Flow Performance of Two-Phase Fluid in Carbonate Fractured-Vuggy Media under HTHP Conditions

Abstract In the middle-late stage of depletion development, water influx and channeling are usually unavoidable in deep carbonate fractured-vuggy reservoirs, which leads to a rapid increase in water cut of production wells, thus significantly reducing the total oil recovery. This study focuses on flow performance of oil and water in carbonate fractured-vuggy media under high-temperature and high-pressure conditions, the two-phase flow characteristics of porous vs. porous-fractured media and fractured vs. fractured-vuggy media are investigated and compared respectively based on lab tests. It is found that oil recovery of waterflooding in the porous-fractured media is only 37.36%, which is much lower than that in the porous media (60.69%), indicating that the presence of fracture can greatly reduce the co-seepage time of oil-water and result in a decrease of total oil recovery. The oil recovery of the fractured and fractured-vuggy media is 85.97% and 53.09%, respectively. The quite obvious difference shows that when the injected water flows into the vug structures along the fracture at a pretty low speed, only part of the oil can be displaced out by the effect of gravity differentiation. The other rest of oil would be widely distributed in the upper part of the vug structures and sealed as remaining oil, which is quite difficult to be driven out. This study reveals the flow law of two-phase fluid in fractured-vuggy media under HTHP conditions, providing novel insights into flow mechanisms of carbonate reservoirs with different scales of flow and storage structures.