A numerical model for simulating single-phase gas flow in anisotropic coal

Abstract

Numerical simulation has become an important approach for investigating coalbed methane (CBM) recovery. This demand has enabled the development of numerical simulators and each simulator has its own features. This paper first modifies the mathematical model of single-phase gas flow in coal by incorporating the anisotropic permeability model presented in our previous work. A numerical model is then developed based on this modified mathematical model by using the finite difference method. The numerical model is solved by using the Gauss-Seidel iteration method. A simulator is developed with the C++ programing language to solve the iteration equation. The numerical model is validated with a set of published experimental data and a set of published production data modeled by commercial CBM simulators. The results show that the numerical model developed in this paper agrees well with both data sets. A series of numerical simulation is conducted to evaluated the effects of permeability anisotropy on dry CBM production by using the numerical model developed in this paper. The results show that if the equivalent permeability is equal to the isotropic permeability, the permeability anisotropy has few effects on gas rate but impacts the distributions of pore pressure and gas content significantly. These results may be meaningful for dry CBM production with multiple vertical wells.