Numerical simulation study of gas-cap reservoir barrier water injection fluid interface migration laws

Based on the reservoir property of Zhanazhol oil reservoir with gas cap in Kazakhstan, the numerical model of oil reservoir is built to explore the migration law for oil reservoir with gas cap barrier waterflooding: before the barrier formation, barrier water flows towards gas cap and oil ring according to the migration law of radial flow to supplement the formation energy of the oil area and gas area, respectively, effectively inhabit the expansion energy of gas cap, reduce the migration velocity of the oil-gas interface. After the barrier formation, the barrier cuts off the channel communicating the oil area with the gas area to separate the oil reservoir with gas cap into an oil reservoir with big gas cap and an oil reservoir with small gas cap, so as to realize the separate exploitation of gas cap and oil ring and effectively prevent the mutual channeling of oil and gas. In combination with the barrier water injection migration laws, the reservoir engineering methods of gas-cap reservoir barrier water injection exploitation before and after the formation of the barrier are set up and the fluid interface migration speeds at different development phases are calculated according to the material-balance principle. And in accordance with the calculation results, before the formation of the barrier, the oil-gas interface migration speed decreases with the increasing of the barrier injection-production ratio, and it slows down more seriously when the barrier well is nearer the outside oil-gas interface, however, there are risks of invasion of crude oil into gas cap. After the formation of the barrier, the oil gas interface is translated into oil-water interface and gas-water interface, the oil-water interface migration speed increases with the increasing of oil recovery rate, and the gas-water interface migration speed increases with the increasing of gas production rate. The fluid interface migration laws at different stages of gas-cap reservoir barrier water injection are further studied respectively by means of laboratory experiments and reservoir engineering methods and the study results have guiding significance for field personnel in the control of fluid interface migration direction and speed.