Sequestration of anthropogenic CO2 in geological media is a potential solution to the release into the atmosphere of CO2, a greenhouse gas. Basically, there are five ways of sequestering CO2 in geological media: 1) through enhanced oil recovery (EOR), 2) storage in depleted oil and gas geological reservoirs, 3) replacement of methane by CO2 in deep coal beds (ECBMR), 4) injection into deep saline aquifers, and 5) storage in salt caverns. Criteria in assessing the suitability of a sedimentary basin for CO2 sequestration are 1) tectonism and geology, 2) the flow of formation waters, and 3) the existence of storage media (hydrocarbon reservoirs, coal seams, deep aquifers, and salt structures). Because of CO2 properties, identification of the depths of the 31.1 degrees Celsius isotherm and the 7.38 MPa isobar is essential in establishing if CO2 could be sequestered as a gas, as a liquid, or in a supercritical state.
Alberta's subsurface is tectonically stable. The geology of the undeformed part of the Alberta Basin underlying most of Alberta is very favourable for CO2 sequestration due to its layer-cake structure and the existence of confined regional-scale aquifers, oil and gas reservoirs in various stages of depletion, uneconomic coal seams, and extensive salt beds. There are six regions in Alberta with various degrees of suitability and different characteristics in terms of CO2 sequestration in geological media:
Northeastern Alberta; generally not suitable; possibly in gas reservoirs and salt caverns
Eastern Alberta; reasonably suitable; in oil and gas reservoirs and salt caverns
Southeastern Alberta; suitable; in oil and gas reservoirs and deep aquifers
Northwestern Alberta; suitable; in oil and gas reservoirs and deep aquifers
Central Alberta; extremely suitable; in oil and gas reservoirs, deep aquifers, coal seams, and salt beds
Southwestern Alberta; extremely suitable; in oil and gas reservoirs, deep aquifers, and coal seams
Major CO2 producers in Alberta are found in the northeast (oil-sands plants), in the east (heavy-oil and power plants), in the central part (refineries and power, petrochemical, and cement plants), and in the southwest (power, cement, and gas plants). Future work should identify specific sites and means for sequestering CO2 in the vicinity of major CO2 producers, and characterize these sites in terms of capacity and retention time.
Bachu, S., Brulotte, M., Grobe, M. and Stewart, S.A. (2000): Suitability of the Alberta subsurface for carbon dioxide sequestration in geological media; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2000-11, 88 p.