Mining Publication: Control of Longwall Gob Gas With Cross-Measure Boreholes (Upper Kittanning Coalbed)
The cross-measure borehole technique is being studied by the Bureau of Mines as an alternative to the use of surface gob boreholes as a means of controlling methane in gobs during longwall mining. Small-diameter holes are drilled from underground locations into strata overlying the mined coalbed. When the roof strata are fractured by the mining operation, a partial vacuum applied to the boreholes draws the methane out of the fractured strata and prevents it from entering the mine ventilation system. Tests in the Upper Kittanning coalbed showed that 50 pct of the methane produced by the longwall mining operation was captured by the cross-measure boreholes. Borehole inclination and penetration into the gob are two important borehole parameters that affect the performance of the cross-measure borehole system.