Effects of gas diffusion from fractures to coal matrix on the evolution of coal strains: Experimental observations

Wang, Chunguang; Liu, Jishan; Feng, Jili; Wei, Mingyao; Wang, Changsheng; Jiang, Yujing

doi:10.1016/j.coal.2016.05.012

Cited by 56 publications

(18 citation statements)

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“…In our previous studies [37,38], gas permeability evolution resulting from competition between gas adsorption effect and mechanical compression has been investigated by using numerical modeling. We also observed the deformation evolution of porous structure of coal sample during gas injection process [39]. It is experimentally found that gas convection between the matrix and the cleat can dynamically control bulk deformation of coal.…”

Section: Introductionmentioning

confidence: 88%

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Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

et al. 2019

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Gas transport through porous coal contains gas laminar flow in the cleat network and gas adsorption/diffusion in the matrix block. Since permeable capacity of the cleat is greater than that of the matrix, change of the matrix pressure readily lags behind change in the cleat pressure. Such unsynchronized pressure changes can result in a complex compatible deformation of a cleat-matrix system, significantly affecting the coal permeability. In this paper, we investigated the cleat-matrix interaction on coal permeability by using a modified pressure pulse decay method integrated with numerical analysis. The experimental results indicate that the bulk volume of the coal sample rapidly expanded at the beginning of gas injection, and then the volume expansion rate of the coal sample slowed down as the downstream pressure of the coal sample gradually equilibrated with the upstream pressure. During this process, the coal permeability was observed to gradually decrease with time. Numerical analysis results indicate that gas transport from the cleat to the matrix can attenuate the differential pressure between the cleat and the matrix. A smaller ratio of initial matrix permeability to initial cleat permeability can prolong decay duration of the differential pressure inside the cleat-matrix system. Although the coal sample is subjected to a stress-controlled condition, the coal permeability response to gas diffusion is closer to the case using a constant volume boundary. The dynamic change of coal permeability is significantly affected by the cleat-matrix interaction, in cases where the short-term change is mainly attributable to the cleat network and the long-term change is controlled by matrix swelling/shrinkage.

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Section: Introductionmentioning

confidence: 88%

“…The present work also gives insight into how the evolution of coal permeability is associated with the dual-pore pressure system. [39]. Permeability measurements are completed on high-volatile bituminous coal (2.5 cm in diameter and 5.0 cm in length) cored from a block collected from the Juye coalfield in eastern China.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

et al. 2019

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“…Tectonic deformation has a control effect on the development of fractures (Çiftçi & Bozkurt, ; Jiang, Chen, et al, ; F. Yang, Ning, & Liu, ). The marginal areas of the North China Craton sedimentary basins are at the intersection part of different blocks, and these areas tend to have multi‐periods of structural changes in the evolution of the Mesozoic and Cenozoic tectonic stress fields (J. S. Liu et al, ; Yin & Ding, ; C. Wang, Liu, Feng, Wei, & Wang, ). The variation and superposition of the stress fields in different tectonic periods affect the formation of fractures, and the complexity restricts the characterization and prediction of fractures from the mechanical mechanism (Ju et al, ; Laubach, ; Y. M. Pang et al, ; Yin, Lv, & Ding, ).…”

Section: Introductionmentioning

confidence: 99%

“…Yang, Ning, & Liu, 2014). The marginal areas of the North China Craton sedimentary basins are at the intersection part of different blocks, and these areas tend to have multi-periods of structural changes in the evolution of the Mesozoic and Cenozoic tectonic stress fields (J. S. Liu et al, 2017;C. Wang, Liu, Feng, Wei, & Wang, 2018).…”

Section: Introductionmentioning

confidence: 99%

Developmental characteristics and distribution law of fractures in a tight sandstone reservoir in a low‐amplitude tectonic zone, eastern Ordos Basin, China

Yin

Tian²,

2019

Geological Journal

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In recent years, a large number of vertical and horizontal sliding fractures were found in the Upper Palaeozoic sandstones in the eastern margin of the Ordos Basin, China, However, the effect of fractures on the distribution of tight sandstone gas is still unclear. Therefore, in this paper, a large number of cores, thin sections, petrophysical property test results, conventional and FMI (Formation MicroScanner Image) image logs, and gas‐testing results were used to study the developmental characteristics of fractures and the gas control effects in a tight sandstone reservoir, in the eastern margin of the Ordos Basin. It was found that the average linear density of the core fractures is generally less than 2 m−1, and the microfractures are characterized as ruptures of quartz particles. The underlying Taiyuan and Benxi formations have the highest fracture development degrees, and the fracture index (FI) values are 0.68 and 0.72, respectively. However, the fracture development degrees in the overlying Shanxi to Shiqianfeng formations are significantly lower, and the FI values are generally less than 0.63. There is a good positive correlation between the fracture development degree and the contents of quartz mineral or brittle minerals (quartz + feldspar). On the whole, the fractures in the uplift and slope parts of the low‐amplitude structure areas are more developed, while in the depression zones, the fractures are generally less developed. The fractures in the Zijinshan Uplift area are extremely well developed; thus, the preservation conditions of the reservoir are poor. In this case, the fractures are unfavourable for the accumulation of natural gas. For the gentle tectonic zones, the over‐developed fractures in the Benxi and Taiyuan formations are unfavourable for the preservation of natural gas. However, the moderately developed fractures in the overlying Shanxi to Shiqianfeng formations are beneficial to the enrichment of natural gas. Finally, we compared the relationship between fracture index (FI) and open‐flow productivity of the gas wells, and it was found that FI values of commercial gas wells (Types I, II, and III gas wells) are generally greater than 0.55, while the FI values of Type IV low‐yield gas wells are generally less than 0.55.

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“…[1][2][3][4][5][6] A great number of ways such as theoretical models, experimental methods and simulation approaches have been adopted to characterize the water-gas flow, among which some analytical solutions for the hydraulic properties of unsaturated hydraulic properties of fracture networks have been proposed. [7][8][9][10][11][12] Besides, the fractal dimension that can be used to quantify the geometric properties such as fracture length and aperture distributions of rock fractures has been widely accepted and incorporated into these models. [13][14][15][16][17][18][19] However, these analytical and/or semi-empirical models did not consider the influence of triaxial stresses that are commonly encountered in the practical engineering.…”

Section: Introductionmentioning

confidence: 99%

Analytical Solutions for Water–gas Flow Through 3d Rock Fracture Networks Subjected to Triaxial Stresses

Liu

Jing

et al. 2018

Fractals

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This study presented the analytical solutions for water-gas flow through three-dimensional (3D) fracture networks subjected to triaxial stresses. The relationship between fractal dimension for fracture aperture distribution subjected to triaxial stresses and that subjected to no stresses is established, and the analytical solutions for fractal dimensions for aperture distribution and the equivalent permeability of both fluid and gas phases were derived. The results show that the calculated relative permeability of water phase-saturation curves agree well with those reported in the literature, which indicates that the proposed solutions are validate. With the increment of normal stresses applied on the fracture surface, both the maximum aperture and § Corresponding author. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. 1850053-1Fractals 2018.26. Downloaded from www.worldscientific.com by 52.183.12.225 on 04/09/19. Re-use and distribution is strictly not permitted, except for Open Access articles. R. Liu et al.minimum aperture decrease; however, their ratio increases first and then decreases. The fractal dimensions for fracture aperture distribution of water and gas phases with respect to saturation are axisymmetric along saturation = 0.5. With the increase in saturation, the fractal dimension for fracture aperture distribution of water phase increases significantly when the saturation is less than 0.1, and then gently when the saturation is continuously increased by up to 1.0. The normal stress increased by two orders of magnitude for a larger normal stress (i.e. increased from 10 −2 MPa to 10 MPa) corresponds to smaller variations in equivalent permeability of both water and gas phases for a smaller normal stress (i.e. increased from 10 −4 MPa to 10 −2 MPa).

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Effects of gas diffusion from fractures to coal matrix on the evolution of coal strains: Experimental observations

Cited by 56 publications

References 52 publications

Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

Developmental characteristics and distribution law of fractures in a tight sandstone reservoir in a low‐amplitude tectonic zone, eastern Ordos Basin, China

Analytical Solutions for Water–gas Flow Through 3d Rock Fracture Networks Subjected to Triaxial Stresses

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