Crack propagation patterns and energy evolution rules of coal within slotting disturbed zone under various lateral pressure coefficients

Lin, Baiquan; Liu, Ting; Zou, Quanle; Zhu, Chuanjie; Yan, Fazhi; Zhang, Zhen

doi:10.1007/s12517-014-1728-9

Cited by 34 publications

(8 citation statements)

References 47 publications

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“…Methane predrainage could help preventing coal and gas outbursts. Drilling gas extraction boreholes into coal seam forms channels for gas flow and relieves stress around the borehole. , However, many CBM reservoirs are characterized by high gas contents, low permeability, and strong heterogeneity. − To improve the gas extraction effect, borehole enlarging methods, such as hydraulic slotting and hydraulic flushing, are often adopted in low-permeability coal seams, thus achieving permeability enhancement. , It should be pointed out that borehole drilling and enlarging methods often cause damage, forming different ranges of fractured zones or collapsed zones around the borehole. This damage effect significantly affects geological engineering projects and gas extraction design as permeability could rise by hundreds of times in damaged coal. , …”

Section: Introductionmentioning

confidence: 99%

“… 3 − 5 To improve the gas extraction effect, borehole enlarging methods, such as hydraulic slotting and hydraulic flushing, are often adopted in low-permeability coal seams, thus achieving permeability enhancement. 6 , 7 It should be pointed out that borehole drilling and enlarging methods often cause damage, forming different ranges of fractured zones or collapsed zones around the borehole. This damage effect significantly affects geological engineering projects and gas extraction design as permeability could rise by hundreds of times in damaged coal.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Mechanical Properties on Gas–Water Flow Characteristics around Boreholes: Implementation of Damage-Based Coupling Models

Zheng,

Wu,

et al. 2024

ACS Omega

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Neglecting the coal damage effect around a borehole could result in low accuracy of gas extraction seepage analysis. A fluid–solid coupling model incorporating coal stress and damage, gas diffusion, and seepage was established. Reliability of the proposed model was validated using field data. Variation characteristics of gas–water phase parameters in the borehole damage zone during gas drainage were analyzed. Meanwhile, effects of equivalent plastic strain, lateral pressure coefficient, internal friction angle, cohesion, Young’s modulus, and Poisson’s ratio on the damage state and spatiotemporal change properties of gas extraction flow were investigated. Results indicate that due to coal damage, permeability shows a three-zone distribution around the borehole, among which the fracture zone has the highest permeability, approximately 40 times of the original value. Permeability in the plastic zone decreases rapidly, while permeability is the smallest in the elastic zone. Coal permeability within the damage zone increases with continuous gas extraction. A smooth and low-value zone occurs for both fracture and matrix gas pressures. With the increase in equivalent plastic strain, the damage zone decreases, while peak permeability in the damage zone rises, and gas pressure in the smooth low-pressure zone continues to drop. The damage zone becomes smaller with an increasing lateral pressure coefficient, while those plastic and elastic zones become larger. The damage zone area corresponding to the lateral pressure coefficient of 0.89 is 82.3% smaller compared with that of 0.56. As internal friction angle and cohesion rise, the damage zone gradually decreases and shifts from a butterfly shape to elliptical shape. When Young’s modulus is heterogeneously distributed, except for concentrated shear damage zones around the borehole, punctate microdamage zones are also found at positions far from the borehole. Those damage zones gradually become smaller as shape parameters of the Weibull distribution get larger. The above findings are expected to offer theoretical support and practical guidance for borehole drilling and efficient extraction of clean methane resources.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Mechanical Properties on Gas–Water Flow Characteristics around Boreholes: Implementation of Damage-Based Coupling Models

Zheng,

Wu,

et al. 2024

ACS Omega

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“…Laboratory experiments (Haimson 2007 ; Labiouse et al 2014 ; Labiouse and Vietor 2014 ; Yang et al 2018 ; Li et al 2019 ) and theoretical and numerical simulations (Perras et al 2010 ; Perras and Diederichs 2016a , b ; Vazaios et al 2019a , b ; Sun et al 2021 ) were also conducted to explore the failure mechanism of the surrounding rocks. The lateral pressure coefficient can affect the shape and the dimension of the EDZ (Bai-quan et al 2015 ). Yi et al ( 2020 ) investigated the progressive fracture processes around tunnels triggered by blast disturbances under different lateral pressure coefficients and found that the influence of the disturbance is the smallest when the lateral pressure coefficient is 1.0.…”

Section: Introductionmentioning

confidence: 99%

Dynamic failure characteristics of surrounding rocks under different lateral pressure coefficients in deep tunnel transient excavation

Yao

et al. 2023

Geomech. Geophys. Geo-energ. Geo-resour.

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A novel transient unloading testing system was adopted to simulate the transient excavation of tunnels under different lateral pressure coefficients (k0). The results show that the transient excavation of a tunnel induces significant stress redistributions and concentrations, particle displacements and vibrations to the surrounding rocks. The decrease of k0 enhances the dynamic disturbance of transient tunnel excavation, and especially when k0 = 0.4 and 0.2, the tensile stress can be observed on the top of the tunnel. The peak particle velocity (PPV) of the measuring points on the top of the tunnel decreases with the increasing distance between the tunnel boundary and measuring point. The transient unloading wave is generally concentrated on lower frequencies in the amplitude-frequency spectrum under the same unloading conditions, especially for lower k0 values. In addition, the dynamic Mohr–Coulomb criterion was used to reveal the failure mechanism of a transient excavated tunnel by involving the loading rate effect. It is found that the excavation damaged zone (EDZ) of the tunnel is dominated by the shear failure, and the number of the shear failure zones increases with the decrease of k0. The EDZ of tunnels after transient excavations varies from ring-shape to egg-shape and X-type shear with the decrease of k0. The evolution of the EDZ induced by the transient unloading is associated with k0, i.e., the shear failure of surrounding rocks mainly occurs in the stress redistribution stage under high k0 (1.0–0.7), while the dramatic destruction of surrounding rocks is more prone to occur after the transient unloading process when k0 ≤ 0.6.

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“…High-pressure water jet slotting [12][13][14][15][16] has been widely applied to enhance CBM extraction from underground coal seams with extremely low permeability, as shown in Figure 1. The coal seams may undergo tensile, compressive, or shear failure under the dynamic loading of the highpressure water jet [15,17,18], which can enhance intrinsic cracks and propagate new cracks. Discoid caves can reduce the effective stress in coal seams and exponentially increase their permeability [19,20].…”

Section: Introductionmentioning

confidence: 99%

Effective Methane Extraction Radius after High-Pressure Water Jet Slotting

Xia

Liu

et al. 2020

Geofluids

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The effective radius of methane extraction after high-pressure water jet slotting is the most important parameter for borehole optimization and extraction time planning. We applied a steady flow model and thermal-hydrological-mechanical (THM) coupling model to calculate the effective radius after high-pressure water jet slotting. Field measurements at the Zhongliangshan coal mine show that both the steady flow model and the THM coupling model can accurately represent the effective radius, and the THM coupling model provides further information regarding extraction time. After that, a variety of factors, including extraction time, coal burial depth, slot radius, initial permeability, and initial methane pressure, are discussed. The effective radius of a slotted borehole is 1.94 times larger than that of a conventional borehole.

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Crack propagation patterns and energy evolution rules of coal within slotting disturbed zone under various lateral pressure coefficients

Cited by 34 publications

References 47 publications

Effects of Mechanical Properties on Gas–Water Flow Characteristics around Boreholes: Implementation of Damage-Based Coupling Models

Effects of Mechanical Properties on Gas–Water Flow Characteristics around Boreholes: Implementation of Damage-Based Coupling Models

Dynamic failure characteristics of surrounding rocks under different lateral pressure coefficients in deep tunnel transient excavation

Effective Methane Extraction Radius after High-Pressure Water Jet Slotting

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