New Technology of Mechanical Cavitation in a Coal Seam to Promote Gas Extraction

Linghu, Jianshe; Chen, Haidong; Wang, Liguo; An, Fenghua

doi:10.1021/acsomega.2c01962

Cited by 5 publications

(3 citation statements)

References 41 publications

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“…However, there are still many problems with the technology and process of gas extraction in Chinese mines at present. The average gas extraction rate in mines is still less than 30% and the level of gas extraction and utilization is still relatively low [9][10][11][12]. One important reason is that there are many and widely distributed soft coal seam mines in China, and the low strength and poor stability of soft coal seams have led to the problem of difficult sealing of gas extraction boreholes in soft coal seams, which has directly led to the current situation of poor gas extraction efficiency in soft coal seams.…”

Section: Introductionmentioning

confidence: 99%

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

Jiang,

Bao,

Lei

2024

Processes

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In order to find the optimal expansion effect of a new curing expansion material so that it can better meet the requirements of the efficient sealing of drilled holes, the expansion and creep characteristics of the new curing expansion material were studied. Based on the creep results of graded loading, the Kelvin–Volgt model was selected to analyze its mechanical parameters, and a new “concentric ring” reinforcement sealing method was proposed. Numerical simulation was employed to analyze and discuss the reinforcement radius and depth of the “protective wall rock hole ring” in the “concentric ring” model, and on-site application experiments were carried out in a soft coal seam. The results show that the “concentric ring” reinforcement sealing method can effectively solve the problems of easy collapse and stress concentration instability in the sealing section of soft coal seams, ensuring long-term and efficient sealing of gas extraction boreholes in soft coal seams. When the diameter of the extraction drilling hole is 100 mm, the optimal reinforcement radius for the “protective wall rock hole ring” is 0.16–0.18 m. A reasonable reinforcement depth of the “protective wall rock hole ring” for drilling in soft coal seams is about 0.8–1 times the width of the roadway. In the on-site application process, experimental boreholes using “concentric ring” reinforcement sealing technology did not show any collapse phenomena, and the volume fraction of extracted gas remained above 30% for the first 30 days. Moreover, the gas volume fraction on the 30th and 60th days was 2.5 times and more than 3 times that of bag sealing boreholes using expanded cement, further proving that the sealing quality of boreholes using “concentric ring” reinforcement sealing is higher.

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Section: Introductionmentioning

confidence: 99%

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

Jiang,

Bao,

Lei

2024

Processes

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“…The energy structure of “rich coal, poor oil, and little gas” determines that coal will be the main energy source in China for a long time in the future. According to statistics, 48% of China’s coal mines are coal and gas outburst or high gas mines, and the number, scale, and losses caused by coal and gas outburst accidents are among the highest in the world. − …”

Section: Introductionmentioning

confidence: 99%

Research on Directional Hydraulic Coal Cutting and Outburst Prevention Technology in Soft and Hard Composite Coal Seams

Shan

Zhong

et al. 2023

ACS Omega

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Affected by tectonics, soft and hard composite coal seams are widely distributed in China; the soft stratification in the soft and hard composite coal seam is the key to controlling the occurrence of coal and gas outburst accidents. Based on this, for soft and hard composite coal seams, in order to accurately extract soft layers, a directional hydraulic coal mining equipment has been developed, including a drilling rig pump truck system, a directional coal wireless measurement system, and a cutter drill pipe system. By constructing a mathematical model and conducting numerical simulations, it was found that the vertical stress, horizontal stress, and gas pressure of the coal body around the borehole after coal extraction decreased significantly compared to normal borehole conditions; the on-site test results indicate that the hydraulic coal extraction volume of directional hydraulic coal extraction boreholes reaches 0.25 m3 per meter. The total amount of coal extracted accounts for more than 3‰ of the total amount of coal within the coverage area. The average concentration of gas extraction in the coal extraction area is 80.15%, and the net amount of gas extraction from 100 m boreholes reaches 0.17 m3/(min·hm). After extraction, the measured residual gas content in the coal extraction and non-extraction areas decreased by 59.27 and 40.38%, respectively. Directional hydraulic coal mining technology can effectively solve the problem of coal and gas outburst prevention in soft and hard composite coal seams and has good application prospects.

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“…31 In recent years, the new technology of the mechanically over-excavated cavity along the borehole is used in soft coal seams to overcome the problems (Figure 1). [32][33][34] A mechanically over-excavated drill bit was used to cut coal to generate a series of cavities along the borehole similar to the structure of 'candied haws on a stick' (Figure 1c). The mechanism of permeability-increasing is the same as hydraulic flushing.…”

Section: Introductionmentioning

confidence: 99%

Mechanical behaviour and fracture evolution of coal specimens containing an over‐excavated hole: Experimental study and numerical modelling

Man

Liu

Mingyao

et al. 2023

Strain

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Utilising a series of mechanically over‐excavated cavities along borehole is a novel technique for enhancing the permeability of soft coal seams and, consequently, gas drainage. The evolution of cracks induced by a wide range of pressure‐relief around an over‐excavated hole is intrinsically complex. In this study, the mechanical behaviour and crack evolution of the specimens containing an over‐excavated hole under uniaxial compression loading were studied by experimental and 3D numerical simulation. The results indicated that the peak strength and elastic modulus of the specimens gradually decrease with increasing cavity diameter and length, which is also verified by the numerical simulation. The inclusion of cylindrical cavities in over‐excavated holes results in reduced crack initiation stress and a greater degradation of peak stress and elastic modulus, despite having an equivalent volume to the ellipsoidal cavity. This is likely attributed to the difference in stress concentration between the cylindrical and ellipsoidal cavities. The crack propagation process can be classified into four stages based on the acoustic emission (AE) event counts, initial crack compaction, stable crack propagation, unstable crack propagation and post‐peak failure stage. The two AE indices, rise angle and average frequency value, demonstrated that the failure is dominated by tensile crack and gradually transformed to shear crack. Stress redistribution is essential in the initiation and propagation of cracks. Tensile stress concentration leads to cracks forming at the top and bottom of the hole, which propagate in the direction of loading. Compressive stress concentration results in shear cracks forming at the left and right sides of the hole, which propagate diagonally. The failure pattern of the specimen is ultimately determined by a combination of tensile and mixed crack propagation. The experimental and numerical results contribute to a deeper understanding of the crack evolution mechanism of coal seams with over‐excavated holes.

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New Technology of Mechanical Cavitation in a Coal Seam to Promote Gas Extraction

Cited by 5 publications

References 41 publications

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

Research on Directional Hydraulic Coal Cutting and Outburst Prevention Technology in Soft and Hard Composite Coal Seams

Mechanical behaviour and fracture evolution of coal specimens containing an over‐excavated hole: Experimental study and numerical modelling

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