Coupled modeling of multiphase flow and poro-mechanics for well operations on fault slip and methane production

Pore pressure variations owing to fluid injection-extraction from deep sedimentary basins can potentially trigger shear slipping along pre-existing faults. We use a coupled two-phase flow and geomechanical model to better understand the physical processes associated with simultaneous injection of \(\hbox {CO}_{2}\) and production of \(\hbox {CH}_{4}\). The model considers permeability changes induced by deformation and slip-dependent friction of the sliding fault. The simulation results show that a sudden stress drop associated with fault reactivation occurs after 46 days of simultaneous fluid injection-extraction. The gas production rate instantaneously decreases as a result of the pressure drawdown applied at the wellbore and then approaches a relatively stable state that cumulatively produces coalbed methane of \(5.90 \times 10^{7}\,\hbox {kg}\). A sensitivity study shows that the arrangement of well operations affects the fault slip timing and corresponding sliding distance, as well as the cumulative gas production. Increasing production-injection or injection-production cycle number advances the timing of fault reactivation and reduces the maximum slip. More cycles result in higher peak production and hence promote the corresponding cumulative gas production, which significantly improves methane productivity efficiency. The results of this study demonstrate the importance of well operations on fault reactivation and cumulative methane production during \(\hbox {CO}_{2}\)-enhanced coalbed methane recovery.