Research On Gas Injection For Enhancing Oil Recovery In Fractured Low-permeability Reservoir

Generally, the reserves of worldwide oil fields with low permeability are tremendous and the significance of reservoirs with low permeability is increasingly fortified as most of reservoirs with middle and high permeability come into the stage of high water cut. Since the rock densification increases coupled with increasing intensity and brittleness of rock in low-permeability reservoir, the reservoir will develop various degrees of fractures under the effect of tectonic stress field, which cause the formation of fractures associated with low-permeability reservoirs, and that of fractured low-permeability reservoir. The development of fractures coupled with the complexity of its distribution makes it very tough to develop low-permeability reservoirs. Gas injection, as an effective technology for enhanced oil recovery, can promote the recovery effectively when it is applied in fractured low-permeability reservoir. Thus, developing the research on gas injection for EOR in fractured low-permeability reservoir occupies strategic significance for petroleum industry all over the world.Combining experiments and simulation, this article studied and compared the advantages of N2 injection for EOR in fractured low-permeability. The properties of microballon and foam were evaluated followed by optimizing injection mode of N2 with fractured core, and at last, the parameters in targeted block such as the injection volume of N2 were optimized with numerical reservoir simulation.It is concluded from the results of experiments that the injection timing of N2 has a large effect on EOR, and N2 injection in early stage of water producing and liquid-alternating-gas make for the development of fractured low-permeability reservoir; the results of fractured core flooding experiments show that the optimum injection way of N2 is that foam-alternating-N2, and the alternating slug should be as small as possible.The results of simulation show that the optimum injection way in experimental site is foam-alternating-N2 with injection volume of 1475×104Nm3 in targeted block.