Numerical Simulation And Application On Low Permeable Reservoirs With Micro Fractures

The low permeability reservoir has become an important basis for many oil field to increase the reserves and production in China. The low permeable reservoir is featured by complex pore structure, small pore throat radius, poor connectivity and high flow resistance. Because of the boundary layer and the interaction between the fluid and porous media, the flow behavior of fluid in porous media is non-linear and exists threshold pressure. Tectonic stress often cause micro fracture developed in the geological history, whose original state is closed. During water-flood development, if the injection pressure exceeds the fracture strength, fracture will open, spread, and interconnected, make the heterogeneity more serious. So the low permeable reservoirs are unbalanced developed, in the direction of the fractures, production wells floodout early, the water cut rise rapidly while in the lateral direction of the fractures, production wells produce at very low level.Currently the reservoir simulation technology of low permeability reservoirs and fracture dynamics is not mature. It cannot effectively characterize the nonlinear flow in low permeability reservoir and fracture dynamics change. To solve these problems, we summarize the literature on the basis of the law of site development and establish a nonlinear mathematical model based on flow characteristics of low permeability reservoirs. Then a "directional pressure sensitive " approach is proposed for the dynamic characteristics of fractures. A dynamic relationship between the fractures’ directional permeability and water injection pressure is established based on laboratory experiments and field statistics. At last, we can characterize the phenomenon that the fracture conductivity changes with water injection pressure changing by setting different " parameter directional sensitive ". On this basis, the numerical simulation method of the micro-cracks in low permeability reservoir is formed.The simulation method is applied to the Wangyao experiment area in Ansai Oilfield, work out the effects of different parameters of the micro-fractrures on the development effect in low permeability oilfield. Based on the well pattern,make research on the pressure field and residual oil field, and further work out the reasonable develop policy using the combined technology of numerical simulation and reservoir engineering, including well pattern, well space, infilling time, well type and injection and production parameters. Studies have shown that under the conditions of the existence of the fractures, the development approach which allocate the injection well line parallel to the fractures and the production line perpendicular to the fractures can maximize the advantage of the fractures, reducing the adverse effects of fractures, therefor achieve better development results. The results not only provide appropriate adjustment plan for Ansai Oilfield, but also set up guideline for the development of the same type of low permeability reservoir.