Potential impact of CO2 on subsurface microbial ecosystems and implications for the performance of storage reservoirs

Studies of the potential environmental consequences of carbon capture and storage (CCS) have, to date, focused on the physical and chemical impacts of CO 2 within stable geological formations together with associated monitoring systems to assure that no significant leakage occurs. If leakage did occur after formal closure of the injection site, this is likely to be restricted to discrete point sources, such as abandoned wells, resulting in locally high concentrations of CO 2 in near-surface ecosystems. Consequently, environmental impacts of localised elevated CO 2 on terrestrial and marine ecosystems are areas of active research. However, the CO 2 storage site could also impact on the deep subsurface microbial ecosystem and biogeochemical processes. This paper describes short pilot studies (2136 h/ 89 days) investigating the changes in physical transport properties that are mediated by microbial activity, within samples of sandstone under experimental conditions simulating deep aquifer and reservoir environments in the North Sea. They showed, for the first time, that P. aeruginosa and indigenous microbial populations can survive exposure to saline fluids saturated with CO 2 . However, little impact on fluid transport under these conditions in these short experiments was observed. It is possible that the microbes require a period of acclimatisation to the extreme environmental conditions generated by the presence of CO 2 before any impacts can be detected. Thus, long-term experiments are needed to clarify the role of microbes on rock transport properties.