Wettability Alteration in Near-Wellbore Regions of Gas Reservoirs to Mitigate Liquid Blockage Using Super Water- and Oil-Repellent ZnO/SiO2 Nanofluid Treatment

In gas-condensate reservoirs as the bottom hole pressure drops below the hydrocarbon dew point of the reservoir fluid, liquids drop out from the gas phase and establish condensate banking near the wellbore, resulting in lower gas productivity. Changing the reservoir rock wettability from liquid-wetting to gas-wetting has outstanding potential in improving the productivity of gas wells. In this work, we report the highly water- and oil-repellent properties of carbonate reservoir rocks treated with a nanofluid based on synthesized ZnO/SiO2 nanocomposites and fluoro-containing materials PTFE, TFE, and PFOS. Carbonate plates coated with the prepared nanofluid exhibits a high contact angle of 162° for brine (contact angle hysteresis=0° and roll-off angle <2°), together with 135° for liquid gas-condensate, supporting significant super-amphiphobicity with self-cleaning properties. Surface characterization of the rock using SEM, SP, and EDX analyses reveals that the rough morphology of ZnO/SiO2 nanocomposites combined with low surface energy of fluorochemical provides the surface superamphiphobicity. Moreover, the efficiency of the nanofluid in wettability alteration of carbonate core from liquid-wetting to ultra gas-wetting under reservoir conditions was investigated by performing gas/liquid two-phase flow tests with single-phase liquid-injection into the gas-saturated core. The results indicate that the mobility of liquid for both gas/brine and gas/ liquid-condensate systems increases significantly after wettability alteration.