New method for evaluation of fluid interface movement in oil reservoir with gas cap and weak aquifer

Abstract

For the development of oil rim reservoir with gas cap and weak edge water, the management of oil-gas and oil-water interface movement is extremely critical. In this paper, a new method for evaluation of fluid interface movement has been put forward, from which the law of fluid interface movement can be recognized clearly and production strategy can be designed reasonably. The new method is based on the material balance principle and the conditions of water influx, fluid expansion and oil & gas production. By analyzing the volume of gas intrusion and water influx, the rate of movement of oil-water and oil-gas interface can be obtained. Then we studied the regular of fluid interface movement and pressure variation, and gave a single reasonable production strategy and a stage reasonable production strategy. Finally, the applicability analysis was carried out. The method can be used to predict the movement speed, movement distance of fluid interface and water influx at different times and different production strategies. Meanwhile, it can be applied to analyze the influence degree of each factor, which affects the moving of fluid interface. The results indicate that: i) The rate of the oil-water interface increases with the increase of the oil production rate and injection-production ratio. The rate of the oil-gas interface increases with the increase of the injection-production ratio, while the gas production rate has less influence on it. ii) For single reasonable production strategy, when time and injection-production ratio is constant, with the increase in oil production rate, the reasonable gas production rate also increases as cubic function correspondingly; When the oil production rate is constant, with the increase in injection production ratio, the corresponding reasonable gas production rate decreases. iii) The earlier the reasonable production strategy is implemented, the slower the formation pressure drops, and the more favorable for development.