Research of Near-Wellbore Fracture Morphology, Formation Mechanism, and Propagation Law for Different Perforation Modes During the Perforation Process

Perforation plays an important role in the fracture morphology near the wellbore and the propagation of hydraulic fracturing fractures. Therefore, it is of great significance to find out the fracture morphology and propagation law during perforation for optimizing perforation technology, enhancing fracture control, and realizing complementary advantages of different perforation schemes. Based on analyzing the characteristics of perforation fracturing at each stage and existing perforation technology, two types of deep-penetrating perforating bullets were used to carry out large-scale perforation shooting experiments. The real processes of spiral perforation, directional perforation, conventional fixed-plane perforation, and interlaced fixed-plane perforation were simulated, respectively. The near-wellbore fracture morphology, formation mechanism, and propagation rule during perforation with different perforation modes were analyzed. The results show that (1) perforation is accompanied by the formation of tunnels, and there are three kinds of source microfractures developed around the tunnels, namely Type I radial microfractures, Type II oblique microfractures, and Type III perforation tip divergent microfractures. The three microfractures are interconnected to form more complex near-wellbore fractures. (2) Under different perforation modes and parameters, the near-wellbore fracture morphology and propagation law formed by microfractures around tunnels are also different. (3) The existence and expansion of near-wellbore fractures validate Chen et al.’s (2005) conjecture that there are “pre-existing fractures” in perforation and negate the assumption that the perforation tunnels are complete. There are no near-wellbore fractures when the perforation method is optimized. The research results in this paper can provide guidance and reference for improving the perforation fracturing effect in oil and gas reservoirs.