Gas Permeability of Fractured Sandstone/Coal Samples under Variable Confining Pressure |
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Authors: | Weiqun Liu Yushou Li Bo Wang |
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Institution: | 1.Department of Earth and Planetary Science,University of California,Berkeley,USA;2.College of Sciences,China University of Mining and Technology,Xuzhou,China |
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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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