The experience gained since the start of the first acid-gas injection operation in Canada in 1989 shows that, from an engineering point of view, acid-gas disposal is a well-established technology. Close to 1.5 Mt CO2 and 1 Mt H2S have been successfully injected into deep hydrocarbon reservoirs and saline aquifers in Alberta and British Columbia. A major issue that has not been addressed is the containment and long-term fate of the injected acid gas. Although no incidents of long-range migration or leakage have been detected and reported to date, both operators and regulatory agencies should consider this issue.
The Alberta Energy and Utilities Board recently approved injection of acid gas into the Nisku Q Pool in the Pembina-Brazeau area in Alberta. The operator has met all the current requirements for obtaining regulatory approval; however, the application does not contain a comprehensive hydrogeological analysis because currently it is not required.
If only the natural setting is considered, including geology and flow of formation waters, the basin to site-scale hydrogeological analysis indicates that injecting acid gas into the Nisku Q Pool is basically a safe operation with no potential for acid-gas migration to shallower strata, potable groundwater and the surface. There are many physical and hydrodynamic barriers to acid-gas migration from the injection formation 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. and Michael, K. (2008): Subsurface characterization of the Brazeau Nisku Q pool reservoir for acid gas injection; Energy Resources Conservation Board, ERCB/AGS Special Report 95, 62 p.