Numerical Study on the Field-Scale Criterion of Hydraulic Fracture Crossing the Interface Between Roof and Broken Low-Permeability Coal

Li, Hao; Liang, Weiguo; Jiang, Yulong; Wu, Pengfei; Wu, Jianjun; He, Wenjun

doi:10.1007/s00603-021-02539-3

Cited by 10 publications

(6 citation statements)

References 30 publications

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“…where σ s is the stress vector; E 0 is the stiffness matrix of the solid element; ε s and ε p s are the total and plastic strain vectors, respectively; I is the identity matrix; d is the damage tensor, and its evolution law is determined according to the research results [24].…”

Section: Elastic-plastic Constitutive Relation Of Intact Coal and Rockmentioning

confidence: 99%

“…where G is the plastic potential function; δ is a parameter of the control curve in the stretching stage and δ = 0.1; σ U is the tensile strength of coal; ψ is the angle of dilatancy. On this basis, combined with plastic mechanics and its corresponding numerical solution [24], ε p s values can be obtained.…”

Section: Elastic-plastic Constitutive Relation Of Intact Coal and Rockmentioning

confidence: 99%

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Finite–Discrete Element Method Prediction of Advanced Fractures in Extra-Thick Coal Seams Based on a Constitutive Model of Rock Deformation–Fragmentation Failure Process

Guo-qiang

2023

Processes

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Roof fall is a frequent and destructive disaster in the working face of extra-thick coal seams. The important technology for disaster elimination is roof grouting, and the key to its success is to accurately predict the distance of the advanced fractures based on a reasonable rock constitutive relationship. In this paper, the constitutive relationship reflecting the progressive failure process of rock was established, including the elastic–plastic constitutive relation of intact rock, the fracture constitutive relation of non-penetrating fracture, and the shear friction constitutive relation of penetrating fracture. On this basis, the finite–discrete element method (FDEM) numerical calculation method was developed. Taking Yushupo Coal mine with a 16-m-thick coal seam as an example, the numerical results showed that the fractures in the roof appear 15~35 m ahead of the working face, and the maximum value of advance bearing pressure is between 16 and 30 MPa. Meanwhile the laboratory test results showed that the compressive strength of the grouted coal is 14.91 MPa after solidification for 7d. The above data mean that the grouting slurry can solidify the broken roof into a whole without roof fall disaster. At the same time, the rock pressure of the extra-thick coal seam can effectively crush the top coal, which is conducive to the top-coal caving operation. The in situ test shows that when the pre-grouting is carried out in the range of 20~30 m in front of the working face, the roof fall disaster can be effectively avoided, which is consistent with the numerical simulation results. It shows the rationality of the FDEM numerical method and the constitutive model of rock deformation–fragmentation failure process.

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Section: Elastic-plastic Constitutive Relation Of Intact Coal and Rockmentioning

confidence: 99%

Section: Elastic-plastic Constitutive Relation Of Intact Coal and Rockmentioning

confidence: 99%

Finite–Discrete Element Method Prediction of Advanced Fractures in Extra-Thick Coal Seams Based on a Constitutive Model of Rock Deformation–Fragmentation Failure Process

Guo-qiang

2023

Processes

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“…The core idea of this technology is that the horizontal well is drilled in the roof or the floor, and the hydraulic fracture initiating in the roof or floor propagates into the coal seam. To date, the indirect fracturing technology has been successfully applied in Luling mine of Huaibei and in Zhaozhuang mine of Jincheng in China [7].…”

Section: Introductionmentioning

confidence: 99%

“…Huang et al [17][18] using the block discrete element method to explore the influence of engineering parameters on the behaviour process of hydraulic fractures penetrating bedding planes. Li et al [19] studied the propagation law of hydraulic fracture across the coal-rock interface based on Plasticity Fracture-Seepage (PF-S) model, and found that the in-situ stress and the interfacial shear strength are the dominant factor controlling the propagation of hydraulic fracture across the coal-rock interface. Escobar et al [20] studied the effect of stress interference on the penetration ability of multiple fractures using XFEM method, and the results showed that stress shadowing facilitate the propagation of hydraulic fracture from shale into roof rock.…”

Section: Introductionmentioning

confidence: 99%

Propagation Law of Hydraulic Fracture across the Coal-Rock Interface under the Co-Effect of Natural Fractures and Tectonic Stress

Zhu¹,

Li²,

Dong³

et al. 2023

Preprint

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Indirect fracturing from roof rock to coal using a horizontal well is a new and promising technology for coalbed methane surface exploitation in soft and low-permeability coal seams. In order to study the propagation law of hydraulic fracture across the coal-rock interface, a pore pressure cohesive element is used to establish a numerical model for indirect fracturing. Combined with practical engineering in 3# coal seam in Xinjing mine in China, the propagation behavior of hydraulic fracture across the coal-rock interface was researched, and the range of horizontal well position for indirect fracturing was determined. The results show that: (1) the pore pressure cohesive element can be used to simulate accurately the interaction between hydraulic fracture and natural fracture, and the propagation of hydraulic fracture across the coal-rock interface. (2) As the vertical distance between the horizontal well and coal-rock interface decreases, the breakdown pressure of perforation decreases; while the injection pressure increases when the hydraulic fracture crosses the coal-rock interface. (3) For the indirect fracturing engineering in 3# coal seam in Xinjing mine, the vertical distance between the horizontal well and coal-rock interface should not be larger than 2.0m to make the hydraulic fracture propagate into the coal seams.

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“…ey found that only when the interface strength is relatively high would HFs will pass through the interface. According to the CT test and the nonlinear mechanicsleakage hypothesis, Li et al [9] developed a three-dimensional discontinuous network model and a plastic-nonlinear fracture-leakage-coupled constitutive formula. According to the numerical simulation results, Oyedere et al [10] believe that in low-permeability media, too high a fracturing fluid injection rate will stop the propagation of hydraulic fractures.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Indirect Fracturing Process Parameters Based on Mechanical Properties of Fractured and Low-Permeability Coal

2022

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The coal-bed methane (CBM) resources in soft and low-permeability coals are assumed to be as much as 15 × 1012 m3 in China. Indirect fracturing technology can be an effective method to successfully extract methane within soft coals. The key to the success of this technique is to optimize the parameters, such as water injection flow rate and fracture initiation location, so that the hydraulic fracturing parameters enable the fractures to pass through the interface between coal and rock and propagate sufficiently into the coal. This paper focuses on solving the above problems by focusing on discontinuities and plastic characteristics of soft coals. Voronoi polyhedron was used to simulate the discontinuities of coal, and the constitutive relations of ductile fracture-seepage and elastoplastic damage-seepage are, respectively, given to the discontinuities and coal matrix. A numerical model was established based on the above theory to simulate the effect of stress difference Δσ, coal-rock interface friction coefficient fc,r, water injection flow rate i w , and distance between the well and the interface Dop on indirect fracturing fractures. The results show that the HFs area in the coal is positively correlated with Δσ, fc,r, and i w , and it first increases and then decreases with the decrease of Dop. The above results were applied in the Zhaozhuang mine of Qinshui Basin by optimizing Dop = 1 m and iw = 8 m3/min, so that CBM production has been greatly increased. The results can provide theoretical support for the efficient development of CBM in fractured and low-permeability coal seam areas.

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Numerical Study on the Field-Scale Criterion of Hydraulic Fracture Crossing the Interface Between Roof and Broken Low-Permeability Coal

Cited by 10 publications

References 30 publications

Finite–Discrete Element Method Prediction of Advanced Fractures in Extra-Thick Coal Seams Based on a Constitutive Model of Rock Deformation–Fragmentation Failure Process

Finite–Discrete Element Method Prediction of Advanced Fractures in Extra-Thick Coal Seams Based on a Constitutive Model of Rock Deformation–Fragmentation Failure Process

Propagation Law of Hydraulic Fracture across the Coal-Rock Interface under the Co-Effect of Natural Fractures and Tectonic Stress

Optimization of Indirect Fracturing Process Parameters Based on Mechanical Properties of Fractured and Low-Permeability Coal

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