Experimental study on permeability variation in argillaceous sandstone caprock subjected to impact loading
摘要
Underground gas storage is a key solution for future energy storage, where the caprock's ability to prevent gas leakage, typically assessed by its permeability, is critical for operational safety. This study investigates the permeability evolution of argillaceous sandstone, a common caprock, under dynamic impact loads using a triaxial split Hopkinson pressure bar (SHPB) system at varying confining pressures (2 ~ 8 MPa) and incident energies (107 ~ 701 J). Microcrack characteristics and permeability were analyzed pre- and post-impact via computed tomography (CT) scanning and a multi-field coupled permeability testing system, respectively. The permeability test results under varying pore pressures indicate the presence of slippage effects in the impacted argillaceous sandstone. The Klinkenberg factor and absolute permeability were quantified, showing that despite no macroscopic failure, permeability varied by two orders of magnitude with changing impact energy or confining pressure. For instance, increasing incident energy from 107 to 701 J (at confining pressure of 4 MPa) raised permeability from 1.7 × 10⁻1⁷ m2 to 343.1 × 10⁻1⁷ m2, while elevating confining pressure from 2 to 8 MPa (at incident energy of 496 J) reduced it from 452.3 × 10⁻1⁷ m2 to 4.2 × 10⁻1⁷ m2. The relationship between absolute permeability and microcrack parameters, such as crack volume and crack area, are correlated. Based on these findings, a predictive model for permeability under combined incident energy and confining pressure was developed.