Geochemical aspects of CO2 sequestration in deep saline aquifers: A review

Abstract

Abstract Carbon dioxide has been identified as one of the main compounds affecting the stability of the earth’s climate. The reduction of the total volume of greenhouse gases emitted to the atmosphere is considered a key mechanism to mitigate climate change. Geological storage of CO2 in deep saline aquifers is currently a well-accepted method of storage, because saline aquifers have larger storage capacities than other geological media. Rock–water–CO2 interactions initiated in the aquifer with CO2 injection play a vital role in CO2 sequestration in saline aquifers, and include different trapping mechanisms: geological trapping, hydrodynamic trapping and geo-chemical trapping (solubility trapping and mineral trapping). Of these, geological trapping and solubility trapping are more effective in the short term, but mineral trapping is safer and more economical in the long term. Current knowledge of geochemical trapping is still at an early stage compared to other trapping mechanisms due to the extensive time required to complete the process. To date, very few studies have been conducted on sandstone reservoirs, which are considered to have the largest storage capacity among geological formations. However, due to the long-term safety of CO2 storage with geochemical trapping, there has been a recent trend to research this process. Both solubility and mineral trapping processes in saline aquifers depend on injecting CO2 and the fluid–rock mineral properties of the aquifers. Until very recently, although it was assumed that temperature, pressure, the salinity of the formation water and the mineral composition of the formation rock are the only parameters which affect mineral trapping, recent research has shown that a number of other reservoir parameters, such as layer thickness, tilt angle, anisotropy and bedding pattern may also significantly affect geochemical trapping. This review provides a comprehensive examination of the current knowledge of the geo-chemistry of solubility and mineral trapping processes in deep saline aquifers.