Optimization of Construction Parameters and Fracture Propagation Law for Horizontal Well Directional Layer-Crossing Fracturing in Soft and Fragmented Coal Seam Roof

Roof horizontal well technology represents an effective methodology for achieving efficient development of coalbed methane in fractured soft coal seams. Cross-layer fracturing serves as a critical technique for enhancing gas production and recovery rates in horizontal wells within the roof of fractured soft coal seams. Currently, there exists a significant research gap in the optimization of construction parameters for cross-layer fracturing in roof horizontal wells, which substantially constrains the efficacy of layer penetration fracturing. To address this limitation, this study employs an integrated approach combining numerical simulation with engineering verification to optimize the fracturing process in roof horizontal wells. The findings demonstrate that stress differential, directional perforation technique, horizontal well placement, and construction displacement constitute the primary controlling factors influencing the fracturing effectiveness of roof horizontal wells across layers. The efficiency of cross-layer fracturing deteriorates with increasing perforation azimuth (angle relative to the vertical direction) and the distance between the horizontal well and the coal seam. Furthermore, as perforation depth and stress differential increase, the impact of construction displacement on fracture propagation becomes more intricate, with construction displacement showing a strong correlation with coal seam thickness. The numerical simulation study indicates that horizontal wells should be strategically positioned in areas where the vertical and horizontal stress differential exceeds 4 MPa. Optimal fracturing sections should be selected where the horizontal well is in close proximity to the coal seam, preferably within a distance of less than 1.0 m. The implementation of directional perforation technology, characterized by vertical downward orientation and a perforation depth exceeding 800 mm, is recommended. Based on coal seam thickness analysis, an optimized construction displacement range of 8–12 m3/min has been determined to facilitate efficient fracturing operations in roof horizontal wells. This parameter optimization significantly contributes to achieving high-efficiency fracturing objectives in roof horizontal wells. The research findings establish a robust theoretical foundation for optimizing fracturing construction parameters and evaluating fracturing effectiveness in horizontal wells within fractured soft coal seam roofs.