Research On Experiments Of Developing Oil Reservoir And Gas Injection Of Hyperosmotic Thick Oil Layers

Most of main oil layers of main oil fields in China belong to thick oil layers and mainly adopt water injection development. Since the difference between the reservoir lithology and the physical property of the thick oil layers is bigger, the heterogeneity in the reservoirs and the plane is stronger, under the effect of gravitational differentiation, an existing mode of water injection development easily generates water breakthrough, the efficiency of washing the bottom with water and displacing oil on the top is low, the contradiction in the layers is prominent, an existing technique can not solve the problem of a whole set of big and thick layer that the efficiency of flood sweep is low.According to domestic and overseas investigation and study materials, America California Buena Vista Oil Field and Daqing Oil Field carry out water and gas alternate injection to solve the problems of washing the bottom of the oil layer with water and low water flooding efficiency, and the water and gas alternate injection increases the water flooding recovery efficiency. However, as for the hyperosmotic thick oil layers, whether the gas injection development can increase the final recovery efficiency also needs further investigating. Aiming at the problem, we consult relevant materials of the thick oil layers, artificial core simulated reservoirs are manufactured, plane models are adopted to simulate basic well patterns (a five-point method), simulated oil is prepared, and laboratory experiments of long core and plane model water driving oil, natural gas driving oil, water-gas alternate driving oil, saturation distribution experiments after the oil is driven of three displacement modes are carried out successively.Oil driving effects under different displacement modes are compared, phenomena which are generated in the displacement process and mechanisms of action are deeply analyzed, and finally an optimum driving mode and injection parameters are selected. The experimental results show that as for the hyperosmotic thick oil layers, the flood sweep coefficient is low, the natural gas driving recovery efficiency is low, the gas breakthrough is rapid, the recovery efficiency of adopting water-gas alternate driving is high, water breakthrough and gas breakthrough are slow, the ascending velocity of water content and production gas oil ratio is slow, and the water-gas alternate driving time is earlier, the oil driving effect is better.Three oil driving modes are compared, water injection development is better than gas injection development, the recovery efficiency of water-gas alternate driving is higher than single water driving and single gas driving since after water and gas are injected alternately, three-phase flow of oil, gas and water is formed in the oil layers, the flow resistance of the water is increased, thereby, the contradiction between and in the layers is reduced, the suction profile is improved, and the suction thickness is increased. Simultaneously, residual oil on the top is driven and swept due to the effect of gravitational differentiation of injected gas. The rational gas-water ratio of water-gas alternate driving should be 1:1, and the slug injection is 0.02PV.