Shale rocks are rich in organic minerals, also it contains multi-scale micro-nano pores, making flow mechanism of fracturing fluid in microscopic pores of shale and the interactions between fracturing fluid and shale very complicated. In this study, firstly, the initial microscopic pore structure of shale before hydration was analyzed by field emission electron microscope. Secondly, the dynamic changes of microscopic pore structure in shale hydration was observed at fixed points with the scanning electron microscopy to find out the correlation between induced micro-fractures and mineral components. Finally, the influence of hydration on the changes of shale physical properties was analyzed. The test results of shale sample from Longmaxi formation (LF) in the Sichuan Basin indicate the micro-fractures induced by shale hydration weremainly shale bedding fractures, with obvious directionality. Clay minerals play a leading role in the formation and expansion of induced fractures. After 10 days of hydration, the porosity can be increased by 2.1 times, and the permeability can be increased by 273.7 times. Therefore, an appropriate shut-in treatment can dramatically enhance post-fracturing performance. The research results can guide the optimization of flowback system and provide scientific basis for efficient development of shale gas reservoirs.

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