| With the rapid development of shale gas exploitation,the huge difference between single-well output and the fact that most of the shale gas wells have low outputs has become increasingly prominent,it's necessary to develop production-enhancing technologies that increase recovery.To this end,the 973 project(Number:2014CB239200)team proposed a new technology that uses supercritical CO2 to enhance shale gas recovery.As part of the research of the 973 project,the thermo-flow-solid coupling seepage model of CH4-CO2 gas in shale is established in this paper,which provides a theoretical basis for supercritical CO2 enhanced shale gas exploitation.Based on previous research results,this paper analyzes the characteristics of shale reservoir media,gas migration characteristics in multi-scale porous media,the effect of temperature changes and shale skeleton deformation on gas flow,and the characteristics of gas flow state change in multi-scale porous media of shale,this paper illustrates the gas flow characteristics in multi-scale porous media.On this basis,the thermo-fluid-solid coupling seepage model of CH4-CO2 gas in shale was established,then the corresponding seepage numerical model is obtained with the finite difference method,finally the corresponding computer program is finished.The simulation and calculation of the case are carried out to confirm the correctness and validity of the model,method and technology.The acquired achievements are as follows:1.A scheme for the classification of gas flow in multi-scale porous media of shale is proposed.Based on the analysis of the characteristics of gas migration in porous media are summarized.It is found that shale reservoir has special low porosity,permeability and other characteristics of the pores,and in the shale porous medium gas adsorption,desorption,diffusion and seepage flow four flow patterns,and then according to the size of the pore diameter shale porosity is divided into matrix nanopores,nano-micro holes and fractures,and elaborated The flow pattern and flow characteristics of the gas at different pore scales.2.A thermo-fluid-solid coupling mathematical model of CH4-CO2 gas in shale was established.Firstly,a mathematical model of gas flow in porous media with different pore sizes was established according to the scheme of gas flow in multi-scale porous media.The flow equation in nanopores,the flow equation in nanometer pores and the influence of effective stress and matrix shrinkage on the permeability and porosity of shale reservoirs were analyzed on the basis of analyzing the influence of reservoir pressure on the shale gas development process.Considering the effect of temperature on shale skeleton and shale reservoir fluids,an energy conservation equation for shale reservoirs was established.Finally,coupled with the auxiliary equation,the physical parameters of the coupling equation and the conditions of the solution,together constitute the shale CH4-CO2 gas thermo-flow-solid coupling mathematical model.3.A thermo-fluid-solid coupling numerical model of CH4-CO2 gas in shale was established.According to the different mass transfer mechanism,the flow equation is divided into the flow equation in the grid block and the flow equation between the grid blocks.The finite difference method is used to discretize the mathematical model of the thermo-fluid-solid coupling seepage flow.The mesh system adopts the block center grid,and then the resulting difference equation is linearized,and finally the successive line relaxation in the super relaxation method(LSOR)Iterative solution to the linear equation.4.Completed the preparation of the mathematical model calculation program.The calculation results are analyzed by the calculated calculation program,which proves the correctness and validity of the model,method and technology. |
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