Creep Rupture and Permeability Evolution in High Temperature Heat-Treated Sandstone Containing Pre-Existing Twin Flaws

Utilizing underground coal gasification cavities for carbon capture and sequestration provides a potentially economic sustainable solution to vexing environmental energy problem. The thermal influence on creep properties long-term permeability evolution around the chamber is key issue in UCG-CCS operation containing fugitive emissions. We complete multi-step loading unloading tests with measurement at confining stresses of 30 MPa pre-cracked sandstone specimens thermally heat-treated 250, 500, 750 1000 °C. Observations indicate critical threshold temperature 500 °C required initiate thermally-induced cracks subsequent strength reduction occurring Comparison histories creep, visco-elastic visco-plastic strains highlight existence strain jump certain deviatoric stress level—where intervening rock bridge between twin starter-cracks eliminated. As level increases, make up an important composition total strain, especially pre-treated higher temperatures, development leads time-dependent failure rock. pre-treatment produces their closure resulting increased instantaneous elastic plastic strains. With increasing ratio, steady-state rates increase slowly before ratio but rise suddenly over final failure. However, has no clear apparent steady rates. Rock subject temperatures exhibit permeabilities. pre-existing close under compression coplanar shear crack propagating from ultimately linking these formerly separate cracks. In addition, it that accommodate greater damage.