Experimental and numerical investigation on fracture evolution in horizontal wells of coalbed methane

Coalbed methane (CBM) is a significant unconventional natural gas resource, and its efficient development relies on hydraulic fracturing technology. The optimal design of perforation parameters constitutes a critical step in determining fracturing effectiveness. Coal rock reservoirs are characterized by strong heterogeneity and a high propensity for coal fines generation. However, current understanding of the influence of perforation parameters on fracture propagation remains insufficient. To address this issue, this study integrated physical experiments employing distributed fiber-optic monitoring with numerical simulations to investigate the effects of perforation density, number, depth, and phase angle on breakdown pressure, fracture propagation morphology, and fluid entry efficiency of perforations. The number of effective perforations was identified as a key factor governing fracture complexity, while the phase angle exerted synergistic control over both breakdown pressure and fracture complexity. Building on these findings, an optimal range of perforation parameters tailored to reservoir characteristics is proposed. The laboratory fracturing experiments further demonstrated that distributed fiber-optic sensing technology can effectively capture the dynamic fracture propagation process, thereby providing a validation benchmark for the numerical simulations. For horizontal-oriented perforation, the simulations indicate an optimal perforation count of 24–36 holes. A perforation density exceeding 16 holes/m markedly reduces the proportion of effective perforations, and perforation depth primarily affects fracture complexity. Comparative analysis of different phase angles demonstrates that the spatial arrangement of helical 60° perforation achieves the lowest breakdown pressure and the simplest fracture morphology. Considering field engineering risks, perforation design parameters conditioned on reservoir conditions are proposed. This study reveals the central role of effective perforations and the synergistic regulatory mechanism of the phase angle, thus providing a crucial theoretical foundation and practical guidance for the refined fracturing design and execution of horizontal wells in CBM reservoirs.