Analysis of longwall goaf gas drainage trials with surface directional boreholes

摘要: Abstract Surface directional boreholes (SDB) were recently trialled at two Australian coal mines as a new application to longwall goaf gas drainage. This method has become increasingly attractive for use where surface access drill large numbers of vertical wells are limited or restricted. To demonstrate the performance and effectiveness SDB help improve future design implementation, results field trials Australia analysed presented in this paper. The SDBs, drilled with medium-radius-drilling techniques, had different configuration parameters, including number branches, diameter, relative locations above mining seam from tailgate. No borehole stability issues encountered during drainage operation. methane flow rate varied all SDBs; however, if applied properly, they can gain consistent high about 1000 L/s. It was observed that efficiency significantly influenced by local geological settings, horizontal placement, branching, water filling. key having is maintain sufficient connection mining-induced fracture zone. In addition, drilling quality control such also crucial, avoid any concave sections might fill groundwater block borehole. trial SDBs have potential common