Four coreholes were drilled (two before and two after mining) at a longwall mine to obtain coal and rock samples from overlying strata to determine their gas content at various times in the mining cycle. Test results indicate that 91 pct of the gas removed from the overlying strata came from coalbeds.

Four coreholes were drilled (two before and two after mining) at a longwall mine to obtain coal and rock samples from overlying strata to determine their gas content at various times in the mining cycle. Test results indicate that 91 pct of the gas removed from the overlying strata came from coalbeds.

The National Institute for Occupational Safety and Health, Office for Mine Safety and Health Research, is investigating the geologic and mining factors influencing the migration of longwall gob gas. One goal of these studies is to optimize methane drainage strategies to reduce the volume of gob gas that reaches the underground workplace. As part of this research effort, longwall gob gas flow paths in a mine operating in the Pittsburgh Coalbed, PA, were investigated using SF6 tracer gas. Tracer gas released into the ventilation airflow underground generally stayed in the bleeder system and was vented at the associated bleeder fan shafts. Tracer gas injected into an inactive (intaking) gob gas venthole migrated to the two inby producing ventholes on the study panel, indicating that all three ventholes were in communication. The tracer gas that was injected into the gob generally stayed in the gob and only migrated to the ventilation system in response to the venthole on the study panel closest to the injection hole going off production. Tracer gas flow velocities in the longwall gob reservoir and factors influencing the production performance of gob gas ventholes in the study area are also discussed.