One of the most significant problems of underground mining is sudden methane outbursts occurred during the production. To reduce the probability of these incidents and bring down the level of emission it is necessary to carry out actions for preliminary degassing of rock mass. According to experimental data there is the relationship between the gas flow from the coal seam and its stress state which is characterized by opening of natural fracture system and release of methane during process of mass stress relief. It is proposed to use this relationship to increase the effectiveness of degasification work by hydraulic fracturing in degassing wells or excavating of slots. This paper presents the results of mathematical modeling of rock mass stress-relieving process performed using Itasca’s FLAC finite-difference software. The main goal was determination of the optimal geometry and location of slots or fractures to increase the stress-relief area of the coal measure rock. The resulting stress pattern was analyzed and recommendation for degasification works of coal seams was made.
To ensure the safety of mining operations, to prevent sudden rock and gas outbursts and for economic efficiency increase through the usage of associated gas, more attention should be paid to improving the technology of coal seams degassing. It is necessary to understand the mechanism of methane emissions from coal beds, as well as relationship between all factors that affect this process. In general, the un-mined coal seam has a low gas recovery. It is considered that the best way to increase the efficiency of the degassing process is to maximize the stress-relief area within the rock mass and the most commonly used methods are hydraulic fracturing and stress-relieving slots. The artificial fractures formation provides partial stress unloading of the rock with methane desorption in affected areas.
