Effects of Mobile Water on Multiple-Contact Miscible Gas Displacements

This paper presents the effects of mobile water on multiple contact miscible displacements under water-wet and oil-wet conditions. Tests were conducted in 8-foot (244 cm) water-wet and oil-wet Berea cores in which CO/sub 2/ and water were injected both separately and simultaneously to displace a reservoir oil. The data presented focus on effects of water in the oil-moving zone where the CO/sub 2/ is generating miscibility with the oil and mobilizing residual oil to waterflooding. Special emphasis is placed on understanding the effect of mobile water saturation on the oil displacement efficiency and the component transfer between phases necessary to develop miscibility in the CO/sub 2/-reservoir oil system. This study demonstrates that reservoir wettability is a key factor in the performance of AGWIP. Gas-water injection can, under certain conditions, have adverse effects on the characteristics of the oil moving zone. These effects are in part caused by the water trapping portions of the oil and solvent. It was observed that mobile water did not change the mass transfer process by which miscibility develops in a multiple contact miscible displacement. (JMT)