Study on the Fractal Characteristics of Coal Body Fissure Development and the Law of Coalbed Methane Migration of around the Stope

Abstract

Due to the complicated coalbed methane (CBM) occurrence conditions and the diverse geological structures in China, the promotion and application of the coal and gas simultaneous extraction technology have been seriously restricted. In view of this, this paper chooses Qingdong Coal Mine protection layer mining and CBM extraction field practice as the research background. Firstly, based on the similar material simulation experiment that simulates coal mining, the dynamic changing pattern of a mining field’s overburdened strata and corresponding stress are obtained, the relationship between gas desorption and stress can then be clarified. Further, with the help of the fractal theory and box counting method, the fracture development characteristics of the overlying strata are quantitatively described on the basis of experimental images. Finally, by building a model for calculating the penetrability coefficient of coal seam based on fractal dimension of mining fissure and analyzing the relationship between fissure development and fractal dimension, the gas migration law and the fissure development areas of #7 and #8 overburden strata where CBM concentrates can be revealed and determined. According to the orientation of the area mentioned above, the location of the CBM pumping field in relation to the coal seam roof and the arrangement of CBM extraction boreholes can be optimized, which make CBM extraction efficient. Meanwhile, the risk of coal and gas outburst is significantly reduced when the CBM concentration is controlled within 0.2% to 0.6% outside the corner of the working face and 0.1% to 0.35% in return flow, which is lower than 0.8%, the threshold of CBM concentration.

Recapitulation and Prospect of Research on Flow Field in Coal Mine Gob

“…Xu et al [43] used the physical similarity simulation method to realize the qualitative study of wind flow state by analyzing the smoke flow state. Yang et al [44] established a model of coal seam permeability coefficient based on similar material experiments simulating coal mining with fractal dimension of mining fractures.…”

The Effect of Hydraulic Coupling on Mechanical Deformation Characteristics of Shallow Coal Seam in Western Mining Area

“…The simulated coal seam depth is 220 m, and the coal seam thickness is 8 m. As shown in Figure 5, the dimension of the model was 180 × 20 × 120 cm (length × height × thickness). Based on similarity theory and previous related research [6,15,34,35], it is determined that the geometric similarity ratio is 200 : 1 and the bulk density similarity ratio is 1.5 : 1. The simulation material uses river sand, calcium carbonate, and gypsum as materials, uses mica as auxiliary materials, and adds a certain proportion of fly ash to the coal seam.…”

“…The failure characteristics of rock materials under different loads are discussed. At the same time, through physical similarity to simulate field conditions, the overburden migration and evolution laws can be studied more intuitively fractal, and the evolution of overburden breaking spatial structure and the occurrence of roof dynamic disasters during the entire mining process are systematically studied [12,[29][30][31][32][33][34][35]. Most of the above is the study of the law of overburden fault development.…”

Study on Gas Migration Law of Mining Coal Seam under the Influence of Normal Fault

“…Gao et al [23] used FLAC 3D to study the stress of stope and crack propagation according to the stress state of coal body in front of the work and simulated and analyzed the gas migration law under the influence of mining through the self-established solid-gas coupling constitutive model considering gas pressure and gas adsorption. Yang et al and Cheng et al [24,25] studied the fracture development characteristics of overlying strata under the influence of mining and simulated and analyzed the gas migration law in the fracture area. In [26] in view of the technical problems of safe mining caused by high gas and low permeability of coal seams in mining areas in China, based on the theory of pressure relief gas drainage, the pressure relief gas drainage technology and coal and gas comining technology system were established.…”