Pulse hydraulic fracturing technology and its application in coalbed methane extraction

The sealing and operating procedures of pulse hydraulic fracturing (PHF) were systematically introduced to increase the methane reservoir permeability. The results of a pilot application conducted at Sv719 working face in Daxing coal mine, China, shown that both the sealing and cracking were successfully operated. The injection time and water quantity were positively correlated with the fracturing initiation pressure. The fracturing mechanism of PHF was theoretically analysed, and the relationship between fatigue-loaded coal strength and injecting frequency was studied. A criterion for determining the fracture pressure was established. Compared to conventional hydraulic fracturing and deep-hole blasting, PHF technology is superior in gas-extraction performance, with a relatively high extraction concentration and less gas attenuation. Moreover, the content and pressure of residual gas in the fractured coal seams were reduced below the regulatory limits, with decrease of 46.15-83.67% and 61.61%, respectively.