Research on the main controlling factors of low permeability coal seam under the action of high-pressure water jetting

The difficulty of underground gas extraction in coal mines depends on the permeability of the coal body, and coal body permeability enhancement is one of the keys to gas extraction research. To improve the permeability of low-permeability coal seams, artificial measures to increase the cracking of coal seams are an effective means to improve the permeability of coal seams. By analyzing the principle of high-pressure water jet seam making, experimental research on the influencing factors of jet flat drag seam making was carried out with a true triaxial test device, and the influencing laws of jet angle, number of drilling holes, jet pressure, ground stress, and seam strength on the seam making effect were analyzed, and on-site applications were carried out. The test results show that the high-pressure water jet can form evenly distributed 'tooth-like' cracks on both sides of the slit hole, and with the increase of the jet angle and the increase of the strength of the coal seam, as well as the increase of the ground stress, the length of the cracks is gradually reduced; On the contrary, the crack length becomes progressively longer as the jet pressure increases.Field test results show that the optimal cutting pressure is 80 MPa, when the cutting time is 12 min, the corresponding depth of cutting is about 1.75 m, at this time, the reasonable optimal cutting hole spacing is 6 m, the optimal cutting slot spacing is 4 m. The experimental results can provide a reference for similar coal mine gas extraction and hydrometallisation measures for gas management.