Abstract
Rock fractures transmit underground gas effectively once they have sufficient widths and interconnection. However, the fracture geometries needed for gas transport are strongly influenced by surrounding pressure conditions. In order to inspect and quantify the influence of surrounding pressure, we design and manufacture a set of gas flow apparatus that can be connected to the MTS815 material testing system, which provides loads and exhibits external pressures in the experiment. With the apparatus and MTS815, we test the fractured samples of sandstone and coal and obtain their relationship between permeability and external pressure. In particular, our permeability calculation based on collection of gas flux and pressure difference has involved the influence of non-Darcian flow. In addition, our study also includes a numerical simulation in the RFPA software platform to display the internal field changes of cracks. The results show that fracture permeability strongly depends on confining pressure, and a critical pressure probably occurs, about 1.5–2 MPa in our experiments, to split each of the permeability curves into two stages, a slow climb and an exponential rush. As a complement, the numerical simulation also demonstrates one more stage for the permeability curve, the post-rush steady fluctuation.
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Acknowledgements
The authors highly appreciate the reviewers’ suggestions. This study was supported by National Natural Science Foundation of China (No. 50774083), Chinese Program for New Century Excellent Talents in University (No. NCET-07-0803) and Special Subject Grant of National “973” Basic Research Program of China (No. 2005CB221502).
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Liu, W., Li, Y. & Wang, B. Gas Permeability of Fractured Sandstone/Coal Samples under Variable Confining Pressure. Transp Porous Med 83, 333–347 (2010). https://doi.org/10.1007/s11242-009-9444-8
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DOI: https://doi.org/10.1007/s11242-009-9444-8