Study on crack propagation of the CO<sub>2</sub> presplitting blasting empty hole effect in coal seam

Pan, Hongyu; Li, Jingwen; Zhang, Tianjun; Li, Shugang; Zhang, Lei

doi:10.1002/ese3.785

Cited by 9 publications

(9 citation statements)

References 20 publications

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“…However, the high-pressure gas blasting technology as a measure to increase the permeability of low-permeability coal seams is still in the development stage, and the related theoretical research is not perfect. Domestic and foreign scholars have carried out a large number of studies on the anti-reflection field of high-pressure gas in unconventional gas low-permeability reservoirs using theoretical analysis, physical experiment, and numerical simulations. − It is found that the amount of high-pressure gas, impact mode, and in situ stress have a great influence on the crack initiation mode and crack propagation law of coal. Some scholars − detected the macroscopic mechanical properties and microstructure changes of coal and rock mass before and after high-pressure gas blasting by uniaxial/triaxial loading, acoustic emission detection, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) to reveal the cracking mechanism under a high-pressure gas impact.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

et al. 2022

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High-pressure air blasting (HPAB) is one of the main feasible technologies to improve the extraction efficiency of unconventional gases. At present, there are few visual studies on the evolution characteristics of pore structure in coal under HPAB, resulting in an unclear understanding of the mesoscopic damage evolution mechanism of coal under HPAB. To study the dynamic response and mesoporous structure evolution characteristics of coal under HPAB, simulated coal specimens were used in HPAB experiments. The pore structure characteristics of coal at different locations away from the blasthole after HPAB were analyzed by using computed tomography scanning and 3D reconstruction technology. The maximum sphere algorithm was used to study the law of pore connectivity and reveal the mesoscopic damage evolution mechanism of coal under HPAB. The results indicate that the stress wave and attenuation and the crack propagation direction are greatly affected by the confining pressure. Compared without confining stress, the radial strain attenuation index decreases by 11.97% and the lateral strain attenuation index increases by 15.36% under confining pressure. Without confining pressure, the crack direction is disordered. On the contrary, the crack expands along the σ 1 and σ 2 directions with confining pressure, while the expansion along other directions is inhibited. The stress wave has a great influence on the pore structure in the nearby zone. Compared with before HPAB, at 25 mm distance from the blasthole, the number of pores increased by 24.80%, the number of throats increased by 12.96 times, the maximum equivalent radius of throats increased by 52.15%, and the maximum channel length of the throat increased by 56.06%. With the increase of the distance, the stress wave has little influence on the pore structure in the middle and far zones. The porosity of representative elementary volume and the distance from the blasthole decay in a power function trend. The maximum disturbance distance under HPAB can reach nearly 110 times of the blasthole radius. The study results provide a theoretical basis for enhancing the coal seam permeability and gas drainage of low-permeability coal seam by HPAB.

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Section: Introductionmentioning

confidence: 99%

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

et al. 2022

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“…Coal bodies around boreholes are affected by different moisture contents and exhibit distinct force characteristics. The crack sprouting, expansion and development processes in each stage are more complex and difficult to observe and characterize, especially regarding their influences on borehole sealing technology and the extraction effect [1][2][3][4][5]. Therefore, it is of great engineering significance to perform research on the image grayscale characteristics of coal bodies around boreholes with different moisture contents.…”

Section: Introductionmentioning

confidence: 99%

“…When the moisture content increases, the peak grayness corresponding to the peak stress point significantly decrease; the peak grayness of the moisture-bearing specimen rapidly increases, the grayness distribution rapidly changes to "high and narrow", the third-order moment µ arc increases, and the internal strain field is not uniformly distributed. These phenomena occur because the moisture-bearing specimens have a certain energy storage period before the stable crack extension stage when energy is released, stress concentration zones appear, and microscopic cracks are formed[25] 3. After the stress is loaded to σ f , the peak grayness of the dry specimen more rapidly decreases, the grayness distribution shifts to "low and narrow", the third-order moment µ arc decreases, and the grayness distribution remains in the(40,110) interval.…”

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confidence: 99%

Study on the Grayscale Characteristics of Borehole Images of Progressive Failure of Coal Bodies with Different Moisture Contents

Pan

et al. 2022

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The failure process of a coal body around a borehole has progressive characteristics. Image characteristics can visually characterize the stress and failure characteristics of the coal body around a borehole during progressive failure. To investigate the effect of the moisture content on the progressive failure of the coal body around the borehole, an image test system for the deformation and fracture of coal rock was used, and progressive failure tests of coal body specimens with different moisture content conditions around boreholes were performed. We acquired images of the deformation field during the entire process of specimen failure. Based on the grayscale image theory, the variation in the grayscale characteristic parameters of the progressive failure process was analyzed. The results show that throughout the progressive failure of coal bodies with different moisture contents around a borehole, the main specimen failure can be divided into six stages: compression density, elastic deformation, crack initiation and stable extension, crack nonstable extension, post-peak softening, and post-peak failure. With increasing moisture content, the σcd/σf values of the 20%- and 40%-moisture-content specimens were 5.1% and 11.3% lower than those of the dry specimens, respectively, and the maximum uniaxial compressive strength σf was 5.1% and 17.4% lower than those of the dry specimens, respectively. The number of cracks that developed decreased. The grayscale histogram had a reduced grayscale peak at each stage, and the surface distortion diminished. The declining grayscale mean curve indicates a lagging development of stress concentration zones. The declining grayscale entropy curve indicates that macroscopic cracks form. The rising grayscale standard deviation curve indicates the delayed development of strain localization zones and weakening of specimen damage. The study explains the deformation and failure characteristics of the coal body around the borehole and the variation in grayness.

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“…In summary, most of the LCPTB research focuses on phase-transition mechanism [22,26,31], rock blasting [32,35], blasting antireflection [2][3][4]7,20,21] and blasting fracture propagation [11,20,36,37]. However, there is a lack of research on the initiation of the fracturing pipe and especially research on the relationship among controllable blasting parameters, blasting pressure and blasting effect in the LCPTB.…”

Section: Introductionmentioning

confidence: 99%

Research on Initiation of Carbon Dioxide Fracturing Pipe Using the Liquid Carbon Dioxide Phase-Transition Blasting Technology

et al. 2021

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Liquid carbon dioxide (L-CO2) phase-transition blasting technology (LCPTB) has caused wide concern in many fields, but there is a lack of research on the initiation of the carbon dioxide fracturing pipe. Studies regarding the carbon dioxide fracturing pipe initiation are critical for controlling and optimizing the LCPTB. Therefore, in this article, a series of exploratory experiments of carbon dioxide blasting were carried out to investigate the qualitative and quantitative relationships between the carbon dioxide fracturing pipe initiation and the three key variables (the filling mass of liquid carbon dioxide (L-CO2) (X1), the amount of chemical heating material (X2) and the thickness of the constant-stress shear plate (X3)). The failure mechanisms of three variables on the phase-transition blasting process of a carbon dioxide fracturing pipe was analyzed qualitatively based on experiment temperature, strain curve and failure form of constant-stress shear plate. An empirical model between the carbon dioxide fracturing pipe initiation (Y) and the three key variables (X1, X2, X3) was obtained after processing experiment result data quantitatively. Based on the phase-transition and blasting process of carbon dioxide, two methods, the Viral–Han–Long (VHL) equation of gas state (EOS) and the strength-failure method were used to calculate the blasting pressure and determine the failure mode of the fracturing pipe. The proposed blasting empirical model can be used to optimize the structural design of carbon dioxide fracturing pipes, guide on-site carbon dioxide blasting operations and further achieve the best blasting effect of LCPTB, so this work can enable LCPTB to be better applied to practical projects.

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Study on crack propagation of the CO₂ presplitting blasting empty hole effect in coal seam

Cited by 9 publications

References 20 publications

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Study on the Grayscale Characteristics of Borehole Images of Progressive Failure of Coal Bodies with Different Moisture Contents

Research on Initiation of Carbon Dioxide Fracturing Pipe Using the Liquid Carbon Dioxide Phase-Transition Blasting Technology

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Study on crack propagation of the CO2 presplitting blasting empty hole effect in coal seam

Cited by 9 publications

References 20 publications

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Study on the Grayscale Characteristics of Borehole Images of Progressive Failure of Coal Bodies with Different Moisture Contents

Research on Initiation of Carbon Dioxide Fracturing Pipe Using the Liquid Carbon Dioxide Phase-Transition Blasting Technology

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Study on crack propagation of the CO₂ presplitting blasting empty hole effect in coal seam