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Geology of the Gull Lake North ASP

Flood, Upper ShaunavonFormation, Southwest

Saskatchewan

By Sid Leggett, Husky Energy

(sid.leggett@huskyenergy.com)

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Acknowledgements

Husky Energy

Members of the Gull Lake ASP Team

Graham Jackson

Curtis Cymbaluk

Dorian Holgate

Wendy Shier

Doug Flaig

Kent Barrett

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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

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What is Alkali Surfactant Polymer Flood?

Alkali: Sodium Hydroxide (NaOH) or Sodium

Carbonate (Na2CO3).

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.

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ASP Screening Criteria

Sandstone preferred over carbonates

Thick unstratified reservoir with few barriers

No bottom water or gas cap

Low clay content ( 100md

Porosity > 15%

Residual oil saturation after water flood > 35% Size

Light to intermediate crude with organic acids

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Location Gull Lake

North Pool

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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.

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The Upper

Shaunavon at

Gull Lake

NW-SE trendingtidal channel thatforms the reservoirfor the Gull Lake

North pool. Channel is up to

10.3m thick.

Discovered in 1953.

Waterflood initiatedin 1956.

22.3API, 24 cpintermediate crudeA2 Member Channel Isopach

Upr Shaunavon Fm.

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Coquina and

Calcareous

Sandstone

Thin walled bivalve coquinas, crinoids, peloids, and raregastropods.

Marine environment of deposition.

Early calcite cementation during a period of subaerialexposure.

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Trapping

Mechanism

Fluid flow towards anorth-southhydrodynamic low.

Gas structurally updipto the northeast.

Oil only along the mainfairway (green).

Oil is trapped instructural highs andupdip pinchouts (blue).

Gull Lake N is locatedat transition.

Gull Lake N

Oil and Gas Hydrodynamic Fairway

Map

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Reservoir Details

Estimated reserves for

the entire reservoir:110MM bbls OOIP.

Gull Lake North poolreserves: 76MM bblsOOIP, recoverable withwater flood 26MMbbls(34.5%).

Average net pay of 4.6m(up to 9.6m), porosity of20% and averagepermeability of 384md.

Downdip water leg withan oil/water contact of -372.5mSS.

Clays: between 0.5 and0.9% Kaolinite and 0.2and 0.6% Illite.

Upr Shaunavon, A2

Channel, Net Porosity

Map

Water

Oil

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Summary

Gull Lake North Upper Shaunavon pool is a large incised tidalchannel composed of a mixture of porous sandstone and tightlimestone.

Hydrodynamic/structural trap resulted in oil accumulating in theupdip 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