Estimate of the optimum horizontal well depth for gas drainage using a numerical method in the tabas coal mine

One of the hazards in underground coal mining operations is the sudden coal gas emission leading to coal outburst. To reduce the risk of gas emissions to enable safer mining, it is necessary to pre-drain coal seams and surrounding strata. According to the experimental data, there exists a relationship between the gas flow from the coal seam and the stress changes in the upper layers above the coal seam. This is achieved by drilling horizontal drainage holes in the coal seam. Phase2 commercial software was used to investigate induced stresses caused by methane drainage operations during mining. The optimum depth of horizontal borehole from the coal face was calculated based on the actual gas production. Results of the numerical simulation showed that boreholes with a minimum distance of 30 m from the coalface provide the optimum gas drainage performance for the underground Tabas Coal mine in the South East of Iran