Research on application of ultra-high pressure water jet slotting + nitrogen injection displacement technology

In view of the basic characteristics of high gas content, poor permeability and short effective extraction time of No. 2 coal seam in 217 working face of Huangling No.2 well, the technical measures of ultra-high pressure water jet + nitrogen injection displacement coal seam gas enhanced extraction were put forward. Based on the theoretical analysis of the technical principle of ultra-high pressure water jet slotting + nitrogen injection displacement, the technology of ultra-high pressure water jet slotting + nitrogen injection displacement and the secondary sealing technology of nitrogen injection drilling were proposed. By means of COMSOL Multiphysics multi-field coupling software numerical simulation, the mathematical model of gas extraction effect after different technical measures were analyzed and summarized, which was basically consistent with the field industrial test results. The results show that the effect of water jet slotting + nitrogen injection displacement on borehole gas extraction was the most obvious. The gas extraction effect of borehole was mainly affected by the secondary cracks caused by the fracture of surrounding coal body caused by water jet slotting. Nitrogen injection displacement plays a driving role in the gas migration of secondary cracks, which promoted the radial flow of gas and improved the efficiency of gas extraction.