Study on the mechanism of coal-rock interface hindering hydraulic fracture propagation in the process of indirectly fracturing broken soft coal seam

Li, Hao; Liang, Weiguo; Wu, Yanxia

doi:10.1088/1755-1315/861/6/062104

Cited by 3 publications

(1 citation statement)

References 11 publications

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“…e interface between the rock layers will still strongly hinder HF propagation. However, the above phenomenon will be more obvious for fractured low-permeability coal because the hydraulic energy will also be consumed in the plastic work, which is not conducive to HF propagation [18]. erefore, a new constitutive equation reflecting the toughness failure of coal needs to be established.…”

Section: Status Of Cbm In Zhaozhuang Minementioning

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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Section: Status Of Cbm In Zhaozhuang Minementioning

confidence: 99%

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

2022

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Experimental investigation of flow regime transition characteristics of fractured coal bodies around gas extraction boreholes

Pang

Pan

et al. 2023

Energy

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Interaction behavior between hydraulic fractures and interface in coal-rock complex rock layer: Experimental study and application exploration

Li,

Shi,

Zhang

et al. 2024

Physics of Fluids

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To achieve long-term and efficient gas extraction in soft, low-permeability coal seams, this study conducted hydraulic fracturing experiments on coal-rock complexes under true triaxial conditions. The pattern of hydraulic fractures (HFs) was reconstructed based on the fractal dimension concept. The results indicate that the tendency of the complex rock layers to initiate fractures toward the coal weakens the trend of increasing fracture initiation pressure with rising geostress. When HFs interact with the interface, the extension pressure significantly decreases. With the lateral pressure coefficient decreasing, HFs tend to extend toward the coal and be captured by the interface, transitioning from a single-wing to a double-wing shape and approaching a symmetrical conjugate state. Only when the vertical principal stress is sufficiently large can HFs separate from the interface. Based on the derived distribution function of induced stress in the coal-rock matrix around the HFs, the displacement conditions of the coal, rock, and interface were examined. The interaction process of rock layer HFs and the interface was divided into three stages: deflection, capture, and separation. The applicability of this study to high-gas soft coal seams was discussed, and a gas management plan involving roof fracturing and full-period extraction was proposed, with the aim of providing a theoretical foundation for the co-extraction and efficient utilization of coal and gas in mines.

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Study on the mechanism of coal-rock interface hindering hydraulic fracture propagation in the process of indirectly fracturing broken soft coal seam

Cited by 3 publications

References 11 publications

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

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

Experimental investigation of flow regime transition characteristics of fractured coal bodies around gas extraction boreholes

Interaction behavior between hydraulic fractures and interface in coal-rock complex rock layer: Experimental study and application exploration

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