Field Investigation of Hydraulic Fracturing in Coal Seams and Its Enhancement for Methane Extraction in the Southeast Sichuan Basin, China

Zhang, Zuxun; Wang, Hongtu; Deng, Bangming; Li, Minghui; Zhang, Dongming

doi:10.3390/en11123451

Cited by 15 publications

(9 citation statements)

References 27 publications

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“…The fluidsolid coupling equations utilized in RFPA 2D -Flow simulation mainly involve equilibrium equation, geometric equation, constitutive equation, seepage equation, and governing equation [31], as shown in Eq. (1).…”

Section: Damage Mechanics Model Of Fluid-solid Couplingmentioning

confidence: 99%

“…To improve the gas-extraction efficiency and control gas-outburst, the permeability of composite thin coal seam needs to be enhanced. To date, hydraulic fracturing, fracturing the rock with high-pressure water, is widely used to improve the poor permeability of composite thin coal seam [1][2][3][4]. Therefore, understanding of hydraulic fracture (HF) propagation and permeability evolution in the composite thin coal seam is fundamental to stimulate the composite thin coal seam.…”

Section: Introductionmentioning

confidence: 99%

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Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Liu

Huang

et al. 2021

Geofluids

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Hydraulic fracturing can improve the permeability of composite thin coal seam. Recently, characterizing hydraulic fracture (HF) propagation inside the coal seam and evaluating the permeability enhancement with HF extension remain challenging and crucial. In this work, based on the geological characteristics of the coal seam in a coal mine of the southwest China, the RFPA2D-Flow software is employed to simulate the HF propagation and its permeability-increasing effect in the composite thin coal seam, and a couple of outcomes were obtained. (1) Continuous propagation of the hydraulic microcrack-band is the prominent characteristic of HF propagation. With the increment of the injection-water pressure, HF generation in the composite thin coal seam can be divided into three stages: stress accumulation, stable fracture propagation, and unstable fracture propagation. (2) The hydraulic microcrack-band propagates continuously driven by the fluid-injection pressure. The microcrack-band not only cracks the coal seam but also fractures the gangue sandwiched between the coal seams. (3) The permeability in the composite thin coal seam increases significantly with the propagation of hydraulic microcrack-band. The permeability increases by 1~2 magnitudes after hydraulic fracturing. This study provides references to the field applications of hydraulic fracturing in the composite thin coal seam, such as optimizing hydraulic fracturing parameters, improving gas drainage, and safe-efficient mining.

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Section: Damage Mechanics Model Of Fluid-solid Couplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Liu

Huang

et al. 2021

Geofluids

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“…However, in terms of permeability enhancement effect of hydraulic fracturing, most of them are judged by means of on-site detection. Zhang et al [22] conducted a hydraulic fracturing test study on the Nantong Mine in the southeast of the Sichuan Basin. Field investigations show that hydraulic fracturing can significantly increase the methane extraction rate of boreholes, which is more than 10 times higher than that of conventional boreholes.…”

Section: Introductionmentioning

confidence: 99%

Simulation Study on the Effect of Coal Seam Hydraulic Fracturing to Increase Permeability

Wang

Zhang

Wang

et al. 2021

Preprint

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Hydraulic fracturing is mainly used to improve coal seam permeability, extract coal seam gas and prevent coal-gas outburst. However, in the aspect of anti-reflection effect, it is judged by the method of field inspection, and there is no good prediction method before the engineering application. In this work, PFC2D software is used to simulate the process of coal seam hydraulic fracturing, and the results are introduced into the mathematical coupling model of the interaction between coal seam deformation and gas flow for analysis. The results show that the particles are moving towards the direction of the minimum principal stress, the moving speed of the particles at the crack tip increases, and the crack will finally expand towards the direction of the maximum principal stress. The gas pressure decline rate and permeability increase rate of the fractured model are both higher than that of the unfractured model. With the increase of extraction time, the decrease rate of gas pressure and the increase rate of permeability both decrease rapidly and gradually approach 0. The longer the hydraulic fracturing time is, the more complex the fracture network is, and the faster the gas pressure drops. However, the difference between the horizontal and vertical gas pressure drops will become larger and larger, and the impact of fracturing on gas drainage effect will gradually become smaller. With the increase of fracturing time, the difference of permeability increase at different monitoring points becomes larger and larger, but with the increase of gas drainage time, the difference will gradually decrease. The higher the initial void pressure is, the faster the gas pressure drops and the greater the permeability increase. However, the influence of the initial void pressure on the permeability increase will gradually become smaller. The research results could provide certain guidance for the prediction of anti-reflection effect of hydraulic fracturing in underground coal mines.

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“…When hydraulic fracturing is applied to a composite rock reservoir, the existence of a weak bedding plane will significantly affect the extension path of hydraulic fractures [1]. How to control the propagation of hydraulic fractures in such reservoirs is a critical problem in a hydraulic fracturing design [2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Experimental and Numerical Investigation on Hydraulic Fracture Propagation Law of Composite Rock Materials considering the Disturbing Stress Effect

Zhang

2021

Geofluids

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The stress disturbance effect will significantly affect the propagation path of hydraulic fractures in the composite rock reservoir. To reveal the influence mechanism of stress disturbance effect on the hydraulic fracture propagation, several groups of laboratory tests and simulation tests were carried out. The test results showed that the hydraulic fracture tip formed a disturbing stress field because of the pore water pressure. Before the hydraulic fracture was extended to the bedding plane, the bedding plane had been damaged under stress disturbance, and the disturbed fracture zone was formed. The propagation mode of hydraulic fracture at the bedding plane was highly sensitive to the formation of the disturbed fracture zone. The sensitivity is mainly reflected from two aspects. (1) Under the action of the hydraulic fracture tip disturbance stress, many microfractures are generated and penetrated into the disturbance fracture zone on the bedding plane. This behavior is accompanied by energy dissipation causing the bedding plane material to be significantly softened, and the energy required for hydraulic fracture propagation is reduced dramatically. (2) The formation of the disturbed fracture zone improves the degree of fragmentation of the bedding plane, and the permeability of the local area increases significantly, forming the dominant circulation path. The higher the development of the disturbed fracture zone, the greater the hydraulic fracture propagation tendency along the bedding plane. According to the formation characteristics of the bedding plane disturbed fracture zone, the author proposed a nonlinear fracture model of the bedding plane disturbed fracture zone and established the hydraulic fracture propagation path criterion. This paper further analyzed the influencing factors of the disturbed fracture zone’s formation conditions and found that the bedding plane’s cementation strength was the main factor affecting the development degree of the disturbed fracture zone.

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Field Investigation of Hydraulic Fracturing in Coal Seams and Its Enhancement for Methane Extraction in the Southeast Sichuan Basin, China

Cited by 15 publications

References 27 publications

Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Simulation Study on the Effect of Coal Seam Hydraulic Fracturing to Increase Permeability

Experimental and Numerical Investigation on Hydraulic Fracture Propagation Law of Composite Rock Materials considering the Disturbing Stress Effect

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