Effects of Slick Water Fracturing Fluid on Microscopic Pore Structure and Properties of Shale Reservoirs

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Shale oil reservoirs are characterized by nanopores and low permeability, which hinder extraction using conventional methods and result in low efficiency. Hydraulic fracturing is a common technique in shale oil extraction, using fracturing fluids to propagate cracks and pores in the rock, thus creating a network of fractures. In field applications, slick water fracturing fluids exhibit lower operational friction and better drag reduction performance compared to other fracturing fluids, providing effective technical support for improving shale oil and gas development efficiency and reducing construction costs. This study investigates the transformation of shale oil reservoirs using hydraulic fracturing fluids. Shale samples were treated with slick water fracturing fluids, and the microstructural characteristics of the pores were qualitatively and quantitatively analyzed using nitrogen adsorption, high-pressure mercury intrusion, and scanning electron microscopy. Finally, the changes in reservoir properties and the rheological behavior of rock samples before and after hydraulic fracturing fluid treatment were examined, along with an analysis of the main factors influencing these changes. The experiments showed that the connectivity of tiny pores in the fractured rock samples improved, with an increase in micro- and mesopores smaller than 50 nm. Both porosity and permeability were enhanced, with a 35.12% increase in permeability under low-pressure conditions. The changes in pore structure were mainly controlled by clay minerals, with a significant correlation between clay mineral content and larger pores, as indicated by a correlation coefficient of R2 = 0.47128.