Water-wettability reduction of an anionic hybrid fluorinated surfactant and depressurizing behavior in super-low permeability sandstone reservoirs

Abstract

A Novel hybrid fluorinated surfactant, sodium 2-[2-(perfluorooctyl)] acetoxy ethanesulphonate (HFS8) was synthesized. The objective of HFS8 was to reduce the amount of trapped water on the rock surface and the capillary pressure in super-low permeability sandstone reservoirs. Its critical micelle concentrations (cmcs) were 0.4 g/L in water and 30 g/L NaCl at 30 °C. The diameters of globular micelles were mostly circa 30 nm in water at the cmc. For the brine at the cmc, the contact angle reached 75.62°; the surface and interface tensions were 13.72 and 2.81 mN/m respectively. The micellization of HFS8 was entropy-driven and easier than the hydrocarbon surfactants. The water phase permeability of core and the oil recovery ratio were increased substantially using HFS8 as a wettability-altering agent, and wettability alteration was more effective than interface activity for depressurization. The amount of injected water increased observably after small amounts of HFS8 was injected into the super-low permeability core.