Investigation of the influence of gas fracturing on fracturing characteristics of coal mass and gas extraction efficiency based on a multi-physical field model

Numerical evaluation on multiphase flow and heat transfer during thermal stimulation enhanced shale gas recovery

In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock (TMR), a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed. The simulation results were then compared with field monitoring data. The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects, i.e., displacement field, stress field and energy field. The results show that in comparison to the full caving mining method, the bearing capacity of the goaf after backfilling was enhanced, the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body, and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture. Before TMR fracture, the subsidence displacement of TMR was reduced by 65.3%, the front abutment stress of panel decreased by 9.4% on average and the high energy concentration zone around panel was also significantly reduced. Overall, the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.

Dynamic disaster control of backfill mining under thick magmatic rock in one side goaf: A case study

Investigation on crack initiation and propagation in hydraulic fracturing of bedded shale by hybrid phase-field modeling

There are many karst collapse columns in coal seam roof in the southern coal field in China, which are different from those in coal seam floor in the northern coal field, due to the stratum characteristics. The karst collapse column in coal seam roof tends to reactivate and conduct water and induce the serious water inrush disaster, when the karst collapse column communicates with the overlying aquifer. In order to reveal the evolution mechanism of water-conducting channel of collapse column in karst mining area of southwest China, the aquifers and water inflow rule in 1908 working face in Qianjin coal mine are analyzed. Besides, the particle size distribution and mineral component of collapse column are researched by the X-ray diffraction test and the screening method, which are the basis for researching the water inrush mechanism in karst collapse column. On this basis, the water inrush of roof collapse column under the influence of mining is researched by establishing the numerical calculation model with the UDEC numerical software. The results show that the water flowing into the 1908 working face comes from the Changxing formation aquifer and Yulongshan formation aquifer above the coal seam, and the proportion of coarse particles and fine particles in collapse column is 89.86% and 10.14%, respectively. With the advance of working face, the water-conducting channel connected the working face with the aquifer, or the surface is formed by collapse pits, karst caves, and collapse column. The research results can be treated as an important basis for the water-preserved mining in southern coal field in China.

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Evolution Mechanism of Water-Conducting Channel of Collapse Column in Karst Mining Area of Southwest China

The mining of underground coal seam often induces the dynamic disasters of coal seam, such as rock burst and gas outburst. The determination of evolution characteristics of mechanical parameters and seepage parameters of coal mass after excavation is the basis for analyzing the formation mechanism of dynamic disasters. In this study, a coupled hydromechanical numerical approach is developed and their complex interactions are analyzed using the energy method to study the influence of outburst factors during underground excavation. A finite element model of porous media, which represents the gas flow field, the coal deformation field, the coal damage field and the cross-couplings between them, is established and the reliability of the model is ensured by numerical and experimental validation. Subsequently, during underground excavation, the coal deformation and gas flow properties around the borehole associated with different factors, including gas sorption, the matrix-fracture characteristics of coal and the seepage characteristics, are analyzed quantitatively using numerical simulations. Furthermore, an energy index is developed based on the energy method to analyze the comprehensive influence of in situ stress and gas pressure on coal mass. The results revealed that in the damage zone, coal permeability increases greatly by one to two orders of magnitude and the gas pressure remains low. Gas adsorption not only affects the stress and deformation of coal, but also affects the extent of the damage zone. High in situ stress, high gas pressure and low coal strength cause the failure range to increase.

https://link.springer.com/content/pdf/10.1007/s11053-020-09644-0.pdf

Tongqiang Xia

Papers

Analysis of Deformation, Permeability and Energy Evolution Characteristics of Coal Mass Around Borehole After Excavation