Fracture characterization in Sc-CO2 quasi-static and shock fracturing: laminated shale and PMMA visualization experiments

ABSTRACT: The loading method of Sc-CO2 significantly impacts the fracturing effectiveness in shale oil and gas reservoirs. This study conducted true triaxial fracturing and visualization experiments on laminated shale and PMMA under quasi-static and shock fracturing conditions, using CT scanning and high-speed photography. Results show that quasi-static fracturing forms a complex but narrow, bedding-controlled fracture network with weak cross-layer propagation. In contrast, shock fracturing creates wider fractures, overcoming bedding and stress constraints. PMMA tests revealed that quasi-static fracturing occurs through slow erosion, while shock fracturing happens in milliseconds, driven by impact loading and fluid migration, leading to surface stress concentration, spalling, or fragmentation. Sc-CO2 shock fracturing produces 7.28% higher fracture concentration, 8.96% higher fractal dimension, 5.20% higher complexity, 5.40 and 3.18 times greater width and volume than quasi-static fracturing, forming wider, more complex networks. These findings provide a theoretical foundation for the further development of Sc-CO2 shock fracturing technology.