Flow characteristics and EOR mechanism of foam flooding in fractured vuggy reservoirs

Abstract

Deep fractured vuggy reservoirs are characterized by complex structures, harsh formation conditions and strong heterogeneity. Accordingly, foam stability was first assessed under high-temperature, high-pressure conditions. A microetched physical model mimicking the fractured vuggy reservoir was constructed. Then, the static features of the foam in the model was inspected. The flow characteristics and EOR mechanism of foam flooding in the microetched model were analyzed. Foam stability results show that at low pressures, the foam volume first increases and then decreases with increasing temperature. With increasing pressure, the influence of temperature on foam stability gradually declines. Within the microetched model, the foam displayed better fluidity in karst caverns, whereas better static stability is attained in the fractures. Gravity impacted oil recovery during water and foam flooding. Bottom water flooding induced uniform rise of the oil-water interface, hence achieving highest oil recovery of 49%. Foam flooding following helped recovering residual oil near the top of the caverns. Employing high-velocity foam flooding following low-velocity foam flooding increased the sweep efficiency of oil entrapped in the dead-end pores. Coupling bottom water flooding with foam flooding is the most promising technique.