Injection of acid gas into the Wabamun Group in the Pembina area of west-central Alberta has taken place since 1994. To date, close to 40 million m3, or 60 kt, acid gas have been injected into this aquifer.
If only the natural setting is considered, including geology and flow of formation waters, the basin to local-scale hydrogeological analysis indicates that injecting acid gas into the Wabamun Group in the Pembina area is basically a safe operation with no potential for acid gas migration to shallower strata, potable groundwater and the surface. Although the Wabamun Group is characterized as a regional aquifer, the average permeability in the Pembina area is relatively low, and intervals of high porosity and permeability occur only locally and are not well connected. There are many physical and hydrodynamic barriers to acid-gas migration from the injection zone into other strata, and the flow process, if it will ever happen, would take an extremely long time on a geological time scale. Any acid-gas plume would disperse and dissolve in formation water during flow on such large time and spatial scales.
Based on available data, it seems there is no potential for acid-gas leakage through fractures. However, the possibility for upward leakage of acid gas exists along wells that were improperly completed and/or abandoned, or along wells whose cement and/or tubing have degraded or may degrade in the future as a result of chemical reactions with formation brine and/or acid gas.
Bachu, S., Buschkuehle, B.E., Haug, K. and Michael, K. (2008): Subsurface characterization of the Pembina-Wabamun acid-gas injection area; Energy Resources Conservation Board, ERCB/AGS Special Report 93, 60 p.