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Abstract
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Altering the wettability of a gas-liquid system from liquid-wetting to intermediate gas-wetting is a novel strategy
for removing condensate from gas condensate reservoirs. In this paper, the role of a silica nanofluid modified by
fluorine groups in the wettability alteration of seven carbonate samples was investigated. An acid test and Energy
Dispersive X-ray Spectroscopy analysis were carried out to identify the levels of calcite and dolomite as dominant
carbonate minerals and evaluate the coating ability of the proposed chemical used on carbonate surfaces. Contact
angle measurements and spontaneous imbibition experiments were conducted before and after wettability
alteration. In addition, gas flooding experiments were conducted on three permeable core samples to investigate
the effect of the nanofluid on the fluid flow at the core scale. Contact angle measurements demonstrated that the
wetting tendency of core samples altered from liquid-wetting into gas-wetting after surface treatment, and a
higher contact angle was achieved for carbonate cores with less dolomite than calcite. EDX analysis showed more
fluorine and silica adsorption on calcite, compared to dolomite cores. After surface modification, the brine
imbibed into carbonate core samples 1 to 7 decreased by 0.104, 0.174, 0.0016, 0.773, 0.355, 0.056, and 0.279,
respectively. Core flooding results demonstrated that the recovery factor of three permeable core samples
increased from 56.52%, 49.69%, and 65.33%–69.34%, 56.75%, and 76.72%, respectively.
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