Coalbed Methane Seepage Process Mid-stream Solid Coupling Problems

Coal gas is a kind of energy source holding in the coal measures, according to estimate, there is about (30-50) 1012m3 coal gas containing in our country, its reserves almost amounts to the normal natural gas storing in sandstone. So, if we can utilize it effectually, great contribution will be made to our national economy.On the other hand, the storage and seepage of coal gas is different from normal natural gas, all these is just because the coal bed owns its special geologic particularities. This leads to the result that we can hardly mining for it by routine method and technology. How much we know about the storage and seepage of coal gas will determine weather we can make effective exploitation about it. In current years, with the development of petroleum industry and the technologies for solving petroleum engineering problems, the research of fluid-solid coupling is playing a more and more important role in the field of exploitation of oil and gas, especially for coal gas. Now , people have realized that the action of coal-body and the fluid in it is interact in the course of methane developing, the flow is two media flow of methane and water. Therefore, it is necessary to study the interacting of the two media seepage. This possesses important significance for the real simulation of the groundwater seepage conditions.This paper faces to the special particularity of the coal gas reservoir directly and discusses the geologic character of the coal measures. First, we summarize the evolvement of the coal, the geologic environment of the coal, the coal origin, and the movement, storage, and seepage of the coal gas. And then, depending on the geologic particularity, we provided the basic static parameters for fluid-solid coupling. Moreover, the coal skeleton is assumed to have elastic-plastic behavior, according to the elastic-plastic theory, the deformation equations are given. On the basic of Darcy's law, the authors have given the seepage field equation. The coupled mathematical model to describe the complex interaction of two fluid (methane and water) is developed by comprehensive analysis method. The model is useful in the numerical simulation of methane reservoir development.After we established the mathematical model of fluid-solid coupling according to the parameters, in the same time, on the basic of principle of finite difference, the finite difference model and methods for solving mathematical model for fluid flow coupled with reservoir deformation are studied. At last, we developed the computer program for solving way of reservoir numerical model with the coupling of multiphase fluid flow and reservoir deformation studied according to the basic principle of software engineering. Meanwhile, a case study is conducted to verify the correctness and effectiveness of the theory and method presented, and to verify the validity of the software that we have development. The results show that mechanisms of dynamic coupling of two-phase fluids flow and reservoir elastic-plastic deformation in recovery process of reservoir have strong effect on the flow of two-phase fluids and reservoir recovery. Therefore, reservoir numerical simulation with the coupling of significance, but also has important role for guiding coal gas field development.