Monitoring of fluid-rock interaction and CO2 storage through produced fluid sampling at the Weyburn CO2-injection enhanced oil recovery site, Saskatchewan, Canada

Addition of CO2 to water-rock mixtures comprising carbonate minerals causes dissolution of carbonates and production of alkalinity. Geochemical modeling suggests dissolution is taking place, however more detail on water-oil-gas ratios needs to be gathered to obtain more accurate estimates of pH at the formation level. Geological storage of CO2 relies on the potential that, over the longer term, silicate minerals will buffer the pH, causing any added CO2 to be precipitated as calcite. Some initial modeling of water-rock reactions suggests that silica sources are available to the water resident in the Midale Formation, and that clay minerals may well be capable of acting as pH buffers, allowing injected CO2 to be stored as carbonate minerals. Further work is underway to document the mineralogy of the Midale Formation and associated units so as to define more accurately the potential for geological storage.