Abstract
The Brazeau Nisku Q-Pool in west-central Alberta is one of more than forty acid gas injection operations currently active in western Canada. The Nisku Q-Pool, mineralogically essentially dolomite and anhydrite, is a depleted sour gas reservoir in the Upper Devonian Nisku Formation. The Nisku is an oil, sweet and sour gas condensate play at depths ranging from about 2300 m in the northeast to more than 4200 m in the southwest, with a thickness of about 80 to 100 m. A unique feature of this play is that the hydrocarbons are contained in numerous closely spaced pools that have been essentially isolated hydrodynamically from one another since hydrocarbon migration and entrapment about 50-60 Ma ago, as shown by initial reservoir pressures and gas compositions. The hydrodynamic isolation renders these pools suitable for acid gas (H2 S + CO2 ) injection and/or carbon dioxide (CO2 ) sequestration. A thorough stratigraphic, diagenetic, mineralogical, and hydrogeological evaluation of the Nisku Formation suggests that the injected acid gas will remain in the structure that contains the Nisku Q-Pool on a geological time scale. In the highly unlikely case of migration out of the Q-Pool, the acid gas plume would disperse and dissolve in deep formation waters along the flow path. The only possibility for upward leakage of acid gas rapid enough to be of human concern is through wells that were improperly completed and/or are abandoned and are not monitored.
Highlights
Over the past two decades, oil and gas producers in western Canada have been faced with a growing challenge to reduce atmospheric emissions of produced H2S from sour hydrocarbon pools
As of November 2003, there were 42 active acid-gas injection operations in western Canada in depleted oil or gas reservoirs (Figs. 1 and 2), and other locations are under consideration for acid gas injection
Injection gas composition varies from about 4 to 95% in H2S-CO2 or CO2-H2S mixtures, which are the byproducts of sour gas processing
Summary
Over the past two decades, oil and gas producers in western Canada have been faced with a growing challenge to reduce atmospheric emissions of produced H2S from sour hydrocarbon pools. H2S is commonly injected as acid gas, a mixture of H2S and CO2 that is a byproduct of “sweetening” sour hydrocarbons. As of November 2003, there were 42 active acid-gas injection operations in western Canada in depleted oil or gas reservoirs Injection gas composition varies from about 4 to 95% in H2S-CO2 or CO2-H2S mixtures, which are the byproducts of sour gas processing. One of these injection sites is the Brazeau Nisku Q-Pool, a carbonate reef buildup in the Upper Devonian Nisku Formation. The Nisku Q-Pool is a depleted sour gas reservoir, in operation as an injection site
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