Geol 40310 Lecture A10: Reservoir Development and Production 2 (Autumn 2023-24) PDF

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A10: Reservoir Development and Production 2. Autumn 2023-24 T. Manzocchi, University College Dublin 1 1 Reservoir Development and Production 2. Ekofisk reservoir example: Reservoir geology: naturally fractured chalk Production me...

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A10: Reservoir Development and Production 2. Autumn 2023-24 T. Manzocchi, University College Dublin 1 1 Reservoir Development and Production 2. Ekofisk reservoir example: Reservoir geology: naturally fractured chalk Production mechanics: Primary production phase: pressure depletion Secondary production phase: water floodings Compaction drive contribution 4D seismic Infrastructure and pipelines Current production and investment 2 Geol 40310 Lecture A10 1 Ekofisk: Norway’s First offshore producer Original recoverable reserves: 3.3 billion bbls oil, 5.6 TCF gas Extended Production test Primary recovery: Pressure depletion/ Solution gas drive Secondary recovery: Water injection Four drive mechanisms: Pressure depletion Solution Gas Drive Water Drive Compaction Drive Development decision: 1972 http://elvisekofiskproducts.com/84/ 3 Chalk Reservoirs Global data (10,000+ carbonate reservoirs), with chalk reservoir highlighted. P10 P50 P90 Chalk reservoirs Erenberg and Nadeau (2005) SEM Photomicrograph of Chalk porosity. (Strand et al. 2007) 4 Geol 40310 Lecture A10 2 Naturally-fractured Chalk Reservoirs Faults and fractures in chalk at Flamborough Head (England) Natural Fractures at Ekofisk result in an effective permeability of 50-100 mD despite matrix permeabilities < 1 mD 5 Ekofisk initial development plan Planned Ekofisk oil: Density: 38°API, Viscosity: 0.25 cp, Solution GOR: > 1,500 scf/STB Actual (Typical volatile oil) Extended production test (1971-1974) demonstrated that sustained production was possible, resulting in the decision to develop the field. Development plan: 20% Recovery factor via Pressure depletion / Solution Gas Drive http://www.norskpetroleum.no/en/production/resource-management-in-mature-areas/ 6 Geol 40310 Lecture A10 3 Depletion Drive and Solution Gas Drive – Ekofisk Reservoir Initial Pressure: 7135 psi Bubble point: 5443 psi Once reservoir drops below bubble point (1980): Slower pressure decline. Stabilised oil production rates Increased gas production rate. 7 Ekofisk primary recovery Planned initially (primary recovery only) Actual primary recovery behaviour (to 1985) Estimated final primary recovery factor ca. 24% (NB: This includes compaction drive – see later) 8 Geol 40310 Lecture A10 4 Ekofisk Secondary Recovery Phase: water injection Extended Production test Primary recovery: Solution gas drive + compaction drive Development decision: 1972 Secondary recovery: water injection Secondary recovery planning: mid 1980s. 9 Water-flooding In a reservoir with poor aquifer support, a water-flood can be generated by injecting the water Higher pressure injection well Lower pressure production well 10 Geol 40310 Lecture A10 5 Drainage and imbibition Drainage: Decrease of the wetting phase saturation Imbibition: Increase of the wetting phase saturation A. Hysteresis: the property depends on historical as well as current conditions Migration and trapping: DRAINAGE B. water oil Drainage Imbibition Oil Recovery: IMBIBITION (if water-wet reservoir) C. B. Capillary pressure water oil 0 C. Water saturation A. 1 11 Spontaneous imbibition – Ekofisk chalk Spontaneous imbibition results of Tor formation samples Water saturation (%) • Strongly water-wet rocks will perform better during waterflooding as the water will spontaneously fill the smallest pores. • Laboratory testing indicates good results in the Ekofisk chalks. Displaced hydrocarbon After exposure to water Initial samples Porosity (%) (Sulak et al. 1990) 12 Geol 40310 Lecture A10 6 Ekofisk Planned water-flood, ca. 1985 Predicted Bbl/day Historical • Expected recovery factor from primary drive of 24% • Expected increase in Recovery to ca. 30% from water injector Injector Producer (Sulak et al. 1990) 13 Ekofisk primary and secondary recovery Planned initially (primary recovery only) Actual recovery behaviour (to 1995) Secondary peak production rate 1994 Primary recovery: Pressure depletion + Solution gas drive Secondary recovery: water injection 14 Geol 40310 Lecture A10 7 Ekofisk Secondary Recovery Phase: water injection Extended Production test Production start: 1974 Primary recovery: Solution gas drive + compaction drive Start secondary recovery: 1987 Secondary recovery: water injection Ekofisk II redevelopment: 1996 15 Ekofisk primary and secondary recovery Planned initially (primary recovery only) Actual behaviour (to 2014) Primary recovery: Solution gas drive + compaction drive Secondary recovery: water injection Secondary recover + field redevelopment 16 Geol 40310 Lecture A10 8 Ekofisk Field production by platform - 2011 X-ray Charlie Bravo Alpha 17 Ekofisk Subsidence – recognised in 1984 18 Geol 40310 Lecture A10 9 Ekofisk Subsidence Subsidence rate of 30-40 cm / year curtailed by water injection repressurisation 19 Compaction of Ekofisk Chalk 20% decrease in porosity due to pore pressure reduction. This compaction is believed to contribute a recovery factor of ca. 10% 20 Geol 40310 Lecture A10 10 21 Ekofisk: Norway’s First offshore producer Original recoverable reserves: 3.3 billion bbls oil, 5.6 TCF gas Extended Production test Primary recovery: Pressure depletion/ Solution gas drive Secondary recovery: Water injection Four drive mechanisms: Pressure depletion Solution Gas Drive Water Drive Compaction Drive Development decision: 1972 Ekofisk: 45% recovery factor of which: ca. 15 % from depletion drive / solution gas drive. ca. 10 % from compaction drive. ca. 20 % from water flooding. http://elvisekofiskproducts.com/84/ 22 Geol 40310 Lecture A10 11 4D seismic at Ekofisk • Repeat seismic survey 1999, 2003, 2006, 2008 • 2010: Installation of permanent reservoir monitoring system (200km of seismic cables trenched 1.5 m into the seabed connecting 3996 sensors) Principal of 4D seismic acquisition: Survey 1 Survey 2 23 Improved seismic acquisition and processing: Streamer vs. Ocean Bottom Network (OBN) Streamer Mander et al. (2013) OBN OBN: Records S-waves too. 24 Geol 40310 Lecture A10 12 Use of time-lapse seismic on Ekofisk Ekofisk Formation Tor Formation 4D seismic amplitude changes between Sep/Oct 2019 and May/Jun 2020 revealing a sub-seismic fault/fracture causing an unwanted flow connection between water injector I1 and producer P1. Folstad et al. (2021) 25 Ekofisk Field, Historical significance Ekofisk: Production test Primary recovery Secondary recovery 26 Geol 40310 Lecture A10 13 Ekofisk Field – Initial Infrastructure - 1970s 3 drilling / production platforms. Field terminal platform. Living quarters Million barrel concrete storage tank 1974: Oil pipeline to Teeside (England) 1977: Gas pipeline to Emden, (Germany) 27 North Sea Oil and Gas pipelines (2010) Ekofisk Teeside Emden 28 Geol 40310 Lecture A10 14 Gyda Ula STATPIPE Gyda Ekofisk Infrastructure 2015 J-Block Teeside Emden Water Oil Gas Gas lift gas Fuel Gas Valhall & Hod Valhall 29 Ekofisk field in 2021: 50 years of oil production 1972: Ekofisk A, B, C platforms 1989: Ekofisk W (water injection) 1987: Ekofisk K (water injection) 1996: Ekofisk X (well heads) 1998: Ekofisk J (fluid processing) 2005: Ekofisk M (well heads) 2009: Ekofisk VA (subsea: injection) 2013: Ekofisk Z (well heads) and Ekofisk VB (subsea: injection) (Ekofisk south) 2017 Ekofisk VC (subsea: injection) April 2022: Ekofisk production license extended to 2048. Source: NPD (Norwegian Petroleum Directorate) 30 Geol 40310 Lecture A10 15 Ekofisk field: production and investment Source: NPD (Norwegian Petroleum Directorate) 10,000 million NOK = ca. 1 billion euro 6 million m3 of oil = ca. 2 billion euro (at $50/bbl) 31 Reservoir Development and Production 2. Ekofisk reservoir example: Reservoir geology: naturally fractured chalk Production mechanics: Primary production phase: pressure depletion Secondary production phase: water floodings Compaction drive contribution 4D seismic Infrastructure and pipelines Current production and investment 32 Geol 40310 Lecture A10 16