The imbibition mechanism for enhanced oil recovery by gel breaking fluid of SiO2-enhanced seawater-based VES fracturing fluid in offshore low permeability reservoir

Nanoparticles have been proven to be potential additives for hydraulic fracturing fluid. However, the application of nanoparticle-enhanced fracturing fluid systems in offshore low-permeability reservoirs are limited, and the mechanism by which the corresponding gel breaking fluid enhances oil recovery (EOR) is unclear. In this work, a SiO 2 -enhanced seawater-based viscoelastic surfactant (VES) fracturing fluid system was initially prepared, and the imbibition influencing factors of the SiO 2 -enhanced gel breaking fluid were systematically investigated. Subsequently, the imbibition mechanism by SiO 2 -enhanced gel breaking fluid was explored through examining its synergistic effect on interface properties and the distribution laws of oil-water phases in micropores during the imbibition process. The results showed that proposed system could maintained stability for more than 6 months, and exhibited rheological performance, yielding an increase 26% in temperature/shear resistance. Moreover, the corresponding gel breaking fluid performed an exceptional capacity for imbibition oil production, the oil recovery was increased by 7.92% compared to the conventional gel breaking fluid system and the imbibition time was extended from 30 h to 70 h. The synergistic adsorption of nano-SiO 2 and surfactants on the interface was responsible for wettability alteration and interfacial tension (IFT) reduction. Imbibition primarily occurred in mesopores, nano-SiO 2 reduced the flow resistance of oil-water two phases in pores, and the residual oil within the pores was exceedingly mobilized. This work provides foundation research of application of SiO 2 -enhanced seawater-based VES fracturing fluid in offshore low permeability reservoirs.