Study On Mass Transfer And Numerical Simulation In Tight Oil Reservoirs

Tight sandstone reservoirs have rich resource prospects,but the depletion development is fast and the ultimate recovery is low.Gas injection is a potential development mode for tight reservoirs.However,for the seepage environment of tight reservoirs with complex fracture network and micro-fracture formed by fracturing,the traditional characterization of oil and gas mass transfer is too general,and conventional seepage mathematical model is difficult to accurately simulate the process of oil and gas mass transfer under different mechanisms in complex fracture network.In this paper,the study is carried out from the following four aspects: microscopic seepage simulation of oil and gas,characterization of mass transfer between matrix and fracture,numerical simulation method of oil and gas mass transfer and optimization design of gas injection.First of all,based on the result of real scanning in strong inhomogeneous core,the application of morphological operations is used to depict the microscale pore throat structure model of high precision,coupling NS equation and the level set equation to simulate the micro process of two phase flow of oil and gas,has realized the micro simulation of mass transfer in the matrix,and the process and mechanism of gas flooding and the five types remaining oil are summed up.Gas pre-injection is put forward to improve the degree of use of crude,and the mechanism of is analysed from the pressure gradient,the fluid properties,interfacial tension.Secondly,for the complex oil and gas mass transfer process between the matrix and fracture,microcosmic concentration diffusion and mass transfer model under different fracture morphology is constructed.Effective diffusion coefficient considering the micro cracks is revised based on the equivalent flux method.Mass transfer effect of the nonuniform mechanical diffusion caused by the process of high-speed interporosity gas flow the fracture is summarizd.The effect of reservoir conditions and development policy is clarified in the differential pressure mass transfer.Comprehensive characterization of the concentration diffusion,mass transfer of speed and pressure difference is built.Then,to clarify the influence of complex oil and gas mass transfer mechanism for production capacity,embedded discrete fracture model considering the role of oil and gas mass transfer is established.Mass transfer mechanism is characterized based on the vectorization programming method and the discrete grid is used to depict the complex contact relationship of matrix and fracture.Compared with the traditional commercial software,new model can depict the mass transfer mechanism and scope more accurately.The field example shows that the fitting effect is better considering the mechanism of oil and gas mass transfer.Finally,the fluid property changing law form the improved PVT experiment is used combined the traditional numerical simulation of oil and gas flow to realize the simulation of different gas injection problems.And the vector storage is used to solve the simulation of multi-well variable production system problems.For typical well groups,the key seepage parameters are calculated,and the influence of different fracture network forms on gas injection is analyzed,and the optimization charts of injection mode,injection fluid,well pattern and other influencing factors are drawn by response surface design method.In this paper,characterization,simulation and evaluation of oil and gas mass transfer laws in tight reservoirs are carried out,which provided certain methods and ideas for research on gas injection to replenish energy in tight reservoirs and provided certain reference for production and development of Chang 7 tight reservoirs in Ordos Basin.