Geology of the Gull Lake North ASP Flood, Upper Shaunavon Formation, Southwest Saskatchewan By Sid Leggett, Husky Energy (sid.leggett@huskyenergy.com)
Acknowledgements Husky Energy Members of the Gull Lake ASP Team Graham Jackson Curtis Cymbaluk Dorian Holgate Wendy Shier Doug Flaig Kent Barrett
Talk Outline What is Alkali/Surfactant/Polymer (ASP) flooding? Criteria for pool selection. Gull Lake Upper Shaunavon pool. Stratigraphy, sedimentology and environment of deposition. Reservoir details. Summary
What is Alkali Surfactant Polymer Flood? Alkali: Sodium Hydroxide (NaOH) or Sodium Carbonate (Na 2 CO 3 ). Reduces adsorption of the surfactant on the rock surfaces Reacts with acids in the oil to create natural surfactant. Surfactant (Soap!) Reduces interfacial tension. Polymer Improves the sweep efficiency.
ASP Screening Criteria Sandstone preferred over carbonates Thick unstratified reservoir with few barriers No bottom water or gas cap Low clay content (<5%) Permeability > 100md Porosity > 15% Residual oil saturation after water flood > 35% Size Light to intermediate crude with organic acids
Location Gull Lake North Pool
PALEOZOIC MESOZOIC CRETACEOUS Regional Stratigraphy U. SHAUNAVON L. SHAUNAVON Top of the Middle Jurassic. Mixed siliciclastic/ carbonate unit. Transition from a carbonate depositional setting to one dominated by terrigenous sediments. Bounded by low relief regional unconformities.
Upper Shaunavon Regional Geology Isopach Top Mississippian to Top Lower Shaunavon Modified from J.E. Christopher, 1964 Mississippian to Lwr Shaunavon isopach reflects Upr Shaunavon depositional surface. Center of the Williston Basin to the southeast. Truncated to the northwest by the Sweetgrass Arch. Gull Lake North area located on the Gull Lake Front east of the Tompkins Apron.
A2 Member Channel Isopach Upr Shaunavon Fm. The Upper Shaunavon at Gull Lake NW-SE trending tidal channel that forms the reservoir for the Gull Lake North pool. Channel is up to 10.3m thick. Discovered in 1953. Waterflood initiated in 1956. 22.3API, 24 cp intermediate crude
Porous Sandstone (A2) Very fine grained sandstone. Minor calcareous cement. Crossbedding, flaser bedding, shale ripups and drapes, shale couplets and back climbing ripples. Tidal influence.
Coquina and Calcareous Sandstone Thin walled bivalve coquinas, crinoids, peloids, and rare gastropods. Marine environment of deposition. Early calcite cementation during a period of subaerial exposure.
Shaunavon Environment of Deposition Turks and Caicos Platform - Large shallow marine platform - Skeletal grainstones, peloidal grainstones and packstones and oolitic grainstones. German Bay - Complex of intertidal flats and tidal channels. - Channels oriented perpendicular to the general shoreline. - No beach or barrier bar.
Oil and Gas Hydrodynamic Fairway Map Trapping Mechanism Gull Lake N Fluid flow towards a north-south hydrodynamic low. Gas structurally updip to the northeast. Oil only along the main fairway (green). Oil is trapped in structural highs and updip pinchouts (blue). Gull Lake N is located at transition.
Oil Upr Shaunavon, A2 Channel, Net Porosity Map Water Reservoir Details Estimated reserves for the entire reservoir: 110MM bbls OOIP. Gull Lake North pool reserves: 76MM bbls OOIP, recoverable with water flood 26MMbbls (34.5%). Average net pay of 4.6m (up to 9.6m), porosity of 20% and average permeability of 384md. Downdip water leg with an oil/water contact of - 372.5mSS. Clays: between 0.5 and 0.9% Kaolinite and 0.2 and 0.6% Illite.
Summary Gull Lake North Upper Shaunavon pool is a large incised tidal channel composed of a mixture of porous sandstone and tight limestone. Hydrodynamic/structural trap resulted in oil accumulating in the updip part of the tidal channel. The pool met most of the key criteria for an ASP tertiary flood: Sandstone. Thick unstratified reservoir. No gas cap. Low clay content. Permeability > 100md. Porosity > 15%. Residual oil saturation > 35%. Intermediate crude with organic acids. Size. Only one negative criteria: water leg. X Srl, 4/09