Research on damage effect of compound perforating technology on soft coal seam

The soft coal seam has the characteristics of low elastic modulus, low compressive strength and high Poisson's ratio. At the same time, joints and cleats are developed, and there are a large number of natural fractures. A large number of research data show that the stimulation effect of hydraulic fracturing technology on coal seam is not ideal, so scholars at home and abroad gradually turn their attention to compound perforation technology.In view of the damage effect of compound perforating technology on soft coal seams，a combination of experiment and numerical simulation was adopted to conduct triaxial compression test and SHPB test by using coal samples in soft coal seams，and numerical simulation calculations were also carried out. The results show that:coal and rock exhibit partial plasticity under static compression，exhibit obvious brittleness under high strain rate conditions with strong aerodynamic impact compressibility; the composite perforation technology has a significantly larger shear and tensile failure range than ordinary perforation，with more damage cracks and longer crack propagation; HMX-HTPB propellant has a long delay time for pressure rise and high peak pressure. It has obvious fracturing effect on the perforation channel and coal rock around the wellbore，so it is more suitable for composite perforation; the external propellant has a more obvious effect on coal fracturing near the perforation tunnel，forming multiple damage cracks that extend far away，and the damage and destruction effect on casing and cement ring is relatively weak.