Preparation and laboratory evaluation of an effective depressurization composite system for medium–low permeability reservoirs

Nano depressurization and injection enhancement are important issues to alleviate the problems of injection volume reduction and recovery reduction in the development of an oilfield waterflooding process. However, there are few depressurization reports about hydrophobic organic nano materials in nano depressurization technology. In this study, a hydrophobic polystyrene nanoparticle (32.2 nm) was prepared as a depressurization agent. A novel polyoxyethylene ether-modified betaine surfactant (AEC-SBe) was synthesized to improve the dispersion stability, depressurization, and injection augmentation of hydrophobic polystyrene nanoparticles. The composite system demonstrated a 48.91% reduction in water injection pressure and exhibited good stability at 95 °C, outperforming both the individual AEC-SBe and typical hydrophobic nano SiO₂. The combined effects of low interfacial tension (of the order of 10⁻² mN/m), a high anti-swelling rate (95%), and alterations in rock surface wettability are considered to be the primary mechanisms contributing to the good depressurization effect observed. This work offers theoretical support for the efficient development of medium–low permeability reservoirs by introducing effective reagents.