Gas extraction technology of staged fracturing with comb hole in soft seam floor

This paper has investigated 15# broken soft and low permeable coal seam in Yangquan Mining Area. In order to improve the gas drainage effect of the broken soft coal seams, features of the coal seam and its floor rock were analyzed. The staged fracturing method for each comb-shaped branch hole has been formed integrating long comb-shaped boreholes in the coal seam floor and staged hydraulic fracturing. The fracture propagation and extension of hydraulic fracturing is theoretically analyzed using the method. Based on the test using this method, the design and construction technology of long comb-shaped boreholes that meet the requirements of segmented fracturing technology have been studied. Also, the fracturing parameter design and fracturing construction process based on the combination of open-hole packer and sliding sleeve ball segmented fracturing tool have been constructed. The test finally formed a comb-shaped long drilling hole with a main hole length of 534 m, five branch holes, and a main fracturing tool string of 490 m. The four holes branch fracturing was achieved, with a maximum water injection of 611 m3 and the maximum pumping pressure of 17.18 MPa per stage. After the test, the gas drainage concentration increased by 10.53 times and the gas drainage volume of the 100-meter borehole increased by 2.02 times compared with the gas drainage technology of drilling through layers.