Experimental identification of CO2-oil-brine-rock interactions: Implications for CO2 sequestration after termination of a CO2-EOR project

Carbon dioxide enhanced oil recovery (CO2-EOR) has been widely applied to the process of carbon capture, utilization, and storage (CCUS). Here, we investigate CO2-oil-water-rock interactions under reservoir conditions (100 °C and 24 MPa) in order to understand the fluid-rock interactions following termination of a CO2-EOR project. Our experimental results show that CO2-rich fluid remained the active fluid controlling the dissolution-precipitation processes in an oil-undersaturated sandstone reservoir; e.g., the dissolution of feldspar and calcite, and the precipitation of kaolinite as well as solid phases comprising O, Si, Al, Na, C, and Ti. Mineral dissolution rates were reduced in the case that mineral surfaces were coated by oil. Mineral wettability and composition, and oil saturation were the main controls on the exposed surface area of grains, and mineral wettability in particular led to selective dissolution. In addition, the permeability of the reservoir decreased substantially due to the precipitation of kaolinite and solid-phase particles, and due to the clogging of less soluble mineral particles released by the dissolution of K-feldspar and carbonate cement, whereas porosity increased. The results provide insight into potential formation damage resulting from CO2-EOR projects.