Mining Publication: Numerical Analysis of the Impact of Longwall Panel Width on Methane Emissions and Performance of Gob Gas Ventholes
In coal mining, longwall mining is a preferred method to maximize production by extracting large blocks of coal that have been outlined with a set of development entries. In U.S. mines, longwall panels are typically 1,000 ft wide (with a continual trend toward even wider panels) and usually over 10,000 ft long. The increasing size of longwall panels, while helping to increase coal production, may also increase methane emissions because of the exposure of the mining environment to a larger area of fractured, gas-bearing strata. Thus, understanding the impact of increased panel widths on methane emissions and designing gob gas ventholes and bleeder systems accordingly can enhance the safety of underground workers by reducing their exposure to potentially explosive accumulations of methane/air mixtures. As part of its mine safety research program, NIOSH's Pittsburgh Research Laboratory has initiated a reservoir modeling effort to better understand the interaction of the various geotechnical factors influencing gas flow within and to the underground longwall mining environment. A focus of this modeling effort has been (1) the prediction of the incremental amount of methane emissions to be expected due to increasing longwall panel widths and (2) optimizing gob gas venthole completion practices to capture more of the gas in the subsided strata above longwall panels before it can enter the ventilation system of the underground workplace. The history-matching phase of the study has been carried out on a 1,250-ft-wide panel in the Pittsburgh Coalbed. Simulations have also been completed for a 1,450-ft-wide panel to estimate the incremental increase in methane emissions and the performance of current gob gas venthole placement configurations. Additional venthole placement configurations were simulated to investigation options for optimizing methane capture from the subsided strata above the wider longwall panel.