scholarly journals Experimental Investigation on Mechanics and Seepage Characteristics of Tectonic and Intact Coal Containing Gas

2020 ◽  
Vol 10 (20) ◽  
pp. 7290
Author(s):  
Chaolin Zhang ◽  
Enyuan Wang ◽  
Jiang Xu ◽  
Shoujian Peng
Keyword(s):  
Coalbed Methane ◽  
Triaxial Compression ◽  
Coal Mines ◽  
Gas Pressure ◽  
Extraction Time ◽  
Gas Extraction ◽  
Effective Measure ◽  
Pressure Stage ◽  
Tectonic Coal ◽  
Seepage Characteristics

Coalbed methane is a double-edged sword with two attributes of energy and hazard in coal mines. Gas drainage is the most direct and effective measure for gas recovery and disaster prevention in coal mines, which is seriously affected by the mechanics and seepage characteristics of coal. In this work, we experimentally simulated the triaxial compression and gas depletion processes using both tectonic coal and intact coal. The mechanics and seepage characteristics of tectonic and intact coal under the coupling effect of stress and gas pressure were analyzed and compared. The results show that during the triaxial compression, the damage stress and peak stress of tectonic coal is only half that of intact coal, while their compaction stress or residual stress are almost the same. Meanwhile, the permeability recovery value after tectonic coal failure is very limited, even smaller than that of intact coal, although its primary permeability is much larger than that of intact coal. On the contrary, the permeability recovery value after intact coal failure is more than twice of its primary permeability. During the gas depletion, the rebound gas pressure of tectonic coal is smaller than that of intact coal, and the permeability of tectonic coal is one order of magnitude larger than that of intact coal before the gas pressure drops to 2 MPa. The broken of tectonic coal and the low permeability of intact coal may be the two principal reasons. Therefore, in the tectonic coal area, the gas extraction time at high gas pressure stage should be stabilized, while in the intact coal area, the gas extraction time at low gas pressure stage should be increased, and the coal permeability enhancement measures should be combined to achieve the goal of high and stable production of coalbed methane.

Micro-Nanostructure of Coal and Adsorption-Diffusion Characteristics of Methane

2021 ◽  
Vol 21 (1) ◽  
pp. 422-430
Author(s):  
Tianrang Jia ◽  
Cao Liu ◽  
Guoying Wei ◽  
Jiangwei Yan ◽  
Qinghao Zhang ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Adsorption Isotherms ◽  
Primary Structure ◽  
Coalbed Methane ◽  
Large Error ◽  
Gas Pressure ◽  
Diffusion Characteristics ◽  
Fundamental Reason ◽  
Tectonic Coal ◽  
Adsorption Amount

The adsorption and diffusion characteristics of coal are important parameters for coalbed methane (CBM) extraction and mine gas control. However, the adsorption test can only obtain the apparent adsorption amount, and it cannot obtain the actual adsorption amount, which leads to a large error during the calculation of the coal diffusion coefficient. Taking the anthracite coal in the Jiulishan Mine as the research object, the micro-nanostructure and instantaneous apparent methane adsorption isotherms of the primary structure coal and tectonic coal were determined by low-temperature CO2 adsorption, mercury intrusion and methane diffusion kinetics tests, and the instantaneous apparent adsorption isotherms of methane were corrected to the instantaneous actual adsorption isotherm by the Langmuir model. The results demonstrate that the micro-nanopore, Density Function Theory (DFT) pore volume and specific surface area values below 1–2 nm in tectonic coal are larger than those in the primary structure coal, which is the fundamental reason why the ultimate adsorption capacity of tectonic coal is larger than that of the primary structure coal. The apparent adsorption amounts of the tectonic coal and the primary structure coal reach the maximum at 8 MPa and 10 MPa, respectively. Thereafter, the instantaneous isotherms of the apparent adsorption amount decrease with increasing of gas pressure. However, the instantaneous isotherms of the actual adsorption amount tend to be stable. The diffusion coefficient undergoes a rapid decay with time under low gas pressure, and undergoes a slow decay with under the high gas pressure.

scholarly journals A Novel Hydraulic Mode to Promote Gas Extraction: Pressure Relief Technologies for Tectonic Regions and Fracturing Technologies for Nontectonic Regions

2019 ◽  
Vol 9 (7) ◽  
pp. 1404 ◽  
Author(s):  
Shaojie Zuo ◽  
Zhaolong Ge ◽  
Zhe Zhou ◽  
Li Wang ◽  
Hanyun Zhao
Keyword(s):  
High Efficiency ◽  
Coal Mines ◽  
Clean Energy ◽  
Extraction Time ◽  
Efficient Production ◽  
Gas Extraction ◽  
Coal Seams ◽  
Pressure Relief ◽  
Gas Concentration ◽  
Coal Roadway

Extraction of gas (coalbed methane) produces clean energy and can ensure that coal mines maintain high-efficiency production. The currently available coal seam permeability enhancing technologies and modes have certain application restrictions. Therefore, a novel mode is proposed to promote gas extraction. This mode divides complex coal seams into tectonic regions and nontectonic regions based on geological structures. Then, the characteristics of different regions are matched with the advantages of different hydraulic technologies; thus, pressure relief technologies are proposed for tectonic regions, and fracturing technologies are proposed for nontectonic regions. The permeability of coal seams will be sharply increased without leaving unfractured areas. This mode will promote the effectiveness of gas extraction, shorten the extraction time, and ensure safe and efficient production in coal mines. A field application shows that this mode has a better effect than slotted directional hydraulic fracturing technology (SDHFT). The gas concentration and pure gas flow were increased by 47.1% (up to 24.94%) and 44.6% (up to 6.13 m3/min), respectively, compared to SDHFT over 9 months. The extraction time was reduced by 4 months. This mode reduced the number of times that gas concentration exceeded government standards during coal roadway excavation, and the coal roadway excavation speed was increased by 16% (up to 158 m/month).

scholarly journals Coal Seam Gas Extraction by Integrated Drillings and Punchings from the Floor Roadway considering Hydraulic-Mechanical Coupling Effect

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-10
Author(s):  
Chaojun Fan ◽  
Haiou Wen ◽  
Sheng Li ◽  
Gang Bai ◽  
Lijun Zhou
Keyword(s):  
Coal Seam ◽  
Coal Mines ◽  
Coupling Model ◽  
Gas Pressure ◽  
Gas Content ◽  
Engineering Practice ◽  
Gas Extraction ◽  
Coal Seam Gas ◽  
Mechanical Coupling ◽  
Gas Disasters

Owing to the exhaustion of shallow coal resources, deep mining has been occupied in coal mines. Deep buried coal seams are featured by the great ground stress, high gas pressure, and low permeability, which boost the risk of gas disasters and thus dramatically threaten the security about coal mines. Coal seam gas pressure and gas content can be decreased by gas extraction, which is the primary measure to prevent and control mine gas disasters. The coal mass is simplified into a continuous medium with dual structure of pores and fractures and single permeability. In consideration of the combined effects of gas slippage and two-phase flow, a hydraulic-mechanical coupling model for gas migration in coals is proposed. This model involves the equations of gas sorption and diffusion, gas and water seepage, coal deformation, and evolution of porosity and permeability. Based on these, the procedure of gas extraction through the floor roadway combined with hydraulic punching and ordinary drainage holes was simulated, and the gas extraction results were used to evaluate the outburst danger of roadway excavation and to verify the engineering practice. Results show that gas extraction can reduce coal seam gas pressure and slow down the rate of gas release, and the established hydraulic-mechanical coupling model can accurately reveal the law of gas extraction by drilling and punching boreholes. After adopting the gas extraction technology of drilling and hydraulic punching from the floor roadway, the remaining gas pressure and gas content are reduced to lower than 0.5 MPa and 5.68 m3/t, respectively. The achievements set a theoretical foundation to the application of drilling and punching integrated technology to enhance gas extraction.

scholarly journals Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2303
Author(s):  
Congyu Zhong ◽  
Liwen Cao ◽  
Jishi Geng ◽  
Zhihao Jiang ◽  
Shuai Zhang
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Coalbed Methane ◽  
Coal Sample ◽  
Fine Particles ◽  
Particle Sizes ◽  
Tectonic Coal

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

scholarly journals Coupled Effects of Stress, Moisture Content and Gas Pressure on the Permeability Evolution of Coal Samples: A Case Study of the Coking Coal Resourced from Tunlan Coalmine

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1653
Author(s):  
Guofu Li ◽  
Yi Wang ◽  
Junhui Wang ◽  
Hongwei Zhang ◽  
Wenbin Shen ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coalbed Methane ◽  
Gas Permeability ◽  
Axial Stress ◽  
Gas Pressure ◽  
Pressure Curve ◽  
Permeability Evolution ◽  
Confining Stress ◽  
Qinshui Basin ◽  
Gas Seepage

Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH4 gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin.

scholarly journals Guiding Effect of Soft Tectonic Coal on Coal and Gas Outburst and its Experimental Study

2021 ◽  
Author(s):  
Qingyi Tu ◽  
Sheng Xue ◽  
Yuanping Cheng ◽  
Wei Zhang ◽  
Gaofeng Shi ◽  
...  
Keyword(s):  
Physical Simulation ◽  
Local Existence ◽  
Coal Pillar ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Control Group ◽  
Long Distance ◽  
Gas Outburst ◽  
Soft Coal ◽  
Tectonic Coal

Abstract Soft tectonic coal commonly exists in coal and gas outburst zones. The physical simulation experiment was carried out to reproduce the influences of soft coal area on the outburst, and the guiding action mechanism of soft tectonic coal on the outburst was investigated. This study concludes that the amount of outburst coal in the experiments of group with local existence of soft coal area are relatively lower. The outburst coal amount (3.8035 kg) and relative outburst intensity (21.02%) in the GR5# experiment were both lower than that in the GN6# experiment of control group. However, the outburst coal in the experiments of group with local existence of soft coal area could be commonly migrated to a long distance, the maximum throwing distances in the three experiments were all over 16.73 m, reaching as high as 20.10 m. Under the gas pressure of 0.30 MPa in the group with local existence of soft coal area, the outburst coal amount (2.7355 kg) was smaller than the amount (2.803 kg) of pulverized coal filled, and the 2.0 cm coal pillar experiences failure only nearby the outburst mouth. As the gas pressure increases, the failure degree of the coal pillar becomes higher and higher until complete failure. The outburst development sequence is changed due to the existence of the soft tectonic soft area. Once the sealing conditions are destructed, the outburst firstly develops in the soft tectonic coal area. Nevertheless, sufficient energy is supplied to transport the coal mass in the soft tectonic coal area to a farther distance, while the residual outburst energy can just result in the outburst of a small quantity of coal masses in the normal area. This research will be of great scientific significance for explaining the soft tectonic coal-induced change of outburst starting and development sequence.

scholarly journals Model development and analysis of coal permeability based on the equivalent characteristics of dual-porosity structure

2019 ◽  
Vol 17 (2) ◽  
pp. 313-327
Author(s):  
Haijun Guo ◽  
Kai Wang ◽  
Yuanping Cheng ◽  
Liang Yuan ◽  
Chao Xu
Keyword(s):  
Coalbed Methane ◽  
Model Development ◽  
Gas Pressure ◽  
Dual Porosity ◽  
Permeability Evolution ◽  
Evolution Law ◽  
Fracture Width ◽  
Coal Permeability ◽  
Porosity Structure ◽  
Gas Seepage

Abstract Mining is a dynamic fracture process of coal and/or rock. The structural failure of coal bodies will change the coal matrix-fracture characteristics and then affect the distribution characteristics of the coalbed methane (CBM). Because of the structural complexity of coal, the coal matrices and fractures will be assumed to the geometries with rule shapes when the gas seepage characteristics in coals are analyzed. The size of the simplified geometries is the equivalent scale of dual-porosity coal structures (i.e. the equivalent fracture width and equivalent matrix scale). In this paper, according to the reasonable assumptions with regarding to dual-porosity coal structures, a new coal permeability evolution model based on the equivalent characteristics of dual-porosity structure (ECDP model) was built and the effect of the equivalent characteristics of dual-porosity structure on the coal permeability evolution law was analyzed. It is observed that if the initial fracture porosity is constant and the equivalent matrix scale increases, the range in which the permeability of coal rises with rising gas pressure increases; if the equivalent fracture width decreases and the equivalent matrix scale is constant, the range in which the permeability of coal rises with rising gas pressure decreases. The ECDP model is more suitable for revealing the evolution law of the coal permeability when large deformations occur in the coal bodies and/or the coal structure is damaged irreversibly, especially during enhancing CBM recovery.

scholarly journals Laboratory Study on Changes in the Pore Structures and Gas Desorption Properties of Intact and Tectonic Coals after Supercritical CO2 Treatment: Implications for Coalbed Methane Recovery

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3419 ◽  
Author(s):  
Erlei Su ◽  
Yunpei Liang ◽  
Lei Li ◽  
Quanle Zou ◽  
Fanfan Niu
Keyword(s):  
Pore Structure ◽  
Coalbed Methane ◽  
Supercritical Co2 ◽  
Total Pore Volume ◽  
Experimental Results ◽  
Methane Recovery ◽  
Enhanced Coalbed Methane Recovery ◽  
Gas Desorption ◽  
Pore Structures ◽  
Tectonic Coal

Tectonic coals in coal seams may affect the process of enhanced coalbed methane recovery with CO2 sequestration (CO2-ECBM). The main objective of this study was to investigate the differences between supercritical CO2 (ScCO2) and intact and tectonic coals to determine how the ScCO2 changes the coal’s properties. More specifically, the changes in the tectonic coal’s pore structures and its gas desorption behavior were of particular interest. In this work, mercury intrusion porosimetry, N2 (77 K) adsorption, and methane desorption experiments were used to identify the difference in pore structures and gas desorption properties between and intact and tectonic coals after ScCO2 treatment. The experimental results indicate that the total pore volume, specific surface area, and pore connectivity of tectonic coal increased more than intact coal after ScCO2 treatment, indicating that ScCO2 had the greatest influence on the pore structure of the tectonic coal. Additionally, ScCO2 treatment enhanced the diffusivity of tectonic coal more than that of intact coal. This verified the pore structure experimental results. A simplified illustration of the methane migration before and after ScCO2 treatment was proposed to analyze the influence of ScCO2 on the tectonic coal reservoir’s CBM. Hence, the results of this study may provide new insights into CO2-ECBM in tectonic coal reservoirs.

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