Numerical Simulation Of Low Permeability Fractured Reservoir Based On Nonlinear Flow Law

The proportion of proven reserves in low permeability is growing in recent years. Because of the distribution of developed fracture and the complexity of the nonlinear fluid flow in low permeability media, the low permeability oil field is difficult to develop. As a result, the degree of reserve recovery is low and the development effect is not good. So it is important to study on the numerical simulation technology of low permeability fractured reservoir with considering the influence of nonlinear flow. And the research will prompt the development of low permeability fractured reservoir.This paper studied water-oil two phase flow law of low permeability reservoirs based on the experimental data acquired by our research group before. The results show that nonlinear flow exists in low permeability media and it has three characteristic parameters which are the minimum threshold pressure gradient, the pseudo-threshold pressure gradient and pseudo- permeability. For the water-oil two phase flow, the minimum threshold pressure gradient decreases with the increase of water saturation, and the pseudo-threshold pressure gradient increases at first and then decreases with the increase of water saturation. Moreover the proposed definition of pseudo-permeability makes the relative permeability curves of the low permeability reservoir different from that of high permeability reservoir.The two-dimensional mathematical model of water-oil two phase flow in low permeability fractured reservoirs has been established on the basis of a continuous non-linear flow model with clear physical meaning acquired through the introduction of the minimum threshold pressure gradient and pseudo-threshold pressure gradient. And then the fully implicit method is used to solve the difference equation and a numerical simulation program is completed. Finally, the program is applied to the analysis of factors influencing the development of low permeability fractured reservoirs. It is suggested that the influence of the minimum threshold pressure gradient on oil production is more obvious than that of the pseudo-threshold pressure gradient, because the minimum threshold pressure gradient determines whether formation fluids to flow or not while the pseudo-threshold pressure gradient just affects the flow property. The smaller the value of two threshold pressure gradients, the closer to the Darcy flow formation fluids are, and the more conducive to the development of low permeability fractured reservoirs. Stress sensitivity of the fracture system has some influence on the yield, that the poor recovery capability of the fracture system permeability will give a low oil production. However, the influence of stress sensitivity on the yield is less obvious in comparison with that of threshold pressure gradient. The influence of producing pressure drop and producer injector spacing on the yield ultimately depends on the nature of the matrix system and the fracture system. Only taking advantage of the low permeability fractured reservoir flow characteristics through determining reasonable pressure drop and well spacing according to the nature of the reservoir can the reservoir be effectively developed.