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Coal mine water outburst under fluid-solid coupling is a hot topic in coal geology. In this paper, the FLAC 3D simulation method is used to systematically study the water outburst problem of fluid coupling with coal mine floor. The results show that the vertical stress of the floor in the goaf has an obvious downward trend after coal seam excavation. Under the joint influence of mine pressure and bearing water pressure, the working face before the old roof pressure can be affected by two stages: the first stage is the advance pressure compression section on both sides of the working face, and the other stage is the pressure relief expansion section under the goaf. Before the old roof is pressed, the shear stress near the roof and floor is also affected to some extent. The front and rear displacement value of the goaf is negative, which is the result of the advance supporting pressure. The effective thickness of the floor waterproof layer decreases gradually with the advance of the working face. When the working face continues to advance, there will be a risk of water outburst. With the increasing width of the working face, the height of the guide belt increases. Therefore, in the process of mining activities, a variety of factors should be considered comprehensively, and a reasonable width of the working face should be selected to ensure the safety of mining. [ABSTRACT FROM AUTHOR]

This paper addressed the rockburst hazards caused by tectonic stress in the "three hard" coal mine in Datong Coalfield. We analyzed tectonic stress characteristics in the mining area and the mechanism of tectonic stress inducing rockbursts. We built the stress analysis model for rockburst-inducing tectonic stress. The roadway of the coal seam 12# in Xinzhouyao Coal Mine of Datong Coalfield was explicitly analyzed as an example. It was found that roof bedding separation was very likely to happen under the action of local tectonic stress in the roadway of the "three hard" coal seam, causing rockbursts that pushed out the coal wall. Numerical simulation was performed to analyze the occurrence of rockbursts induced by tectonic stress. We validated that stress concentration was more likely to happen in the coal-rock masses under the action of the tectonic stress, causing rockbursts. Besides, a large horizontal stress gradient would be formed near the roadway coal wall when the principal stress was perpendicular to the roadway axis. Rockbursts were highly probable in the coal-rock masses under this situation. [ABSTRACT FROM AUTHOR]

China is rich in primary energy resources. Due to specific terrain conditions, different types of problems may occur in the process of development. When the coal seams are located under the oil layers, due to the physical characteristics of oil, the exploitation of coal seams will cause losses to the oil layers, and the volatile oil may also cause threats to coal mining. To analyze the fracture development and leakage characteristics of overburden strata for this type of geological conditions, we have carried out physical simulation experiments and performed a further numerical simulation to study and verify the evolution of fractures. Based on numerical simulation results, methods have been proposed that may effectively reduce the air leakage in the working face and control the parameters, including viscous resistance, distance, and the construction period of the blocking. In this paper, based on the 30100 face in the Nanliang coal mine as an example, we have proved that the proposed measures can provide good theoretical guidance for the prevention of spontaneous combustion of residual coal and control of water in coal mine production. The developed method offers good economic benefits for safe production in coal mines. [ABSTRACT FROM AUTHOR]

In order to provide production safety and determine the optimal ventilation scheme in coal mining, the mines should be classified by their gas emission and mine security rank. In this paper the three models of mine classification, mine insecurity, and the optimal ventilation required by the mine are established and solved by MatLab and Lingo software. In answer to question 1, firstly, the daily absolute gas emission amount and relative gas are evaluated by average values of absolute and relative gas emission rates. It is shown that average values distribution complies with the normal distribution and fluctuation around the stable value. Finally, according to the standard requirements, the mine is classified as a high gas mine. In answer to question 2, the relationship is established between the gas concentration and the lower limit of coal dust explosion concentration, and a specific function relationship between gas concentration and coal dust explosion concentration is obtained by logarithmic fitting. The fuzzy membership function is derived, and the fuzzy statistical evaluation model is established to evaluate the mine safely. The probability safety value calculated by MatLab software is 4.63 %. In answer to question 3, firstly, according to the relationship between gas concentration, coal dust concentration and ventilation speed, the minimum air volume actually required by the coal mining face under the condition of safe production is established. Through MatLab programming calculation, the minimum air volume of coal mining face 1 and face 2 is 385.10 and 531.08 m3/min, respectively. According to the diversion of the air volume of each working zone and the specific requirements for ventilation speed in each zone, a ventilation optimization model is established and solved by Lingo software. The calculated air volume of the local ventilator and the optimal (total) air volume required by the mine are 150 and 1491.18 m3/min, respectively. Finally, through the solution and analysis of the model, it is shown that the simulation method is reasonable and can produce reliable guidance for management of high-risk coal mining enterprises. [ABSTRACT FROM AUTHOR]

Geological coalbed methane (CBM) reserves buried at a depth of about 2000 m in China amount are estimated at 36.81 trillion m, ranking China as third in the world. Resources buried at depths greater than 1000 m account for 61.2% of total reserves. Compared with currently developed shallow coal seams, the deep beds have much more complex mechanical engineering characteristics: high in situ stress, high temperature, high karst water pressure, considerable mining disturbance, etc. Therefore hydraulic fracturing operations for deep coalbed methane (DCBM) are associated with problems that are not typical for shallow beds. Accordingly, in order to develop deep bed fracturing technology, we need to study types of proppants, fracturing fluids, fracturing supporting technology, etc. based on results of hydraulic fracturing of shallow coal seams. [ABSTRACT FROM AUTHOR]