Experimental study of coal matrix-cleat interaction under constant volume boundary condition

Wang, Chunguang, Zhai, Peicheng, Chen, Zhongwei, Liu, Jishan, Wang, Linsen and Xie, Jun (2017) Experimental study of coal matrix-cleat interaction under constant volume boundary condition. International Journal of Coal Geology, 181 124-132. doi:10.1016/j.coal.2017.08.014

Author Wang, Chunguang
Zhai, Peicheng
Chen, Zhongwei
Liu, Jishan
Wang, Linsen
Xie, Jun
Title Experimental study of coal matrix-cleat interaction under constant volume boundary condition
Journal name International Journal of Coal Geology   Check publisher's open access policy
ISSN 0166-5162
Publication date 2017-09-01
Year available 2017
Sub-type Article (original research)
DOI 10.1016/j.coal.2017.08.014
Open Access Status Not yet assessed
Volume 181
Start page 124
End page 132
Total pages 9
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 2103 Fuel Technology
1907 Geology
1905 Economic Geology
1913 Stratigraphy
Abstract Interaction of coal cleat and matrix plays an important role in determining the dynamic change of coal pore structure and its permeability. Majority of the experimental studies on the cleat-matrix interaction are carried out by measuring the correlation between coal permeability and pore pressure. Under this condition, it is commonly believed that the cleat pressure is equalized with the matrix pressure, in which the permeability is available only for gas flow/adsorption reaching equilibrium state. In this study, the coal cleat-matrix interaction is to uncover during helium unsteady flow from the cleat network to matrix blocks. This objective is achieved by measuring local deformation of coal sample and its permeability under a constant volume boundary. The results show that the incremental of coal strain firstly increases from 184 mu epsilon for 2.0 MPa to 440 mu epsilon for 4.5 MPa, resulting from the opening of the fractures and the compression of the matrix blocks, and then recovers to 105 mu epsilon for 2.0 MPa and 222 mu epsilon for 4.5 MPa, due to expansion of the coal matrix. Such a transition of the coal deformation reveals that the gas injection process generates a dynamically imbalance pressure between the cleat and matrix, and then gas diffusion around the vicinity of the cleat causes non-uniform expansion of the coal matrix. Recovery ratio of 0.5 for the matrix strain was observed, quantifying the contribution of matrix expansion to the cleat aperture. Through comparing the measured permeability data with two predicted permeability by the constant volume model and the matchstick model, it is found that the variation of coal permeability is controlled not only by the change of cleat aperture, but also affected by the matrix expansion process. This work offers a new direct observation into the dynamics of gas mass transfer from the cleat to the matrix and a new understanding of coal permeability evolution in response of the transition. It sheds light on the development of new permeability model that incorporate the fracture-matrix interaction.
Keyword Swelling Area Propagation
Permeability Evolution
Effective Stress
Q-Index Code C1
Q-Index Status Provisional Code
Grant ID 41772154
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mechanical & Mining Engineering Publications
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Created: Sun, 05 Nov 2017, 09:04:53 EST