The release of methane into the working area of coal mines can affect safety and production. Therefore, methane drainage reduces the risk of explosion and can be used as a fuel and energy source. One methane drainage method is cross‐measure borehole drilling, which involves drilling boreholes from tailgate roadways to the roof or floor layers of a mined seam. In this method, determining the appropriate distance between methane drainage stations has a significant impact on increasing the efficiency of operation and reducing drilling costs and the time required for drainage operations from each station. In this paper, a new 3D numerical model is developed for methane drainage from an underground coal mine to determine the suitable distance between methane drainage stations in the cross‐measure borehole method using COMSOL Multiphysics software. For this purpose, by considering the porous media flow module and the laws related to the movement of gas in the goaf, different numerical models for distances of 10, 15, 20, 25, and 30 m were simulated. The simulation results showed that by reducing the distance between methane drainage stations, the speed of gas flow in the borehole and the amount of gas removed from the boreholes in a similar period of time increase to an acceptable level. In addition, the implementation of this model in a case study showed that a distance of 10 m between drainage stations increases the efficiency of boreholes to approximately 20%. Numerical simulation in this study can provide basic support for the design of drainage boreholes and reduce the risk of gas in underground coal mines.

A large amount of gas is emitted during underground mining processes, so mining productivity decreases and safety risks increase. Efficient methane drainage from the coal seam and surrounding rocks in underground mines not only improves safety but also leads to higher productivity. Methane drainage must be performed when the ventilation air cannot dilute the methane emissions in the mine to a level below the allowed limits. The cross-measure borehole method is one of the methane drainage methods that involves drilling boreholes from the tailgate roadway to an un-stressed zone in the roof or floor stratum of a mined seam. This is the main method used in Tabas coal mine N 1. One of the effective parameters in this method is the distance between methane drainage stations, which has a direct effect on the length of boreholes required for drainage. This study was based on the measurement of ventilation air methane by methane sensors and anemometers placed at the longwall panel as well as measuring the amount of methane drainage. Moreover, in this study, the obtained and analyzed data were used to determine the suitable distance between methane drainage stations based on the cross-measure borehole method. In a field test, three borehole arrangements with different station distances in Panel E4 of Tabas coal mine N 1 were investigated. Then, the amounts of gas drained from these arrangements were compared with each other. The highest methane drainage efficiency was achieved for distances in the range of 9-12 m between methane drainage stations.

Methane release during mining exploitation represents a severe threat to miners’ safety. Methane gas can be removed from coal seams using predrainage and postdrainage techniques and used to generate electricity or for household purposes. One of the postdrainage methods is the cross‐measure borehole method, which involves drilling boreholes from the tailgate roadway to an unstressed zone in the roof or floor layers of a mined seam. To achieve high efficiency of gas draining, predicting and determining the optimum range of design elements in gas drainage operation is necessary. The distance between the methane drainage (MD) stations is one of the most important parameters for determining the amount of gas removed. This study was conducted on the basis of the measurement data of MD in the Tabas coal mine. In this study, hybrid multilayer perceptron (MLP) neural networks and gray wolf optimizer (GWO) algorithm were employed to predict and optimize the gas drainage process. Therefore, the technical parameters of MD boreholes, including panel properties, advanced speed, and joint density, were considered. Then, a hybrid artificial neural network (ANN)–GWO algorithm was developed in the MATLAB programing environment, and the performance of the model was evaluated using statistical criteria such as regression relationships, correlation coefficients between actual and predicted values, and average relative error percentage. Applying the presented model can increase the MD efficiency to an acceptable range. The results showed an average reduction in the distance between the MD stations from 20 to 10 m (assuming that other technical parameters of the boreholes remain constant in the cross‐measurer boreholes method), and the MD efficiency increases by ~20%–50%. Finally, the efficiency of gas output from the mine will be improved, and a balance will be struck between methane removed with ventilation air methane (VAM) and MD.

Underground coal mining is known as one of the major sources of methane emissions which mainly occurs after underground coal extraction. Rock strata in-situ methane can potentially be the most significant hazard in coal mining operations. To prevent or minimize the risks of methane emissions, methane drainage approaches have been adopted by coal mines. Rock mass methane drainage is the most efficient and effective approach toward controlling methane hazards as it prevents and reduces the frequency of methane emissions, outflows into the working area and sudden outbursts of methane and rocks. The method includes drilling boreholes from the tailgate side to the unstressed zone in the roof and floor strata above and below a working coal seam. The coal seam gas content in Tabas Parvadeh I is estimated to be about 16 m3 /t, which is relatively high. Based on exploration data, five distinct coal seams have been identified (B1, B2, C1, C2 and D) at the coal deposit and currently C1 is being worked. Considering the high value of C1 gas content and surrounding rocks, the Methane Drainage System (MDS) has been utilized for gas drainage. This paper tries to determine the desorption area which is essential and helpful for the selection of an effective drilling pattern into the adjacent coal seams. In this study, the methane drainage zone in the E4 panel of the Tabas coal mine was calculated using experimental equations and a drainage borehole pattern was determined.