Research On The Stress Sensitivity Effect And The Law Of Matrix/Fracture Transfer Flow In Tight Reservoirs

The study of the stress sensitivity effect and the matrix/fracture intermedium transfer law are the basic problems of the tight reservoir fracturing development,which are directly related to the accuracy of the numerical simulation and affect the design of the development plan.In view of the present commercial numerical simulation software is generally based on the stable seepage theory,the stress sensitivity model is simple,the low reliability prediction results,in this paper,the matrix stress sensitivity experiments of the Glutenite,Turbidite and the Beach bar sand types tight reservoirs in Jiyang depression is carried out,and the matrix stress sensitivity laws of the different sedimentary types tight reservoirs is clarified.In order to expand the universality of the stress sensitivity model,the generalized stress sensitivity model based on the Young’s modulus and the pore structure parameters of the rock is established by combining the Poiseuille’s law,the Hertz contact deformation theory and the CT scanning experiments.Through the micro fracture stress sensitivity experiments,the micro fracture stress sensitivity laws with different permeability grades are clarified,and the empirical model of the micro fracture stress sensitivity considering the initial value of micro fracture permeability is established.Through the main fracture conductivity experiments,it is clear that the long-term depression of the main fracture conductivity can be divided into the initial closing period and the stable closing period.Based on the mechanical deformation theory,the initial conductivity value calculation model is established considering the proppant performance,the proppant concentration,the reservoir sedimentary rock type,the reservoir permeability and the closure stress at the initial stage of main fracture closure;Based on the experimental results,the long-term conductivity variation model of tight reservoir considering the initial conductivity value and time is established to calculate the continuous variation process of the main fracture conductivity.According to the dual media characteristics of the matrix and microfracture in the fractured zone of tight reservoir,the pressure diffusion equation of matrix/fracture transfer flow is established considering the threshold pressure gradient and the stress sensitivity effect.The pressure distribution and average pressure of the matrix system in the early stage of transfer flow(the pressure does not propagate to the matrix center)and the late stage of transfer flow(the quasi stable period)are solved respectively.Thus,the matrix/fracture nonlinear transfer flow model of tight reservoir is established.Through the design of the matrix / fracture transfer flow experiments,the experimental verification of different matrix permeabilities,bedrock sizes,matrix lithologies and fracture permeabilities of the theoretical transfer model is completed;According to the experimental results,the theoretical model is modified,and the accuracy of the modified model is 26.5% higher than that of the W & R and Kazemi classical models.By introducing the established matrix stress sensitivity model,the micro-fracture stress sensitivity model,the main fracture conductivity model and the matrix/fracture nonlinear transfer flow model,the matrix/micro-fracture/main fracture triple-media nonlinear seepage coupling mathematical model of the tight reservoir is established.The large sparse coefficient matrix is constructed by the difference discretization of the mathematical model,and the incomplete LU preprocessing method of the coefficient matrix and the generalized global conjugate gradient square algorithm are proposed.In this paper,the seepage mathematical model,the coefficient matrix and the solution methods which can reflect the development characteristics of the tight reservoirs are established,which provides the theoretical support for the development of numerical simulation software of tight reservoir.The nonlinear seepage coupling mathematical model is applied to the Turbidite tight reservoir of Wang587 Block in Jiyang depression,Bohai Bay basin,the accuracy of the production calculation in the initial stage of development is increased by 13.3% compared with the commercial software Eclipse.The reasonable development policy of the Wang 587 Block optimized by the nonlinear seepage coupling model is to adopt staggered well pattern,the well spacing of 350 m,the row spacing of 150 m,the fracture half length of 120 m and the formation pressure coefficient of 1.1.