Evolution Mechanism of Permeability Characteristics of Shale Reservoirs During Supercritical Fluid Fracturing and Displacement

Supercritical CO2 (ScCO2)-enhanced shale gas recovery technology offers dual advantages: improving shale gas recovery while reducing CO2 emissions. The permeability of shale reservoirs during CO2 displacement of CH4 is a crucial issue in evaluating the efficacy of shale gas production and CO2 sequestration. In this study, ScCO2 fracturing and displacement experiments were carried out for shale samples, and the fracturing and permeability characteristics of shale were analyzed. The findings indicate that ScCO2 significantly enhances fracturing and permeability, with an overall increase in permeability by three orders of magnitude. Higher injection pressures and lower stress lead to an earlier breakthrough of CO2. The CH4 production rate after CO2 displacement is higher than that under conventional recovery conditions. The cumulative flow of CH4 initially rises with increasing pressure of injection, but subsequently declines throughout the later phases of displacement, leading to a reduced CO2 storage rate and CH4 generation rate. High stress can inhibit CO2 injection and CH4 outflow, reduce CH4 production rate, and promote shale to preferentially adsorb CO2, resulting in higher CO2 storage rate.