Effect of supercritical CO2/water interactions on geomechanical behavior of quartz-rich sandstone for CO2 geological storage

In the course of CO2 injection into a storage reservoir, understanding of a volumetric change (e.g., swelling), induced by interacting among CO2, water and rock into pores of rocks should be a critical step for modeling of hydro-mechanical response relevant to CO2 capture and storage (CCS) technology. For the majority of ongoing and planning CCS sites in the globe, hard sedimentary rocks, which is main component of quartz and feldspars with less clay minerals (e.g., smectite, illite), is a representative reservoir rock. It is well-known that caprocks (i.e., mudstone and shale) occur the swelling behavior of a rock matrix in the presence of water and/or CO2 due to intercalation and exchange reactions between layers of clay minerals. However, such volumetric change effect for quartz-rich rocks is not yet being investigated enough. In this study, we investigate geomechanical behavior of quartz-rich sandstone (Berea sandstone) in supercritical CO2 (scCO2)-water system under effective pressure of 10 MPa for up to approximately 1 week, the condition of which assumes that CO2 is injected into a storage reservoir at 1 km depth. Our results demonstrated that quartz-rich sandstone had a significant potential for changes in geomechanical properties (i.e., axial stress, displacement, volumetric strain) in scCO2-water system, like that do clay-rich caprocks, although little the change being observed for only water-saturation under the same effective stresses, and its maximum value was approximately 0.3 % for scCO2/water system. Also, increasing axial stress induced by the change in volumetric strain of the rock sample tested were more than 1 MPa for all experimental runs. A comparison results suggested that the obtained volumetric strains for this system could not be explained fully by change in bulk modulus before and after introducing scCO2 into the rock sample. The findings of our study might provide a significant contribution for the coupled hydro-mechanical behavior in storing CO2 into hard sedimentary rocks.