Dual Medium Gas Reservoir Fluid-solid Coupled Numerical Simulation Study

With the recent development of oil industry and the need of solving complicated petroleum engineering problems, fluid-solid coupling study which is highly valued is becoming more and more important in oil drilling, oil production and oil development. For the moment, the main progress of the research in fluid-solid coupling study in oil & gas field development numerical simulation is focus on simple porous media. The particularity of coupled modle about dual porosity media manifested that it is hard to get the full coupled modle and complicated to find the numerical simulation techniques. This thesis is focus on theory problems and analytical solutions in coupled problem of dual porosity media. Double effective stress theory and finite element method were introduced. Based on that, calculation program was established. It is avial to frame scientific development plan and improve veracity and scientificaalness of the decision-making.On the basis of a great number of experiments and theoretical studies performed by former researchers, the work finished in this paper concerning fluid-solid coupling theory in dual porosity media reservoir focuses on several aspects of the following:1.Based on the analysis of the limitation of theory Terzaghi effective stress in study of rock and the studying by it will take the inadaptability in numerical simulation of dual porous media gas reservoir. Double effective stress theory was introduced to study numerical simulation of dual porous media gas reservoir.2. As to the elastic plastic distortion characteristics under the condition of changeable stress in low permeability reservoir, elastic reservoir and elastic plastic reservoir constitutive model are established and corresponding matrix description and matrix expressions are given, either.3. Based on analysis of reservoir stress and strain with double stress theory and rock skeleton constitutive relation, a dual media reservoir rock skeleton deformable mathematical model was presented. The models relate the porosity, permeability with fluid pressures or effective stresses. The mathematical model of dual porosity media gas reservoir include solid phase equilibrium equation and liquid flow equation, which taking into account the interactive effect of rock deformation and fluid flows. Each equation is not stand, which is coupled by coupling term. They are a suit of full coupled partial differential equations.4. Due to the complexity resulting from coupling and nonlinearity of the governing equations, analytical solutions are very difficult to obtain. Therefore thenumerical simulation techniques must be used. The finite difference, method has historically been widely used for solving many reservoir problems. However, in many cases such as flow regimes which give rise to shock front development, and especially in the fluid-solid coupled problems, there are inherent difficulties if the finite difference method is used. Recently, the finite element method has become increasingly popular due to its natural flexibility in being able to handle the boundary conditions for simulating complex geometric problems. A finite element numerical model for multiphase fluids flow in a deforming porous medium is presented. The displacements and the fluid pressures are taken as primary unknowns of the model. A finite element simultaneous solution of the fully coupled governing equations in the space domain by Galerkin finite element method is given. To solve the finical semi-discretized governing differential equations in the time domain fully implicit numerical scheme are presented. A linear analysis is used to study the stability conditions of the present model.5. On the basis of finite element equations of the fluid-solid coupling presented in this paper, a finite element computer program has been developed. FEPG was used to develop this program. One dimension simplex model analytic solution was brought to compare with the program. The result is shown that the outcome of numerical model and analytic solution are accordant.6. The computer program was used to simulate a typical naturally fractured gas reservoir compared with the conventional uncoupled model and the coupled model based on Terzaghi effective stress theory. The result show that the porosity and permeability will depressed because the fall of fluid press lead to the increase of effective stress. Compared with the conventional uncoupled model, the change of the porosity and permeability will influence the result of numerical simulation; Compared with the coupled model based on Terzaghi effective stress theory will magnify the influence. So, It will be more accurate that using double stress theory in study of coupled.