Experimental study of natural gas flooding to improve the recovery of tight glutenite reservoir

Abstract

ABSTRACT Tight glutenite reservoir in Mahu area are usually put into production by volume fracturing of horizontal wells. In the process of production, there are some problems such as rapid production decline, low recovery factor, and so on. Therefore, experimental study of natural gas flooding to improve the recovery of tight glutenite reservoir was carried out. Using cores of different diameter sizes from the target interval of the target area, the whole development process of different gas injection speeds and different development methods is simulated by the core displacement devices with high temperature and high pressure resistance. The characteristics of exhaustion, displacement, development effect, and action mechanism were evaluated and analyzed systematically. The study shows that the better the physical properties of the tight glutenite, the higher the recovery degree of the exhaustion development. As the pressure is reduced from 55MPa to 10MPa, the recovery degree can reach about 6%. Natural gas flooding after exhaustion can greatly improve oil recovery. The results of laboratory experiments show that the recovery efficiency of natural gas flooding after depletion can be improved by 38%–62%. The higher the gas injection rate is, the lower the final recovery rate is. With the displacement velocity increasing from 0.02 ml/min to 0.1 ml/min in laboratory experiments, the corresponding ultimate recovery rate decreased from 67.03% to 44.67%. Therefore, field operations need to control the gas injection rate to ensure higher gas flooding recovery. According to the experimental results of natural gas flood-soaking-natural gas flooding, the final recovery is 38.54% under miscible condition. The recovery of gas flooding stage before soaking is 27.97%. Compared with natural gas flooding, the oil displacement efficiency can be improved by nearly 10% in the development mode of natural gas flooding-soaking-natural gas flooding, which is due to its mechanism including the following three stages. First is near-miscible flooding which plays a role in intergranular pores, micro-fractures, and pressure fractures in the gas flooding stage before soaking. Second is miscible dissolution replacement which plays a role in intergranular dissolved pores in the soaking stage. Third is gas carrying oil recovery which plays a role in pressure fractures in the gas flooding stage after soaking. Finally, the development mode of natural gas flooding-soaking-natural gas flooding can achieve enhanced tight glutenite recovery.