Optimization of drilling arrangement for static fracturing and penetration enhancement technology in coal seams

In order to improve the effect of static fracturing and penetration enhancement in low permeability coal seams and optimize the fracturing distribution method, a static fracturing stress-damage coupling model was constructed based on COMSOL software by combining laboratory experiments and numerical simulation, and the influence of the drilling arrangement on the effect of static fracturing was investigated, which revealed the evolution of the stress field and the distribution of the damage zone of the coal body under different construction parameters. The results show that: the superposition effect of expansion pressure generated by double-hole fracturing obviously enhances the fracturing effect, and the existence of free surface inside the coal body under the guided hole arrangement can guide the direction of fracture expansion, which makes the fracture expansion more significant; the evolution of the damage zone in the process of static fracturing is affected by the expansion pressure, the parameters of hole arrangement and the elastic modulus, and the increase of expansion pressure accelerates the migration of the stress inflection point, which results in the decrease of the elastic modulus of the coal body and the emergence of the damage zone. In the late stage of static fracturing, the area of the damage zone with guided holes and prefabricated cracks is 5.98 m² and 4.78 m², respectively, which is 2.3 times and 1.8 times higher than that of the single-hole arrangement, and the area of the damage zone is increased from 5.47 m² to 5.98 m² by adding guided holes on top of the double-hole arrangement, which indicates that the arrangement of guided holes and prefabricated cracks can significantly improve the fracturing effect of the coal body. The fracturing effect of "double holes+guide holes" is the best.