Risk Evaluation Sleipner CO 2 Storage

Transcription

1 1 Risk Evaluation Sleipner CO 2 Storage Authors: Helga Hansen, Statoil and Hans Aksel Haugen, Statoil Licence partners: ExxonMobil E&P Norway, Norsk Hydro AS, Total E&P Norway

2 Outline 2 1. Introduction 3. EU- and industry-funded SACS, SACS2 and CO2STORE 2. Risk evaluation pre-injection 4. Risk evaluation post-drilling, after ten years of injection 5. Further work

3 Introduction Sleipner Vest Production start 1996 Natural gas with 9 mol% CO 2 GIIP: 5.6 TSft 3 (160 GSm 3 ) 3 CIIP: 427 mill.bbl (70 MSm 3 ) NORWAY km Sleipner Øst Production start 1993 Natural gas with < 1 mol % CO UK Gas sales specifications: < 2.5 mol% CO 2

4 4 1. Extraction Sleipner B Sleipner T Amine Plant Sleipner A Injection Well 2. Compression Gas with CO 2 1 Mtons Injected and vented CO Injected Vented 0.80 Gas with CO 2 CO 2 3. Injection M tons CO 2 Utsira Fm 4. Subsurface storage Sleipner Vest

5 Outline 5 1. Introduction 3. EU- and industry-funded SACS, SACS2 and CO2STORE 2. Risk evaluation pre-injection 4. Risk evaluation post-drilling, after ten years of injection 5. Further work

6 6 Approval from the Norwegian Authorities: - Plan for Development and Operation (PDO) for the Sleipner Vest field (1991) No separate application - No Quantitative Evaluation Risks mentioned: - injectivity, potential overpressure -wetco 2 corroding the casing in the production wells - hydrate formation in the Utsira Formation unlikely

7 Main issues focused on prior to injection 7 Evaluation of injectivity Petrophysical evaluation Reservoir Simulation No migration of the CO 2 back to the Sleipner wells Mapping of the Top Utsira Fm important to locate the optimal injection point Caprock Cuttings and geophysical well logs Gas seapage study

8 8 Main issues focused on prior to injection - INJECTIVITY Æ Petrophysical evaluation of the Utsira Fm based on six wells; main results were Net sand and Porosity for seven different zones W E ? Sand wedge Sand wedge (b) (d)? 1200??? 1200 gr ild 15/8-1 gr gr ild ild 15/8-115/9-7 gr gr ild ild 15/9-7 15/9-8 gr gr ild ild 15/9-8 15/9-18 gr ild gr sflu 15/ /9-16 grgr sflu rt gr gr rt sflu gr gr sflu rt 15/ /9-A16 15/9-A16 15/ / /7-3 Hordaland G Hordaland G (c)? Utsira Sand 800 (a) Nordland G. 600 Inj. well Utsira Sand 400 TVD TVD Inj. well 400 E Nordland G. W gr rt 16/7-3 Net Sand Porosity Horizontal (%) (%) permeability * ~ D * estimated

9 9 Main issues focused on prior to injection - INJECTIVITY Reservoir Simulation (black oil, oil-gas model) Temperature critical, 27 0 C SGAS (CO 2 ) after 10 years of injection Shale barriers

10 10 Main issues focused on prior to injection - MIGRATION Assumed CO 2 migration direction No migration of the CO 2 back to the Sleipner wells New seismic survey in 1994 changed the location from NW to 2.8 km NNE of the SLA (the current location) SLA Structural trap identified, saddle area northwards Predicted migration direction northwards Base Utsira Fm shows shale diapirs east of SLA expected to reduce the horizontal distribution of the CO 2 towards the SLA

11 11 Main issues focused on prior to injection - CAPROCK - Cuttings and geophysical well logs of the Nordland shales no detailed studies performed, considered an effective seal - Gas seapage study performed in 1994 Mapped existing shallow gas accumulations and pre-existing gas pathways around the storage site. Concluded that there are no indications of gas seepage which may signify a leakage risk from the CO 2 storage site.

12 Outline Introduction 3. EU- and industry-funded SACS, SACS2 and CO2STORE 2. Risk evaluation pre-injection 4. Risk evaluation post-drilling, after ten years of injection 5. Further work

13 13 SACS-project - a multi-institutional research project The project has been divided into 5 scientific work areas: Regional geology and reservoir characterisation Geochemistry Monitoring Well Geophysics Reservoir Simulations

14 14 Seismic monitoring of Sleipner CO2 injection difference maps km 8,4 million tonnes injected in period Area of CO2 plume: 2,8 km2 Length of CO2 plume: 3760 m 1 km 200 ms 1 km

15 Sleipner Area: Top Utsira Time Map Plume extension & top Utsira time map Summed amplitudes 15 Assumed CO2 spill directions 3,76 km saddle Injection CO 2 point SLA Injection point Plume outline June 2006 Plume outline Oct km

16 Outline Introduction 3. EU- and industry-funded SACS, SACS2 and CO2STORE 2. Risk evaluation pre-injection 4. Risk evaluation post-drilling, after ten years of injection 5. Further work

17 17 The Risk Evaluation Process A group of experts, including international expertise, were invited to join a workshop on risk associated with the CO 2 injectiononsleipner, 29. and 30. May 2006 Aim of workshop: Identify risks of CO 2 escape and effects on neighbouring wells and licences Current injection rates Increased injection rates Identify mitigating measures Evaluate whether risk is within acceptable limits

18 Risk classification 18 High CO 2 injection must cease until compensating measures have been performed Medium CO 2 injection can continue but compensating measures should be implemented to control and/or reduce the risk Low CO 2 injection can continue and compensating measures should be considered in the longer term to control and/or reduce the risk Very low Insignificant contribution to the risk picture and CO 2 injection can continue with no need for implementation of compensating measures

19 19 Cap rock Utsira Fm Wells High CO 2 injection must cease until compensating measures Medium Low CO 2 injection can continue but compensating measures should be implemented to control and/or reduce the risk CO 2 injection can continue and compensating measures should be considered in the longer term to control and/or reduce the risk Very low Insignificant contribution to the risk picture and CO 2 injection can continue with no need for implementation of compensating measures

20 20 Increased* Current injection rates, rates, Utsira Utsira Fm Fm * ~ 10 times current injection rates Risks affecting the Sleipner Licence Risks affecting neighbouring licences Medium risk: Migration below Top Utsira Fm or internal shale layers to adjacentwells Medium risk: Utsira Fm Injection induced degradation of reservoir, e.g.subsidence Medium risk: Migration below Top Utsira Fm or internal shale layers to neighbouring licence blocks: - problems for future exploration wells (gas pockets, corrosive environment) - destroy seismic response below plume Low risk: Reduce / misinterpret storage capacity due to degradation or other unknown factors Low risk: Migration below Top Utsira Fm to up-dip sands in cap rock seal seabed Compromise future use of Utsira water for injection purposes

21 21 Increased* Current injection rates, rates, cap cap rock rock * ~ 10 times current injection rates Risks affecting the Sleipner Licence Risks affecting neighbouring licences Cap rock Medium risk: Leakage through undetected faults/fractures: to shallow fms seabed Low risk: Differential pressure due to buoyancy effects creates fractures Migration through sand injections (pre-existing permeable zones)

22 22 Increased Current injection rates, wells * ~ 10 times current injection rates Risks affecting the Sleipner Licence Risks affecting neighbouring licences Medium risk: CO 2 reaches adjacent exploration and wellsproduction wells - loss of well integrity - leakage outside/inside casing surface Wells Low risk: Injection system failure leakage back to SLA through injection well risk to personnel

23 23 Key findings from the workshop The risk of CO 2 release from Utsira Formation is considered low and acceptable Increased injection rates would accelerate the identified risks A selection of mitigating measures to reduce risk and improve control of the CO 2 plumewereproposed

24 Further work 24 EU- and industry-funded SACS, SACS2 and CO2STORE Risk evaluation post-drilling, after ten years of injection CO2ReMoVe Mitigating measures - Time lapse seismic surveys are the main monitoring tool - Update the Top Utsira Depth map based on the time lapse seismic survey - Update the reservoir simulation model based on the Top Utsira map update CO 2 migration prognosis - Evaluation of the exposure and long-term integrity of wells in the area