Experimental study on the influence of coal-rock interface strength on crack propagation law of supercritical carbon dioxide fracturing

Supercritical CO2 (SC-CO2) fracturing technology has become a new way of waterless fracturing of coal seams, which not only changes the fracture structure of coal, but also achieves the purpose of CO2 geological storage. When the SC-CO2 cracks propagate to the roof and floor of coal seams, the sudden change in the rock mass properties on both sides of the coal-rock interface makes the crack propagation law more complicated. To study the influence of coal-rock interface on crack propagation of SC-CO2 fracturing, the preparation method of different coal-rock interface strength specimens was proposed. Moreover, the true triaxial SC-CO2 fracturing test system was used to study the influence of different coal-rock interface strengths on the SC-CO2 fracturing injection pressure-time evolution law, and the SC-CO2 fracturing acoustic emission signal response of different coal-rock interface strengths was also analyzed. Meanwhile, the propagation mode of the SC-CO2 cracks in the coal-rock interface area was analyzed, and the influence of coal-rock interface strength on crack propagation law was revealed. The research results show that the SC-CO2 cracks in the coal-rock interface area have various types of crack propagation, such as extending along the interface, directly passing through the interface, and compound propagation. The higher the coal-rock interface strength is, the more likely the SC-CO2 crack is to propagate across the interface. The results can provide theoretical guidance for applying and promoting SC-CO2 fracturing technology in coal mines.