• Energy Research

ABSTRACTThe multi‐field coupling relationship and temperature evolution mechanism of gas‐containing coal in areas affected by geological structures were investigated, focusing specifically on the engineering aspects of a reverse fault in the No. 3 coal seam at the Xinjing Coal Mine. An analysis was conducted to examine the thermal‐fluid‐solid coupling behavior of gas‐containing coal. A thermal‐fluid‐solid coupling model for gas‐containing coal, accounting for the effects of damage, was developed to simulate the incubation process of coal and gas outbursts within the fault zone during the advancement of the working face. The study has indicated that faults not only degrade the mechanical properties of the surrounding coal‐rock mass, but also disrupt the continuity of coal seam stress. Gas tends to accumulate near fault zones, resulting in differences in the gas pressure and content on either side of the fault, thereby substantially increasing the likelihood of coal and gas outbursts. The primary factors influencing temperature variations include deformation energy, energy from gas expansion, thermal convection, thermal conduction, and the thermal effects associated with adsorption and desorption. Among these factors, the endothermic effect associated with adsorption and desorption significantly influences the temperature fluctuations in coal. The results of this study provide a theoretical foundation for exploring the mechanisms underlying coal and gas outbursts, improving the interdisciplinary coupling theory for coal and gas systems and employing temperature metrics to predict such outbursts.

ABSTRACTBased on the engineering background of coalbed methane block in Liujia District of Fuxin with complex geological conditions, a seepage mathematical model considering the dynamic changes of porosity and permeability of coal reservoir caused by coal matrix shrinkage under the conditions of gas adsorption, desorption, and stress change is established. A geological model of heterogeneous coalbed methane reservoir is established, which includes igneous rock and fault geological structure. The influence of permeability on coalbed methane productivity and reservoir pressure under complex geological conditions is studied by numerical simulation. The results show that the permeability of coal seam is an important factor affecting the yield of coalbed methane. The higher the permeability, the faster the output rate of coalbed methane, the higher the output, the faster the pressure drop of coal reservoir, and the faster the desorption rate of coalbed methane. Under the premise that the horizontal wellbore is perpendicular to the maximum permeability direction of the coal seam, the productivity of the well arrangement method is higher than that of the parallel maximum permeability direction. However, the length of the horizontal well in the Liujia block is limited by the dense igneous rock distribution, and the desorption area of the coalbed methane is reduced and the production is reduced when the vertical arrangement is arranged. Therefore, the horizontal wells in the Liujia block should be parallel to the maximum permeability direction and set along the direction of igneous rock. The greater the vertical permeability of the coal seam, the faster the reservoir pressure decreases, and the better the horizontal well productivity.

AbstractWhen pressure relief mining of a non‐all‐coal protective layer, to realize the accurate regulation of the pressure relief range and pressure release value of mining height, it is necessary to carry out research on the migration of overburden and the stress distribution law of stope under mining height control. Through similar material simulation experiments, four groups of similar material simulation experimental models were established. The laws of rock strata movement and stress distribution at 2, 4, and 5 m mining heights under different geological conditions, and the laws of rock strata movement and stress distribution at 5 and 8 m mining heights under the same geological conditions were obtained. The research results show that the geological conditions and mining height do not affect the evolution of the rock strata movement range. The highest position of the strata movement and deformation is linearly related to the advancing distance of the coalface. The maximum height of rock strata movement increases abruptly when encountering the key strata, but it still has a linear relationship. The highest position of each expansion of the fracture zone has an exponential relationship with the advancing distance of the coalface. When the key strata are encountered, the maximum height of the fracture zone increases abruptly. The change in mining height only affects the distribution range of the “three zones.” The mining height controls the stress distribution of stope by adjusting the “three zones” of the roof. With the increase in mining height, the caving zone and fracture zone range increase. The corresponding pressure relief range and pressure relief value show the change law of first increasing and then decreasing. There is an optimal mining height, which can make the pressure relief effect of stope best.

AbstractWith the shift of coal resources to deep mining, the occurrence of long‐distance coal seams has increased, and protective layer mining is facing new challenges. This paper attempts to explain the stress evolution law of the upper coal group in the long‐distance mining of the lower coal group in Pingdingshan No. 8 Coal Mine. A simulation model of advance mining of lower‐group coal long‐distance was established. The stress evolution law of the upper coal seam under the influence of advanced mining disturbance of the lower coal seam is studied. The following conclusions were obtained: The advance mining of the lower coal group had a positive or negative impact on the stress distribution of the upper coal seam group. With the recovery of the lower coal group of the F‐21030 working face, the overburden of the F‐21030 goaf finally formed a “Y” type pressure relief area. The pressure relief effect of the E‐21070 working face near the stopping line was obvious. The coal seam of Group E was divided into three areas affected by the advance mining of the lower coal seam. The maximum pressure relief value was 6.6% lower than the initial stress. According to the simulation results, the E‐21070 working face was divided into three regions, namely, the pressure relief region, the stress increase region, and the original stress region. According to the field drainage results of pressure relief gas, the extraction curve could be divided into three parts, namely, the stable area, pressure relief area, and stress recovery area. The maximum pure gas drainage volume could reach seven to eight times of the original area. The pressure relief extraction effect was remarkable, and the optimal extraction range was 22–210 m behind the coal face of the group.

Upper protective seam mining has been widely applied in China, but the theory of long-distance multiple upper protective seam mining is not yet perfect. In order to investigate the overburden stress evolution law of repetitive mining of long-distance coal seam groups, an experimental study was conducted to simulate similar materials under repeated mining conditions in the long-distance double upper protective layer in the background of Pingmei Group 8th coal mine. By analyzing the roof-collapse structure and the stress evolution law of different layers of the floor during the superposition mining, the pressure-relief range of the protective layer after the mining of the double upper protective layer was determined. The study results showed that: the pressure relief of the protective layer in the long-distance upper protective layer mining was a dynamic process. After the mining of Group D coal seam, the maximum impact depth of the bottom plate could reach 182 m, and the pressure-relief angle of the upper side of Group E coal seam was 65°, and the pressure-relief angle of the lower side was 75°. The distance behind the vertical projection of the working face of Group D was 42 m. The overlapping back mining would affect the stress distribution of Group F coal seam. The pressure-relief angle of the upper side of Group F coal seam was 88°, and the pressure-relief angle of the lower side was greater than 78°. The distance behind the vertical projection of the working face of Group E was less than 61 m. The superposition and staggered mining of double protective layers could expand the protective layer. Through the verification of the measurement of gas parameters on site, it can be seen from the results that it has a certain protection effect. The research results can enrich the theory of long-distance multiple upper protective layer mining, and provide theoretical guidance for long-distance Coal Seam Group Mining in Pingmei coal-mine area.