Hydrodynamic trapping of injected acid gas in the Alberta Basin, Western Canada

Publisher Summary This chapter discusses that various operators in Alberta are currently injecting CO2 and/or CO2-H2S-mixtures into deep formations, for acid gas disposal. The long-term containment of acid gas appears to be relatively certain in depleted reservoirs as indicated by the previous accumulation and trapping of hydrocarbons in these structures. Also, the reservoir capacity is well known from the volumes of the produced oil or gas. Conversely, aquifers represent migration pathways for fluids, and potential travel times of injected acid gas and injection capacity depend on the flow regime and aquifer permeability. In the Alberta Basin there are many hydrostratigraphic and hydrodynamic barriers to acid gas migration, resulting in a long migration pathway from the injection zone into shallower strata and ultimately to the ground surface. Migration times 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 acid-gas injection in Alberta has shown that the process of CO2-injection into deep geological media is technically feasible. However, the theoretical analysis of the long-term containment of the injected gas still needs to be confirmed by actually monitoring the movement of acid gas in the subsurface.