The inter-salt shale in the Qianjiang formation of Jianghan Basin in China are characterized by multiple bedding planes, low rock strength, complicated mineral compositions and high heterogeneity of rock mechanics. The brittleness evaluation of the inter-salt shale has not been investigated. Core samples of intersalt shale from the fourth member of the Qianjiang Formation were tested by using CT scan, X-ray diffraction, tri-axial rock testat the in-situ condition. An integrated investigation was conducted on the brittleness evaluation of inter-salt shale from the perspective of bedding planes, brittle mineral components, elastic parameters and the complete stress-strain characteristicsof rocks. The results indicate that the intersalt shale exist with bedding planes andglauberite, which leads to high anisotropy and heterogeneity. Theargillaceous dolomite of the fourth member of the Qianjiang Formation is rich in brittle minerals which is beneficial to fracturing. The elastic parameters of the inter-salt shale obtained at the in-situ conditions are quite different with that of the gas shale. The brittleness index of argillaceous dolomiteand dolomitic claystone can becalculatedthrough a modified model. The transformation model of the dynamic-static mechanic parameters has been built based on the logging data and the laboratory data in order to obtain the brittleness index profile along the wellbore.The post-peak stress-strain relations indicates the rock has high residual strength at confined stress state, which explains that the rock is damaged through shear failure along the bedding plane and fails to generate complex fractures. This study would provide theoretical basis for fracability evaluation model used in theinter-salt shale oil reservoir.

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