Fracture Network Propagation And Productivity Prediction Based On Fluid-solid Fully Coupling Of SRV-fractured Horizontal Wells In Tight Oil Reservoirs

Horizontal well and stimulated reservoir volume(SRV)fracturing have become the most effective technology in tight reservoir formation treatment.SRV fracturing often induces complex fracture-network growth to enhance horizontal well production in tight oil reservoirs.The comprehensive research method — percolation theory,mathematical modeling and numerical simulation are adopted in this dissertation.Meanwhile,the modified displacement discontinuity method(DDM)and finite element method for the numerical solution are used to simulate the fracture network propagation with SRV-fracturing and predict the horizontal well productivity.On the basis of fully considering the characteristics of tight reservoir,the following four parts are mainly carried out.First of all,we derive and establish a theoretical model about fracture network propagation with SRV-fracturing for tight reservoirs,using the modified displacement discontinuity method(DDM),mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation.Through analyzing the variation rules of formation stress fields,fracture propagation pattern(FPP)and branch fracture propagation angles and pressures,the mechanical mechanism of fracture network propagation with SRV-fracturing for tight reservoirs are revealed.The results show that whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments.Secondly,in view of the problem of stress interference between adjacent fractures in the process of multi-fracture propagation,the mathematical model of injection fluid distribution inside the fractures is proposed.The process of fracture network growth with SRV-fracturing is simulated.And the influence geologic factors and SRV-fracturing parameters of tight reservoir on the shape and structure parameters was analyzed.According to the different FPPs ofSRV-fractured horizontal wells,the parameter description and characterization method of fracture network structure with multiple porous media system of SRV-fractured horizontal well for tight reservoir is presented.Thirdly,in terms of the characteristic of different fracture network stimulated patterns for SRV-fractured horizontal wells in tight oil reservoirs,considering the dual porosity property of matrix and natural fractures,based on the flowing feature of fracture network stimulated system of discrete-fracture mode(DFM),a mathematical unsteady flow model for SRV-fractured horizontal well in tight oil reservoir is presented.The finite element techniques is used to obtain the numerical solution.The differences of flowing patterns between dual-porosity,dual-permeability and dual-porosity,single permeability model are analyzed,and the characteristic of unsteady pressure and productivity for SRV-fractured horizontal well in tight oil reservoir are revealed.Finally,the numerical simulation method of SRV-fractured horizontal wells in tight oil reservoirs based on fluid-solid fully coupling is introduced.According to the effective stress principle and regional flow characteristics,the fluid-solid fully coupling mathematical model considering multiple pore medium characteristics of complex fracture networks is presented.The fully coupling numerical solution of the stress field and flow field is solved by the finite element method.The variation law of stress-strain and reservoir physical property parameters is revealed.For the non-coupled and full-coupled model,the productivity difference and the production contribution ratio of multiple porous media are compared and analyzed.And the productivity characteristics and influencing factors of full-coupled SRV-fractured Horizontal Wells in Tight Oil Reservoirs are analyzed.The results show that when considering the stress field,the initial production rate of SRV-fractured horizontal well is large but declines quickly,which has a fundamentally different characteristics from traditional flow model.Summing up,an efficient fracture network propagation and productivity prediction simulation theory and method of SRV-fractured horizontal wells in tight oil reservoirs are developed,which provides a certain theoretical and technical guidance for the optimization design of horizontal wells with SRV-fracturing and efficient development of tight oil reservoirs.