Coupled fluid-flow and geomechanics for triple-porosity/dual-permeability modeling of coalbed methane recovery

A coupled fluid-flow and geomechanics model for simulating coalbed methane (CBM) recovery is presented. In the model, the fluid-flow process is simulated with a triple-porosity/dual-permeability model, and the coupling effects of effective stress and micro-pore swelling/shrinkage are modeled with the coupled fluid-flow and geomechanical deformation approach. The mathematical model is implemented with a finite volume method. First, a case without considering coupling between fluid-flow and geomechanics is simulated and compared with an existing simulator. The effects of coupled fluid-flow and geomechanics are then studied in detail with two illustrative examples. The first one is designed for testing the effective stress effect without micro-pore swelling/shrinkage effect, and the other for testing the coupling effects of the effective stress and micro-pore swelling/shrinkage on the methane production. The numerical results indicate that both the effective stress and the micro-pore shrinkage make a significant contribution to fluid-flow in CBM reservoir and to methane production. The methane production sensitivity to Young’s modulus and Langmuir sorption strain are investigated as well. Finally, we make a dynamic analysis of the coupling effects of fluid-flow process and geomechanics.