Reservoir scale CO2-water-rock interactions and geochemical evolution of sandstone reservoirs due to CO2 geo-storage process

CO2 injection into geological formations is essential for enhanced oil recovery and CO2 geological sequestration. Although sandstone saline aquifers are considered as important CO2 storage sites, the reservoir scale CO2-water-rock interactions and the associated geochemical evolution due to the CO2 sequestration process in the sandstone reservoir and their effect on CO2 mineral trapping of sandstone reservoirs has not been addressed effectively. Thus, in this paper, we studied the impact of CO2 injection on CO2-Water-sandstone interactions by simulating a three-dimensional permeable sandstone reservoir overlying by a shale caprock layer. The chemical compositions of the sandstone and shale samples were measured using a quantitative X-ray diffraction (XRD) instrument. The simulated sandstone reservoir consisted mainly of quartz, kaolinite, chlorite, and illite, while the shale layer consisted of quartz, ankerite, calcite, illite, albite, and chlorite. CO2 was injected at a depth of 1865 m for a period of 10 years at a rate of 1Mt per year and then stored for the next 100 years. Our simulation results show that CO2-water-sandstone interactions lead to significant variations in the mineral compositions of the sandstone reservoir. The simulation results show that chlorite was dissolved and illite was participated for the whole sandstone reservoir. However, the reactions of quartz and kaolinite vary with the reservoir depth and storage time. In addition, the results show that CO2-water-sandstone interactions lead to decrease the pH of the formation. Thus, we conclude that CO2 injection in the sandstone reservoir leads to significant geochemical reactions (dissolution and precipitation). These results have important implications for CO2 storage in estimating CO2 flow in porous media and its entrapment and fluid spreading in the sandstone reservoir.