Laboratory study of nitrogen/foam enhanced oil recovery from vuggy-fractured carbonate reservoirs

Abstract

Aiming at a special vuggy-fractured carbonate, the mechanism of nitrogen flooding, co-injection of water and nitrogen (CWN), water alternating gas injection (WAG) and foam flooding was studied by slate model. Experimental results showed that mechanism of nitrogen flooding was displacing attic oil, which was similar to other vuggy fractured reservoirs. While to CWN, the main mechanism was not relieve of gas channeling. It was found that gas mainly flowed through the upper hole or the upper location of hole and water mainly flowed along the lower hole or the lower location of hole. The main reason why CWN recovery was higher than nitrogen flooding was that during nitrogen flooding, nitrogen would substitute attic oil, so some oil would flow to the water channel and form remaining oil in water channel. During CWN, water flowed mainly along the water channel in previous water flooding, so remaining oil in water channel would not occur during CWN. While to WAG, it had lowest recovery. Among the previous three flooding methods, remaining oil named “sandwich oil” was found between gas and water.