Effect of coal permeability evolution on CO2 storage capacity under phase partial pressure in ScCO2-ECBM processes

In the technology of Supercritical Carbon Dioxide Enhanced Coalbed Methane (ScCO2-ECBM), permeability evolution is a critical factor influencing the widespread application of this technique. Existing theoretical studies primarily focus on factors like pressure, but the influence of phase pressures on permeability evolution remains underexplored due to the coexistence of multiple fluids in coal. The evolution characteristics of phase pressures are crucial for impacting coal permeability in multiphase collaborative actions. The evolution characteristics of phase pressures in the multiphase synergistic process play a crucial role in influencing coal permeability. In this study, we quantitatively characterize the energy generated by CO2 phase transition and propose a new permeability model. The results indicate that fluid pressure exhibits an initial rise and then decline, with the existence of fluid peak pressure. Simultaneously, ScCO2 injection induces a U-shaped permeability evolution trend in space and a rapid increase followed by a decrease over time. Furthermore, Under high-pressure conditions, reservoir methane has minimal impact on CO2 storage capacity. Building on these findings, we discuss a stepwise pressure-raising injection method for effective ScCO2 injection into coal. However, this method exacerbates permeability decay and increases fluid peak pressure significantly. This research has significant implications for deep coalbed CO2 sequestration.