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International Journal of Coal Geology
Article . 2016 . Peer-reviewed
License: Elsevier TDM
Data sources: Crossref
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Effects of gas diffusion from fractures to coal matrix on the evolution of coal strains: Experimental observations

Authors: Jiang Yujing; Mingyao Wei; Jili Feng; Changsheng Wang; Chunguang Wang; Chunguang Wang; Chunguang Wang; +2 Authors

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

Abstract

Abstract In this study, we investigate coal matrix swelling during the process of gas diffusion from cleats and its impact on the evolution of strain. We inject helium into both jacketed and unjacketed coal samples within a pressurized core holder. In the unjacketed experiment, the coal sample was exposed to hydrostatic gas pressure. In the jacketed experiment, the coal sample was constrained by fixed displacement at the two ends and by constant confining pressure laterally. In both experiments, strains were measured continuously both parallel/perpendicular to the bedding plane of the coal as internal pressure of helium is increased. For the unjacketed test the initial rapid compactive deformation of the sample rebounds to dilative at long term — attributed to the gas diffusion-induced swelling of the coal matrix. For the jacketed test both axial and circumferential coal strains are first dilative due to the decrease in effective stress with subsequent changes of coal strain induced by the gas diffusion closely associated with the specific boundary conditions. For a constant stress boundary, the circumferential strain first remains unchanged for some time and then gradually increases to steady state. Such a phenomenon suggests that when gas diffuses from the cleat to the matrix, the coal matrix-cleat system probably undergoes a transition from local swelling to macroswelling. In contrast, for a fixed displacement boundary, the axial strain first decreases and then reaches a steady state. It also indicates that the swelling of the matrix not only decreases the aperture of the fracture, but also expands the circumferential profile of the coal sample due to the Poisson effect. In addition, helium diffusion in the matrix is estimated by using the bidisperse diffusion model. The calculated effective diffusivity increases with pore pressure. This suggested that the gas diffusion coefficient is a pore pressure-dependent parameter. These results demonstrate that gas diffusion from the cleat to the matrix can cause the swelling of the coal matrix, change the aperture of the cleat, and in turn impact the evolution of the coal permeability.

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
57
Top 10%
Top 10%
Top 10%