Quantification of oil recovery efficiency, CO2 storage potential, and fluid-rock interactions by CWI in heterogeneous sandstone oil reservoirs

Abstract

Significant interest exists in improving recovery from oil reservoirs while addressing concerns about increasing CO2 concentrations in the atmosphere. The combination of Enhanced Oil Recovery (EOR) and safe geologic storage of CO2 in oil reservoirs is appealing and can be achieved by carbonated (CO2-enriched) water injection (CWI). So far, through several flooding experiments, the potential of carbonated water injection as an EOR scenario has been investigated. While several coreflood experiments on homogeneous cores have been performed, there is no information on the effectiveness of CWI for oil recovery and CO2 storage potential on heterogeneous cores. Since not all the oil reservoirs are homogenous, understanding the potential of CWI as an integrated EOR and CO2 storage scenario in heterogeneous oil reservoirs is essential.With this objective, a series of high-pressure and high-temperature coreflood experiments were performed on a heterogeneous sandstone core. Based on the results, the heterogeneity of rock dominated water and carbonated water flow paths led to early breakthrough. However, interestingly, the ultimate oil recovery by CWI, either as the secondary or tertiary injection scenario, was higher than that of conventional waterflooding. Both secondary and tertiary CWI showed a strong potential for increasing oil recovery from the heterogeneous core and re-mobilized part of the trapped oil. In addition to the strong oil recovery by CWI, CWI demonstrated the good potential for safe underground storage of CO2 in heterogeneous reservoirs. Furthermore, carbonated water-sandstone rock interactions led to the slight mineral dissolution of the rock and separation of the submicron inorganic particles from the surface of the rock. These inorganic particles, which were previously interacting with asphaltenes and polar components of the oil during the ageing period, produced a hydrogen bond with water and formed oil in water emulsion. This phenomenon is called “Pickering emulsion” which can lead to wettability alteration from oil-wet towards more water-wet conditions and in turn a better oil recovery by CWI.