The Final Disposal of Disused Pipelines and Cables by PItEY5iY


									  The Final Disposal of Disused
      Pipelines and Cables
           LANDING                                          PIPELINES


                                              Gas pipeline
                                              Oil / condensate pipeline
                                              Projected gas pipeline                                                                              Norne


                                                                                                                                                 HALTEN PIPE
                                                                                                                           SP        Njord
                                                                                                                D R

     60°                                                Murchison
                                 Shetland                                         Veslefrikk                              FLORØ
                                                                                      Brage Troll
                                                                                                  OTS                      Sture

                                                                    Frigg                                               Kollsnes


                                                                     Heimdal               II A
                                               FNA                                   IPE
                                                                                           II B

                                                                                   EP                                     Kårstø


                 St Fergus                                                                          PIP
                                                                                            ST    AT
                                                        Sleipner                                               STAVANGER
                                                                                Draupner S/E

                                                                    Cod            Gyda
     55°                                                 Tommeliten
                                         IP    E                                Hod









                        Bacton                                                                                               Emden
                                 INTE ECTOR

                  Dunkerque                        Zeebrugge
     50°                      France                       Belgium

            0°                                                              5°                                                         10°

Summary of the Findings of a Norwegian
     Assessment Programme
                                          Unofficial translation
Steering Committe Members:
Erik Johnsen (MPE) – leader
Halvor Musæus (MPE)
Peter Reine (FIN)
Roald Paulsen (FID)
Robert Misund (FDIR)
Sveinung Oftedal (MD)
Else Karen Norland (NPD)
Kjell Arild Anfinsen (NPD)
Inger Caspersen (SFT)
Erling Gjertveit (Statoil)
Johan Nitter-Hauge (MPE) – secretary

Editorial assistance by Martin Ivar Aaserød (Agenda)

Ministry of Petroleum and Energy (MPE)

Oslo, December 1999


A few petroleum fields on the Norwegian Continental Shelf have ceased or are about to cease
production. The Norwegian Parliament has accepted the decision of OSPAR (The Convention on
the Protection of the Marine Environment in the Northeast Atlantic) which imposes a general ban
on sea disposal of disused offshore installations. The decision does not cover pipelines and cables.
There are today no international rules for the removal and disposal of offshore oil and gas
pipelines. The requisite legal authority for decisions regarding pipeline and cable disposal is found
in the Petroleum Act.

In order to acquire the proper basis for a decision on the disposal of Odin's gas pipeline, the
Ministry of Petroleum and Energy started a 3-year assessment programme in 1996 for improving
the factual basis of disposal options dealing with the offshore industry's pipelines and cables. At the
same time the Ministry made known that no decision about the final disposal of any pipelines
would be made until the assessment had been reviewed. The final disposal decision on the Odin
pipelines was thereby postponed until 2000, and the decision pertaining to Mime's pipelines was
likewise put off.

To implement the assessment programme the Ministry of Petroleum and Energy aappointed a
steering committee consisting of Erik Johnsen, Ministry of Petroleum and Energy (leader), Halvor
Musæus, Ministry of Petroleum and Energy, Peter Reine, Ministry of Finances, Roald Paulsen,
Ministry of Fisheries, Robert Misund, Directorate of Fisheries, Sveinung Oftedal, Ministry of
Environment, Else Karen Norland, Norwegian Petroleum Directorate, Kjell Arild Anfinsen,
Norwegian Petroleum Directorate, Inger Caspersen, Norwegian Pollution Authority, Erling
Gjertveit, Statoil, and Johan Nitter-Hauge, Ministry of Petroleum and Energy (secretary). Martin
Ivar Aaserød of Agenda Utredning & Utvikling AS was engaged to compile the assessment
programme's results. The English translation is done by Nicholas Wade, Scanews.

The purpose of this report is to document the availability of knowledge in the various implicated
disciplines and to summarise the programme's sub-projects. It is intended that this document may
serve as a basis for making a choice among the various disposal options for disused pipelines and
cables. The steering committee has contributed qualified inputs to the summary report and supports
its conclusions.

Ministry of Petroleum and Energy,
December 1999




    1.1   BACKGROUND





    4.2   REMOVAL
    4.3   RE-USE AT SEA








    8.2   REMOVAL
    8.3   RE-USE AT SEA

The Final Disposal of Obsolete Pipelines and Cables              5

Acronyms and abbreviations
FDIR           Directorate of Fisheries
FID            Ministry of Fisheries
FIN            Ministry of Finances
IMR            Institute of Marine Research
MD             Ministry of Environment
NCS            Norwegian continental shelf
NPD            Norwegian Petroleum Directorate
MPE            Ministry of Petroleum and Energy
OSPAR          Oslo-Paris Convention
SFT            Norwegian Pollution Authority
UNCLOS         United Nations Convention on Law of the Sea


A few petroleum fields on the Norwegian            The comparable standing for infield pipelines
Continental Shelf (NCS) have ceased or are         and cables is respectively 77% and 90%.
about to cease production. The Norwegian
Parliament decided what was to be done with        An NPD pipeline compilation made in
the disused installations at North East Frigg,     1997/98 listed just about 400 km of steel
Odin and Mime. A decision was not taken            pipelines and 20 km of flexible pipelines shut
with regard to the final disposal of Mime and      down because of terminated production or
Odin pipelines. The termination and removal        outphased infrastructure. Additionally about
plans for several other field will be submitted    100 km of cables are no longer operative.
to the Parliament in the near future, of which     These pipelines and cables are for the most
East Frigg and Tommeliten Gamma will come          part located in the Ekofisk and Frigg areas. It
first. Subsequently parts of Ekofisk and the       is expected that another 240 km of pipelines
remainder of Frigg installations, both with        and 80 km cables will be shut down in
extensive pipelines, will be shut down.            1999/2000.

There are today no international rules about
                                                   Disposal options
the removal and disposal of offshore oil and
gas pipelines. National legal authority has        Chapter 4 describes alternative means of
been established in the Petroleum Act and in       disposing of disused pipelines and cables and
the Removal Cost Allocation Act, cfr. chapter      their technical feasibility. The assessment
1.2.                                               comprises leaving in place, removal, re-use
                                                   offshore, recycling and dumping.
When the final disposal of the Odin facilities
was under review, the Ministry of Petroleum        By leaving in place is meant that the pipeline
and Energy started a 3-year assessment             or the cable is shut down and left where it is.
programme in 1996 to improve the factual           A pipeline or cable may either be left as it is
basis for dealing with options for the final       or measures may be taken to reduce
disposal of the offshore industry's pipelines      undesirable impacts. Such measures may be
and cables. The programme aimed to clarify         rock/gravel dumping or trenching with or
the full extent of disposal decisions required     without backfill. The different ways of
in the future and possible disposal options.       covering/burial are by and large based on
The intent was also to assess the conse-           known technology.
quences of the alternatives with regard to cost,
safety, the marine environment, energy             Certain knowledge about the course of
consumption and other users of the sea. A list     degradation of steel pipelines is lacking since
of the commissioned studies is found in            model results cannot be verified by field
chapter 2.                                         observation. A rough estimate of the total
                                                   degradation time is in the range of 300 - 500
                                                   years. Differing circumstances, if for instance
Pipelines and cables on the Norwegian
                                                   the concrete coating is intact, can prolong the
continental shelf
                                                   period to a great degree, while damage can
Chapter 3 covers pipelines and cables on the       reduce it.
NCS. As of 1999, according to the Norwegian
Petroleum Directorate (NPD), there were            A pipeline that is left as is for a while
about 9300 km of pipelines on the NCS              following shutdown, but is meant to be
connected to the production and transmission       removed at a later date, is known as
of oil and gas. 7400 km of those were export       "temporarily left in place." Leaving
lines and 1900 infield lines, while 6200 km of     temporaryly in place may be desirable for
the pipelines were in the Norwegian sector         safety reasons (removal may be very
and the remainder were export lines crossing       complicated in an area of ongoing petroleum
foreign sectors. In addition, there are about      activity) or to cut costs by co-ordinating
1850 km of cables. About 33% of the export         removal operations.
lines are trenched or covered with gravel/rock.
The Final Disposal of Disused Pipelines and Cables                          7                   7

Removal means taking pipelines and cables            coatings will need special attention. Several
out of the marine environment where they             ways of securing pipeline removal operations
have lain for further use or recycling or            in order to safeguard the workforce are
dumping. Pipeline and cable metals are               proposed.
recyclable. If no realistic use or recycling
alternative is found, the materials must be          Environmental impacts
deposited on land.
                                                     The environmental impacts of the various
Methods of removing all kinds of pipelines           alternatives are discussed in Chapter 6. Such
and cables exist. What is most suitable              aspects as metals leaching, emissions to the
depends on type (rigid or flexible), size,           atmosphere, sea and land and bottom
weight, coatings, and water depth. All               sediments and habitats are described.
removal methods derive from reversed
installation, so they are not necessarily            It is not expected that the environmental
optimal for removal. As a general rule it is         impacts from leaching metals and other
easier to remove flexible pipelines than rigid       pipeline and cable materials will be serious,
ones.                                                regardless of what option is chosen.

Partial removal of pipelines and cables entails      Mercury and cadmium, which are used
that some parts are removed and others left. It      primarily in anodes, are the metals thought to
is not considered a separate alternative.            have negative environmental impacts. Both
                                                     are heavy metals that accumulate in the food
By re-use offshore is meant re-utilisation in        chain. The critical level of mercury and
the petroleum activities or for another              cadmium is about to be attained in certain
offshore purpose. Worldwide experience of            especially vulnerable species. It is not
pipeline re-use is very limited. As of the           expected that the other materials can have
present only pipelines of relatively short           serious environmental impacts.
lengths and modest diameters have been
reused. Re-use requires satisfying the               Mercury is found in aluminium anodes on
specification and quality requirements of the        pipelines installed before 1980. There are
new user. The use of requalified materials will      about 30 km of such pipelines in Ekofisk and
always entail some uncertainty. Cables are           Statfjord, with totally about 80 kg mercury
mostly made-to-order for highly specialised          installed. These pipelines have been in use for
objectives and have thereby limited re-use           more than 20 years and a good part of the
options. Re-use signifies a postponement of          material has eroded. Mercury and cadmium
final disposal.                                      leaching from the pipelines are estimated to
                                                     constitute maximum respectively 0.02% and
                                                     0.04% of total anthropogenic inputs of these
Impacts on the working environment
                                                     elements in the environment.
Chapter 5 compares the working environment
during lifting, removal, transport ashore and        The relevant pipelines in the Ekofisk area are
final disposal to the working environment            buried, while those in the Statfjord area are
during installation. Not many differences have       assumed to be either buried or subsided. It is
been found. In removal the most demanding            assumed that parts of the mercury released by
operations are transferring the removed pipe         the anodes are bound in particles to bottom
from the lift vessel, stowing and securing it in     sediments and can be released into the sea
the transport vessel.                                should the pipelines be removed.

In any landbased operation disposing of              The area covered by pipelines is quite small in
removed pipe in accordance with safety               relation to the total NCS area and the total
regulations, there will be a limited serious         impact on bottom habitats of the various
accident risk, but the minor work accident risk      disposal alternatives is considered
is significant since many of the operations          insignificant.
will become routine. Analysis of this subject
indicates that the handling of anti-corrosion
8                                                                                 Summary Report

Calculations on energy consumption and             Rockdumping can actually lead to closed
emissions show that leaving in place leads to      areas and reduced catches.
the lowest direct emissions to air, fresh water
and the marine environment. Account taken of       Backfilling of a pipeline or cable left in place,
the environmental cost of producing materials      does not entail any hindrance for trawling
to replace those left, primarily steel and         once the work is finished. This method is
concrete, deposit on land gives the highest        particularly appropriate for trawling grounds.
emissions. Recovery of pipeline steel or re-       Trenching without backfilling, may cause
use options for the pipe on land or at sea will    provisional problems or blocked access for
lower total emissions compared to new              trawlers, until the trench has been naturally
production. NOx and dust emissions on the          filled.
other hand are increased by re-use or
recovery. That conclusion presupposes that         Removing the pipeline or cable from the sea
there is a re-use market. Disposal on land will    bottom or beneath the surface will reduce
require a lot of space and can cause local         operational problems once the removal is
pollution of fresh water recipients.               completed. If they have been rockdumped,
                                                   removal may lead to spreading the rock over a
Impacts on fisheries                               larger area and thus increasing the operational
The impacts of the various alternatives on         problems.
fisheries are treated in Chapter 7.
                                                   Re-use at sea may have the same
A pipeline would normally not obstruct             consequences for fisheries as leaving the
fishing with passive gear, such as net and         pipeline or cable in place, depending on its
lines, or with ring net or pelagic trawl. In       new location.
1990-1998 on the average 94% of Norwegian
                                                   Cost considerations
North Sea catches were taken by trawl and
purse net. It is indifferent for purse net         The costs of the disposal options are discussed
fisheries whatever final disposal alternative is   in Chapter 8.
chosen. This report, therefore, focuses on
significant factors for bottom gear fisheries      The leaving in place of pipelines and cables as
(bottom trawl in particular).                      they are does not entail extra costs in
                                                   principle. Rockdumping proud pipelines and
It is not very likely that existing pipelines      cables and trenching all pipes that are
cause any significant reduction of catches for     uncovered have been considered. Rock-
the Norwegian trawler fleet in the North Sea.      dumping costs come to NOK 25 billion.
That is a valid presumption so long as the         Trenching the same pipelines and cables
pipelines are not externally damaged. Most         without backfilling will cost between NOK
pipeline problems for trawling today are           2.0 and 5.0 billion, provided that trenching is
related to rockdumping.                            possible.

The leaving in place of pipelines or cables that   Removal of pipelines and cables is estimated
are buried in stable sea bottoms does not          to amount to almost NOK 44 billion,
hinder trawling. Pipelines lying proud can         including costs for handling and depositing on
cause some operational problems on trawling        land. Development of new technology may
grounds, but provided there is no serious          lead to substantial cost savings. There is little
external damage, the extent of the problems        to be saved by recycling. Re-use costs have
will be as in the operating phase. If abandoned    not been estimated. The costs of removal and
pipelines are severely damaged or develop          disposal at sea are of the same order as
free spans, operational problems in the form       bringing ashore for disposal there.
of lost catches and restricted access may be
significant.                                       Cost computation demonstrates that 40%-50%
                                                   of the cost of the various disposal options are
As a general rule gravel and rock dumping on       linked to marine areas that are important or
a pipeline or cable left in place, will create     very important for trawling.
more operational problems for trawlers.
The Final Disposal of Disused Pipelines and Cables                        9                  9

Costs are computed on the premise of optimal         one-by-one as they come out of use, the
implementation of the work, with mobilisation        additional mobilisation and demobilisation
and demobilisation of vessels in the same            costs will add about 30%. This supplementary
season. Estimated costs of Frigg removals            cost may vary from field to field.
show that if pipelines and cables are removed
The Final Disposal of Disused Pipelines and Cables                        11                    11

A few petroleum fields on the Norwegian Continental Shelf (NCS) have ceased or are
about to cease production, which entails the shutdown of oil and gas pipelines. The
Ministry of Petroleum and Energy started a 3-year assessment programme in 1996 to
improve the factual basis for decisions about the final disposal of pipelines and cables.
This chapter describes the background, organisation and implementation of the assessment
and ends with a short review of international rules pertaining to the removal and disposal
of facilities (installations and pipelines) that have been taken out of use.

1.1 Background
A few petroleum fields on the NCS have
                                                     1.2 Organisation and
ceased or are about to cease production. The               implementation
Parliament decided what was to be done with
the disused installations at North East Frigg,       To get the assessment underway a working
Odin and Mime. Reference is made to the              seminar was held on 23-24 Sept 1996
white papers St prp nr 36 (1994-95), St prp nr       attended by representatives of the competent
50 (1995-96) and St prp nr 15 (1996-97). For         ministries, directorates, oil companies, other
Odin and Mime no decision was made about             organisations and research institutions. The
the final disposal of their disused pipelines.       point of the seminar was to identify, document
The decommissioning plans for several other          and co-ordinate relevant project proposals
fields will be submitted to the Parliament in        with the themes presented in table 1.1.
the near future, of which East Frigg and
Tommeliten Gamma will come first, followed           To implement the programme MPE set up a
by parts of Ekofisk and the remainder of             steering committee in 1996 with the
Frigg. All in all, this represents extensive         participation of the Ministry of Fisheries,
lengths of pipelines.                                including the Fisheries Directorate, the
                                                     Ministry of Environment, including the State
The Ministry of Petroleum and Energy (MPE)           Pollution Control Authority, the Ministry of
started a 3-year assessment programme in             Finance and MPE, including the Norwegian
1996 to improve the factual basis for                Petroleum Directorate. One of Statoil's
decisions on the final disposal of offshore          veteran pipeline engineers participated in the
pipelines and cables, cfr. St prp nr 50 (1995-       work as professional advisor. For editorial
96) and St prp nr 58 (1995-96). The purpose          assistance in the compilation of the
of the assessment was i.a. to clarify                programme's findings an independent
                                                     consultant was engaged.
   the scope of future disposal decisions and
    options                                          The steering committee was made responsible
   what materials the pipelines consist of and      for implementing the assessment programme
    their contents                                   and soliciting and acquiring tenders for the
   the consequences of the various disposal         thematic studies from appropriate consultants.
    options with regard to cost, safety, the         The committee has released a report summing
    environment and other sea users.                 up the results of the commissioned studies. It
                                                     is a public document. The steering committee
At the same time the Ministry advised that no        was not empowered to give any advice in
final decision on pipeline disposal would be         respect of any specific disposal option or
taken until the assessment had been done. The        general guidelines in the subject area.
final disposal decision for the Odin pipelines
as thereby postponed until 2000, and the same
applied to Mime.
12                                                                                  Summary Report

Table 1.1: Appropriate themes at assessment inception
Theme               Keyword
Fishery             fishery methods, fishing gear, damage risk, fish availability along pipelines,
                    maintenance, safeguarding, liability
Marine              residual hydrocarbon and chemical leakage, bottom sediments, water quality,
environment         background values, pipelines as nurseries for marine organisms, general
On land             scrapping, handling waste, fumes, noise, atmospheric emissions, material
                    handling, transport, working environment/safety, resycling
Technical factors mapping and localising of pipelines, re-use possibilities, removal methods,
                  securing methods, pipe corrosion, cracks, degradation

                                                      licensees have no right to such tax deductions
1.3 Legislation on removal of                         on a year to year basis, but each licensee is
      offshore facilities                             entitled to an allocation from the state when
                                                      the final disposal is taking place. The
Norwegian legislation on removal and                  allocation is based on the licensee's tax
disposal of disused offshore facilities               liability in the years when the installation was
(installations and pipelines) are found in the        in use. This means that each disposal decision
Petroleum Act of 29 November 1996, No 72              must be sanctioned by the Parliament.
and the Installation Removal Cost Allocation
Act of 25 April 1986, No 11 (Cost Allocation          The UN Convention on the Law of the Sea of
Act).                                                 1982 requires the removal of disused offshore
                                                      installations to safeguard shipping in
The Petroleum Act's chapter 5 treats the              accordance with internationally accepted
termination of petroleum activities. It requires      standards, the environment and fisheries.
the licensee to submit a decommissioning plan         International Maritime Organization (IMO)
prior to the shut down of an offshore facility,       has adopted the relevant guidelines. They do
with proposals for its disposal. Disposal may         not pertain to pipelines. The appropriate legal
include continued use in the petroleum                basis for decisions on disposal of pipelines are
activities, other re-use, entire or partial           incorporated in the Petroleum Act.
removal or leaving in place. On the basis of
the plan MPE makes a decision on disposal             In summer 1998 the Commission on the
and fixes a time limit for its implementation.        Convention for the protection of the marine
The evaluation which constitutes the basis of         environment in the North East Atlantic,
the decision shall i.a. emphasize technical,          OSPAR, reached agreement on banning the
safety, environmental and economic factors            dumping of disused offshore installations at
and regard for other users of the sea. If the         sea. Exceptions are granted for certain kinds
disposal decision is for leaving the facility in      of installations or parts of installations if an
place, the licensee or the owner is liable for        overall assessment in a specific case shows
any damage or interference the facility may           that there are significant reasons for disposal
cause, whether wilfully or by negligence on           at sea. The OSPAR decision entered into force
his part, unless the Ministry decides other-          on 9 February 1999. St prp nr 8 (1998-99)
wise. Reference is made to Ot prp nr 43               describes in more detail the decision and the
(1995-96).                                            applicable exemptions, while St prp nr 36
                                                      (1994-95) provides a more thorough review of
The costs of the final disposal are allocated         other applicable rules and international
among the Norwegian state and the licensees           guidelines.
pursuant to the Cost Allocation Act. The
The Final Disposal of Disused Pipelines and Cables                             13                 13

This chapter presents the subject matter of the studies commissioned in the scope of the
assessment programmme. Reference is made to Chapter 9 for a complete list. The chapter
division of this report is by study subject matter, on each of which a chapter is based.

NCS pipelines and cables                             Environmental impacts
NPD has prepared compilation of pipelines            Four studies analyse environmental impacts
and cables on the Norwegian continental              of the removal or leaving in place of pipe-
shelf which describes pipeline types,                lines and cables:
materials used and lie. (NPD 1999)
                                                     Pipeline degradation over time
Disposal options                                     This study treats the degradation rate of
Three studies of disposal options have been          pipelines left in place, including the leaching
prepared.                                            rate of potential environmental harmful
                                                     metals and other compounds. Consideration
Methods of lifting and removing pipelines            is also given to the need of pipeline
and cables, and re-use possibilities                 inspection, maintenance and safeguarding
                                                     measures. (Dames & Moore et al. 1999c)
This project clarifies the various lifting and
removal methods and the equipment required           The impact of harmful substances in
and discusses the possibilities and technical        pipelines on the marine environment
constraints of re-use. (JP Kenny et al. 1999)
                                                     This study focuses on the impacts on the
Disposal of flexible pipes and cables                marine environment of leakage of harmful
                                                     substances from pipelines and cables left in
This study analyses the removal of flexible          place. Dispersion pathways and mechanisms
pipes and cables and discusses the                   of bioaccumulation are reviewed in respect of
possibilities and technical constraints              particularly vulnerable organisms and areas.
applying. (Halliburton Subsea 1999)                  (Aquateam 1999)
Recovery and recycling of pipeline and cable         Impacts on the outer environment
                                                     The impacts on the outer environment of the
This study considers issues and possibilities        various disposal options are covered. As far
related to removing protective coatings as           as possible energy consumption, emissions to
well as the recovery and recycling of pipeline       air, sea and fresh water, and amounts of
and cable materials. Pipelines with and              wastes are quantified. (RC Consultants 1999)
without a concrete weight coating are
covered. (Taraldrud 1998).                           Impacts on marine habitat

Impacts on the working environment                   This study looks at impacts which the various
                                                     disposal options have on sea-bedhabitats,
This study discusses the consequences of             classifies natural North Sea habitats, and
pipeline and cable removal and final disposal        assesses restitution time after physical
on the working environment. It clarifies how         impacts. (Det norske Veritas 1999)
these operations impact the working
environment compared to the impacts of the           Impacts on fisheries
installation phase. (Dames & Moore et al.
1999a)                                               Two studies take up consequences for
                                                     fisheries. Some findings of the operators'
                                                     recently-released North Sea Regional Impact
                                                     assessment are cited. (Agenda 1999b)
14                                                                            Summary Report

The availability of fish along pipelines         The costs of alternative disposal options
                                                 This is a cost analysis of the various disposal
The availability of fish along North Sea oil
                                                 options. The costs of removal and subsequent
and gas pipelines has been investigated to
                                                 treatment on land are based on the use of
find out whether commercial kinds of fish
                                                 existing equipment for the production,
aggregate around pipelines and if so whether
                                                 installation and operation of pipelines and
there are quantities able to sustain a viable
                                                 cables. (Dames & Moore 1999b)
fishery. (Nøttestad 1999)
                                                 Cost estimates for burying and covering
Grounds and extent of Norwegian trawl
fisheries in the North Sea
                                                 Methods have been described and burying
Important areas for Norwegian trawling in
                                                 and covering costs with/ without backfilling
the North Sea are described, and important
                                                 of pipelines that today lie on the seabed have
fishing grounds are mapped and graded on
                                                 been estimated. The assessements derive
the scale of importance in 1990s fisheries.
                                                 from Statoil's experience in recent pipelaying
(Agenda 1999a)
                                                 projects. (Gjertveit 1999)
Cost factors
Two studies analyse cost factors applicable to
the various disposal options.
The Final Disposal of Disused Pipelines and Cables                                                            15                              15

               CONTINENTAL SHELF
To date approx. 9300 km of pipelines and 1850 km of cables have been installed for the
exploitation and transmission of oil and gas on the Norwegian continental shelf. This chapter
presents a compilation of essential pipeline data, supplemented with a review of lie of pipelines
and cables in or on the seabed. A good 400 km of pipelines and just about 100 km of cables have
already been taken out of use. It is expected that about 240 km of pipe and about 80 km of cable
will be taken out of use in 1999/2000. The chapter ends with a close description of expected
pipeline and cable outphasing.

                                                                                     pipelines crossing foreign sectors. There are
3.1 Review of Norwegian                                                              about 1850 km of cables, all within the
                 pipelines and cables                                                Norwegian sector.

The NPD manages the CODAM database on                                                3.1.1    Export pipelines
all pipeline systems for exploitation and                                            Figure 3.1 gives the length in km of the export
transmission of oil and gas on the Norwegian                                         pipelines laid between 1975 and 1999
continental shelf, including transmissions                                           including Jotun Gas Export, Europipe II, Troll
from Norway to the UK and the Continent.                                             Oil Pipe II and Åsgard Transport. Figure 3.2
The database also covers all types of offshore                                       shows existing and planned or approved gas,
cables used in the petroleum activities. It is                                       oil and condensate export lines from NCS.
continously updated.
                                                                                     Table 3.1 shows that about 1/3 of export pipe-
There are some 9300 km of pipelines                                                  lines are trenched, covered or rockdumped.
connected to the exploitation and transmission                                       The greater length of these pipelines are lying
of oil and gas, 7400 km of which are export                                          in shallow water on foreign continental
lines, the majority for gas, and about 1900 km                                       shelves.
inter field lines (either pipelines inside a field
development or flow lines between                                                    The breakdown of export pipelines by
neighbouring fields). About 6200 km are                                              dimension and transported medium is shown
within the Norwegian sector and the                                                  in table 3.2.
remaining 3100 km are parts of the export

                                                                    Export pipelines









                      1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

                                                                         Oil   Gas    Condensate
16                                                                                                                                                                   Summary Report

Figure 3.1: Development of export lines over time (NPD)
       LANDING                                               PIPELINES


                                          Gas pipeline
                                          Oil / condensate pipeline
                                          Projected gas pipeline                                                                                        Norne


                                                                                                                                                       HALTEN PIPE
                                                                                                                                SP         Njord

                                                                                                                   D R
60°                                                 Murchison
                             Shetland                                                 Veslefrikk                               FLORØ
                                                                                          Brage Troll
                                                                                                      OTS                        Sture

                                                                        Frigg                                              Kollsnes


                                                                         Heimdal               II A
                                           FNA                                           IPE
                                                                                               II B

                                                                                       EP                                      Kårstø


                                                                                                      P      E
             St Fergus                                                                             TPI
                                                     Sleipner                                   STA                STAVANGER
                                                                                    Draupner S/E

                                                                        Cod            Gyda
55°                                                   Tommeliten
                                     IPE                                            Hod


                                                                                                                  PE I

                                                     I E






                    Bacton                                                                                                        Emden
                             INTE ECTOR

              Dunkerque                      Zeebrugge
50°                       France                            Belgium

        0°                                                                      5°                                                           10°
The Final Disposal of Disused Pipelines and Cables         17   17

Figure 3.2: Norwegian pipeline systems automn 1999 (NPD)
18                                                                                            Summary Report

Table 3.1: Lie of pipelines and cables by type and location (NPD))

Lie                                     Export lines                          Infield lines            Cables

                             NCS         Foreign       Sum            Steel     Flexible      Sum
Trenched, covered              8%            25%       33%              62%         15%        77%           90%
On the seabed                 50%            17%       67%              20%         23%        23%           10%
Sum                           58%            42%       100%             82%         18%       100%       100%

Table 3.2: Distribution of export lines by                    remaining 100 km burial or cover depth has
dimension and transported medium in km                        not been recorded.
                                                              3.1.3     Cables
Dimensjon     Gas    Oil      Condensate       Sum
                                                              On the Norwegian continental shelf there are
< 20”          362      85       198            645
                                                              about 1850 km of cables connected to the
20” – 40”     1809   543         228           2580           petroleum activities. They fall in 4 categories,
> 40”         4211       -          -          4211
                                                              see table 3.4. Usually cables are installed at
                                                              the same time as pipelines but their alignment
Sum           6382   628         426           7436           may be different.

                                                              Tabel 3.4: Cables by main categories in km
3.1.2    Infield lines                                        length
Infield lines may be split in two categories:
steel and flexible pipelines. The division                     Category                              Total
between these and the medium transported is                    Control cables                           400
shown in Table 3.3. Injection pipelines                        Power cables                             130
comprise both gas and water injection.
"Other" covers methanol, nitrogen, service                     Fiber-optic power cables                 130
and test pipelines. Most infield pipelines are                 Other fiber-optic cables                1200
less than 14" in diameter.
                                                               Total                                   1850
Table 3.3: Distribution of infield pipelines by
type and transported medium in km length                      90% (1650 km) of the cables on the
                                                              Norwegian continental shelf are buried or
 Medium         Steel        Flexible       Total             covered. Of these 1390 km are buried or
 Oil             378             23          401              covered up to 1 meter depth, and 180 km at
                                                              more than 1 m depth. The buried or covered
 Gas             431                2        433              depth of the remaining 80 km is not recorded.
 Multiphase      328            187          515

                                                              3.2 Pipeline outphasing
 Injection       256             79          335
 Other           142             45          187
 Total          1535            336         1871              The projected design lifetime of pipelines and
                                                              cables on the Norwegian continental shelf
Just under 80% of all infield pipelines are                   may vary. The longest is until 2050 and is
trenched, covered or other wise protected, see                valid for a major part of the big oil and gas
table 3.1. About 600 km are buried or covered                 export lines to the Continent. It is antisipated
up to 1 meter depth and 750 km are buried or                  that lifetime of these export lines may be
                                                              prolonged when needed.
covered to more than 1 m depth. For the
The Final Disposal of Disused Pipelines and Cables                                             19                               19

                                                                                                    P la nne d e xpo rt line
                3000                                                                                o ut pha s ing
                2500                                                                                O f whic h o n f o re ign
                                                                                                    s he lf
  Km pipeline

                                                                                                    P la nne d inf ie ld line
                1500                                                                                o ut pha s ing

                       B e f o re   1997-2010 2010-2025   2025-2040 A fter 2040

Figure 3.4: Expected pipeline outphasing. The figures are from CODAM as of June 1997 and do
not cover Åsgard Transport and Europipe II. (JP Kenny et al. 1999)

The infield pipelines have by and large shorter                      More than 80% or 362 km of the pipelines
lifetimes and many of them will be taken out                         taken out of use are buried while the
of use within 15 years from now. Yet it is                           remaining 20% (81 km) are proud. The
assumed that if need be their lifetime can also                      pipelines in the Ekofisk area are mainly
be prolonged. Figure 3.4 illustrates the extent                      buried with 1 m of cover.
of pipelines to be taken out of use on the basis
of their design lifetime. (JP Kenny et al. 1999)                     T able 3.5: Amounts of materials in
                                                                     Norwegian pipelines, excluding Åsgard
Table 3.5 shows the quantities of steel and the                      Transport and Europipe II (JP Kenny et
types of coating in the pipelines that will be                       al.1999)
decommissioned by 2050. The cables are
additional, see chapter 3.1.                                           Kind of material                             Amount
The NPD compilation shows that a good 400                                                                           in 1000
km of steel pipelines and 20 km of flexible                                                                         tonnes
pipelines have been taken out of use following                         Carbon steel in export lines                   2 970
the end of production or infrastructure                                Carbon steel in infield lines                    184
outphasing. Their outer pipe diameter varies                           Duplex steel (only infield line)                   6
between 2" and 36". About 100 km of cables                             Duplex steel (only infield line)                 183
are also taken out of use. The total pipeline
                                                                       Coal tar coating                                  12
systems taken out of use amount to not quite
                                                                       Concrete                                        4000
6% of total installed pipeline length. Most of
the pipeline systems taken out of use are
located in the southern part of the Norwegian                        Besides those that are already shutdown, it is
North Sea sector (Ekofisk area) and in the                           expected that approx. 240 km of pipelines and
Frigg area.                                                          80 km of cables will be taken out of use in the
                                                                     course of 1999/ 2000.
20                                                                                Summary Report

The disposal options discussed in this chapter are leaving in place, removal and re-cycling
or deposit, see chapter 1.3. Methods exist for removal of all kinds of cables and pipelines.
Which methods are most appropriate depend on i.a. pipeline type, pipe size, weight, kind of
coating and water depth. Removal methods have not been optimised because they make use
of equipment designed for installing pipelines and cables.

                                                       coating beneath. This is a very uncertain
4.1 Leaving in place                                   parameter.
                                                   •   Degradation of the pipe itself will start
By leaving in place a pipeline or cable is
                                                       locally from any protective coating
meant that it is shut down and left lying as it
                                                       damage and at the pipe ends. Protective
is. A pipeline or cable may be left in place
                                                       coating cracks will promote locally higher
without any form of measure or measures may
                                                       corrosion rates.
be taken to reduce undesirable impacts.
                                                   •   Once the protective coating and the weight
                                                       coating have degraded¸ metals leaching
4.1.1   Leaving in place as is                         will occur during a very long period of
This option requires no other measures than            time before the pipeline corrodes away -
purging,flushing if needed, plugging and               300 to 500 years according to the model
securing of the free ends. However, out of             calculation. If the concrete coating is
regard for other users of the sea, it may be           intact, degradation time will be greatly
desirable to keep some control of pipeline             extended.
degradation.                                       •   The leaching rate will likely peak about
                                                       200 years after the pipeline has started to
Degradation sequence of steel pipelines                degrade.
Knowledge of the course that degradation           •   Changes in natural forces acting on the
takes in steel pipelines is lacking since it has       pipelines, as for instance, damage from
not been possible to verify model calculations         trawl doors, are apt to increase the rate of
by observations. The longest projected                 degradation.
lifetime for the pipelines installed today is 50   •   Buried pipelines can be expected to
years. The lifetime of some pipeline systems           degrade at a slower rate than uncovered.
that have been in operation for up to 20 years
is being prolonged past design lifetime            Degradation sequence of flexible pipes and
because the fields have proven capable of          cables
producing longer than expected and the
pipelines still meet all the technical             A separate study was made on disposal of
requirements.                                      flexible pipes and cables with attention given
                                                   to the degradation sequence. (Halliburton
A study was commissioned to analyse                Subsea1999)
pipeline degradation over time, including i.a.
the leaching of metals and compounds. It also      Flexible pipelines are composed of layers of
addresses the need for inspection,                 steel and plastic materials and their lifetime is
maintenance and safeguarding of pipelines          determined by the lifetime of each of those
left in place. (Dames & Moore et al. 1999c)        material layers and the shocks they are
The major conclusions are:                         subjected to during their normal use. The steel
                                                   of the various layers is exposed to corrosion
• Anodes can be expected to protect the pipe       and mechanical and dynamic loads, all of
  against corrosion for 50-70 years.               which affect lifetime. No independent
• Pipeline degradation once the anodes are         assessment has been made of the steel lifetime
  expended depends on the condition of the         of these pipelines.
  concrete weight coating and the protective
The Final Disposal of Disused Pipelines and Cables                         21                    21

The plastic and composite layers are not             pipelines and cables. This might for instance
affected by corrosion and mechanical and             be in areas where a damaged or partially
dynamic loading in the same way as the steel         broken up pipeline or cable would interfere
layers. Unlike steel, plastic is vulnerable to       with fishing. The following measures could be
ageing, which weakens resistance and leads to        suitable:
degeneration of the material. Plastics'               Cover with gravel/rock.
chemical and mechanical characteristics               Trench the pipe without backfilling and let
change over time, which may affect the                  nature take care of natural backfill in due
flexible pipeline's lifetime. Just how extensive        time.
the ageing process is depends on the kind of          Trench the pipe with backfilling of the
plastic and what it has been exposed too                excavated masses.
during use.
                                                     Covering with gravel or rock
Cables have typically lifetimes ranging from
30-40 years up to 100 years depending on             To cover a pipeline lying on the seabed a
kind and design. Among other factors their           profile as sketched in figure 4.1 will need be
lifetime depends on insulation quality and           built up by gravel or rock. To calculcate the
whether they have an inner metal, watertight         needed gravel/rock volume a continuous
layer. Design lifetime presumes no external          cover comprising a 0.75 meter overburden
damage such as blows, stress and movement            and a 3:1 slope is needed to achieve a stable
beyond the forces the cable is fabricated to         cross section.

Inspection and reporting
It is not considered necessary to maintain
pipelines that are permanently left in place on
the seabed. Degradation and final collapse
will most likely occur at different places
during a long course of time. The experience
                                                     Figure 4.1 Typical pipeline cover profile
of operating pipelines that lie on a sandy
                                                     (Gjertveit 1999).
seabed shows that most of them tend wholly
or partially to "burrow down on their own."

Buried and covered pipelines will usually not
need more safeguards, but the risk of exposure
by erosion and other factors affecting stability
will have to be evaluated for each and every
pipelineFrom an environmental point of view
it is not necessary to monitor or inspect
abandoned pipelines.

Pieces of broken pipeline will be a hindrance
in areas where productive fishing with bottom
gear like trawl and seine net takes place. A         Figure 4.2: Cover volume (m3) per meter
flow of information from other sea users             pipeline length (Gjertveit 1999)
should be channelled to the responsible parties
so that any sign of break up, exposure of            This approximation gives an average rock/
buried pipelines or development of free spans        gravel volume between 3 m³ and 11 m³ per
may be recorded when and where needed.               meter of pipeline with 10"- 42" diameter, see
                                                     figure 4.2 In practice some segments of pipe-
4.1.2   Leaving in place with                        lines will already be partially covered or
        safeguarding measures                        subsided in the seabed. In other places several
                                                     times the volume will be needed for adequate
Out of regard for other sea users it may be          cover.
appropriate to cover over or bury abandoned
22                                                                                 Summary Report

Burial of pipeline without backfilling              It is expected that as a pipeline deteriorates
                                                    structurally, there will be fewer suitable
A pipeline can be buried with many kinds of
                                                    removal methods and removal costs will
equipment, of which there are several
                                                    increase. Efforts to safeguard and maintain
suppliers in the market. The effective use of
                                                    pipelines to be removed at a later date will
the various kinds of equipment depends on the
                                                    need to be assessed also in the light of method
type of seabed and how deep the pipeline is to
                                                    suitability at that time. The removal method
lie. Appropriate equipment is :
                                                    will dictate what condition and what residual
 ploughs of various kinds and size                 strength the pipeline will need have and the
 water jet sleds                                   condition of its protective coating. (Dames &
 mechanical trenchers                              Moore et al. 1999c)

These tools make each their own form of             Decommissioning and maintaining
trench profile. A plough working in                 There is today little experience worldwide of
consolidated bottom typically leaves a sharply      the decommissioning of offshore pipelines.
profiled trench with masses piled up                Decommissioning of pipelines entails
alongside. A water jet sled in loose sand           purging, flushing and securing of the free
leaves a broad, sloping trench profile.             ends. The anodes will provide external
                                                    corrosion protection for many years and until
Natural backfilling takes place gradually over      they are eroded, there will be no corrosion. If
time, and the natural overburden of pipelines       the pipelines are temporarily abandoned, rust
that are buried below the surface of the seabed     monitoring will become necessary once the
will vary. In sea depths from 20 to 100 m           anodes are eroded. Free spans must be secured
experience points to relatively active and          against fatigue loading and environmental and
quick natural backfilling. In 2-10 years after      specific weight loads, protective coating
trenching most of the pipeline ought to be          deterioration and corrosion, so that when it is
naturally covered. In deeper water where there      time to remove the pipeline, it is in a state that
is little movement of the seafbed sediments         satisfies the requirements set by removal
natural backfilling will take much longer, and      method and final disposal solution.
it can be expected that the trench profile to a
greater extent will remain.                         If the cut ends of the pipeline are left open,
                                                    water will circulate inside and rust will
Burial with backfilling                             spread. Cut, unplugged ends will therefore
                                                    need corrosion and degradation monitoring.
If natural backfilling does not take place or       Damage to a pipeline may complicate
takes too long, natural sea bottom masses can       removal.
be ploughed back. Special ploughs are
available for such work.                            Besides corrosion, pipelines are exposed to
                                                    seabed movement and subsidence in certain,
4.1.3   Temporary leaving in place                  delimited areas. In such events the pipeline
                                                    should be checked to determine their effect on
By temporary leaving in place in this report is
                                                    the structural integrity of the pipeline, the
meant leaving in place in view of subsequent
                                                    choice of removal method and final disposal
removal. Since removal of a pipeline in the
vicinity of infrastructure that is in current use
is very risky, a postponement may be
                                                    An inspection and maintenance programme is
preferable. Moreover, the objective of
                                                    recommended established in order to promote
temporary leaving in place is to be able to co-
                                                    the desired course of events. Such a
ordinate the removal of several pipelines and
                                                    programme would be especially appropriate
cables for the costwise benefits it entails, cfr.
                                                    for pipelines temporarily left in place on
chapter 8. Leaving in place for the purpose of
                                                    productive, bottom gear fishing grounds.
subsequent re-use or other use is treated in
chapter 4.3
The Final Disposal of Disused Pipelines and Cables                         23                     23

4.1.4   Technical feasibility                        weight coating are also recyclable. It is
                                                     assumed that ways to re-use substantial parts
Covering and burial methods for pipelines and        of the concrete can be developed, while the
cables are proven and based on Statoil's latest
                                                     rest has to be deposited. As for bituminous
experience with pipelaying projects. (Gjertveit
                                                     coatings no good technical solutions for re-use
1999)                                                are available at present.
                                                     (Taraldrud 1998)
4.2 Removal
                                                     In flexible pipelines it is likely that only the
By removal is meant lifting and recovering           metal layers have scrap value, as the plastic
pipelines and cables for the purpose of re-use,      layers are probably contaminated and
recycling or deposit. Re-use at sea is               saturated with oil and gas components from
discussed in chapter 4.3.                            the transport phase. This applies in particular
                                                     to internal plastic layers. Metals can be
                                                     recovered from cables. The more copper and
4.2.1   Re-use on land                               steel there is per unit of length, the more
Among the assessed re-use options for                routine is the recovery of these metals.
pipelines on land are:                               (Halliburton 1999)

   structures and weight-bearing elements           The only solution for components for which
   piles and foundations                            there are no realistic re-use or recycling
   conductors for water and drainage                options is deposit in waste tips on land or in
   industrial pipe assemblies                       suitable ocean sites. In practice there will be
   reforming by machining to minor                  very great amounts of waste to be deposited.
    components.                                      The waste created by partial recycling of steel
                                                     amounts to less than in the production of new
Cables are mostly so specialised that there are      pipes, the main reason being the great
very few re-use options. If multipurpose             amounts of waste materials produced in ore
cables are to be re-used, they will probably         mining and iron smelting.
have to be stripped so the useful component(s)
may be removed.                                      4.2.3   Technical feasibility

Globally there has been very limited                 A special study has been made of appropriate
experience of re-using pipelines, and the            methods and equipment for removing and
current market appears to be too little to take      retrieving disused pipelines and cables (JP
on great amounts. It is usual that wreckers-         Kenny et al. 1999). These and their scope of
scrap dealers take over steel pipelines and          application are listed in table 4.2, which
reduce them to material components for               makes clear there are ways to remove all
recycling, energy recovery, or deposit.              pipelines and cables. Which method is the
(Taraldrud 1998)                                     best in the specific case depends on pipeline
                                                     type, pipe diameter, weight, kinds of coatings
                                                     and water depth. In general the removal of
4.2.2   Recycling and dumping                        flexible pipes and cables is an easier operation
The collection of offshore pipelines and             than the removal of rigid pipes.
cables will lead to great amounts of materials.
There are as of yet no industrial processes          The tow method followed by the reel barge
developed which may in a cost efficient              method is the most suitable for direct re-use,
manner separate pipeline components of               in particular when it is a matter of short
recycling value.                                     infield lines without concrete coating. The
                                                     advantage of these two methods is that short
The steel can be remelted and recycled once          infield pipelines may be retrieved in their full
the concrete and asphalt has been removed.           length, which in the re-use context adds up to
Substances and materials that can contaminate        less cutting, welding and re-applying field
the melt must be removed beforehand.                 coatings on welded joints.
Reinforcement steel bars in the concrete
24   Summary Report
The Final Disposal of Disused Pipelines and Cables                                 25                       25

Table 4.2: Uses and application scope of various removal methods (JP Kenny et al.1999)

Removal method:          Use and scope of use

Reversed S-curve         This laying method is characterised by the S curve the pipe has on its way from
                         the lay vessel to the sea bottom. The pipe is pulled out of the lay vessel and down
                         the stern ramp and stinger. This method is used in the North Sea for laying pipe
                         wider than 14" and pipe with a concrete coating. Reversed S-curve can be used
                         with all kinds of steel pipelines and is most suitable for the big, heavy pipelines.
Reversed J-curve         Characteristic of this method is the J-curve of the pipeline as it hangs almost
                         vertical in an inclined ramp and descends to the seabed, bending toward the
                         horizontal as it approaches.
                         The method is designed for great depths and has not yet been used in the Norrh
                         Sea. It can be used for all kinds of steel pipelines but it is not applicable in
                         shallow water and is best suitable for small and medium diameter pipelines. It can
                         also be used for cables and flexible pipelines if cutting is done as the pipeline is
Reel barge               Small diameter pipelines (<16”) have been installed in the North Sea from giant
                         reels by this method and it can be used to recover all kinds of cables and flexible
                         pipelines. The removal of rigid pipe usually is limited by the reel diameter. This
                         method cannot be used with concrete-coated pipelines.
Cutting on the seabed    This method consists of cutting the pipeline or cable in segments on the seabed
                         and lifting them to a ship or barge. It is suitable for all kinds of cables, flexible
                         pipelines and steel pipelines, but is very costly.
Towing                   Removal is accomplished by various ways of towing, known as bottom pull,
                         above-bottom pull , half-submerged tow and floatation. These methods are used
                         for big-inch steel pipelines in short sections and are not suitable for pipe with
                         weight coating.

A drawback of the tow method is the                       direct re-use in oil and gas transportation. The
comprehensive preparation and the long                    accumulated plastic deformation that the
execution required, which put strict demands              material undergoes from repeated reel
on inspection, quality assessment, repair and             winding and unwinding can damage the
requalification.                                          protective coat and cause fatigue and material
                                                          deterioration in the form of increased

                                                          The other removal methods have greater
                                                          capacities than the towing method and the reel
                                                          barge method, but they require that the
                                                          pipeline be cut in sections as it is pulled up.
                                                          Cutting at the field welds gives either 12 m or
                                                          24 m sections. If re-use of the pipeline is
                                                          planned, it all adds up to a lot more work to
Figure 4.3: Reversed S-curve from lay barge
                                                          prepare for re-installation.

                                                          For removing pipelines and cables from the
                                                          sea bottom a lot of equipment is required for
                                                          effective operations. All removal methods are
                                                          based on reversed installation and are thereby
                                                          not necessarily suitable for removal.
                                                          Development of better methods for removing
                                                          overburden and cutting pipe would be
Figure 4.4: Reel barge                                    worthwhile in the aim of achieving a higher
                                                          removal rate.
A drawback with the reel barge method is to
what extent the recovered steel is suitable for
26                                                                              Summary Report

4.2.4   Partial removal/leaving in place           state of pipes before removal (corrosion
Partial removal of pipelines and cables and         and fatigue level, damage and defects)
leaving in place of the remaining parts has not    stresses during removal, transportation,
been studied as a separate disposal option. It      inspection, requalification and
is in effect a combination of the options           reinstallation
described in chapter 4.1 and 4.2.                  new use requirements (corrosiveness,
                                                    temperature and pressure, transport
                                                    capacity, water depth, loadings and
4.3 Re-use at sea                                   lifetime).

By re-use of pipelines and cables at sea is       It is probable that material can be requalified
meant re-use for the same objective or another    for re-use with existing methods, even though
objective in the petroleum activity or other      there are no established routines for the
marine activity. Such re-use postpones the        requalification of pipelines and cables today.
choice of the final disposal solution.            Requalification for direct re-use in oil and gas
                                                  transport on site will most often require
There is very limited experience of the re-use    internal inspection of pipelines with
of pipelines, even on the world scale. As of      custommade tools. As concerns re-use
the present only relatively short lengths of      involving removal and transport to shore, the
pipe with small to medium diameters have          requalification of steel pipelines can be done
been re-used. Flexible pipelines are re-used in   with proven methods that give reliable
Brazil. There are few re-use possibilities for    evaluations of the state of the material. The
cables because on the whole they are designed     re-use challenge is mainly to document that
and made for a specific use. It has proved        the new user's specification and quality
impossible to find examples of the direct re-     requirements can be met. There will
use of steel pipelines and cables for             nonetheless always be some uncertainty in the
transmission of oil and gas.                      use of requalified materials.

4.3.1   Requalification of materials              Rockdumped electric power cables are
                                                  exposed to such a risk of damage during
Re-using a pipeline or cable puts specific        removal that a priori they are not considered
conditions on their technical state before        suitable for direct re-use.
removal. The requirements of the intended
new use as well must be mapped to determine       4.3.2   Technical feasibility
whether or not they can be met. The
assessment will be related to:                    For re-use requiring removal or displacement,
                                                  reference is made to chapter 4.2.3.
The Final Disposal of Disused Pipelines and Cables                          27                    27

Theworking environment impact study compared the impacts from the removal, transport,
bringing ashore and final disposal of pipelines to those of the installation phase. Few
differences between the two phases of activity were identified. The correct handling of
corrosion resistant coatings and an industrial process for materials separation will be
essential for the working environment in the final disposal phase on land. Several
proposals were made to secure that the operations in the removal and final disposal phase
are carried out with proper regard to the working environment.

                                                     consequences correspond to those identified
5.1 Retrieval and removal                            for reversed S-curve procedures, that is,
                                                     cutting, moving, lifting and stowing pipe.
This chapter demonstrates how the working
environment is affected by pipeline removal
compared to installation. Physical and               5.1.3   Reel barge method
chemical working environment factors, as             The hazard in the reversed reel lay method is
well as dangerous situations that can occur          in the first place linked to a rupture of the pipe
during removal have been pinpointed by the           because of structural weaknesses. This can
commissioned study. (Dames & More et al.             cause the pipe to fly up and spin out of control
1999a) The retrieval and removal methods             and strike personnel close by. When being
that have been assessed are those listed in          unwound on land before cutting in shorter
table 4.2.                                           lengths, small residual stresses in the pipe can
                                                     make the ends unexpectedly strike out and hit
5.1.1   Reversed S-curve method                      personnel.
A review of these removal procedures has
identified the following as impacts:                 5.1.4   Sea bottom cutting of pipe
                                                     An accident while pipe and equipment are
• Cutting pipe: machine operators are                being lifted to the surface in the vicinity of
   exposed to injury while being in contact          operating installations can damage subsea
   with the cutting machine. They are also           equipment, which could cause oil and gas to
   exposed to noise, dust that may contain           leak out and harm personnel, the environment
   asbestos, low radioactive substances, oil         and equipment. When pipe are being stowed
   residues, etc. There is also a risk of fall and   on board the vessel, pipe rolling on deck can
   crush injuries.                                   injure personnel.
• Moving and recovering cut pipe. These
   activities carry a risk of crush injuries.
   Work entailing the lifting of pipe carries        5.1.5   Towing lengths of pipe
   the risk of pipe being dropped causing            If the pipe under tow fills with water, there is
   personnel injury, notably because the pipe        a risk it will sink. The risks of this happening
   clamps used by cranes today were not              are greater during removal than during
   designed to lift pipe covered with concrete       installation because of the state of the pipe. To
   at both ends.                                     avoid accidents that can lead to spills of oil or
• Receiving and stowing pipe on the                  gas, towing should not be done in the vicinity
   transport vessel. Pipe can roll and injure        of operating oil and gas installations.
   personnel. This risk is significantly higher
   than when the pipe was shipped out for            5.1.6   Summary
5.1.2 Reversed J-curve method                        The difference between the working
                                                     environments of the installation and removal
Review of reversed J-curve procedures shows          phases is not seen as significant. Some pipe
that that their working environment                  installation procedures that are risky for the
28                                                                               Summary Report

working environment are not part of the            5.2.2   Purging the pipe
removal phase, but to a certain degree are
                                                   Even if pipelines and cables have been purged
replaced by procedures which also carry
                                                   at sea, it is likely that some of them will need
negative consequences. The most demanding
                                                   more cleaning when on land because they
removal operation is the transportation and
                                                   may still contain production residues,
stowing of pipe from the removal vessel (S-
                                                   including some containing heightened
curve and J-curve methods) and aboard the
                                                   concentrations of LRA (low radioactive)
pipe transport vessel when pipes are cut on the
                                                   scale. It is especially considered hazardous to
                                                   health to inhale pulverised LRA scale during
                                                   the removal of such deposits.
Several measures are proposed in the
assessment for assuring worker safety. If well
                                                   There is little risk of radiation when working
thought-out, purposeful measures and
                                                   with LRA scale, but everybody who takes part
procedures are followed, no factors have been
                                                   in any work entailing direct contract with it
identified that create a more hazardous
                                                   must be given a thorough briefing on the risk
working environment during removal than
                                                   and means of protection.
during installation.
                                                   The authorities refuse to allow LRA scale to
5.2 Transport and handling
                                                   be dumped in Himdalen national dump for
                                                   radioactive waste. Large amounts of LRA
        on land                                    scale constitute thereby a hazardous waste
                                                   problem needing clarification.
The following transport and handling
operations on land have been identified as         5.2.3   Removing anodes
having potential adverse impacts on the
working environment:                               By the time pipelines are lifted and removed
                                                   from the sea, most anode material will have
    unloading pipe lengths from the transport     eroded and the steel structure, its protective
     vessel and transferring to shore              coating, insulation if any and its concrete
    purging the pipe                              coating remain. If a "hot pass" is used to cut
    removing anodes                               off the anodes, it can liberate gas from the
    removing concrete                             anode material, the pipe steel and what is left
    removing protective coatings                  of the corrosion resistant coating.
    cutting pipe
    crushing concrete                             5.2.4   Removing concrete
                                                   There are three recognised ways to remove
Details of the impacts of these operations are     the concrete coating: by explosives, by
given below.                                       gouging or chipping and by pressing out the
                                                   pipe. None of these methods is an industrial
5.2.1    Unloading pipe lengths from the           process, while all of them have traits of work-
         transport vessel and                      intensive heavy labour with person-injury
         transferring to shore                     risks.
Unloading and stowing pipe are on the whole
                                                   Removal by using explosives runs the risk of
proven procedures. But there may be an added
                                                   causing injury as a result of careless use and
risk of work accidents when unloading and
                                                   storage. Gouging can create great clouds of
using a crane because pipes may be
                                                   dust, which can be harmful for the working
deteriorating, or parts of the concrete coating
                                                   crew. In order to press out a steel pipe its
may drop off. Whole pipe lengths can slip and
                                                   protective coating has to be heated. This
fall because the pipe clamps used today by
                                                   releases gases that are hazardous from the
cranes are not designed to lift pipe coated with
                                                   working environment point of view.
concrete at both ends.
The Final Disposal of Disused Pipelines and Cables                         29                     29

5.2.5   Removing the protective                      dust, which in some cases contains remnants
        coating                                      of glass fiber and asbestos, as well as to
                                                     toxic/radioactive substances and hydrocarbon
There are several methods for removing the
protective coating, but none of them is very
suitable for large scale removal, nor has any
of them yet been used on whole pipe sections.        5.2.7   Cutting concrete
                                                     Concrete is crushed before being transported
There are many kinds of corrosion resistant          to a reception facility for recycling or deposit.
coatings in use on North Sea pipelines. Some         Crushing produces dust and noise, and the
coating components are strong allergens and          dust from crushed concrete will have the same
carry a high risk of causing eczema. The             affect on worker health as from the dust from
further use of some current components has           the weight coating.
been prohibited, because of the health risk and
other reasons.
                                                     5.2.8   Summary
Depending on the kind of coating and the             The landbased final disposal operation entails
removal method, removing a protective                a limited risk of serious accidents. It is heavy
coating can bring about the release of               labour requiring a lot of manpower and
hazardous gases. The work crew can also be           carrying a significant risk of work accidents,
exposed to dust that can precipitate asthma          since many of the work operations gradually
and other allergic reactions or irritate the skin.   become routine for the workers. The study
In some cases they may be glass fibre or             notes the importance of handling protective
asbestos dust from protective layer                  coatings in a way that protects workers.
reinforcement.                                       Several heath safeguards or precautions are
                                                     proposed which will contribute to a better
5.2.6   Cutting pipe                                 working environment. It is believed that the
                                                     technology may be substantially improved if
In cutting there is a risk of injury from            there is carried out steady and major pipeline
rotating machinery. The operator can also be         removal operations.
exposed to concrete and protective coating
30                                                                                Summary Report

Mercury and cadmium are the metals in pipelines and anodes believed to have a potential for
negatively impacting the environment. However, the estimated inputs of mercury and cadmium
from pipelines make up maximum 0.02% and 0.04% respectively of the total, annual anthropogenic
releases to the North Sea. The mercury from pipelines comes from aluminium anodes that may be
in use along some 30 km of buried or subsided infield pipelines installed before 1980. Significant
environmental impacts from other elements is not expected, and the consequences for the marine
environment of the different disposal options are considered very minor.

Calculations of energy use and emissions show that re-use and recycling of pipeline materials are
more favourable as regards impacts on the environment than leaving in place and production of
new pipes due to the level of energy consumption in pipe production. That conclusion presupposes
there is a re-use market and that quality requirements can be met. Among the other options,leaving
in place gives the lowest energy consumption and lowest emissions. Deposit on land requires large
areas and can cause local pollution.

                                                    abundance of species and individuals and high
6.1 North Sea bottom                                biomass. Brittle stars and crustaceans
      conditions                                    compose a large part of fauna.

The Norwegian sector of the North Sea is            Sleipner area: The bottom substrate at
dominated by relatively shallow and flat areas      Sleipner is mainly fine sand. Here depths vary
with a depth of about 100m beyond the               mainly between 100 and 125m. In the areas
Norwegian Trench, while 300-400 m depths            believed free of oil industry impacts a great
are found in the Trench and extend towards          variety of species has been found. Brittle stars
the Norwegian coast to the northeast and east.      make up a large part of epifauna.
The shallow part is at its broadest in the
southern region and gets narrower as it goes        Oseberg area: The bottom substrate at
northward. The bottom conditions in the             Oseberg mainly consists of sands with silty
relevant areas are described below, based on a      deposits in deeper water (depths vary between
Det norske Veritas report (DNV 1999).               100m and 200 m). Benthos are rich in species
                                                    and abundant in number. Brittle stars are very
                                                    common, except in the more contaminated
6.1.1 Habitats and species                          areas in close vicinity of platforms.
The kinds of sea bottom can roughly be split
between hard substrate and soft sediment,           Tampen area: Depths vary between 120 m
both of which can be subdivided in numerous         and 360 m and have thereby a more varied
classes. The ecological term "habitat" is often     bottom substrate from sands to silts. The
defined by physical characteristics. In the         finest-grained soils (high silt ratio) are found
marine environment these are bottom                 in the deepest water. The area's bottom fauna
topography, depth, hydrographic factors             is rich in species and individuals, with species
(salinity, temperature) current and kind of         variety highest in the coarse-grained soils. At
bottom. Several investigations demonstrate          the great depths are registered large colonies
that species richness increases as the ratio of     of Echiura and polychaetous annelids, and in
coarse-grained sediments in the bottom              shallower water great colonies of young
increases.                                          echinoderms.

Ekofisk area: The bottom substrate at Ekofisk       Haltenbank area. Characteristic of the areas
is primarily sand, and the area is relatively       affected by the oil industy are great depths
shallow (< 100m). A wide spectrum of species        and sediments composed mostly of silts and
has been identified with a moderate                 clays. In some places large gravel beds and
                                                    boulders have been found. The fauna is
The Final Disposal of Disused Pipelines and Cables                        31                    31

Figure 6.1: Sea bottom types of the Norwegian continental shelf south of 65° N based on date from
Statoil, the Institute of Marine Research and others. Diamicton is a moraine material with a great
range of particle sizes (DNV 1999).

dominated by Echiura and polychaetous                6.1.2   Distribution of pipelines and
annelids. Species abundance varies with                      cables by habitat
sediment type and depth and is at its greatest
                                                     Table 6.1 presents the relative distribution of
among the coarsest-grained sediments. In the
                                                     pipelines and cables on soft and hard bottoms.
Haltenbank area are also found large coral
                                                     It shows that the majority of both lie in soft
                                                     bottom habitats and what is more, a
Table 6.1:Estimated relative share of                significant share in areas with a great variety
pipelines and cables by length lying in the          of particle sizes (diamicton).
various Norwegian shelf habitats (DNV 1999)
 Habitat             Pipelines      Cables
                                                     6.2 Input of metals
 Soft substrate:
 - Fines                20 %          18 %           Underthe auspices of the North Sea Task
 - Silty sand           12 %          22 %
                                                     Force (NSTF) a great effort was made to map
 - Sand                 55 %          41 %
                                                     the state of the North Sea as marine
 Hard substrate:                                     environment, of which the latest unified
 - Gravel               2%             0%            presentation was published in North Sea
 - Stone/rock           2%             5%            Quality Status Report 1993 (NSTF 1993).
 - Diamicton            9%            14 %           The report shows that large areas of the North
 - Coral reef          <1%            <1%            Sea have concentrations of environmental
                                                     poisons that exceed North Atlantic back-
                                                     ground levels.
32                                                                                  Summary Report

                                                   alloys. Table 6.2 provides a general view of
As a general rule the negative impacts that are    the quantities of metals in Norwegian North
directly attributable to discharges to the North   Sea pipelines.
Sea are easily identifiable close to the
discharge outfalls, as for instance in estuaries   Table 6.2: Total amount of heavy metals, iron
and depositional areas like the Norwegian          and manganese used in Norwegian pipelines
Trench and parts of Dogger Bank. Few               as of January 1999, excluding Åsgard
impacts have been found in the northern and        Transport and Europipe II (Aquateam 1999,
central North Sea, except from localised           Dames & Moore et al. 1999c).
effects of the oil and gas industry. Impacts
increase and are more visible further south in     Material         Carbon steel       Duplex pipe
                                                                    pipe (tonnes)       (tonnes)
the North Sea and in the English Channel and
in the approaches to the coast and estuaries. A    Total             3 000 000             5 000
new environmental status report is expected at
                                                   Mercury                < 0,1                   0
the turn of the year 1999/2000.
                                                   Cadmium                    5                   0
The awareness of offshore oil industry metals      Copper                  210                -
inputs to the marine environment in the North      Nickel                 4 800              325
Sea has been directed to platform discharges       Chrome                  450             1 150
during the exploration and production phases.      Iron              2 932 500             3 500
Little attention has been paid to potential        Manganese            45 000               100
sources in the transport systems. In the
                                                   1) There is up to 2.5% copper in some types of
context of the pipeline and cable removal
                                                   Duplex steel. Information on the copper content in
assessment programme two studies were              the Norwegian pipelines of Duplex steels is not
made of this subject. (Dames & Moore et al         available.
1999, Aquateam 1999)
                                                   Input from anodes and from other sources is
To protect steel pipelines against corrosion       presented in table 6.3 The heavy metals input
sacrificial anodes (cathodic protection) of zinc   from anodes is seen to be very minor
or aluminium alloys are used in addition to        compared to other sources. The table shows
protective coatings. In the course of time the     that with the exception of zinc, the input from
anode material erodes (oxydises) and the steel     pipeline anodes is but 0.001- 1% of the
remains intact. Experience shows that anodes       accumulation from other sources.
last longer than their projected design
lifetime. When a pipeline is shut down, from       Analysis of the composition of North Sea
20% to 50% of its anode mass may be intact.        pipelines and cables has identified mercury,
As long as there is some anode left, the           cadmium, lead, chrome, copper, zinc, and
pipeline will not corrode even though shut         nickel as potentially the most
down. It is expected that the big gas pipelines    environmentally-hazardous materials used.
will be kept in service as long as possible and    These metals erode slowly and are toxic.
that there will be little anode left when they     Some of them are also bioaccumulative. They
are taken out of use. Anodes are a source of       come from human activities and from natural
continuous metals input in the water column.       sources. The ratio between natural and human
Some of these metals may in heavy                  provenance for some of them in the North Sea
concentrations have negative impacts on            is estimated in Aquateam 1999 at:
marine organisms.
                                                   Material         Natural       Anthropogenic
6.2.1 Presence and input of metals                 Mercury          >80%               <20%
      in the North Sea                             Cadmium           50%                50%
                                                   Lead                5%               95%
Various carbon steel alloys dominate in export
lines and rigid infield lines and are in use in    Mercury and cadmium are the metals in
7400 km or 96% of these, Åsgard Transport          pipelines and cables believed to have a
and Europipe II excepted. Of the heavy metals
nickel, chrome and copper are found in these
The Final Disposal of Disused Pipelines and Cables                            33                       33

Table 6.3: Estimated yearly discharges to the North Sea from PARCOM countries (tonnes/year)
(Dames & Moore et al 1999c).
                                  Cadmium          Mercury       Copper          Lead           Zinc

Atmospheric sources                    53             5,1          530           1330          4100
Inputs from land                       54              25         1500           1150          7650
Other accumulations                    71              19         1300           2700          7900
Inputs from Norwegian anodes        0,052           0,001*       0,018          0,026           139
Total                                 178           49,1          3330           5180         19736
*) Revised estimate year 2029 (Aquateam 1999).

potential for negatively impacting the                  importance for the total availability. But for
environment. This is due to negative                    some very vulnerable species the critical level
consequences through bioaccumulation and                of mercury and cadmium content is about to
concentration in the food chain. Sacrificial            be reached. Any increase of mercury in a form
anodes for corrosion protection are not used            that makes it available for organisms will
on flexible pipelines and cables, and the latter        inevitably lead to an increase of organisms'
do not contain elements believed to have a              mercury content over time. The bioavailability
potential of adverse environmental impact.              of particulate-bound mercury from natural
                                                        sources is expected to be lower than for
The local uptake of heavy metals and                    mercury in water solution.
spreading via the food chain is considered to
be more serious than geographical distribution          Piepline mercury comes from sacrificial
in water masses. Along buried pipelines there           anodes of aluminium on a few infield
may be heavy accumulations in the sediments             pipelines installed before 1980. It is not at all
near anodes. The sediments are also liable to           clear how much of these anodes remains. The
bind leaching materials and make them                   Petroleum Directorate's database shows that
unavailable for marine organisms. As a                  aluminium anodes have been used in a few
general rule particulate-bound heavy metals             pipelines at Ekofisk and perhaps also at
are less accessible for organisms than free             Statfjord. The kind of anode material used on
metal ions and organically-bound metals.                Statfjord pipelines is not recorded, but it is
Organisms that feed on sediments take up just           taken for granted that the anodes used were of
a small part of the total availability of heavy         aluminium alloys. Table 6.4 shows the
metals in the sediments, while the heavy                pipelines assumed to have anodes containing
metals at large in the sea are more easily              mercury. Such anodes have been used in 30
accessible. (Aquateam 1999).                            km of infield pipelines at the most, but not in
                                                        any export line.
6.2.2 More about mercury input
                                                        The calculation of the input of heavy metals is
Mercury is the most toxic of the heavy metals.          based on the rate of leaching from pipelines
It accumulates in the food chain. It is                 lying on the seabed. The pipelines believed to
estimated that the accumulation of mercury in           have aluminium anodes with mercury alloys
mammals has increased 2-3 times in the last             in the Ekofisk area are buried, while those in
20 years. Methyl mercury is particularly toxic.         the Statfjord area are believed to be wholly or
Investigations have shown that the                      partially buried. Much of the mercury released
bioavailability of dissolved methyl mercury at          by the anodes will thereby be particulate-
ingestion is nearly 100%. The consumption of            bound in the bottom sediments. When
seafood is one of the major paths by which the          removed these pipelines could release this
human organism is exposed to methyl                     mercury to the water masses. (Aquateam
mercury.                                                1999)

Most of the mercury accumulations in the                Based on the above it is estimated that 156 t
North Sea comes from natural sources. A                 of aluminium anodes have been used in
reduction in inputs from anthropogenic
sources is not expected to have any
34                                                                                              Summary Report

Table 6.4: Infield pipelines on steam before 1980 with aluminium alloy anodes that probably
contain mercury (Aquateam, 1999).
Operator                                                   Pipeline data
              From     To            On steam      Diameter       Length       Anode         Lifetime   Status
                                                   (inches)        (km)       distance (m)    years

Phillips/     2/7-C    2/4-R          01.12.79       12,75         12,3           12           20       shutdown
              2/7-C    2/7-R          01.12.79       10,75         12,2           12           20       shutdown
Statoil/      Stat-A   Stat.B-OLS     01.12.79        36            3,5           48           25       operating
              Stat-A   Stat.B-OLS     24.11.79        36            2,2           48           25       operating

Sum infield pipelines                                              30,3                                 operating
1) Anode material not reported, accepted that aluminium anodes were used.

Norwegian petroleum fields. Provided that                      expected to increase up to approx. 80 kg/year
mercury makes up 0.05% of the anode                            around year 2050. Compared to emissions by
material, the quantity of mercury used will be                 air and by land the amount is minor, see table
80 kg.                                                         6.3. The maximum input of cadmium from
                                                               pipelines will comprise 0.04% of
A good part of the anodes has already eroded,                  accumulations in the North Sea from
and the remainder is expected to be eroded by                  anthropogenic sources.
2100. It is calculated that there will be an
exponential increase of mercury released by
anodes on the Norwegian continental shelf                      6.3 Input of organic
from about 0.8 kg/year in 2029 (50 years after
laying) unto a maximum of 1.8 kg/year in                               compounds
2089. These amounts are relatively small
when compared to others, see table 6.3. The                    T here is a continuous input of organic
input of mercury from pipelines will at the                    compound pollutants to the North Sea. This
most constitute 0.02% of mercury                               chapter's presentation is limited to the organic
accumulating in the North Sea from                             compounds that are believed to have the
anthropogenic sources.                                         heaviest impact, total hydrocarbons THC and
                                                               polycyclic aromatic hydrocarbons PAH.
Since 1985 the input of mercury in the North                   (Dames & Moore et al. 1999c. Aquateam
Sea has been reduced by 90%. 5 tonnes of                       1999)
mercury was released to the atmosphere and
the sea in 1985; by 1998 the emissions had                     6.3.1       Input of THC from pipelines
been reduced to 466 kg. Industrial discharges
constitute almost half of present mercury                      The highest values of THC are recorded near
emissions. The remainder comes from                            trafficked estuaries and oil platforms. Oil-
crematories, tooth fillings, waste incineration,               based mud was discharged without prior
batteries and other products. Mercury is one                   washing in the 1970s and 1980s, and drill
of the toxics with the highest priority of the                 cuttings and mud on the sea bottom are still a
environmental authorities. Their goal is a                     source of THC pollution. The total discharge
major reduction of mercury emissions by year                   of oil to the North Sea is 86,000 - 210,000
2010 at the latest. (SFT 1999)                                 t/year. See table 6.5.

                                                               Even after flushing and pigging, pipelines can
6.2.3       More about cadmium inputs                          still contain residues of low viscosity
The input of cadmium from pipelines comes                      hydrocarbons. It is estimated that 500 t of oil
from erosion of zinc anodes, which can                         may remain in North Sea pipelines, of which
contain 0.03% - 0.05% cadmium, and is                          200 t in the Norwegian sector, corresponding
The Final Disposal of Disused Pipelines and Cables                            35                    35

to 200 kg per km oil or condensate pipelines.           figure up to 15% of coal tar or asphalt content
Inputs of residual hydrocarbons to the water            is composed of PAH compounds. This gives
column will be insignificant and are not                an overall estimate of 20,000 t/PAH in
considered to be a threat to the marine                 protective coatings on North Sea pipelines. It
environment. (Dames & Moore et al. 1999c).              is presumed that when sea water gets to a
                                                        PAHiferous coating, the coating may quickly
6.3.2        Inputs of PAH from pipelines               be transformed into particles, and a certain
                                                        amount will leak over a long period of time
There are few measurements of PAH                       into the sea. The water quality in ports where
concentrations in the North Sea, and the few            sediments are PAH contaminated show high
that exist show great variations. In certain            PAH concentrations in the water column. It is
cases PAH can be acutely toxic for marine               to be expected that PAH compounds in
organisms and they can also be                          marine sediments will have low
bioaccumulative. Several tar derivatives,               biodegradation because of low oxygen and
benzo(a)pyren, are carcinogenic.                        temperature. Since PAH is only minutely
                                                        water soluble, the worse environmental hazard
Table 6.5: Total input of oil to the North Sea          will most likely be in particulate material
in tonne/year (NSTF 1993)                               eaten by organisms. The amounts concerned
                                       Amount /year
                                                        are not thought to be any threat to the marine
                                                        environment. (Aquateam 1999)
    Natural seepage                            1000
    Atmosphere                           7000-15000
    Rivers/ land drainage               16000-46000     6.3.3   Leaching of plastics
    Sewage                               3000-15000
                                                        Infield pipelines may have a protective and
    Refineries                                 4000
    Oil terminals/other land eceptions         1000     insulating outer plastic layer. Plastics contain
    Coastal industry                     5000-15000     phthalamates, softeners, which investigations
    Oil/gas production                       29000*     show biodegrade easily in aerobic conditions
    Sewage sludge                        1000-10000     but, according to some studies, slowly in
    Dumped industrial waste               1000-2000     anaerobic environments (i.e. in sediments and
    Dredging                             2000-10000     deep in earth and ground water.) Biological
    Ship operations                       1000-2000
                                                   **   decomposition will dominate on the whole.
    Accidents/ illegal discharges
    from ships                                          Few pipelines with coatings containing
    Totalt                            86000-210000      polypropylene PP or PVC have been used in
                                                        the North Sea.
      20-30 x 103 t/year in 1984-1990 (PARCOM
      estimates).                                       In the Petroleum Directorate's database there
      The region, except the BeNeLux-countries.         is no information on PVC in pipelines. There
                                                        are 563 km of pipelines covered with PP.
The main source of PAH from pipelines will              Supposing 10" pipeline diameter, 15 grams a
be from corrosion-protective coatings made              day will leach out. It is difficult to estimate
from asphalt or coal tar. The coating will              how long the leaching will last, but it will
begin to degrade when the steel is eaten up by          dwindle down eventually.
internal corrosion or the external protective
concrete coat is damaged. There are no                  It is presumed that when sea water gets to the
records of concrete durability, but it is known         plastic, it may quickly be transformed into
that concrete in the sea decomposes very                particles. There will also be some longtime
slowly. The point in this connection is when            leaching into the sea. Since there are small
steel rusts through and through and when the            amounts of plastics in use, and since
concrete is damaged, such that the                      phthalamates leach mainly out from new pipes
PAHiferous coating begins to deteriorate.               and biodegradability in the anaerobic
                                                        environment is low, it can be assumed that the
Detailed information on the PAH content in              effect of leaving the plastic is insignificant.
protective coatings is lacking, but estimates           (Aquateam 1999)
36                                                                                                     Summary Report

Table 6.6: Calcualted energy consumption and CO2 emissions per kilometer pipeline and cable
(RC Consultants 1999)
                                                            36” pipeline            8” pipeline           4,5” cable
                                                         Energy       CO2         Energy    CO2        Energy     CO2
                                                           GJ           t          GJ         t         GJ          t
 Leaving in place *                                           32            2,4     190           14         -           -
 - re-cycling                                              8130         350        2180       150       1270           130
 - re-use as piles and foundation elements                 1600         120        1780       130            -           -
 - re-use as structural elements and pipe
                                                           2660         260        1590       120            -           -
 - deposit on land                                         1580         120        1700       130        840           130
 Re-use at sea                                             5680         530        4420       330            -           -
 Producing and laying new pipe                            19730        1360        5970       420            -           -
*) The energy consumed in severing pipe and securing loose pipe ends is identical for all options. The figures present
   averages and for the sake of comparison the 36" pipeline is 100 km long and the 8" pipeline is 5 km long.

                                                                   presupposes that the pipeline in question can
6.4 Other environmental                                            be qualified for re-use and that there is a need
        impacts                                                    for which the pipeline's specifications and
                                                                   remaining lifetime are suitable. Big export
The various disposal options can affect the                        lines as a general rule serve many fields and
outer environment in various ways. Energy                          do so over the longterm. It is not considered
consumption and emissions are discussed in                         likely that a used export pipeline will find a
chapter 6.4.1 and direct impacts on the marine                     new application of its former use.
environment and habitats in chapter 6.4.2.
                                                                   On the scale of energy use, waste production
                                                                   and emissions re-use at sea is the best solution
6.4.1     Energy consumption and                                   for the environment. The less transportation
          emissions                                                and reworking is required, the more
A separate study handles the environmental                         advantageous re-use at sea is compared to
impacts of the disposal options. Energy                            other disposal options.
consumption, emissions to the atmosphere and
to the marine environment, fresh water and                         Where re-use at sea is not possible, re-use on
waste generation are the criteria. There is no                     land gives lowest energy use and emissions.
consideration of which disposal option in the                      In this case too the new use with minor needs
total picture is the most preferable or                            for reworking, modification and transportation
probable. Cost, safety and operational factors                     is the best from the environmental point of
have not been considered either. (RC                               view. A major reworking of the pipes will
Consultants 1999). The following are                               lead to a substantial waste production and
evaluated:                                                         discharges to sea and fresh water.

 36" export line (100 km)                                         If there are no good re-use possibilities,
 8" infield line (5 km)                                           recovery of the steel can be a suitable
 4.5" combined cable (5 km).                                      solution. Recycling steel from pipelines is
                                                                   done with much less energy, waste generation
Table 6.6 shows energy use and CO2                                 and emissions of CO2, SO2, and VOC than
emissions of the disposal options described                        production of new steel. Emissions of N0x
and assessed in the study.                                         and dust increase, compared to new
                                                                   production. On condition there are real uses
Global experience of pipeline and cable re-use                     for them, re-cycling of concrete materials can
is very limited, see chapter 4.3. Re-use at sea                    also be an option. Glassfibre-reinforced
The Final Disposal of Disused Pipelines and Cables                         37                     37

asphalt lacks a recovery method and will thus        pipeline route and for as long as it takes the
become hazardous waste on a large scale. See         disturbed habitat to adjust to the changed
as well chapter 4.2.2.                               environment and reconstitute itself.

Deposit proves to be the worst option, account       There will be no impact from pipelines that
taken of the environmental cost of the               were trenched and naturally covered.
replacement materials, primarily steel and           Observations indicate that pipelines on sand
concrete. If nonetheless deposit is chosen,          bottoms will be wholly covered or buried
leaving in place gives the lowest energy use         within 10-15 years after being laid.
and emissions to air and sea. Deposit on land
requires large areas and may cause pollution         On all types of bottom the covering of
in fresh water recipients.                           exposed pipelines or the removal of rock-
                                                     dumped pipelines may cause lasting, local
6.4.2   Impacts on the marine                        changes of habitat.
        environment and habitats
                                                     Where there are soft bottoms with a thin
Colonies of benthic organisms are vulnerable         sediment layer, pipelines or rock fill will not
to impacts from dumping, dredging, cuttings          acquire a natural cover. An exposed pipeline
piles, frequent trawling, loss of oxygen to          that is left in place will serve as an artificial
algae blooms, and input of organic                   habitat for hard bottom organisms for its
compounds and other sources. But because             entire lifetime. The same is the case for
most species have short reproduction cycles,         pipelines that are rockdumped. Such bottoms
stocks are capable of rapid regrowth once the        are found in great areas in the northern part of
source of pollution is eliminated. The longer-       the Norwegian Trench, especially on the
lived species need more time to regain their         eastern slope as well as northern parts of the
normal abundance, and even though an impact          North Sea and the continental shelf off Møre
may have little effect, the natural species          and Trøndelag.
composition of the ecosystem is most likely
adversely affected. (NSTF 1993, SFT 1994)            The area taken over by pipelines is very little
                                                     in relation to the total NCS area and the total
A commissioned study looks at possible               consequences for bottom habitat are seen to
impacts on water quality, pelagic organisms,         be insignificant.
sea bottom topography, sediment quality,
benthos and fish resources in general without
distinction made among the various types of          6.4.3 Organic material
habitat. (Dames & Moore 1999c). A                    Some organic material (fouling) on pipelines
supplementary study takes up the                     and cables will be taken up and transported to
consequences for different habitats of physical      land along with them. Neither the extent nor
disturbance for more thorough analysis, with         the use of this kind of material has been
emphasis put on presumed differences in              assessed.
restitution time requirements. (DNV 1999)

The general conclusion is that there is an area      6.5 Impacts of the different
no more than 100 m wide on either side of a
pipeline that can likely be impacted regardless             disposal options
of the disposal option, and any impacts will
on the whole be insignificant. Rockdumping           The following factors present themselves as
pipes left in place can bring about local            most important for assessing impacts.
changes of bottom topography.
                                                        use of aluminium anodes
The area's sediment type, the way the pipeline           energy use and emissions
is laid, and what disposal alternative is chosen         bottom conditions along the pipeline
determine local consequences for bottom                  route.
habitat. The impacts are limited to local
disturbances in a narrow belt following the
38                                                                                   Summary Report

6.5.1   Leaving in place                              potential of negative impact. Since impacts
                                                      from emissions to the marine environment are
Impacts on the marine environment                     considered minor even if pipeline and cable
Mercury and cadmium are the metals from               are left in place, removal makes no great
Norwegian pipelines that may have negative            contribution to the marine environment in the
environmental impacts. Inputs are limited and         form of reduced inputs of potentially
no leaching of metals is expected to have a           hazardous substances.
significant, adverse environmental impact.
                                                      Other environmental impacts
Of organic compounds THC and PAH are
                                                      If pipelines are to be removed, the lowest
seen as the most hazardous. THC inputs from
                                                      level of emissions and least waste will be
pipelines will be insignificant and are not
                                                      realised by re-use or steel recycling compared
considered to have a noticeable effect on the
                                                      to new production. NOx and dust emissions
marine environment. The main source of PAH
                                                      increase on the other hand. That conclusion is
is the corrosion-protective layer made of
                                                      contingent on a market for these uses.
asphalt or coal tar. Since PAH is water soluble
                                                      Extensive reworking of the pipelines may lead
only to a minor degree, it will be a major
                                                      to large quantities of wastes and emissions to
environmental hazard only when organisms
                                                      the marine environment and fresh water. It
feed on particulate material.
                                                      will also be produced wastes for which there
                                                      is no known recovery method. Concrete
If a pipeline or cable is to be left in place after
                                                      materials may also be recovered, if there is
safeguarding by trenching, burial, rock-
                                                      relevant use for them. Deposit on land
dumping or other means of cover, these
                                                      requires a lot of space and may cause local
measures can impact habitats locally along the
                                                      pollution and contamination of fresh water.
pipeline route, but the area disturbed is very
                                                      Habitat restitution time is short when exposed
                                                      pipelines and cables are removed. The
Altogether the impacts on the marine
                                                      removal of buried, covered or subsided
environment of pipelines and cables left in
                                                      pipelines on a soft bottom may have local
place are found to be very minor.
                                                      effects for habitat along its alignment. The
                                                      disturbed area is small, and the consequences
Other environmental impacts                           are seen to be insignificant.
Calculations of energy consumption and
emissions show thatleaving in place gives the         6.5.3   Re-use at sea
lowest direct emissions both to the
atmosphere and the marine environment. If             Impacts on the marine environment
account is taken also of the environmental            Re-use at sea usually entails the postponement
costs incurred by production of equivalent            of the final disposal decision. For the time the
materials, primarily steel and concrete,              pipelines and cables remain on the bottom,
leaving in place entails high emissions.              their environmental impacts will be the same
                                                      as in the operative phase.
Temporarily left in place
During the time that pipelines and cables             Other environmental impacts
remain on the sea bottom, their                       If there are re-use possibilities at sea for
environmental effects are like those during the       pipelines, energy consumption and emissions
operational phase.                                    to air will be much lower than for producing
                                                      and laying new pipe. NOx emissions are an
6.5.2   Removal                                       exception, as those connected to re-use at sea
                                                      will exceed those connected to leaving in
Impacts on the marine environment                     place and new production. The less
Removing pipelines or cables reduces                  transportation and reworking are necessary,
emissions to the marine environment of heavy          the more advantageous is re-use compared to
metals and organic compounds with a                   the other disposal options. It is not likely that
                                                      cables can be directly re-used.
The Final Disposal of Disused Pipelines and Cables                           39                      39

Trawl and purse net are the most important fishing gear used in the North Sea. It is only
bottom gear like trawl and bottom seine that are impacted by pipelines and cables. A
pipeline or cable buried in a stable bottom carries no risk for trawling. A pipeline lying
proud without free spans or external damage can cause some operational interference in
trawling areas, but as long as it has no external damage, the extent of the interference will
be the same as in the operating phase. Should a pipeline left in place be seriously damaged
or free spans be developed, the operational interference could be serious and entail loss of
grounds and catch. Rockdumped pipelines can cause serious problems and possible loss of
grounds and catch for industrial trawlers and shrimp trawlers.

7.1 Important fishing                                Most Norwegian whitefish catches of cod
        grounds and catches                          fishes by trawling consist of saithe and rise
                                                     and fall much from year to year. In recent
This chapter describes the distribution of           years landings have shown a weak rise
catches in the North Sea in relation to fishing      compared to remote years. (IMR 1998)
methods and fishing grounds. It builds on the
fisheries thematic report that is part of the
North Sea Regional Environmental Statement
which was presented in spring 1999 by the
Norwegian North Sea operators. Use has also
been made of a supplementary report on
trawling’s geographical distribution. (Agenda
1999a and 1999b)

Norwegian North Sea fisheries statistics are
arranged by statistical areas and locations as
shown in figure 7.1 The most detailed
statistics apply to trawling and purse net
seining, of which there are data on both area
and location levels, the latter in area extent
equal to 6 oil blocks. For other gear there is
only statistical area data.

7.1.1   North Sea catches
Table 7.1 shows 1990-98 reported catches
from the North Sea by gear. The 1996-98
statistics are provisional. 30% of all
Norwegian catches in the period 1990-98
came from the North Sea. The table shows
                                                     Figure 7.1: Fisheries statistical areas
that trawl and purse seine fisheries are the         (område = statistical area, lokalitet = location)
most important, accounting for 94% on the
average of North Sea catches in 1990-98.             The industrial trawl fisheries evolved
                                                     positively between 1990 and 1998. It is
Trawl fisheries include such different fish as       typical for industrial trawling that the ratio
whitefish, prawns and industrial fish (sandeel,      between sandeel and Norway pout/blue
Norway pout and blue whiting). Catches are           whiting varies over time. In years when there
allocated by these fisheries in table 7.2.           is a lot of sandeel, trawling concentrates on it,
40                                                                                                    Summary Report

while when there is a lot of Norway pout and          blue whiting, sandeel catches drop.
Table 7.1: Average Norwegian deep sea catches in the North Sea 1990-98 by gear type alongside
total Norwegian catches in all sea areas. All catches in 1000 t round weight. Provisional figures
for 1996-98. (Source: Directorate of Fisheries’ s delivery receipt statistics)
Statistical area                                          North Sea                                   Total Norwegian
                                        2)                                                                       2)
                                Trawl               Net                Other            Sum              catches
Area 08                           121,6             124,7                   9,7          256,0
Area 09                             0,4              16,0                   4,8           21,2
Area 28                            62,4              87,1                  12,6          161,1
Area 41                           121,4              42,0                   0,8          164,2
Area 42                            11,2              39,2                  12,7           63,1

North Sea as unit                 317,0             309,0                  39,8          665,6                2253,8

1) The North Sea defined as statistical areas 08, 09, 28, 41 and 42, see figure 7.1.
2) Not including prawns or other shellfish.

Table 7.2: Norwegian trawl fisheries in the North Sea 1) 1990 – 1998 by main species. All catches
in 1000 t round weight. Provisional figures for 1996-98.(Source: Directorate of Fisheries catch log
Statistical area            Whitefish trawling        Prawns                           Industrial trawling
                             (mostly saithe)                                Sandeel      Norway pout         Blue whiting

Area 08                               9,1                 1,5                  50,0           59,2               13,7
Area 09                               0,1                 1,3                   0,0            0,0                  -
Area 28                              10,2                 0,0                  20,6           29,4               14,2
Area 41                               1,4                 0,0                 120,5            0,3                  -
Area 42                              12,2                 0,0                   0,1            3,2                0,4
Average 1990-98                      33,1                 2,8                 191,2           92,1               28,4

1) The North Sea defined as statistical areas 08, 09, 28, 41 and 42, see figure 7.1.
2) All catches counted as Norway pout and others until 1995. Average is calculated for 1996-98.

Figure 7.2 shows the most important grounds                      direct bottom trawling for whitefish in these
for industrial trawling in the North Sea and                     waters.
catches graded by the individual statistical
locations. Corresponding figures are made for                    Trawling for whitefish, saithe for the most
whitefish and prawn fisheries. (Agenda                           part, takes mainly place from about 160-170
1999a)                                                           m deapths on the slope and westward over the
                                                                 edge. The banks west of the edge are the
The statistics presented in this chapter show                    principal grounds for this fishery. Although
catches. When studying the figures it is well                    whitefish are traditionally caught in the area
to keep in mind that the prices paid for the                     by both industrial trawlers and the big stern
various kinds of fish differ enormously. The                     trawlers, industrial trawlers have not taken
kilo price paid for saithe in the country as a                   part in the last few years, a changeover that
whole in 1990-98 was from 4 to 7 times the                       should be seen in the light of very good
price paid for Norway pout.                                      industrial fish catches.

7.1.2     More about whitefish trawling                          The most important whitefish trawling
Whitefish trawling takes places down to 300
m depth in the North Sea. In the deeper parts                    The biggest whitefish catches in the 1990s
of the western slope of the Norwegian Trench                     have been in the areas around Statfjord and
some whitefish are caught with bottom gear,                      Oseberg, traditional fishing grounds known as
mostly ling and cusk taken as industrial                         Tampen and Viking Bank respectively.
trawling bycatches. There is seldom any                          Foreign fishing
The Final Disposal of Disused Pipelines and Cables                         41                     41

Foreign boats fish for whitefish in much the         whiting catches until 1995 were reported as
same areas as the Norwegians. The exception          Norway pout and others.
is that EU boats in the North Sea fish more
often for flounder. These fisheries use either       Industrial trawling for sandeel
ordinary gear or a beam trawl and take place
                                                     The sandeel fishery takes place in clearly
mainly in the southern North Sea and in the
                                                     delimited areas, which is due to the depth and
Norwegian sector south of the 59th parallel.
                                                     bottom conditions that the sandeel requires.
EU boats fish also for more cod and haddock
                                                     Practically no sandeel is caught in water
than Norwegians on the west plateau in the
                                                     deeper than 110 m, and the most intensive
Norwegian sector of the North Sea with
                                                     fishing is usually found in 100 m although
bottom trawl and bottom seine.
                                                     there are exceptions. A typical trait of sandeel
                                                     ground is that from one year to another there
7.1.3   More about industrial trawling               may be no sandeel, only then to be revived
Figure 7.2 shows the main industrial trawling        and be fished intensively. There has
grounds in the North Sea.                            practically never been good fishing in all
                                                     sandeel grounds in the same year.
The Norway pout fishery
                                                     Sandeel is fished when it hovers just above
Industrial trawling for Norway pout goes             the seabed, which means the trawl gear used
along the slope of the Norwegian Trench from         has a lighter ground line than that used in
south to north. The characteristic of the            trawling for Norway pout. A new type of
fishery in this area is that the fish often stand    ground line developed not long ago, the rock
at a definite depth and trawling stays at that       hopper, has led to an expansion of sandeel
depth as it follows the slope. The main fishery      fishing grounds by making it possible to trawl
occurs most often at 300 m depth and moves           over rocky bottoms.
westward, up the slope toward shallower
water. Not much Norway pout is taken in              The main industrial trawling grounds
water shallower than 130-140m. Between
Heimdal and Balder there used to be trawling         Figure 7.2 shows the biggest industrial trawl
for Norway pout, but no sizable catches have         catches taken on the slope northward from the
been reported in latter years.                       59th parallel, where Norway pout is the most
                                                     important fish. West of Oseberg on the Viking
The Fisheries Directorate says that from one         Bank there is trawling for sandeel. South of
year to another there may be sporadic fishing        the 58th parallel on the shallow banks lying
for Norway pout eastward towards the Troll           west and southwest of the slope big catches
field. There is, however, no regular fishing for     are made, with sandeel the most important
Norway pout at such great depths as found in         fish of the area..
the Troll area. The fishery makes use of trawl
gear that is heavily weighted down forward to        7.1.4   More about prawn trawling
get as close to the bottom as possible.
                                                     The principal grounds for prawn trawling in
                                                     the North Sea are along the bottom and lower
The blue whiting fishery
                                                     western slope of the Norwegian Trench.
Along the slope between the 60th and 62nd            Trawling is done in 250-300 m depth and in
parallels there is also industrial fishing for       winter higher up at 200 m. The biggest
blue whiting. Blue whiting is found as far           catches are taken in grounds on the slope
south as Egersund Bank but south of the 60th         under the Edge. Nearer to shore Skude
parallel it has so far been too widely scattered     Ground off Karmøy and Kvitsøy is the most
to support a commercial fishery. Fishing for         fished, and there is also nearshore trawling for
blue whiting mainly occurs at 280-350 m              prawns west of Øygarden.
deapth with the largest catches down to 300
m. From time to time there may be good               The main prawn trawling grounds
fishing for blue whiting in the Troll area. It is
                                                     The biggest prawn catches are taken in the
not possible to read historical blue whiting
                                                     locations at the bottom of the Norwegian
catches in the fisheries statistics, since blue
42                                                                               Summary Report

Figure 7.2: Important North Sea industrial trawling grounds. Average catch by statistical locations
1990-98 (Source: Directorate of Fisheries and Southern Norway Trawler Society)
The Final Disposal of Disused Pipelines and Cables                                                                            43                            43

Trench south and southeastward from about                                                                No       Fishing in pipeline area
59°N in direction of Skagerrak.
                                                                                                                 Fishing with bottom trawl
7.1.5    More about nephrops trawling
Nephrops trawling is a relatively new fishery                                                                    Somewhat/very important
and is practiced along the western slope of the                                                                       fishing area
Norwegian Trench from 59°30’N towards the

                                                                                                                                                            May cause serious operational problems for trawling
south. The grounds where nephrops are fished

                                                      No operational problems of any consequence
are pretty much co-extensive with the prawn
grounds, but nephrops trawling is also done                                                                                    No

farther west in shallower water. The fishery                                                                            Rockdumped
takes place by and large in depths between                                                                          Yes
130 and 280 m, with most done in the deeper                                                                                                    No

water, 240-260 m.                                                                                                Securely          Wholly/partially
                                                                                                                 covered              exposed
                                                                                                                 Yes     No            No      Yes

7.2 Significant factors for                                                                        Yes
                                                                                                                       Stable bottom
        fisheries                                                                                                                       No

In the context of the impacts for fisheries of                                                           Whitefish trawling             Free spans
the individual disposal options, several factors
are prominent:

 the kind of fishery and its extent in the                                                                                            No external    No
                                                                                                                                     damage on pipe
  pipeline area                                                                                                                                Yes
 what has been learnt from trawling along
  pipelines                                                                                                    May cause some operational
                                                                                                                 problems for trawling
 what has been learnt from trawling over
  rock fill
                                                     Figure 7.3: Decisive conditions for evaluating
 burial and subsidence
                                                     impacts of pipelines and cables on fishing
 free spans                                         (Agenda 1999b)
 the condition the pipeline is in.
Figure 7.3 provides a list of factors relating to    made. This section will therefore concentrate
pipelines and cables on the sea bottom of            on conditions relating to trawling in areas of
significance for fisheries.                          pipelines and cables.

                                                     To find out what problems may be created for
7.2.1    Fishing in pipeline areas                   bottom trawling it is necessary to know the
Chapter 7.1.1 makes clear there is very              extent of the fishery in the area in question. It
limited net and line fishing in the North Sea,       is hardly possible to draw up objective criteria
Norwegian sector, where the main gears are           for classifying fisheries by degree of
trawl and purse net. A pipeline does not             importance: little, somewhat, very. The
hinder fishing with conventional (passive)           baseline report on trawling in the North Sea
gear like net and line or fishing with purse net     defines statistical locations as of little
or pelagic trawl once a pipeline has been laid.      importance when in 1990-98 the annual
Fisheries using these gears are not affected by      catches were on the average less than 500 t of
the choice of any of the disposal options.           whitefish, 2000 t of industrial fish or 100 t of
                                                     prawns. Se figure 7.2. (Agenda 1999a).
Only trawling and bottom seining can be
affected by sea bottom pipelines and cables.
Norwegian bottom seining in the North Sea is
of minor importance, and there are no data
available to show where catches are
44                                                                                      Summary Report

Table 7.3:Summary of data from trawling trials over 40” pipeline in 1993, consisting of 98 of
altogether 111 crossings. (IMR 1993).
Trawl type                  Crossing angle                             Trawl door lands on back
                 30     15-30     <15         Total        30     30-15      <15        Total
Industrial        30         23         3           56            -          6          2           8
Prawn             10         5          1           16            -          1          -           1
Nephrops          17         9          -           26           1*)         -          -           1

Total             57         37         4           98           1           7          2          10
*) Crossing angle 35.

7.2.2   Fishing along pipelines                          Trawling trials in 1988
It is well documented that sea bottom                    In 1988 were held trials crossing the 28”
structures aggregate fish, and this applies also         Statpipe and 30” Oseberg pipelines with
to a degree to pipelines. There are a few                standard bottom gear. Among the conclusions
Norwegian boats that fish with nets and trawl            was that crossing at an angle of 45° or more
along pipelines. This is done usually when               greatly reduced the risk of hooking and
there are no better opportunities elsewhere.             tearing gear. Crossing at flatter angles entailed
IMR investigated the availability of fish along          an increased risk.
North Sea oil and gas pipelines for the
purpose of determining whether fish in                   Trawling trials in 1993
commercial quantities aggregate along the
                                                         IMR undertook more trials of pipeline
pipeline, creating basis for a profitable
                                                         overtrawling in May 1993 with industrial,
fishery. (Nøttestad 1999)
                                                         prawn and nephrops trawls on the 40”
                                                         Zeepipe pipeline. The most important results
The project report concludes that there is no
                                                         are summarised in table 7.3. The trials
measurable aggregation effect of commercial
                                                         demonstrated that trawl doors encountering
fish along the pipelines in the North Sea. The
                                                         the pipeline at a higher angle than 30° passed
catch rate achieved in the project’s fishing
                                                         over without interference. If the crossing
trials gave no basis for a commercial fishery.
                                                         angle was less, there was an increasing
The project was carried out in a short time in
                                                         likelihood that the first trawl door to
spring 1998, and there may be seasonal
                                                         encounter the pipeline fell back against it and
                                                         slid along, such that the distance between
                                                         doors was shortened and the net opening
7.2.3   Experience of trawling over                      reduced. According to the report the doors
        pipelines                                        regained position in 2-7 minutes. When a
According to fishing skippers, trawling over             trawl door has fallen on its back, it is very apt
cables and pipelines no larger than 16” in               to go fast in a soft bottom or get lodged under
diameter is no problem. (Agenda 1999b)                   a free span.
Many of them have been buried for protection
against trawl doors, and that may be a factor            In industrial and prawn trawling the trawl
in the skippers’ opinion. No overtrawling trial          doors did not land on their backs when the
of small pipelines has been made.                        crossing angle was over 30°. When the
                                                         crossing angle was between 15° and 30° the
There is however a difference of opinion as to           trawl door fell over in 1 of every 4 tries.
the extent of interference that large pipelines          Under 15° it fell over half the time. The
can cause trawling. Several trawling trials and          smallest trawl doors crossed the pipeline
investigations have been undertaken to cast              immediately they encountered it regardless of
some light on the subject, the latest in 1988            the angle, with one exception. (IMR 1993)
and 1993 under the auspices of the Fisheries             The trawl crossing trials were conducted on
Directorate and IMR.                                     hard bottoms. No trials have been held to
                                                         clarify how trawl doors performed when they
The Final Disposal of Disused Pipelines and Cables                         45                    45

lie on their backs on soft bottoms after             that the lighter gear with weighted ground line
crossing.                                            was not suitable for crossing rockdumped
                                                     Prawn trawl trials in 1998
The overtrawling trials showed that trawling
across large pipelines caused much less              In the summer 1998 brief trials were held to
interference than expected. Experience has           test overtrawling rockdumped sections of the
shown that pipelines on the whole do not             Sleipner condensate pipeline, which is in an
cause any loss of access that may result in          area of intensive prawn trawling. The
reduced catches. Depending on the angle of           overtrawling was carried out by a prawn
crossing the interference that overtrawling          trawler with daily experience from the area
encounters will vary. Examples of                    and its trawl gear was fitted with a weighted
interference are course adjustments to cross a       ground line. The trials indicated that
pipeline, the need of greater awareness when         overtrawling could be harmless if the trawl
crossing in case a trawldoor might go fast and       was rigged as for usual demersal fish trawling.
reduced freedom of navigation when fishing           (Statoil 1998) It is noteworthy that the rock
boat density is high. There is no material to        fill in these trials had the top layer composed
quantify such problems.                              of gravel in the 1”-3” diameter range and the
                                                     prawn rigging was lighter forward than the
7.2.4   Experience of overtrawling                   industrial trawl rigged for Norway pout. It is
        rockdumped pipelines                         not sure that these observations are significant
                                                     for industrial trawling, but they do show that
Export pipelines as a general rule are laid          overtrawling a rockdumped pipeline may
proud. Along some sections they are rock-            differ according to circumstances from the
dumped for support or stability, and that is         IMR trials findings.
also the case where there are pipeline
junctions. Rock fill can be dragged off a rock-      Boat size
dumped section by bottom fishing gear and
spread about, exposing a pipeline or cable.          In the same area where industrial and prawn
                                                     trawlers had problems crossing rockdumped
Rock fill along a pipeline can be a source of        pipelines in the 1997 trials, whitefish trawlers
problems for bottom trawling. Usually in             were towing their gear without any reported
whitefish and industry trawling the cod end          difficulty. These boats towed trawls that were
does not touch the bottom. Rocks may enter           made of heavier net material and, not least
the net when the trawl crosses a rockdumped          important, had rock protective netting and
pipeline and cause heavy wear-and-tear, and          much bigger bobbins that were used in the
when industrial fish are unloaded, there is a        trials. Nor has there been any reports since
risk that rock will be pumped out with the           that time from whitefish trawler skippers of
catch and damage the pump. Rock in the cod           any problems relating to rockdumped
end can also crush fish. All in all rockdumped       pipelines in the North Sea.
pipelines can cause the loss of fishing
opportunity and add costs.                           Summary
                                                     Pipelines and cables that are securely covered
Institute of Marine Research (IMR) trials in         cause no more serious interference after they
1997                                                 have been shut down than during their
In the summer 1997 IMR conducted another             operative phase. It has been noted above that
overtrawling experiment to assess the risk           there are no categorical observations about the
potential of rockdumped pipelines for bottom         impacts of pipeline rock fill. No noteworthy
gear. (IMR 1997) The trials demonstrated             interference seems to be caused whitefish
damage to prawn trawls and to industrial             trawling with big North Sea trawlers, but trials
trawls. But an industrial trawl equipped with        have not been held, so documentation is
bobbins gear was less vulnerable than                lacking. As for industrial trawling and prawn
industrial and prawn gear with a lead-               trawling the trial results are ambiguous.
weighted ground line. The conclusion was
46                                                                                 Summary Report

Nonetheless the impacts of rockdumped               Going fast with a trawl door in a free span
pipelines constitute today probably the most        entails a serious safety risk. On the Norwegian
serious problem at the trawling-pipeline            shelf no dramatic incident of going fast in a
interface. It therefore seems necessary to carry    free span is known. But on the British shelf a
outmore trials to clarify the significance of       trawler capsized and sank in March 1997 after
rock dumping and the implications with              having lodged a trawldoor inside a free span
regard to rock fill form, size and composition.     on a 30” pipeline. In the British sector of the
                                                    North Sea operators and authorities are
7.2.5   Burial and subsidence                       working to map the state of pipelines in
                                                    relation to tendency to free span by the end of
As already mentioned, about 90% of infield          1999. (Scanews)
lines and cables are either buried or covered
over, but only a small percentage of export
                                                    7.2.7   Pipeline condition
lines are buried. Pipelines and cables that are
securely buried do not interfere in any way         The conclusions in chapter 7.2.4 on
with fishing.                                       overtrawling apply so long as pipelines are
                                                    intact without external damage. In the
On soft bottoms pipelines and cables subside        longterm pipelines can be damaged by
and sink as time goes by. The degree of             corrosion and external events and eventually
subsidence depends on the local bottom              degrade. Small pipelines and cables lying
conditions. Experience of Statpipe shows that       exposed are in principle more vulnerable for
pipelines can sink up to half their diameter in     damage than bigger, sturdier pipelines. A
the course of 3-5 years. Subsidence facilitates     pipeline or cable with external damage lying
the passage of trawl doors. Any pipeline that       exposed on the seabed or halfway subsided
is partially or wholly subsided beneath the         may entail the risk for gear of being snagged
mudline is less exposed to damage than a            or torn. In areas of bottom trawling and
pipeline lying up on it.                            bottom seining this can amount to serious
                                                    interference. When skippers are aware of
In parts of the North Sea there is a constant       these conditions, they will avoid the
flux of bottom sediments under the influence        hazardous sections of pipeline and cable and
of waves and currents. In areas with strong         will thereby lose fishing grounds and have
bottom currents the lie of pipelines and cables     reduced catches.
will change over time. There is less sediment
transport in the Norwegian sector than in the       7.2.8   Conclusions
southern and southeastern parts of the North
Sea.                                                It is not likely that existing pipelines cause a
                                                    loss of catches for Norwegian North Sea
                                                    trawlers. This is a valid conclusion so long as
7.2.6   Free spans
                                                    pipelines have no serious external damage.
Even though a pipeline may be installed             Any pipeline is apt to cause operational
without free spans, they can develop because        interference to trawling. Pipelines and cables
of inner tensions in the pipeline or movement       that are buried and stable pose no hindrance
of the seabed under the influence of bottom         for fishing.
currents. On trawling grounds free spans
impose a heightened risks on trawlers of            Pipeline disturbances for fishing are linked in
going fast with their doors. If it proves           particular to rock dumped sections and pipe
impossible to free the door, the gear and the       with external damage. These disturbances can
catch will be lost, and the fishing trip aborted.   be in the form of important operational
When the location of a free span is known, the      interference in some fisheries and in other
vicinity is avoided and fishing ground area is      cases loss of fishing grounds, damaged gear
lost. In practice there is no difference between    and reduced catch. In the longterm pipelines
a pipeline left in place and one that is in         may be damaged by external events and
operation. On the Norwegian continental shelf       corrosion and eventually degrade totally.
the extent of free spanning is seen as quite
The Final Disposal of Disused Pipelines and Cables                         47                    47

7.3 Impacts of the disposal                          If a pipeline or cable is trenched and not
        options                                      backfilled, the impacts will depend on how
                                                     long nature takes to cover the trench. Before
How fisheries are impacted by the different          that happens, there is an added risk of trawl-
disposal options may be assessed on a three-         doors going fast.
point scale:
                                                     If backfilling accompanies trenching, there
• no operational problems                            will be no problems for trawling once the
• some operational problems for trawling             work is done. This method is especially suited
• serious problems, maybe loss of ground.            for areas of intensive trawling.

The classification according to these criteria is    Temporary leaving in place
shown in figure 7.3. In the following, the           Temporary leaving in place in principle
assessments are focusing on the more                 entails no modification of the current
important areas for trawling.                        situation.

7.3.1   Leaving in place                             7.3.2   Removal
Leaving in place as is                               The consequences of this alternative depends
A pipeline or cable that is buried and stable        on what the pipeline/cable lie is before
does not interfere with trawling. Pipelines          removal. If it is already buried or completely
lying proud without free spans or external           subsided, removal can entail pits and piles of
damage cause someoperational problems on             bottom mass on the seabed, which increase
trawling grounds of any importance. As long          the risk of trawl doors snagging.
as pipelines remain intact, problems will be no
worse than in their operational phase. If the        If the pipeline or cable has been rockdumped,
pipeline suffers external damage or develops         removal may mean that rock gets strewn over
free spans, important operational problems           a larger area, which will cause an increase of
can arise that entail loss of grounds unless the     the operational problems for some trawlers.
pipeline is buried, covered over or removed.
                                                     If the pipeline or cable lies proud or is some-
A rockdumped pipeline does not per se cause          what subsided in the seabed, removal will
significant problems for whitefish trawling.         reduce the risk of interference in the area.
For other trawling it can cause worse                After a partially-sunken pipeline has been
problems and even loss of grounds. These can         removed there may be an increased risk of
probably be reduced by the use of smaller            trawldoors going fast, but it will be a risk of
gravel in the top layer of the rock fill.            short duration, lasting only until the sea
                                                     bottom has levelled itself.
Leaving in place after safeguarding
Leaving a pipeline or cable in place and             7.3.3   Re-use at sea
covered with gravel/stone will most likely           Re-use at sea usually amounts to a
increase the operational problems for                postponement of the final disposal choice. For
industrial and prawn trawling. Such rock fill        the time that pipelines or cables remain on the
may in practical terms also lead to grounds          seabed, the impacts on fishing will be the
loss and reduced catches in these fisheries.         same as by leaving in place.
48                                                                                Summary Report

Costs have been computed on the basis of using existing equipment and methods for the
production, installation and operation of pipelines and cables. These costs are additional
to the cost of leaving pipeline and cable as they are. Removal of pipelines and cables
costs the most, about NOK 44 billion including handling and deposit on land. Rock-
dumping costs are estimated at NOK 25 billion. Trenching will cost substantially less. The
computations give a range of NOK 2.2-5.3 billion for trenching without backfilling. Around
40%-50% of the cost of the various disposal alternatives applies to maritime areas that
are either important or very important for trawling.

This chapter is based on a report prepared by      pipelines. Pipelines and cables are covered in
Dames & Moore (Dames & Moore et al.                their full, reported length to a depth of 0.5 m.
1999b). All these calculations presume that        The comparable costs for rockdumping are
pipelines and cables have all been purged and      estimated at just about NOK 24 billion.
flushed after having been shut down and are
free of hydrocarbons. Costs incurred by those      Trenching without backfilling
operations are not included here. The basic
premise is the optimal execution of the work,      Trenching without backfilling means digging
                                                   a trench with a plough or jet sled for pipeline
with onemobilisation/demobilisation of vessel
per season. This solution is more economical       and cable burial. The trenches are dug to a
than removing pipelines or cables one-by-one.      depth giving minimum 0.5 m overburden
                                                   above the pipeline by natural covering. The
                                                   cost of trenching without backfilling is
8.1 Leaving in place                               estimated at NOK 2.2 billion. No account has
                                                   been taken of pipeline crossings or other
                                                   conditions that would complicate the work.
Calculations have been made for leaving
                                                   The calculations are based on the presumption
pipelines and cables as they are and after
                                                   that trenching is possible.
covering over or trenching with/without
                                                   The computed trenching costs appear low
                                                   compared to the costs Statoil has experienced.
8.1.1 Leaving in place as they are                 (Gjertveit 1999). Taking Statoil's cost figures
This alternative in principle costs nothing. But   puts trenching without backfilling in the range
other sea users would likely want some             of NOK 5.3 billion.
control with the state of the abandoned
pipelines. Such costs have not been                Trenching with backfilling
considered.                                        Trenching with backfilling of pipelines up to
                                                   30" is done in one pass of the plough, while if
8.1.2 Leaving in place with                        the pipeline is bigger than 30", two passes are
                                                   needed. On the same premises as noted above,
                                                   the cost is estimated at NOK 2.2 billion.
Rockdumping or burial costs have been
calculated for all pipes and cables not already
covered as well for the pipes in the NPD           8.1.3 Temporary leaving in place
database for which there is insufficient           Temporary leaving in place is not an
information about cover. This amounts to           independent option and primarily would only
67% of export lines, 23% of infield lines and      be considered in the co-ordination of the
10% of cables.                                     removal of several pipelines and cables in
                                                   order to cut costs. Calculations made on the
Rockdumping                                        premise that Frigg pipelines and cables are
                                                   removed one-by-one show mobilisation and
The calculations are based on the use of the
                                                   demobilisation in the range of 30%
same method as is used to cover over new
The Final Disposal of Disused Pipelines and Cables                                   49                     49

Table 8.1. Computed costs for Norwegian pipeline and cable disposal options. Billions of NOK.
(Dames & Moore et al. 1999b, Gjertveit 1999).
Options                              Pipes/cables     Pipes > 14”         Sum         Important/ very important
                                         <14”                                            trawling grounds
Leaving in place:
- As is                                      -               -               -                         -
- Rockdumping                              0,9            23,7            24,6                 10 – 12,5
- Trenching without backfilling
  - Dames & Moore m fl 1999b               0,3             1,9             2,2                  1,0 – 1,1
  - Gjertveit 1999                         0,3             5,0             5,3                  2,1 - 2,7
- Removal for deposit on land              1,6            40,0            41,6                   17 – 21
- Deposit on land                            -               -             2,2                  0,9 – 1,1
Removal and dumping at sea **)             2,6            41,0            43,6                    17 - 22

*)   Cfr chapter 7.2.1. It is assumed that all export lines in foreign sectors lying on the seabed are in
     important or very important fishing grounds.
**) It is possible that the development of new technology could half these costs.

higher than those cited above. This added cost
may vary from field to field.                               Recycling and dumping
                                                            Many component parts of pipelines and cables
8.2 Removal
                                                            can be recycled, and some components can be
                                                            incinerated for energy recovery. However,
                                                            high costs are associated with removing and
The removal of pipelines and cables is based                separating out components for recycling from
on the use of current installation equipment                the bulk of material where there is a high ratio
and is therefore not optimised. Experience of               of low value components like concrete and
pipeline removal on the Norwegian                           asphalt coating. Materials with a recycling
continental shelf is limited to a few incidents             potential are copper, lead, aluminium, plastic/
in connection with wrong laying and damage                  rubber and duplex steel. The economic benefit
to some pipelines. If it should be necessary to             of recycling is slight, except for steel.
remove a greater amount of pipelines and
cables in the future, experience would be
                                                            The alternative to re-use and recycling is
acquired and in all probability a market for
                                                            depositing. Land-based depositing is done in
better methods and technology would evolve.
                                                            municipal tips, also the destruction of
The study indicates that the development of
                                                            hazardous waste. The total cost for handling
new technology for quicker removal could cut
                                                            on land of the existing pipelines and cables is
costs by half.
                                                            estimated at a good NOK 2 billion net (less
                                                            recycling earnings). These costs are additional
8.2.1 Removal and bringing to                               to removal costs. The total cost amounts to
      shore                                                 just about NOK 44 billion. Any costs for re-
                                                            use on land are not included.
The computed costs include preparations,
inspection to map pipeline conditions,
uncovering, removal and bringing to shore.                  8.2.2 Recycling and dumping at
Factors that can complicate removal are                           sea
crossings, cover, integrated elements such as
                                                            If the pipes are to be dumped in deep water,
T and Y joints, valve stations, other structures
                                                            the operation is the same as for removal and
and pipe ends. Complicating factors like these
                                                            transport to land. On condition the sea
are not accounted for in the estimates, but are
                                                            transport time is about the same as the
often part of many pipeline and cable systems.
                                                            alternative transport to land, the cost will be
The removal costs for all cables and pipelines
                                                            approximately the same. Dumping at sea
will come to about NOK 40 billlion.
50                                                                                 Summary Report

requires transport with crane vessels. This         trenching but without rockdumping in the
means somewhat higher costs compared to             important/very important trawling areas is
removal and bringin to shore. The total cost is     estimated at NOK 1 – 2.7 billion.
about the same as for removal and disposal on
land, that is, not quite NOK 44 billion.
                                                    8.3 Re-use at sea
8.2.3 Partial removal/leaving in
                                                    The direct re-use of steel pipelines and cables
      place after safeguarding                      in oil and gas transportation is not likely, cfr.
Partial removal/leaving in place of pipelines       chapter 4.1.2. Consequently no cost analysis
and cables is seen not as an independent            of this disposal alternative has been made.
option but a combination of the above. A
combined removal option might consist of
leaving pipelines and cables in some areas as       8.4 Time allocation of costs
they are and removing or abandoning them
after safeguarding in other areas.                  The projected lifetime of pipelines and cables
                                                    on the Norwegian continental shelf ends
A computed cost example illustrates the costs       around 2050, cfr. chapter 3.2. This will
of leaving in place in areas of little importance   probably be lengthened if there is a need.
for trawling and of removal or leaving in
place after safeguarding in areas of                Pipeline removal costs will be highest in the
importance/great importance for trawling.           beginning and at the end of the period until
                                                    2050. Infield lines, which on the whole have
NPD estimates that 40%-50% of pipelines in          the shortest lifetime, represent substantial
the Norwegian sector lie within the fisheries       costs as soon as the next 10 years. This is due
statistic locations that are important or very      to the fact that around the turn of the century
important for trawling, cfr. the scale in           some pipelines will, according to their
chapter 7.2.1. The comparable figure for            predicted lifetime, be shut down. Towards the
cables is 90%, but they are believed for the        end of the period the high costs relate to the
most part to be entirely buried. In the foreign     shut down of the export lines, which generally
sectors about 60% of the Norwegian export           have a longer lifetime.
lines are either buried or covered over. The
cost model is based on the remaining 40%            In the case of rockdumping, costs are also
lying in areas of importance or great               expected to be high at the end of the period.
importance for foreign trawling.                    The reason for that is the long lifetime of
                                                    export lines. The rockdumping cost is low at
Based on these figures it is believed that 40%-     the beginning of the period because most of
50% of removal costs are related to areas           the pipes being shut down will be infield lines
where trawling is important or very important.      that are already buried. Trenching has about
Table 8.1 presents a rough estimate of the cost     the same time profile as rockdumping.
of removal or leaving in place after safe-
guarding in these areas. Removal of pipelines       It must be pointed out that extended lifetime
and cables is estimated at NOK 17-22 billion.       of pipelines can make substantial changes to
Comparable cost for leaving in place after          this allocation of costs over time.
rockdumping is estimated at NOK 10-12.5
billion. The cost of leaving in place after
The Final Disposal of Disused Pipelines and Cables                        51                       51

Reference listings are split between studies commissioned in the scope of the assessment
programme and others.

Commissioned studies
Agenda Utredning og Utvikling AS, 1999a: Trålfiske i Nordsjøen. Lokalisering og omfang av det
norske trålfisket omkring rørledninger. Norwegian trawling, grounds & scope

Aquateam – norsk vannteknologisk senter A/S 1999: Virkning på marint miljø av miljøskadelige
stoffer i rørledninger. Rapport nr 99-025, juni 1999. Impacts on marine environment

Dames & Moore Norge, ETPM NorSea A/S og Reverse Engineering Limited 1999a: Virkninger på
arbeidsmiljø i tilknytning til fjerning av rørledninger. Removal & worker safety

Dames & Moore Norge, DSND Subsea og ETPM NorSea A/S 1999b: Kostnadsanalyse av ulike
disponeringsalternativer for utrangerte rørledninger og kabler. Cost analysis of disposal options

Dames & Moore Norge, JP Kenny, og Corresist AS, 1999c: Nedbrytning av rørledninger over tid.
Pipeline degradation

Det Norske Veritas AS, 1999: Konsekvensutredning for habitater på sokkelen. Disponerings-
alternativer for rørledninger og kabler. EIA for habitats

Gjertveit, Erling (Statoil) 1999: Kostnadsoverslag for nedgraving og tildekking av rørledninger.
EIA for habitats

Halliburton Subsea 1999: Disponering av fleksible rør og kabler. Disposal of flexible pipelines &

JP Kenny A/S og Dames & Moore Norge, 1999: Metoder for fjerning og opptak av utrangerte
rørledninger og kabler, og muligheter for gjenbruk. Removal methods & re-use possibilities

Nøttestad, Leif 1998: Fiskeforekomster langs rørledninger i Nordsjøen. Havforskningsinstituttet,
1998. Fish availability along pipelines

Oljedirektoratet 1999: Norske rørledninger og kabler. Notat av 26.04.99 med senere suppleringer.
Norwegian pipelines & cables

RC Consultants as 1999: Disponering av rørledninger og kabler. Påvirkning av ytre miljø ved
fjerning av rørledninger og kabler. Emissions from different disposal options

Taraldrud, Paal Anders 1998: "Gjenvinning/resirkulering av materialer i offshore rørledninger og
kabler". Hovedoppgave ved Høgskolen i Stavanger. Recovery and recycling

Other sources
Agenda Utredning og Utvikling AS, 1999b: Regional konsekvensutredning Nordsjøen. Tema-
rapport 7: Fiskerier og akvakultur - området 58N - 62N. Regional North Sea ES - Fisheries

AURIS 1995. An assessment of the environmental impacts of decommissioning options for oil and
gas installations in the UK North Sea. AURIS MR270.
52                                                                                  Summary Report

Havforskningsinstituttet, 1993. Tråling over 40" rørledning - virkninger på fiskeredskap. Fisken og
Havet, nr 11 - 1993. Overtrawling and bottom gear

Havforskningsinstituttet, 1997. Tråling over steindekte rørledninger i Nordsjøen. Fisken og Havet,
nr 10 - 1997. Trawling over rock fill

Havforskningsinstitutttet,1998: Havets ressurser 1998. Fisken og havet, særnummer 1, 1998. Living
marine resources

North Sea Task Force (NSTF) 1993. North Sea Quality Status Report 1993. Oslo and Paris
Commissions, London. Olsen & Olsen, Fredensborg, Danmark.

Scanews 1998: Westhaven-ulykken i mars 1997 og følgene for britiske fiskere og britisk
oljeindustri. Utarbeidet av Scanews for Fiskeridirektoratet. Westhaven loss & consequences

SFT 1994: Tilstandsrapport for Nordsjøen 1993. Kortversjon av tilstandsrapporten, konklusjoner
og sammendrag for delområdene 1, 6 og 8. SFT-rapport 94:13. North Sea environmental status

SFT 1999: Kvikksølvutslippene i Norge redusert med 90 prosent. Pressemelding, 30. august 1999.
Press release- mercury inputs reduced

Statoil 1998: Tråltest over steinfyllinger på Sleipner kondensatrørledning 06.-14. juli 1998.
Foreløpig rapport. Trawling trials over rockdumped pipeline

St prp nr 36 (1994-95) Om disponering av innretningane på Nordaust Frigg og sal av statlege
eigardelar i Smørbukk og Smørbukk Sør. Disposal of NE Frigg installations

St prp nr 50 (1995-96) Olje- og gassvirksomhet, utbygging og drift av Åsgardfeltet samt
disponering av innretningene på Odinfeltet. Disposal of NE Frigg installations

St prp nr 58 (1995-96) Omprioriteringer og tilleggsbevilgninger på statsbudsjettet 1996. Budget

St prp nr 15 (1996-97) Om endring av løyvingar på statsbudsjettet for 1996 og andre saker under
Nærings- og energidepartementet. Budget appropriations

St prp nr 8 (1998-99) Utbygging av Huldra, SDØE-deltagelse i Vestprosess, kostnadsutviklingen
for Åsgard m.v., og diverse disponeringssaker. Field termination plans.

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