Experimental Investigation Into the Propagation Law of Supercritical Carbon Dioxide Fracturing Cracks Induced by Directional Grooving of Hard Roof

Directional fracturing technology for coal and rock is crucial for preventing accidents resulting from the rupture of the hard roof in coal mines. Supercritical carbon dioxide (SC-CO₂) fracturing, a green and waterless technology, has garnered significant research interest due to its ability to form complex crack networks. This technology holds promise for mitigating the risk of hard roof collapse in coal mines. Understanding the mechanisms to induce optimal crack propagation through SC-CO₂ fracturing is highly valuable. This study employs the true triaxial test platform for SC-CO₂ fracturing to examine the propagation law of cracks induced by directional grooving. A series of SC-CO₂ fracturing tests were performed under varying in-situ stress differentials, groove numbers, and spacing between them, and a method for characterizing the directional fracturing effects in terms of inducing cracks was proposed. The morphology of crack propagation in fractured samples was photographed, and the types, lengths, and directions of surface cracks were statistically analyzed. A three-dimensional model of cracks in the fractured samples was reconstructed, revealing the evolution characteristics of hole-line spacing and the main crack-induced angle of deflection. The influence of grooves on crack propagation during SC-CO₂ fracturing under various conditions was determined, and the interaction mechanism of the stress field at the crack tip within the grooved area was analyzed. These results provide theoretical guidance for applying SC-CO₂ fracturing technology in coal mines.