Influence of supercritical CO2-water soaking on fracture toughness of shale: Implications for shale gas recovery and CO2 sequestration

The fracture toughness of shale influences fracture network formation and CO 2 storage stability in shale reservoirs. To investigate this effect, semi-circular bending (SCB) tests and measurements of surface energy, fracture surface roughness, and mineral compositions were conducted on samples exposed to supercritical CO 2 (ScCO 2 ) for 0–60 days. Fracture toughness increased initially and then plateaued, and the established empirical formula adequately describes this evolution. These changes, attributed to increased surface energy, fracture surface complexity, and bridging effects from mineral dissolution and precipitation, enable the shale to absorb and release more energy during fracture propagation. The increased fracture toughness hinders fracture propagation, limiting the development of complex fracture networks during gas exploitation but enhancing CO 2 storage stability. These findings offer insights into shale gas extraction and CO 2 geological sequestration.