A novel failure control technology of cross-measure borehole for gas drainage: A case study

Abstract

Chinese coal mines, which are generally of complex mining conditions, are threatened by serious coal and gas outburst and explosion accidents. Cross-measure borehole (CMB) gas drainage is one of the widely applied prevention measures, but, unfortunately, it faces some serious problems such as low gas concentration, low gas flow rate and short effective drainage period. Thus, in this study, a new in-situ failure control technology that uses fine particles to seal leakage fractures around the CMB was proposed to improve the gas drainage effect. Based on the geological background in Luling coal mine, this new technology was researched in detail. First, an air-leakage network model was established for the CMB gas drainage, and the results reveal that the gas pressure and the characteristics of leakage fracture around the borehole notably affect the gas concentration. Then, based on the in-situ failure control technology, a pneumatic conveying experiment was performed to investigate the blockage characteristics of particles in narrow straight fractures, and the optimal blockage parameters, including conveying pressure, particle mass flow rate, air flow rate and blockage particle size, were obtained for engineering application. Finally, reasonable schemes for gas drainage were designed and implemented at the new and old drilling fields to evaluate the effect of this technology.Field test results show that gas concentration grows by 40–450% for the old drilling fields and 20–280% for the new drilling fields, and gas flow rate increases by 40–90% and 60–70%, respectively. Meanwhile, the high-concentration gas drainage time is extended for approximately 2−3months. These results indicate that this new technology for CMB gas drainage is a promising measure to significantly improve the gas drainage effect in Chinese coal mines.