A saline aquifer can refer to any one of a number of sedimentary rock types saturated with saline, non-potable water, from which the water can be drawn, and into which fluids can be injected (IEA, 2004). Deep saline aquifers provide the greatest volumetric potential for storage anywhere in the world (as high as 10,000 Gt).
Saline aquifers run deep under all 68 Canadian sedimentary basins, and provide access to storage opportunities in many parts of the country. The Petroleum Technology Research Centre began a project in 2009 that will see CO2 captured from a Regina, Saskatchewan refinery into a nearby deep saline formation. In addition, the Alberta Government is sponsoring projects with CCS fund involving deep saline injection.
Statoil’s Sleipner Project, which is 250 km off the coast of Norway in the North Sea, is the first commercial-scale project dedicated to CO2 storage in a deep saline aquifer. The Sleipner natural gas production field provides approximately 1 MtCO2/yr for storage in the aquifer (IEA, 2004). Since 1996, the site has not experienced any CO2 leakage, and the project is proving technically feasible (IEA, 2004). The entire project will store some 20 MtCO2 in its lifetime, although the total storage capacity is hundreds of times larger (IPCC, 2005).
H2S produced through sour gas desulphurisation cannot be released into the atmosphere. Currently, there are limited markets for sulphur, and the processing of H2S using the Clauss process is uneconomic. Consequently, more and more gas producers in the Alberta Basin in Western Canada are turning to acid gas (H2S & CO2) injection in geological media as a means to deal with the produced H2S from sour gas.
The first acid gas injection operation in Alberta started in 1989 and in 1995 there were 5 operations; in 1998 there were 21, and currently there are 29.
The composition of the injected acid gas varies between 7 to 95 % CO2 and 4 to 83% H2S, with minor amounts of methane. The licensed daily injection rate for CO2 in Alberta is ~900 t/d ( ~ 0.33 Mt/yr). Acid gas is injected in 11 depleted hydrocarbon reservoirs and 23 deep saline aquifers at 29 different locations. Of these, 9 are in sandstone and 25 in carbonate rocks.