Research on fracture propagation process of coal seam hydraulic fracturing based on simulation analysis and microseismic monitoring

Coal structures significantly influence the efficiency of hydraulic fracturing, which is vital for enhancing coalbed methane production. Experiments, models, and microseismic monitoring show how coal structures affect fracture propagation: (1) Different structural combinations affect the initiation pressure and time, with variations in the way cracks expand depending on the structure. (2) An increase in the thickness of clastic coal leads to fracture extension towards it, while the native coal structure facilitates fracture expansion. Cracks propagate along the largest horizontal principal stress direction due to the increased bonding and flexibility of clump coal when exposed to fracturing fluid. (3) In the "two hards sandwiching one soft" structural combination, where hard coal is thick and soft coal is thin, cracks propagate through the soft coal. The hard coal provides effective crack generation, yet the presence of soft coal notably increases fracturing fluid loss.