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					Gullfaks field
    Rune Instefjord
Project leader, Gullfaks IOR
                                                             Key data for GF main field
                                                                                                                                                            • Location: northern North Sea
                                                                                                                                                            • Discovered: 1978
                                                                                                                                                            • Start production: 1986
                                                                                                                                                             • Location: northern North Sea
                                                                                                                                                        •   • Start production: 1986
                                                                                                                                                               Base oil reserves: 356 Mill. Sm3
                                                                Gullfaks
                                                                Gullfaks
                                                                                                                                                             • Discovered: 1978
                                                                                                                                                        •   • Base reserves: 356 Mill. Sm 3
                                                                                                                                                               Produced to date: 327 Mill. Sm

                                                                                                                                                        • • Produced recovery: 327 Mill. Sm3
                                                                                                                                                             Expected to date: 61 %
                                                                                                                                                                –   Recovery pr. 2006: 56%
                                                                                                                                                        •   Expected recovery: 61 %
                                                                                                                                                            • Initial pressure: 310-320 bar at 1850 m TVD
                                                                                                                                                              MHN

                      3 500
                                                                                                                                                            • Bubble point pressure: ~200-240 bar at 1850 m
                      3 000                                                                                                                                   TVD MHN
Rate 1000 Sm3/month




                      2 500



                      2 000
                                                                                                                                                            • GOR: ~ 100 Sm³/Sm³
                      1 500
                                                                                                                                                            • Viscosity: ~ 0.5 – 1 cp
                      1 000



                       500
                                                                                                                                                            • Dip angel in western part: 12-15 deg
                         0
                          1986   1988   1990   1992   1994   1996   1998   2000   2002   2004   2006   2008   2010   2012   2014   2016   2018   2020




                              Basis Water              IOR Water              Basis OIL                IOR Oil              Start prognosis
 Gullfaks Field
-Structural setting and reservoir
 performance, Gullfaks Field
  • Complex fault system
      –   Main fault system trending
          north-south: large faults (50 – 250 m
          throw)
                                                                                                                                      C
      –   Secondary fault system east-west                                                                       B
          (10 – 100 m throw)                                                                                                      C
      –   Three structual areas
                                                                                                             B
  • A major challenge to realise the                                                              A

    IOR potential, is a continuous
    improvement of the structural
    description by
      –   frequent seismic surveillances          Structural Depth Map, top Statfjord Fm. View from south.
                                                                               A
          (conventional time lapse and Ocean      Vertical scale 4x horisontal
          Bottom Seismics)
      –   Use of advanced geological and
                                                    Post-Jurassic
                                                                                                                             5
                                                                                                                                          msl

                                                                                                                             km
          reservoir simulation models               sediments
                                                                                                                                          1000 m
                                                                                                  Accom-
                                                                                  Domino System   modation           Horst

                                                                                                                                          2000 m
                                                   Brent Gr.

                                                                    Statfj.                                                               3000 m
                                                                    Fm.

                                                  Tordis                                                                                  4000 m

                                                  break-            Intra-Teist refl.
                                                  away
                                                                                                                                          5000 m
                                                  fault
                                                                                   Low-angle
                                                                                   detachment                                             6000 m




                                                                                                             Basement                     7000 m




                                                                                                                                          8000 m
Structural interpretation




         W                                                       Line 736                                                     E
                               CDP 400              600              800               1000                1200     1400
          0000                                                                                                                0000
                                                                                         HORST
                                                                                         COMPLEX

          1000                                                      ACCOMODATION                                              1000
                                  DOMINO
                                  SYSTEM

          2000                                                                                                                2000




          3000                                                                                                                3000




          4000   Intra-Lomvi                                                                                                  4000
                 reflector


          5000                                                                                                                5000



                                           Cretaceous/Tertiary       Base Cretaceous               Brent          Statfjord
                                           sediments                 unconformity                  Group          Fm.
Reservoir Quality
            •   Reservoirs: Brent, Cook,
                       Statfjord & Lunde
            •   Complex reservoir, very faulted
            •   Porosity: 25-35 %
            •   Permeability:
                 – Tarbert, Etive, good Ness, good
                    Statfjord and Cook- 3 >1D
                 – Rannoch, poor Ness, poor Statfjord,
                    Cook-2 and Lunde : 100 mD – 1 D

            •   Moderate-to-High Reservoir
                Quality
            •   Contrasting layers
            •   Weak formations
DRAINAGE STRATEGY (primary)
• Aquifer support
• Water injection
• Reservoir pressure over bubble point
• Injectors in the water zone
• Producers high on structure
                              Drainage strategy               (continues)


 Secondary:
Secondary:
  Secondary:
   Secondary:
  Secondary:                               Why?
                                           Why?
                                          Why?
                                            Why?
 • Gas injection, up-dip
•••• Gas injection, up-dip
     Gas injection,up-dip
      Gas injection, up-dip                • Avoid production reduction when gas export is at its
                                           • Avoidproduction reduction when gas export is at itsis at its
     Gas injection, up-dip
 •• WAG injection                         •• Avoid production reduction when gas export is at its
                                                Avoid production reduction when gas export
••• WAG injection
     WAG injection
     WAG injection
      WAG injection                            maximum
                                              maximum
                                              maximum
                                                maximum
                                           • Reduce storage costs and CO tax
                                           • Reduce storage costs and CO2 tax
                                          ••• Reduce storage costs and CO22 tax2 tax
                                                Reduce storage costs and CO
                                           • Produce attic oil
                                               Produce attic oil
                                          ••• Produceattic oil saturation
                                                Produce attic oil
                                               Reduce residual oil
                                           • Reduce residual oil saturation
                                          ••• Reachareas difficultsaturationwith with water injection, ex. LB
                                           • Reach areas difficult to reach with water injection, ex. Ness by LB
                                                Reduce residual oil to to reach water injection, ex. Ness by
                                               Reach areas difficult reach
                                            • Ness by LB injection reach with water injection, ex. Ness by LB
                                               injection
                                              injection
                                                Reach areas difficult to
                                                injection
                                           •
                                           •   Get uniform drainage, decrease sand production
                                               Get uniform drainage, decrease sand production
 • Horizontal wells
• Horizontal wells
• Horizontal wells                         •
                                           •   Drain by-passed oil decrease sand production
                                               Get uniform drainage,
                                               Drain by-passed oil
Horizontal wells                          ••   Get uniform drainage, decrease sand production
                                               Drain by-passed oil
• Reservoir pressure under bubble point   ••   Drain by-passed oil
                                               Create gas lift, save drilling costs
• Reservoir pressure under bubble point    •   Create gas lift, save drilling costs

• Commingle production
• Reservoir pressure under bubble point   •• Create gas lift, save drilling costs
                                             Accelerate production


• Commingle production                    • Accelerate production
                                                              Gullfaks reserves estimates through time

              700                                                                                                                                                                                                                                                                                                   700




              600                                                                                                                                                                                                                STOOIP (3,6 billion bbl)                                                           600
                                                                                                                                              588585               581582 587 582581582
                                                                                                                       574           579
                                    564                                                                         560
                           540        540                                                 538
                530                                                                               522
                                                510
              500                                  502                                                                               Remaining oil                                                                                                                                                                  500
                                                                                   478
                                                              452


              400                                                                                                                                                                                                                                                                                                   400
Olje (MSm³)




                                                                                                                                                                                               352 355
                                                                                                                                                                                                                                                     2,2 billion bbls
                                                                                                                                                                                        342                                                                 BASE PROFILE
                                                                                                                                                                                 332
                                                                                                                                              317319               321 325
                                                                                                                                     309
              300                                                                                                                                                                                                                                                                                                   300
                                                                                                                       284
                                                                                                                257
                           240
                230                                    RESERVES                           230
                                                211210
              200                                                                                                                                                                                                                                                                                                   200




              100
                                                                                                                                                                        PRODUCED                                                                                                                                    100




               0                                                                                                                                                                                                                                                                                                    0
                    1980
                           1981
                                  1982
                                         1983
                                                1984
                                                       1985
                                                              1986
                                                                     1987
                                                                            1988
                                                                                   1989
                                                                                           1990
                                                                                                  1991
                                                                                                         1992
                                                                                                                1993
                                                                                                                       1994
                                                                                                                              1995
                                                                                                                                     1996
                                                                                                                                            1997
                                                                                                                                                   1998
                                                                                                                                                          1999
                                                                                                                                                                 2000
                                                                                                                                                                        2001
                                                                                                                                                                               2002
                                                                                                                                                                                      2003
                                                                                                                                                                                             2004
                                                                                                                                                                                                    2005
                                                                                                                                                                                                           2006
                                                                                                                                                                                                                  2007
                                                                                                                                                                                                                         2008
                                                                                                                                                                                                                                2009
                                                                                                                                                                                                                                       2010
                                                                                                                                                                                                                                              2011
                                                                                                                                                                                                                                                     2012
                                                                                                                                                                                                                                                            2013
                                                                                                                                                                                                                                                                   2014
                                                                                                                                                                                                                                                                          2015
                                                                                                                                                                                                                                                                                 2016
                                                                                                                                                                                                                                                                                        2017
                                                                                                                                                                                                                                                                                               2018
                                                                                                                                                                                                                                                                                                      2019
                                                                                                                                                                                                                                                                                                             2020
                                                                                          Historie                      Basis profil                         Reserver                          STOOIP
                                           Reserves Growth Gullfaks
                                            Sammenligning av prognoser for basis oljeproduksjon
                                                            Gullfaks hovedfelt
                       35
                                                                                                      In additon, tie-in of
                                                                                                      satellite fields has
                       30
                                                                                                      increased the oil and
    mill Sm per year




                                                                                                      gas sales from the
                       25                                                                             field (1994 Tordis,
Mill. Sm3 3 pr. år




                                                                                                                                                 Present prognosis for
                                                                                                      1998 GF Satellites                         economical lifetime:
                       20                                                                             Phase 1, 2001 GF                           Year 2018. Ambition:
                                                                                                      Satellites Phase 2.                        Year 2030
                       15


                       10


                       5


                       0
                            1986

                                   1988

                                           1990

                                                   1992

                                                          1994

                                                                 1996

                                                                          1998

                                                                                 2000

                                                                                        2002

                                                                                               2004

                                                                                                       2006

                                                                                                              2008

                                                                                                                     2010

                                                                                                                            2012

                                                                                                                                   2014

                                                                                                                                          2016
                                          Produsert                     88 Rev PUD               93 Høst                     94 Høst              RSP 96
                                          RSP 00                        RSP 02                   RSP 03                      RSP 04
IOR at Gullfaks
Main reasons for improved recovery

• Continuous focus on reservoir description and monitoring
• An increased no. of drainage points / wells and the use of superinjectors for water
 injection

• Supplementary gas injection (WAG) in selected reservoir segments
• Increased process capacities where necessary both for water (prod/inj), liquid, oil
 and gas

• Reduced inlet separator pressure
• Use of time-lapse (4D) seismic to map remaining hydrocarbons
                  Ambitions in Long Range Plan
• Produce 400 Mill. Sm³ oil in the field life time. Corresponding to around 70%
 recovery factor on the main field.

• Cost reductions and an active IOR implementation is the most important
 instrument to reach the ambition.

• Lengthening the field life time with several years.
• Third parts processing.
Gullfaks Main Field –
oil rate prognosis
                                     35
                          Millions
Oljeproduksjon (Sm3/år)




                                     30

                                     25

                                     20

                                     15

                                     10

                                     5

                                     0
                                          1986

                                                 1990

                                                        1994

                                                                 1998

                                                                        2002

                                                                               2006

                                                                                      2010

                                                                                             2014

                                                                                                    2018

                                                                                                           2022

                                                                                                                  2026
                                                               Basis      Basis+ØOU          Ambisjon
                       Gullfaks ”IOR ambition” project
•   Duration: 2006-2008.
•   Main goal: mature the undefined IOR ambition volumes (and more?) to RC 5.
     – Identify specific measures and demonstrate that they may be economical feasible.



                     Gullfaks Hovedfelt                                                       Mill Sm³
                    Basis profil                                       0-3        Gullfaks         356,7
                    Senfase trykkavlastning Cook                       7A         Cook               1,0
                    Infill Cook                                        4A         Cook               0,2
                    Lavtrykk Cook                                      7A         Cook               1,1
                    Forbedret sweep i Cook ved økt vanninjeksjon       4A         Cook               0,2
                    Nye IOR-brønner i Brent                            4A         Brent             10,6
                    Massiv vannsirkulering i Brent                     4A         Brent              7,0
                    Statfjord IOR                                      7A         Statfjord          0,2
                    Massiv vannsirkulering Statfjord                   4A         Statfjord          1,3
                    Krans/Kyrre IOR                                    7A         Krans              0,5
                    Lunde IOR                                          7A         Lunde              2,1
                    CO2 prosjekt                                       6          Brent              -
                    Ambisjonsprofil                                    7A         Gullfaks          17,4
                    Lunde IOR 0,4<Sw<0,6                               7F         Lunde              1,7
                    Sum all IOR Measures                               Sum        All               43,3
Gullfaks Main Field. Improved oil recovery.

Implemented:                                                     Implemented (continued):
• Water injection from start                                     • Multilateral wells
• Upgrading of water injection capacities                        • Coiled Tubing drilling
• Sand control (screens) in most wells                           • Through tubing drilling
• ”Designer wells” (horisontal, 3D)                              • Rig assisted snubbing
• Extended reach drilling (9 km drilled, 10 km well is beeing    • Underbalanced drilling
  drilled)                                                       • Expandable liners
• Extensive exploration activity within drilling reach from      • 4D seismic
  platforms => new volumes
• Hydraulic fracturing in low perm reservoirs                    Studied, but discarded:
• WAG (Water alternating gas) injection                          • Surfactant injection (pilot)
• ”Huff and puff” gas injection                                  • Gel blocking (pilot)
• Monobore completions                                           • CO2 miscible injection
• ”Intelligent wells”, remotely operated zone isolation valves

                                                                 Under evaluation:
                                                                 • MIOR (Microbiological IOR)
                                   Water circulation
• Main mechanism for IOR at Gullfaks.
                                                            1,0

                                                            0,9
                                                                                                               Krw - Referanse
                                                            0,8                                                Krw - Sor = 0.2

• Done a simulation study with extended                     0,7
                                                                                                               Kro - Referanse
                                                                                                               Kro - Sor =0.2
                                                            0,6




                                              Rel. Perm.
  water injection.                                          0,5

                                                            0,4


• Maximum use of platform capacity for all                  0,3

                                                            0,2


  phases.                                                   0,1

                                                            0,0
                                                                  0                 0,2          0,4             0,6               0,8          1

• Residual oil saturation down to 5% from                                                         Water Saturation




  lab experiments.                                              0,10

                                                                0,09

                                                                0,08

• Drilling infill wells, both injectors and                     0,07

                                                                0,06




                                                   Rel. Perm.
  producers.                                                    0,05

                                                                0,04

                                                                0,03

                                                                0,02

                                                                0,01

                                                                0,00
                                                                       0,6   0,65         0,7   0,75     0,8         0,85    0,9         0,95   1
                                                                                                   Water Saturation
                         Water circulation, results
• Most important mechanism is the
 creeping relative permeability and long        WCT vs cumulative oil, history and
 tail production from each well.                prediction

• One well has historically produced with oil
 rate < 100 Sm³ and wct > 0,9 for 7 years.
• H2S is a problem, but nitrate injection
 seems to control it.
• Water production may be an
 environmental challenge.
            Added use of today’s medicine
            gives the highest contribution
            to the future recovery.
                      Drilling history at Gullfaks
• 3 platforms with 42, 42 and 52 slots.
• Started with vertical wells (less than 60 deg) and 6 sub sea wells.
• After 4-5 years drilled horizontal wells.
• Water breakthrough gave sand problems:
   – Gravel packed wells, screen,
   – Fractured wells with proppants.
• Last 5 years
   – Sidetracks.
   – Through Tubing Drilling.
   – Multilateral incl. DIACS in the well junction.
                                  Sand handling project
Assumption:
                                                                                                           Kurve for MSR-testing
 Most wells on Gullfaks has sand production.




                                                            Sand i sandf elle (gram/time )
                                                                                             100
 Wells classified after probability for erosion.                                             90
                                                                                              80
 Allow higher sand production rate in the cases                                              70
  with low erosion risk.                                                                      60
                                                                                              50
 Monitoring erosion progress.                                                                40
 Started at Gullfaks A in 2003 after a pilot at GFA                                          30
                                                                                              20
  on 3 wells in 2002.                                                                         10

 Installed at all 3 platforms in 2004.                                                        0
                                                                                                   0   2      4        6       8       10      12
 Both accelerate and increase oil recovery.                                                           Tid (timer etter bunn opp på ny rate)




                     •Cumulative gain for ASR in 2003: 216 000 Sm³
                      which gives a daily rate of around 590 Sm3/d
Seismic acquisition on Gullfaks


                           Surface seismic
                           1985, 1996, 1999,
                           2003


                           Shadow area

                            OBS acquired
                            in 2001

                            OBS acquired
                            In 2003
                          Based on 4D/4C seismic…

 Well B-41A successfully drilled late 2000          Well C-44A successfully drilled
                                                             early 2001
                                                                                      After 1996 survey:
                                                     Well C-26AT2 drilled in 2003

                               Well C-15C drilled 2003
                          X                                                           After 1999 survey:
             Potential new well
             location cancelled
                                             Well B-15AT4 successfully drilled 2003
                                                                                      After 2001 survey:
                                             Well B-4A successfully drilled in 1999


                                                                                      After 2003 survey:

                                                     Well C-43 under drilling
Well A-29A successfully
    drilled in 2003


                                                Well A-46T2 drilled mid-2000
    Well A-21A successfully
      drilled early 2000
                                  Status 4D
• Based on 4D seismic we have drilled more than 10 wells with success.
• Top Brent (Tarbert), top Etive, top Cook and top Statfjord are the formations
 where 4D has been most valuable.

• Ness, Rannoch and lower part of Statfjord is more difficult.
• Have seen 4D effects in areas around injectors were the pressure is significance
 higher than initial pressure.

• All wells have hit their target and most of them produced more than expected in
 the ‘Recommendation To Drill’.
                             Flooding map
Reservoir monitoring and management

                Simulation                 Structural
                models                     framework
                                                        Sedimentology, detailed
                                                        stratigraphy


                                                                   Reservoir
                                                                   description and
Time-lapse                                                         initial volume
seismic
1985

             Top reservoir




               OWC
       OWC




                                                        Well position, and
                             Production, injection
1999
                                                        perforation levels
             Top reservoir
                             rates, RST and PLT
                         Flooding map

  Water flooded


Partly water flooded


             Uncertain flooding
                                        Oil producer

Gas flooded or                          Future producer
originally in place
                                        WAG injector

                                        Water injector
Oil filled
                                        Gas injector
                   Alternative recovery methods
• Surfactant pilot in the early 1990’s. Full field project stopped due to:
   – Chemical cost was too high relative too its efficiency.
   – Remaining oil saturation after water flooding was lower than expected.
   – Surfactant system efficiency was too little robust.
• CO2 MWAG Study last years
   – Simulations done on Frontsim and Eclipse 300.
   – Potential of 10-20 Mill. Sm³ oil identified.
   – Too high cost totally and therefore a none economic project with to days
      framework condition.
                                      AMIOR
• Alternative project to reduce residual oil at Gullfaks.
• Add nitrate (doing already due to reduction of H2S), phosphate and oxygen to the
 injection water.

• Reducing surface tension between oil and water and thereby mobilize oil.
                                         AMIOR
• Pilot in well A-41B recommend.
• Closed area with steady-state conditions.
• Good reservoir understanding.
• Good spacing between injector and
 producer.

• A-36 has an established water cut
 growth.

• A-41B is perforated in the oil zone.
                                       Prospects
• A wide range of prospects in the licence.
• Drill from the platforms where possible.
• Use existing infrastructure to produce
 from the discoveries.

• Commercial solutions for prospects
 across licence boundary.

• Coordinate exploration and production
 drilling.

• Combine targets where possible.
                                     Conclusions
• Recovery of 400 mill. Sm³ (app. 70% recovery factor).
• Lengthening the field life time.
• Water circulation is the main IOR method.
• Drilling of new and less expensive wells important.
• Alternative recovery methods may be a substantial part of the future.
• Exploration and third part processing contributes.
• Close collaboration between the different technical disciplines is an important
 premise to reach the ambition.
Requirements to moving volumes from resource category
7a and 6 to 5a
Requirements to moving volumes from resource category
7a and 6 to 5a, cont…
•   Profitable measure
•   Assumptions regarding this evaluation are given in Appendix B
•   Likelihood of implementation equal to or greater than 30 %.
    A way of calculating the likelihood of implementation is given in Appendix C.

•   Prepare plan (studies, eventual technology qualification, manning, budget,) and timing for next phase (when is the
    right time to proceed).
    The level of detail of such a plan depends on the size of the project/measure.
•   Documentation shall include;
    – Production effects (all HC phases) in the targeted reservoir(s)
    – Simple uncertainty estimation for production effects (low-medium-high)
    – Is the measure competing with other measures (yes/no – which ones)
    – Evaluate whether the measure has any consequence for process capacities[1] (yes/no – which ones)
    – Cost(Capex and OPEX) estimate for the measure (class A)
    – Economical evaluation
    – Plan and timing of next phase
•
    [1] If yes; will the measure displace other measures?

				
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