A fully coupled coal deformation and compositional flow model for the control of the pre-mining coal seam gas extraction

The coal seam gas recovery in deep reservoirs often meets high temperature. The change of temperature can greatly influence gas sorption, and couples heat transfer with coal deformation and gas-flow. This paper modifies the conventional Langmuir adsorption equation into a non-isothermal adsorption equation with a set of experimental data. After then, a fully coupled thermo-hydro-mechanical model of coal deformation, gas-flow and heat transfer is established. By using a finite element approach of COMSOL multi-physics, a numerical simulation of coal seam gas recovery from high temperature reservoir is subsequently implemented. The results show that the gas pressure and temperature decrease with production time and increase with the distance from production well, the reservoir permeability decreases with production time due to the compaction of increasing effective stress to coal fracture network, the cumulative gas production increases with production time exponentially whereas the production efficiency decreases negative exponentially, that the gas production in earlier 10 years accounts for 80% of the total production in 30 years. Our fully coupled thermo-hydro-mechanical model can improve the current understanding of coal seam gas recovery from high temperature reservoirs.

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Thermo-hydro-mechanical coupled mathematical model for controlling the pre-mining coal seam gas extraction with slotted boreholes

International Journal of Mining Science and Technology ◽

10.1016/j.ijmst.2017.03.012 ◽

2017 ◽

Vol 27 (3) ◽

pp. 473-479 ◽

Cited By ~ 8

Author(s):

Yi Xue ◽

Feng Gao ◽

Yanan Gao ◽

Xin Liang ◽

Zhizhen Zhang ◽

...

Keyword(s):

Mathematical Model ◽

Coal Seam ◽

Gas Extraction ◽

Coal Seam Gas ◽

Mining Coal

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

Applied Sciences ◽

10.3390/app9214720 ◽

2019 ◽

Vol 9 (21) ◽

pp. 4720 ◽

Cited By ~ 3

Author(s):

Ge ◽

Zhang ◽

Sun ◽

Hu

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Hydraulic Fracture ◽

Scale Model ◽

Gas Extraction ◽

Coal Seams ◽

Directional Hydraulic Fracturing ◽

Coal Mine Methane ◽

Multi Scale ◽

Fully Coupled

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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Experimental Study on Deep Borehole Pre-Cracking Blasting of Drilling through Strata at Low Permeability Seam

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.868.339 ◽

2013 ◽

Vol 868 ◽

pp. 339-342

Author(s):

Jian Liu ◽

Qian Le

Keyword(s):

Coal Seam ◽

Control Area ◽

Low Permeability ◽

Gas Extraction ◽

Test Results ◽

Deep Borehole ◽

Coal Seam Gas ◽

Gas Concentration ◽

Working Face ◽

Outburst Coal Seam

In the process of roadway excavation in the low permeability outburst coal seam, with drilling through strata in the bottom drainage roadway extracting coal seam gas of control area. In order to improve extraction effect, the method that deep borehole pre-cracking blasting is used to increase the permeability of coal in the drilling through strata seam segment is proposed. The calculation formula on crushing circle and crack circle radius of deep borehole pre-cracking blasting are derived, and the effective loosening radius of blasting is calculated in theory, the research achievements are applied to field test, the test results show that deep borehole pre-cracking blasting permeability improvement technology is carried out in the drilling through strata of the low permeability outburst coal seam, the permeability of coal seam is improved by 180 times, the gas extraction scalar is raised by 8-10 tomes, during the process of roadway excavation, gas concentration of the working face is 0.2%-0.3%, and tunneling footage is increased by 2 times.

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Peer review report 2 On “Groundwater methane in a potential coal seam gas extraction region”

Journal of Hydrology Regional Studies ◽

10.1016/j.ejrh.2015.12.043 ◽

2015 ◽

Vol 3 ◽

pp. 120-122

Author(s):

Malcolm Edward Cox

Keyword(s):

Coal Seam ◽

Peer Review ◽

Gas Extraction ◽

Coal Seam Gas ◽

Extraction Region

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Peer review report 1 On “Groundwater methane in a potential coal seam gas extraction region”

Journal of Hydrology Regional Studies ◽

10.1016/j.ejrh.2015.12.042 ◽

2016 ◽

Vol 5 ◽

pp. 3-5

Author(s):

Anonymous

Keyword(s):

Coal Seam ◽

Peer Review ◽

Gas Extraction ◽

Coal Seam Gas ◽

Extraction Region

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Investigation of Large-Diameter Borehole for Enhancing Permeability and Gas Extraction in Soft Coal Seam

Geofluids ◽

10.1155/2020/6618590 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Yongwen Wang ◽

Wanjun Yan ◽

Zhongjiu Ren ◽

Zhiqiang Yan ◽

Ziwen Liu ◽

...

Keyword(s):

Coal Seam ◽

Shear Failure ◽

Large Diameter ◽

Gas Content ◽

Gas Extraction ◽

Extraction Area ◽

Damage Area ◽

Soft Coal ◽

Coal Deformation ◽

Soft Coal Seam

The efficiency of gas extraction from the soft coal seam with ultralow permeability is low. Gas extraction with large-diameter borehole is proposed to deplete gas content for preventing gas outburst disaster in this study. The fractures around the large borehole will enhance the permeability in the damage area to promote gas extraction. We established a damage-stress-seepage coupling model for large-diameter borehole gas extraction in soft coal seam. This mathematical model contains governing equations of gases sorption and transport, coal deformation, and damage, reflecting the coupling responses between gas and coal seam. The model is solved by the finite element method to simulate the gas drainage large-diameter borehole through roadway. Distributions of elastic modulus, damage area, and maximum principal stress in soft coal seam with different borehole diameters including 94 mm, 133 mm, 200 mm, and 300 mm are analyzed. The gas pressure, gas content, and effective extraction area in soft coal seam are discussed. Results show that the shear failure zone appears around the large-diameter borehole, and its permeability rises sharply. This opens up the gas transport channel and is conducive to the rapid extraction. It is confirmed that gas extraction using large-diameter borehole (300 mm) can greatly improve the efficiency of the gas preextraction in soft coal seam by increasing gas extraction rate. These provide a foundation for guiding the operation of gas extraction with large borehole from the soft coal seam in the field.

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