The Influence of Gas-Wetting Nanofluid on the Liquid-Blocking Effect of Condensate Reservoir

Abstract

Abstract Gas condensate reservoirs often experience a sharp reduction in gas deliverability when the wellbore pressure drops under its dew point, this is known as liquid-blocking effect in gas condensate reservoir. Many solutions with limited effectiveness were proposed to figure out the problem, and wettablity alteration is proven to be one of effective measures for liquid-blocking effect. Recent investigations show that the wettability of core near wellbore region can be permanently altered from water-wet or oil-wet to intermediate gas-wetting with the fluorosurfactant treatment, and the mobility and distribution of fluids in porous media can also be significantly improved after gas-wetting alteration. The objective of this study was to find out the effect of gas-wetting alteration by fluorosurfactant modified nano-silica on the gas recovery in methane-liquid-rock system. The fluorochemicals are widely used to change the surface properties of solid to achieve a surface with a low surface free energy. In this study, gas-wetting alteration on solid surface is achieved with fluorosurfactant and fluoropolymer. In order to obtain a super gas-wetting, nano-silica particles with a size of 40 nm was functionally modified by fluorosurfactant. Contact angle measurement, Owens two-liquid method, and capillary rise in methane-liquid-core system were conducted to evaluate the effect of gas-wetting alternation on the cores wettability and gas recovery. Data of Contact angle measurement showed that the core wettability can be altered to gas-wetting or super gas-wetting after FG40, FP-2 and FG40 modified nano-silica solution treatment, the contact angles of brine and decane on core surface increased from 23° and 0° to 152° and 127° after treated by 0.5% FG40 modified nano-silica solution, respectively. The surface free energy of cores before and after treatment shows that the sueface free energy decreased from 70 mN/m to approximately 0.61 mN/m. The results of capillary rise and imbibition test verified that of the contact angle measurement and surface free energy, the liquid levels of brine and decane significantly decreased to -20 and 7 mm when the wettability of capillary atered to gas-wetting. Analysis of SEM and TEM indicated that the gas-wetting nano-silica can form a gas-wetting adsorption layer with coarse structures on core surface, which play a vital role in super gas-wetting. In summary, the cores wettability can be altered from liquid-wetting to super gas-wetting by the novel fluorosurfactant modified nano-silica, and gas deliverability can be significantly improved due to super gas-wetting alteration.