Comparison of shear-induced gas transmissivity of tensile fractures in sandstone and shale under varying effective normal stresses
Comparison of shear-induced gas transmissivity of tensile fractures in sandstone and shale under varying effective normal stresses
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DOI：
10.1016/j.jngse.2021.104218
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发表时间：
2021-11
影响因子：
--
通讯作者：
Nao Shen;Xiaochun Li;Zhang Qiang;Wang Lei
中科院分区：
文献类型：
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作者：
Nao Shen;Xiaochun Li;Zhang Qiang;Wang Lei
Hydraulic transport properties of fractures not only control production flow rates in geo-energy reservoirs, but also affect potential leakage in waste/energy storage reservoirs. Here, we performed shear-seepage tests on tensile fractures in sandstone and shale samples under varying effective normal stress conditions. The experimental results show that hydraulic transmissivity of sandstone fractures decreases with imposed shear stress, which may be caused by elastic-plastic deformation of local asperities on the fracture surface. For shale fractures, hydraulic transmissivity stays almost constant at the initial elastic loading stage, followed by a rapid increase until reaching peak shear stress. We interpreted it as a result of brittle damage accumulated on the shale fracture surface. When progressive sliding persists and shear stress remains nearly constant, the corresponding transmissivity is found to be dependent on applied normal stress for both sandstone and shale fractures. This is possibly due to competition between fracture dilation and development of impermeable gouges. The computed tomography analysis reveals that there is a positive correlation between final fracture transmissivity and final sandstone and shale fracture volumes. The comparison of 3D topography analysis of fracture surfaces before and after shearing demonstrates that the sandstone fracture surface gets smoother locally, whereas the local shale fracture surface becomes rougher. In addition, the wear area of sandstone fracture surface is notably larger than that of shale fracture surface under shearing conditions. Our experimental results highlight that shear-induced transmissivity evolution of a tensile fracture depends on the deformation-damage mode of asperities and on applied effective normal stress.
