ABSTRACT:

Shales are generally anisotropic, which are characterized by low velocity in the bedding normal direction because of the presence of clay minerals, micro-cracks and kerogen. The anisotropy greatly influences the SRV (stimulated reservoir volume) fracturing of shale reservoirs during hydraulic fracturing. In this study, cylindrical shalesamples were cored from the outcrops of two types of shale (Lujiaping and Longmaxi group) along the bedding-parallel and bedding-normal direction. Surfaces of all the samples were rectified and polished to 10µm to ensure parallelism and minimum friction during testing. The velocity and permeability measurements of two types of shale were evaluated. Also the stress sensitivity coefficient of velocities and permeability were carried out. Our results showed that: (1) Longmaxi shale samples are much more anisotropic than Lujiaping shale samples. (2) Elastic velocity anisotropy is in good agreement with the permeability anisotropy. (3) Elastic velocities, permeability and elastic stress sensitivity are orientation-dependent. Nevertheless, the stress sensitivity parameters of permeability are orientation-independent. (4) For Longmaxi shale samples, the permeability of bedding-parallel samples is larger than that of bedding-normal samples. However, the elastic stress sensitivity is in opposite direction. This is influenced by the lamination of Longmaxi shales.

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