Static expansion fracturing mechanism for enhancing gas permeability in low permeability coal seams

Extraction of gas from low-permeability thick coal seams poses challenges globally, attributed to low extraction efficiency, limited enrichment content, and extraction complexities. Investigating static fracturing in low-permeability thick coal seams holds substantial engineering significance and practical utility. This research delves into the current conditions in the Western region, characterized by low gas permeability and challenging extraction in thick coal seams. Through the utilization of FLAC^3D and COMSOL, simulation schemes are devised to analyze the influence of borehole parameters on fracture efficacy, elucidating the mechanisms by which external loads and internal gas pressure impact coal seam permeability. Field monitoring tests are employed to evaluate and model gas extraction enhancement via borehole positioning. The results suggest that the application of a static fracturing agent inducing 40 MPa expansion stress, along with a 75 mm borehole diameter and 0.5 m spacing, effectively fractures low-permeability thick coal seams. The spacing between extraction and fracturing holes adversely affects gas extraction efficiency due to the limited range of static fracturing. Field experiments demonstrate that static fracturing significantly improves gas extraction from low-permeability thick coal seams, resulting in a twofold increase in average gas extraction purity post-fracturing. This study establishes a robust theoretical foundation for optimizing gas extraction and mining activities in challenging low-permeability thick coal seam environments.