Numerical studies of improved methane drainage technologies by stimulating coal seams in multi-seam mining layouts

Szott, W.; Słota-Valim, Małgorzata; Gołąbek, A.; Sowiżdżał, K.; Łętkowski, Piotr

doi:10.1016/j.ijrmms.2018.06.011

Cited by 36 publications

(17 citation statements)

References 17 publications

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“…Some scholars believed that pulsating hydraulic fracturing must be carried out to improve the permeability of coal seam, and both the fissure mechanism and the gas seepage in the crack need to be studied deeply [15,16]. [17] presented the procedures and results of numerical modelling of different stimulation methods and pointed out the hydrofracturing and jet slotting as stimulating methods can potentially enhance methane drainage from the analyzed seam. [18] combined theoretical research and field tests to exploit high-pressure air blasting for cracking and permeability enhancement.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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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.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…erefore, in view of the gas emission laws of coal bodies, experts in the field have adopted many research methods, including gas adsorption and desorption experiments, microscanning, micropore structure analyses, and mercury injection experiments [23][24][25]. However, the majority of the research studies generally utilize one or two of the aforementioned methods to examine the gas desorption laws of coal bodies.…”

Section: Introductionmentioning

confidence: 99%

A Study of the Differences in the Gas Diffusion and Migration Characteristics of Soft and Hard Coal in High Gas Coal Seams

Yuan

2020

Advances in Civil Engineering

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At the present time, it is of major significance to examine the differences in the gas diffusion and migration characteristics of soft and hard coal in order to prevent and control safety hazards in high gas coal seams. In this study, the differences in the gas diffusion and migration characteristics between soft coal and hard coal were examined in detail using macrostructural, mesostructural, and microstructural research methods. The root causes of the differences in the gas diffusion and migration between soft coal and hard coal were revealed in the obtained research results. The study shows that, in terms of the macrostructures, the soft coal particle grains were flakey and with shapes resembling fingernails. Meanwhile, the hard coal particle grains were observed to be in the shapes of complete blocks. In addition, in terms of the mesostructures of the different coal types, it was found that the proportion of granular coal below the particle size limit of 6 mm in the soft coal was much higher than that of the hard coal. Also, from the aspect of the characteristics of the microstructures, the pores and fissures on the soft coal surfaces were observed to be better developed, and the BJH specific surface areas of the soft coal were more than twice those of the hard coal. That is to say, the gas diffusion and migration conditions of the soft coal were better than those of the hard coal. At the same time, the increments of the specific surface areas and volumes of the pores of soft coal were above 100 nm, which provided channels for gas diffusion and migration at rates of more than twice those of the hard coal. Therefore, the soft coal was more conducive to gas emissions. This study conducted gas desorption experiments on both soft and hard coal samples and found that the initial gas desorption speed of the soft coal was significantly higher than that of the hard coal. Since the instantaneous gas emissions of the soft coal were significantly higher than those of the hard coal, it was considered to be more likely that gas outbursts and transfinite accidents could potentially occur in the soft coal layers of a project site. This study’s results provided a foundation and basis for effective gas control measures in coal seams composed of soft coal layers, which will be of major significance to the safety of coal mining activities in the future.

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“…They focused on the impact of critical parameters related to coal seams on the methane production. Through a dynamic flow model, the drainage effect after using different stimulation technologies was investigated by Szott et al [30], where they found that the area of drainage zone after hydraulic fracturing was about 20 times larger than that after hydraulic slotting. However, none of these models is capable of investigating the multi-scale THM coupling behaviors of a coal seam after directional hydraulic fracturing.…”

Section: Introductionmentioning

confidence: 99%

Fully Coupled Multi-Scale Model for Gas Extraction from Coal Seam Stimulated by Directional Hydraulic Fracturing

Zhang

Sun

et al. 2019

Applied Sciences

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Although numerous studies have tried to explain the mechanism of directional hydraulic fracturing in a coal seam, few of them have been conducted on gas migration stimulated by directional hydraulic fracturing during coal mine methane extraction. In this study, a fully coupled multi-scale model to stimulate gas extraction from a coal seam stimulated by directional hydraulic fracturing was developed and calculated by a finite element approach. The model considers gas flow and heat transfer within the hydraulic fractures, the coal matrix, and cleat system, and it accounts for coal deformation. The model was verified using gas amount data from the NO.8 coal seam at Fengchun mine, Chongqing, Southwest China. Model simulation results show that slots and hydraulic fracture can expand the area of gas pressure drop and decrease the time needed to complete the extraction. The evolution of hydraulic fracture apertures and permeability in coal seams is greatly influenced by the effective stress and coal matrix deformation. A series of sensitivity analyses were performed to investigate the impacts of key factors on gas extraction time of completion. The study shows that hydraulic fracture aperture and the cleat permeability of coal seams play crucial roles in gas extraction from a coal seam stimulated by directional hydraulic fracturing. In addition, the reasonable arrangement of directional boreholes could improve the gas extraction efficiency. A large coal seam dip angle and high temperature help to enhance coal mine methane extraction from the coal seam.

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Numerical studies of improved methane drainage technologies by stimulating coal seams in multi-seam mining layouts

Cited by 36 publications

References 17 publications

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

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

A Study of the Differences in the Gas Diffusion and Migration Characteristics of Soft and Hard Coal in High Gas Coal Seams

Fully Coupled Multi-Scale Model for Gas Extraction from Coal Seam Stimulated by Directional Hydraulic Fracturing

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