Laboratory Evaluation of Electrically Enhanced Oil Recovery in Tight Reservoirs

By coupling the electrokinetic phenomenon, the direct current (DC) electric field has recently been considered as a novel process to enhance oil recovery over waterflooding. We conducted a series of coreflood experiments to evaluate the performance of electrically enhanced oil recovery in tight reservoirs and identify the key underlying mechanisms. Results show that the oil recovery induced by the DC electric field is higher than that of waterflooding. The oil recovery increases first and then decreases with the enhancement of the DC electric field. Using 0.05 mol/L NaCl solution with 10 V voltage, the highest oil recovery of 55.6% was increased by 28.4% compared with the average oil recovery (43.3%) of waterflooding. Not only does electroosmosis reduce the required pressure from 19.20 to 15.89 MPa with its variation proportional to the DC voltage and ion concentration but also such an electrochemical reaction changes the core mineral compositions (i.e., increasing the clay content but decreasing the orthoclase and calcite content), evidenced by a decrease in both contact angle up to 27.34% and absolute zeta potential up to 22.21%. By reduction of the flow resistance of water and increase of the oil-water ratio, electroosmosis shortens the time for the water at the displacement front to reach the outlet and reduces the volumetric sweep efficiency. Meanwhile, electroosmosis causes a smooth velocity profile similar to the piston-like displacement and increases displacement efficiency. Once a reduction in volumetric sweep efficiency could not be offset by an increase in displacement efficiency, oil recovery would be first improved with an increase in both voltage and ion concentration and then decreased, among which the effect of ion concentration is not as significant as that of the voltage.