The Effect of Fluoropolymer on Wettability Alteration of Sandstone at Elevated Temperatures

Gas condensate reservoirs are generally recovered using a pressure depletion drive. Gas can condensate into the liquid phase near the wellbore region when the reservoir pressure falls below the dew point pressure, which can kill gas deliverability. Wettability alteration is an effective means of overcoming this problem; core wettability can be altered from liquid-wet to gas-wet to alleviate the effect of condensate accumulation near the wellbore region. To establish the effect of fluoropolymer on wettability alteration in a gas-condensate reservoir, a gas-wetting alteration agent was synthesized by emulsion polymerization using different molar ratios of fluorine-containing monomers and acrylic monomers. FTIR and SEM were performed to analyze the structure of the gas-wetting agent. Contact angle measurements were used to assess surface alteration by the Owens two-liquid method. The effects of alteration agent concentration, salt concentration, pH and temperature on gas-wetting alteration were also evaluated. Results showed that the best molar ratio of fluoropolymer monomer to acrylic monomers was 1:2. The egg-like structure of the fluoropolymer latex on the core surface mainly contributes to gas-wetting alteration. The contact angles of brine and oil can be altered from 23° and 0° to 137° and 67° by 1 wt% FP-2 treatment, respectively. The surface free energy of the core was reduced from 67.52 to 1.66 mN/m. Moreover, the treated cores remain gas-wetting up to 100 g L^?1 of salt solution, 120 °C and within the pH range of 5–7. This novel gas-wetting alteration agent can be used to solve the problem of liquid blocking effects in gas condensate reservoirs and improve gas recovery significantly.