Permeability enhancement of reservoir rocks loaded by repeated low-amplitude stress waves

Abstract

Wave-based loading techniques have been proposed as a potential method for the enhancement of permeability in deep reservoirs, yet the mechanisms governing permeability changes in reservoir rocks under repeated stress wave (RSW) loading remain unclear. This study addresses this gap by employing a modified triaxial split Hopkinson pressure bar (TSHPB) system to simulate coupled hydraulic-mechanical (CHM) conditions and repeated stress wave loading on green sandstone (GS) specimens. In situ permeability measurements are conducted following each impact, with dissipated energy calculated to quantify specimen damage. Experimental results reveal a positive correlation between permeability and dissipated energy, with significant permeability enhancement under RSW loading. Initially, permeability increases with repeated impacts, later stabilizing after a gradual decline. Elevated differential water pressure and decreased confining pressure facilitate crack extension, enhancing permeability, while dissipated energy inversely correlates with these CHM conditions. To model these changes, a micromechanical model incorporating fracture mechanics and the equivalent pore concept is developed, accurately predicting permeability evolution by correlating crack length and pore size with dissipated energy. The model's predictions align closely with experimental data, enhancing understanding of RSW on permeability evolution, and offering a predictive framework to optimize permeability in resource recovery applications.