Numerical Study on Shocking Coal Seam of Multi-Points Explosion with High-Pressure Gas

The permeability of coal seam is an important parameter for the gas extraction and gas outburst control. However, most of the coal seams are low-permeability with outstanding characteristic in China. Therefore，it is a good technology to provide the theoretical basis for increasing the permeability of low-gas- permeability coal seam by shocking with high-pressure air. Based on the percolation theory of porous media and combining the gas pressure change after shocking the coal seam with high-pressure air, the solid-gas coupled mathematical model is presented for the flow in the coal seam. By applying the software, the numerical simulation is computed and analyzed for the gas pressure evolution owing to the multi-spot continuous shocking the coal seam by the high-pressure air under the different pressure values and strata pressure.

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Research and Optimization of Gas Extraction by Crossing-Seam Boreholes from Floor Roadway

Geofluids ◽

10.1155/2021/7499012 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Gang Li ◽

Jiafei Teng

Keyword(s):

Coal Seam ◽

Gas Permeability ◽

Gas Pressure ◽

Gas Content ◽

Gas Extraction ◽

Gas Migration ◽

Governing Equations ◽

Coal Seam Gas ◽

Gas Seepage ◽

Gas Disaster

Deep coal seams are characterized by large stress, high gas pressure, and low permeability. The gas disaster threatens the safe production of coal mine seriously. Gas extraction by crossing-seam boreholes from floor roadway (GECMBFR) can reduce the pressure and content of coal seam gas, which is the main measure to prevent gas disaster. Considering the Klinkenberg effect, governing equations of gas adsorption/desorption-diffusion, gas seepage, and stress fields within the coal seam are established to form the seepage-stress coupling model. The governing equations are embodied into a finite element driven software to numerically simulate gas migration and fluid-solid coupling law in coal seam. On this basis, the process of gas extraction under different borehole spacings and diameters is simulated. The effects of these two key parameters on coal seam gas pressure, gas content, and gas permeability were analyzed. The borehole spacing and diameter were determined to be 5 m and 0.09 m, respectively. Combined with the actual situation of a mine, the process of gas extraction from floor roadway with different cross-sectional schemes, ordinary drilling boreholes and punching combined drilling boreholes, is comparatively analyzed. The results show that the gas extraction effect by ordinary drilling boreholes is lower than that of the punching combined drilling boreholes, and the extraction is uneven and makes it difficult to meet the standard. Hydraulic punching was carried out, and coal was washed out of the borehole, which expanded the contact area between the borehole wall and coal seam. The coal seam around the punching borehole is unloaded, which improves coal permeability and accelerates gas migration towards the borehole, thus promoting the efficiency of gas extraction. It is more reasonable to use punching combined drilling borehole scheme when implementing the GECMBFR technology.

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Coupling Technology of Deep-Hole Presplitting Blasting and Hydraulic Fracturing Enhance Permeability Technology in Low-Permeability and Gas Outburst Coal Seam: A Case Study in the No. 8 Mine of Pingdingshan, China

Advances in Civil Engineering ◽

10.1155/2021/5569678 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Wei Wang ◽

Yanzhao Wei ◽

Minggong Guo ◽

Yanzhi Li

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Complex Structure ◽

Coal And Gas Outburst ◽

Gas Content ◽

Low Permeability ◽

Gas Extraction ◽

Deep Hole ◽

Coal Seams ◽

Gas Outburst

The current study aims to analyze the principles of integrated technology of explosion to tackle the problems of coal seam high gas content and pressure, developed faults, complex structure, low coal seam permeability, and high outburst risk. Based on this, we found through numerical simulation that as the inclination of the coal seam increases, the risk of coal and gas outburst increases during the tunneling process. Therefore, it is necessary to take measures to reduce the risk of coal and gas outburst. We conducted field engineering experiments. Our results show that the synergistic antireflection technology of hydraulic fracturing and deep-hole presplitting blasting has a significant antireflection effect in low-permeability coal seams. After implementing this technology, the distribution of coal moisture content was relatively uniform and improved the influence range of direction and tendency. Following 52 days of extraction, the average extraction concentration was 2.9 times that of the coal seam gas extraction concentration under the original technology. The average scalar volume of single hole gas extraction was increased by 7.7 times. Through field tests, the purpose of pressure relief and permeability enhancement in low-permeability coal seams was achieved. Moreover, the effect of gas drainage and treatment in low-permeability coal seams was improved, and the applicability, effectiveness, and safety of underground hydraulic fracturing and antireflection technology in low-permeability coal seams were verified. The new technique is promising for preventing and controlling gas hazards in the future.

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Permeability Enhancement Properties of High-Pressure Abrasive Water Jet Flushing and Its Application in a Soft Coal Seam

Frontiers in Energy Research ◽

10.3389/fenrg.2021.679623 ◽

2021 ◽

Vol 9 ◽

Author(s):

Xinzhe Zhang ◽

Piotr Wiśniewski ◽

Sławomir Dykas ◽

Guojie Zhang

Keyword(s):

High Pressure ◽

Coal Seam ◽

Water Jet ◽

Gas Pressure ◽

Theory And Practice ◽

Abrasive Water Jet ◽

Gas Drainage ◽

Permeability Enhancement ◽

Soft Coal ◽

Soft Coal Seam

High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this study, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing equations for the evolution of mesoscopic element damage along with coal mass deformation. Numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. Distributions of the seepage and gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed by conducting a field experiment. Conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced and that the gas drainage volume is three times higher than that of a conventional borehole. Field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved and that tunneling speed is nearly doubled. The results obtained from this study can provide guidance to gas drainage in soft coal seams regarding the theory and practice application of the HPAWJF method.

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Micropore Structure and Fractal Characteristics of Low-Permeability Coal Seams

Advances in Materials Science and Engineering ◽

10.1155/2018/4186280 ◽

2018 ◽

Vol 2018 ◽

pp. 1-15 ◽

Cited By ~ 2

Author(s):

Guang-zhe Deng ◽

Rui Zheng

Keyword(s):

Fractal Dimension ◽

Electron Microscope ◽

Scanning Electron Microscope ◽

Coal Seam ◽

Linear Relationship ◽

Surface Area ◽

Pore Volume ◽

Low Permeability ◽

Coal Seams ◽

Scanning Electron

With the raw coal from a typical low-permeability coal seam in the coalfield of South Junger Basin in Xinjiang as the research object, this paper examined six kinds of coal samples with different permeabilities using a scanning electron microscope and a low-temperature nitrogen adsorption test that employed a JSM-6460LV high-resolution scanning electron microscope and an ASAP2020 automatic specific surface area micropore analyzer to measure all characteristic micropore structural parameters. According to fractal geometry theory, four fractal dimension calculation models of coal and rock were established, after which the pore structure characteristic parameters were used to calculate the fractal dimensions of the different coal seams. The results show that (1) the low-permeability coal seam in the coalfield of South Junger Basin in Xinjiang belongs to mesoporous medium, with a certain number of large pores and no micropores. The varying adsorption capacities of the different coal seams were positively correlated with pore volume, surface area, and the mesoporous surface area proportions, from which it was concluded that mesopores were the main contributors to pore adsorption in low-permeability coal seams. (2) The raw coal pore fractal dimension had a negative linear relationship to average pore size, a positive linear relationship with total pore volume, total surface area, and adsorption capacity, and a positive correlation with the mesoporous surface area proportion; that is, the higher the fractal dimension, the larger the pore volume and surface area of the raw coal. (3) The permeability of the low-permeability coal seam had a phase correlation with the micropore development degree; that is, the permeability had a phase negative correlation with the pore distribution fractal dimension, and there was a positive correlation between permeability and porosity. These results are of theoretical significance for the clean exploitation of low-permeability coal seam resources.

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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 ◽

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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Applicability Analysis of Klinkenberg Slip Theory in the Measurement of Tight Core Permeability

Energies ◽

10.3390/en12122351 ◽

2019 ◽

Vol 12 (12) ◽

pp. 2351 ◽

Cited By ~ 2

Author(s):

Jirui Zou ◽

Xiangan Yue ◽

Weiqing An ◽

Jun Gu ◽

Liqi Wang

Keyword(s):

High Pressure ◽

Gas Permeability ◽

Fluid Dynamic ◽

Dynamic Parameter ◽

Low Pressure ◽

Low Permeability ◽

Apparent Permeability ◽

Tight Reservoir ◽

Gas Seepage ◽

The Relationship

The Klinkenberg slippage theory has widely been used to obtain gas permeability in low-permeability porous media. However, recent research shows that there is a deviation from the Klinkenberg slippage theory for tight reservoir cores under low-pressure conditions. In this research, a new experimental device was designed to carry out the steady-state gas permeability test with high pressure and low flowrate. The results show that, unlike regular low-permeability cores, the permeability of tight cores is not a constant value, but a variate related to a fluid-dynamic parameter (flowrate). Under high-pressure conditions, the relationship between flowrate and apparent permeability of cores with low permeability is consistent with Klinkenberg slippage theory, while the relationship between flowrate and apparent permeability of tight cores is contrary to Klinkenberg slip theory. The apparent permeability of tight core increases with increasing flowrate under high-pressure conditions, and it is significantly lower than the Klinkenberg permeability predicted by Klinkenberg slippage theory. The difference gets larger when the flowrate becomes lower (back pressure increases and pressure difference decreases). Therefore, the Klinkenberg permeability which is obtained by the Klinkenberg slippage theory by using low-pressure experimental data will cause significant overestimation of the actual gas seepage capacity in the tight reservoir. In order to evaluate the gas seepage capacity in a tight reservoir precisely, it is necessary to test the permeability of the tight cores directly at high pressure and low flowrate.

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Improvement of Gas Drainage Efficiency of Low-Permeability Coal Seams Using Ultra-High Pressure Hydraulic Cutting Technique

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/472/1/012084 ◽

2019 ◽

Vol 472 ◽

pp. 012084 ◽

Cited By ~ 1

Author(s):

Yongjiang Zhang

Keyword(s):

High Pressure ◽

Low Permeability ◽

Coal Seams ◽

Gas Drainage ◽

Ultra High Pressure

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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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