Acid-Gas Injection at Watelet, Alberta: An Analogue for the Detailed Characterization of a CO2 Sequestration Site

Karsten Michael¹, Beate E. Buschkuehle¹, and Stefan Bachu^2
1 Alberta Energy and Utilities Board, Edmonton, AB
² Alberta Geological Survey, Edmonton, AB

Geological sequestration of CO2 is an option for significantly reducing emissions into the atmosphere. Various operators in western Canada are currently injecting acid gas (CO2 and H2S) into deep formations. The Alberta Geological Survey conducted a comprehensive subsurface characterization of the regional and local-scale geology, reservoir characteristics, mineralogy, in-situ fluid properties, hydrogeology and stress regime at various acid-gas injection operations in the Alberta Basin to assess the long-term fate of injected acid-gas in the subsurface. At Watelet, south of Edmonton, a mixture of approximately 90 % CO2 and 10 % H2S has been injected since 1997 at 1250 m depth into Devonian platform carbonates of the Cooking Lake Formation, which form a regional aquifer. Overlying shales of the Ireton Formation and the underlying tight argillaceous limestones of the Beaverhill Lake Group vertically confine the Cooking Lake aquifer. On the basis of permeability and porosity values for the Cooking Lake aquifer, and of acid gas and brine properties, an order-of-magnitude analysis shows that, once outside the influence of the injection well, the velocity of the updip migrating acid gas is a few metres per year. Migration times to shallow groundwater or the ground surface in the order of thousands to millions of years would lead to the dissolution of acid gas in formation water and dispersion of any acid gas plume along the flow path. The experience with the acid-gas injection at Watelet and other operations in Alberta has shown that the process of CO2-injection into deep aquifers is technically feasible.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005