The Final Disposal of Disused Pipelines and Cables LANDING PIPELINES 65° Gas pipeline Oil / condensate pipeline Projected gas pipeline Norne Heidrun Åsgard HALTEN PIPE Draugen T OR SP Njord AN TR D R ÅSGA TRONDHEIM Tjeldbergodden Statfjord 60° Murchison Snorre Gullfaks Shetland Veslefrikk FLORØ Brage Troll Mongstad Oseberg OTS Sture Norway ST Frigg Kollsnes AT PIP BERGEN E Frøy Heimdal II A FNA IPE II B EP Kårstø ZE E IP EP Sweden ZE E St Fergus PIP ST AT Sleipner STAVANGER Draupner S/E Ula Cod Gyda Ekofisk Valhall 55° Tommeliten IP E Hod NORP EURO Denmark EUR Teesside PIPE OPIP II EI NO R PIP EI E PIP E United PIP ZEE AN Kingdom FR Bacton Emden INTE ECTOR CON R- N Germany Netherlands 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 1 PREFACE 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 TABLE OF CONTENTS 3 EXECUTIVE SUMMARY 1 INTRODUCTION 1.1 BACKGROUND 1.2 ORGANISATION AND IMPLEMENTATION 1.3 LEGISLATION ON REMOVAL OF OFFSHORE FACILITIES 2 COMMISSIONED STUDIES 3 PIPELINES AND CABLES ON THE NORWEGIAN CONTINENTAL SHELF 3.1 REVIEW OF NORWEGIAN PIPELINES AND CABLES 3.2 PIPELINE OUTPHASING 4 DISPOSAL OPTIONS 4.1 LEAVING IN PLACE 4.2 REMOVAL 4.3 RE-USE AT SEA 5 IMPACTS ON THE WORKING ENVIRONMENT 5.1 RETRIEVAL AND REMOVAL 5.2 TRANSPORT AND HANDLING ON LAND 6 ENVIRONMENTAL IMPACTS 6.1 NORTH SEA BOTTOM CONDITIONS 6.2 INPUT OF METALS 6.3 INPUT OF ORGANIC COMPOUNDS 6.4 OTHER ENVIRONMENTAL IMPACTS 6.5 IMPACTS OF THE DIFFERENT DISPOSAL OPTIONS 7 IMPACTS ON FISHERIES 7.1 IMPORTANT FISHING GROUNDS AND CATCHES 7.2 SIGNIFICANT FACTORS FOR FISHERIES 7.3 IMPACTS OF THE DISPOSAL OPTIONS 8 COST CONSIDERATIONS 8.1 LEAVING IN PLACE 8.2 REMOVAL 8.3 RE-USE AT SEA 8.4 TIME ALLOCATION OF COSTS 9 REFERENCES 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 5 6 EXECUTIVE SUMMARY 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 1 INTRODUCTION 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 impacts 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 2 COMMISSIONED STUDIES 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 materials 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 pipelines 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 3 PIPELINES AND CABLES ON THE NORWEGIAN 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 8000 7000 6000 5000 Kilometers 4000 3000 2000 1000 0 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 65° Gas pipeline Oil / condensate pipeline Projected gas pipeline Norne Heidrun Åsgard HALTEN PIPE Draugen T OR SP Njord AN TR D R ÅSGA TRONDHEIM Tjeldbergodden Statfjord 60° Murchison Snorre Gullfaks Shetland Veslefrikk FLORØ Brage Troll Mongstad Oseberg OTS Sture Norway ST Frigg Kollsnes AT PIP BERGEN E Frøy Heimdal II A FNA IPE II B EP Kårstø ZE E IP EP Sweden ZE P E St Fergus TPI Sleipner STA STAVANGER Draupner S/E Ula Cod Gyda Ekofisk Valhall 55° Tommeliten IPE Hod NORP EURO Denmark EUR Teesside PIPE OPI PE I II NO R PIP I E E PIP E United PIP ZEE AN Kingdom FR Bacton Emden INTE ECTOR CON R- N Germany Netherlands 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 continental shelf 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. length 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 3500 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 2000 Km pipeline P la nne d inf ie ld line 1500 o ut pha s ing 1000 500 0 B e f o re 1997-2010 2010-2025 2025-2040 A fter 2040 1997 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 of material 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 4 DISPOSAL OPTIONS 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. stand. 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 solution. 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 retrieved. 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 brittleness. 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 5 IMPACTS ON THE WORKING ENVIRONMENT 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 installation. 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 seabed. 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 residues. 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 6 ENVIRONMENTAL IMPACTS 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 reefs. 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 1) 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 Field 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 Ekofisk 2/7-C 2/7-R 01.12.79 10,75 12,2 12 20 shutdown ¹ Statoil/ Stat-A Stat.B-OLS 01.12.79 36 3,5 48 25 operating ¹ Statfjord 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 Source 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 15000-60000 ** 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 - - Removal - 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 - - assemblies - 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 small. 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 7 IMPACTS ON FISHERIES 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) 1) 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 statistics) Statistical area Whitefish trawling Prawns Industrial trawling (mostly saithe) Sandeel Norway pout Blue whiting 2) 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 grounds 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. Yes No Fishing with bottom trawl 7.1.5 More about nephrops trawling Yes Nephrops trawling is a relatively new fishery Somewhat/very important No 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 Yes south. The grounds where nephrops are fished No operational problems of any consequence Yes Buried 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 Yes Yes In the context of the impacts for fisheries of Whitefish trawling Free spans the individual disposal options, several factors No are prominent: No 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 variations. 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 pipelines. Summary 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 limited. 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 8 COST CONSIDERATIONS 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 backfill. 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, safeguarding 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'**: - 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 9 REFERENCES 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 & cables 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 58N - 62N. 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 appropriations 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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