Prediction of interactive effects of CBM production, faulting stress regime, and fault in coal reservoir: Numerical simulation

Abstract

The stress in coal reservoir is dynamic and redistributes during coalbed methane (CBM) production. It is abundantly evident in the literature that maximum and minimum horizontal stresses reduce with reservoir pressure depletion. This study aims to predict the change of Anderson's faulting (tectonic regimes) in anisotropic coal due to gas production. A series of fully coupled scenario-based numerical simulations are conducted to investigate the effects of anisotropic sorption and mechanical properties of coal reservoir and immediate underlying rock stratum, and faulting on stress redistribution and gas production. For this purpose, the common assumption of uniaxial strain condition and constant overburden stress together with the widely acceptable values for the mechanical properties of coal are used for the simulations. The simulation results show that initial faulting stress regime, anisotropy in coal, and sorption parameters such as modulus of solid expansion have a significant role in prediction of final stress regime. It was also observed that a permeable fault located parallel to a horizontal borehole may contribute to gas production for both cases of the borehole drilled in the horst and graben structures. The simulation results of this study offer implications on the impact of CBM production on stress redistribution, surface subsidence, and transition of faulting stress regime around horizontal boreholes and far-field.