Numerical simulation of rock cracking around a perforation

The distribution of cracks around a perforation, as the initial condition for hydraulic fracturing, has a non-negligible influence on the fracturing process. This work presents a perforating experiment to investigate the crack distribution around the perforation tunnel. The distribution of the number of cracks on samples was statistically analyzed. Then, a 2D cross-section was selected as the research target for numerical simulation. And a numerical model was introduced to describe the rock cracking in the cross-section during perforation based on FEPG (Finite Element Program Generator) software. The meso-mechanical parameters were set to be randomly distributed to ensure a random distribution of cracks. The tensile failure criterion, Mohr-Coulomb criterion, and the fracture toughness criterion were used as the failure criterion. The modulus reduction method was applied to show element cracking. The simulation results show that the damage zone can be divided into four parts after perforation. According to the main causes of cracked elements, the four zones were named as the central crushed zone, the compression-shear damage zone, the tensile damage concentration zone, and the tensile damage propagation zone. The variations of the distribution of cracks under different perforating charge sizes and confining pressures have been analyzed. The reliability of the numerical model was verified by comparing the results of the numerical simulation to the physical experiments.