Displacement mechanisms of air injection in low permeability reservoirs

Abstract By means of physical modeling and numerical simulation, this paper makes a systematic study on oil displacement mechanism by air injection in low permeability reservoirs. Based on the findings, production performance by air drive is studied through the application of a real low permeability reservoir model. Studies show that air intake capacity is far greater than water intake capacity in low permeability reservoirs. Therefore, air injection, which can effectively supplement and maintain reservoir pressure, can build effective pressure displacement system much easier than water injection. Low-temperature oxidization reaction will occur between oil and the oxygen in air, which consumes oxygen and forms nitrogen drive. At the same time, CO 2 and large amounts of heat are generated, and the temperature in some parts of the reservoir can reach about 200°C. Nitrogen drive contributes 69%; temperature increasing and CO 2 generation contribute 26.7% and 4.3% respectively for the total recovery of air drive. Recovery factors by air drive, nitrogen drive and water drive are also studied respectively by using the real low permeability reservoir model. Recovery factor by air drive for 30 years reaches 21.5%, and it is twice as large as that of water drive, which is 10.6% for the same period. Production performance is significantly improved. Air drive is an effective way for improving production performance and increasing recovery factor.