Abstract:

To explore the enhanced permeability of gas-containing coal seams and improve extraction efficiency, high-pressure gas fracturing tests under different impact directions were performed by a self-developed true triaxial high-pressure gas impact rock fracturing test system. The test variable was the angle between gas impact direction and maximum horizontal principal stress. High-pressure gas impact tests were performed under the actions of three triaxial stress, and rock fracture morphology and acoustic emission response were obtained at angles between the impact direction and the maximum horizontal principal stress of 0, 30, 45, 60, and 90°. The results indicated that the rock fracturing process caused by high-pressure gas presented five significant stages including the impact crack initiation stage, air pressure rising stage, crack propagation stage, air pressure stabilization stage, and pressure attenuation stage; High-pressure gas impact caused vertical and horizontal cracks. Vertical cracks were deflected, and the deflection angle increased with the increment of the jet angle. Moreover, the crack deflection points gradually moved away from the drilling hole, and the horizontal fracture surface took on a shape of low in the middle and high in surrounding areas. The maximum gas pressure increased with the angle between the jet direction and the maximum principal stress, and the peak pressure represented a linear increment from 0 to 90°; The acoustic emission signals analysis indicated that rock impact failure was primarily caused by tensile failure and supplemented by shear failure. However, as the jet angle increased, it gradually became a tensile-shear composite failure dominated by shear failure.

Key words: high-pressure gas, fracturing rock, impact direction, acoustic emission, crack propagation