Performance of Electroassisted Carbonated Water Injection (ECWI) for Enhanced Oil Recovery and CO2 Storage in Tight Formations

Abstract In this work, the conventional carbonated water injection (CWI) has been significantly enhanced by adding a direct current (DC) electric field, i.e., the electroassisted CWI (ECWI) process, to improve its injectivity in a tight reservoir for enhancing oil recovery and subsequent CO2 storage. Experimentally, we conducted a series of well-designed tests to evaluate the ECWI performance in a tight reservoir and identify the key underlying mechanisms associated with oil recovery and CO2 storage. Early adoption of the ECWI in a tight sandstone reservoir results in the highest oil recovery, up to 61.9%, compared to 51.2% for the CWI and 41.3% for conventional waterflooding. During the ECWI process, a voltage of 10 V achieves the highest oil recovery, while 15 V provides the best water injectivity. Also, the enhanced oil recovery (EOR) mechanisms are closely associated with both electroosmosis and the enhancement of carbonized water–rock reactions induced by a DC electric field. An increase in voltage during the ECWI enhances these two phenomena, resulting in an increase in displacement efficiency and a decrease in volumetric sweep efficiency, with the former being dominant. During the ECWI process, oil recovery increases with an increase in voltage until the reduction in volumetric sweep efficiency cannot be offset by the increase in displacement efficiency. Also, the ECWI process accelerates CO2 dissolution in formation water and residual oil while enhancing CO2 storage capacity.