Experimental investigation on the shale's time-dependent microphysical characteristics under the fluid-shale interaction

The long-term fracturing process will affect the shale's microphysical characteristics. In this paper, under the fluid-shale interaction with different duration, the evolutions of shale's minerals, pore structure, brittleness, as well as the ions of fluids are investigated. The results show that, as the interaction proceeding, the shale's typical minerals experienced a resolution and regeneration process, while the ions concentration of the fracturing fluid shows negatively correlated with the that of minerals correspondingly. The evolutions of shale's pore volume and the specific surface area show opposite changing trends, which indicates that time-dependent micropore is characterized as dissolution first and then filling. Finally, the shale's time-dependent brittleness model is developed based on the minerals' evolution. These findings will provide a new insight for the optimization of hydraulic fracturing design based on shale's dynamic microphysical characteristics.