Research on Fracture Propagation Mechanism of Deep Coal-Rock Gas Reservoir in Yan'an Gasfield-Taking Y Well as an Example

Deep coal-rock gas resources have abundant reserves and high development potential, playing a crucial role in alleviating energy supply-demand contradictions and ensuring national energy security. However, the fracture propagation mechanism and interlayer penetration behavior in deep coal-rock reservoirs remain unclear. Based on this, this study takes Well Y in the Benxi Formation 8# coal seam of the Yan’an Gas Field as an example. By establishing a three-dimensional directional well fracturing simulation model, the hydraulic fracture propagation mechanism in deep coal-rock gas reservoirs and the post-fracturing production dynamics were investigated. The results show that the fracture network propagates more extensively within the coal-rock reservoir than in the overlying and underlying formations, and interlayer-penetrating fractures mainly originate from secondary fractures. The degree of interlayer penetration is relatively low for both activated cleats and fractures located farther from the wellbore. When cleats near the wellbore are activated, secondary fractures tend to form in the middle of the cleats, whereas cleats farther from the wellbore generate secondary fractures at both ends. Secondary fractures and activated cleats attract each other, causing fractures to deflect and intertwine, forming a complex fracture network. After the injection of 70–140 mesh sand is completed, the complexity and propagation range of the fracture network are already close to the final fracture morphology. For some parts of the fracture network, gas saturation initially increases and then decreases with production time, while the gas saturation in the surrounding reservoir matrix continuously decreases. This study provides a theoretical basis for research on hydraulic fracture propagation in deep coal-rock reservoirs.