Synergistic modification mechanisms of nano-modified slickwater system for enhanced oil recovery in tight oil reservoirs

To address two main challenges, i.e. insufficient proppant support in hydraulic fractures and limited oil mobilization from the matrix, in tight oil reservoirs, this study proposes a concept of “fracturing fluid-rock matrix synergistic modification” to formulate a modified slickwater system based on nano-droplets. This nano-modified slickwater system is investigated for its synergistic modification mechanisms through experimental techniques including rheological measurements, visualized proppant transport tests, three-phase interfacial atomic force microscopy measurements, wettability characterization, and core flood experiments. The results indicate that the nano-modified slickwater system exhibits a low viscosity and high elasticity under high shear rates, which facilitates friction reduction and fracture propagation, and exhibits a sharp increase of viscosity while maintaining the high elasticity through restoring the microscopic association structure under low shear rates, which enhances proppant transport by fracturing fluid in distal and branched fractures. This system releases nano-droplets after fluid breaking, which then migrate to deep matrix pores, altering the matrix wettability and enhancing oil recovery through imbibition. It is concluded that the nano-modified slickwater system formulated following the concept of “fracturing fluid-rock matrix synergistic modification” is adaptive to working conditions, and it can simultaneously expand the volume of conductive fracture-network and enhance matrix productivity, enabling fracturing fluids to “enter, migrate, and modify” tight reservoir matrix economically and effectively. The proposed system offers a reliable technical foundation for efficient development of tight oil reservoirs.