Study on mechanical properties and energy evolution of coal under liquid nitrogen freezing

Huang, Laisheng; Li, Bo; Wang, Bo; Wu, Bing; Zhang, Junxiang

doi:10.1016/j.engfracmech.2023.109158

Cited by 32 publications

(8 citation statements)

References 40 publications

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“…6(a) and (b) shows that the initial stress and energy values of the coal seam are 14.35MPa and 13.76×10 6 J without the influence of mining disturbance and pressure relief. The stress and energy values are increased to 16MPa and 18×10 6 J respectively, and the pressure relief of the main and inferior strata can reduce the stress and energy values within the range of 10-29m to 7MPa and 4×10 6 J, the average stress and energy of the coal seam are both low compared with the initial stress and the average stress and energy values of the mining disturbance, the stress and energy values in the range of 0-10m have increased significantly, which are from 14.52MPa to 15.38MPa, 13.99×10 6 J to 15.80×10 6 J, respectively. Before and after the pressure relief of the key strata, the stress field and energy field distribution of the coal seam in the range of 41-70m along the direction of the excavation face, are shown in Fig.…”

Section: Fracturing Drilling Layout and Scope Of Influencementioning

confidence: 99%

“…Coal seam gas drainage measures can not only improve mining efficiency, but also reduce the occurrence of safety production accidents, and eliminate dangers and potential risks of mining works thoroughly [3][4][5]. Hydraulic measures, such as, hydraulic punching, hydraulic cutting, and hydraulic fracturing are widely used in the practical field of coal seam permeability enhancement [6][7][8][9]. Hydraulic punching increases the expansion and pressure relief space of the coal seam around the borehole [10].…”

Section: Introductionmentioning

confidence: 99%

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Study on stress-permeability change of soft coal seam under hydraulic unloading of overlying key strata: numerical simulation and theory

Wang

Liu

et al. 2023

Preprint

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Based on the geological conditions of low permeability, high gas pressure, high gas content, and high ground stress in soft coal seams, the hydraulic fracturing technology of key strata in overlying strata was proposed. This research mainly focuses on the 8003 excavation working face of a mine in Shanxi as the engineering background, the main and inferior key strata of the overlying strata were determined according to the key strata theory, the hydraulic fracture initiation pressure is measured to be 16MPa, and the influence range is about 15m. `This research established a coal seam permeability model under impacts of effective stress and pore pressure by using simulation software such as FLAC3D to simulate the changes in stress and energy of coal seams before and after fracturing in key strata. Based on results of changes in coal seam permeability and extraction radius, as well as the data of engineering test results, this research also found that fracturing in key strata can cut off the stress transmission path of overlying strata, and thus effectively improving coal seam permeability. The fracturing of the overlying key strata has the effect of unloading and dissipating energy on the coal seam. The stress value and energy values along the inclination and strike of the excavation working face have a varying degree of decreasing trend. With decreasing original stress concentration area of the coal seam, both the stress value and energy values of the deep coal seam are increased. The energy and stress distribution characteristics of the coal seam before and after unloading are basically consistent. After hydraulic fracturing of the key layer, the average gas concentration in the return air flow of the excavation working face decreased from 0.65–0.51%, and the number of coal burst decreased by 95%.

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Section: Fracturing Drilling Layout and Scope Of Influencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study on stress-permeability change of soft coal seam under hydraulic unloading of overlying key strata: numerical simulation and theory

Wang

Liu

et al. 2023

Preprint

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“…The rising effective stress inhibits the flow of coal seam gas and hinders gas extraction. To improve the effect of gas extraction in coal seams, pressure relief and permeability enhancement measures can be adopted on roof strata. , However, due to the geological evolution over time, pore fractures in reservoirs were blocked by minerals such as calcite, montmorillonite, and hematite. − Physical permeability enhancement methods fail to alleviate this situation. Acidification, a multiphase chemical reaction occurring at the liquid–solid interface, can unblock pores and strengthen the development of the pore-fracture system of rock formation through chemical dissolution. − Its process can be roughly divided into three phases: the movement of H + in the acid fluid system to the rock surface, the adsorption of H + on the rock surface and the chemical reaction, and the departure of the products from the rock surface at the reaction end (Figure ).…”

Section: Introductionmentioning

confidence: 99%

“…To improve the effect of gas extraction in coal seams, pressure relief and permeability enhancement measures can be adopted on roof strata. 2,3 However, due to the geological evolution over time, pore fractures in reservoirs were blocked by minerals such as calcite, montmorillonite, and hematite. 4−6 Physical permeability enhancement methods fail to alleviate this situation.…”

Section: Introductionmentioning

confidence: 99%

Damage Characterization and Permeability Variation of Acidified Rock: A Theoretical and Experimental Study

et al. 2023

ACS Earth Space Chem.

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This study aims to explore the damage and permeability enhancement effect of acidification on rock. First, an X-ray diffraction qualitative analysis was conducted on the roof rock in the coal seam of Jiulishan Coal Mine in Jiaozuo City, Henan Province, China, by an X-ray diffractometer. The optimum acid solution ratio (12% HCl+1% HF) was obtained based on the principle of acidification acting on the mineral composition. Based on previous tests, tests for mechanical properties and gas permeability of rock samples before and after acidification were carried out. Under the condition of different acidification times, the rock damage degree was quantitatively characterized by the changes in the mass loss and mechanical properties of rock, and the relationships of acidification time with the rock damage degree and permeability were explored. The results reveal the following. (1) Macroscopically, acidification damages rock by deteriorating its mechanical properties, and the damage mode transitions from brittle damage to ductile damage. The damage degree is positively correlated with the acidification time; however, when the reaction reaches a certain extent, acidification barely causes mechanical damage to the rock. (2) Microscopically, minerals in the rock mass are dissolved, hence promoting the connectivity between pores and enhancing the permeability. In addition, there is a chain causality for rock permeability enhancement; that is, the acidification time determines the amount of minerals dissolved inside the rock, and the mineral dissolution intensifies rock damage, which then enhances the permeability. The evolution of rock permeability with acidification time can be concluded as follows: the permeability increases rapidly first, then rises slowly, and finally levels off; the optimum acidification time is in the range of 8−24 h with permeability enhanced by 220−260%.

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“…The grain-interface stiffness mismatch in induced macro-fractures will have a great effect on the energy and fracturing behavior. Measurements of the damage and fracturing behavior of the fractured coal with fracturing-induced macro-fractures, under uniaxial and triaxial stresses, have been carried out [48][49][50]. Laboratory observations of coal subjected to true triaxial stresses have so far been limited to intact samples, and relevant experimental studies on fractured coal samples are still limited.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Energy Evolution Characteristics of Intact and Fractured Coal under True Triaxial Progressive Stress Loading

Liu,

Zhao,

Yin

et al. 2023

Sustainability

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The underground coal mining process is closely associated with frequent energy storage and consumption of coal mass with natural and induced fractures. Exploring the energy evolution characteristics of intact and fractured coal samples could be helpful for dynamic disaster control. In this study, laboratory true triaxial tests on the energy evolution characteristics of intact and fractured coal samples have been carried out and systematically discussed. The results show that the brittleness and peak strength are weakened due to the presence of macro-fractures in coal. The mean peak strength and brittleness for fractured coal are 29.00% and 74.59% lower than the intact coal samples. For both intact and fractured coal, the energy evolution curves are closely related to the deformation stages under true triaxial stresses. When subjected to the same intermediate stress, intact coal stores more elastic strain energy compared to fractured coal. Additionally, the rate of dissipative energy variation is two–three times lower in fractured coal samples compared to intact coal samples.

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Study on mechanical properties and energy evolution of coal under liquid nitrogen freezing

Cited by 32 publications

References 40 publications

Study on stress-permeability change of soft coal seam under hydraulic unloading of overlying key strata: numerical simulation and theory

Study on stress-permeability change of soft coal seam under hydraulic unloading of overlying key strata: numerical simulation and theory

Damage Characterization and Permeability Variation of Acidified Rock: A Theoretical and Experimental Study

Comparison of Energy Evolution Characteristics of Intact and Fractured Coal under True Triaxial Progressive Stress Loading

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