Wettability alteration of carbonate rocks from liquid-wetting to ultra gas-wetting using TiO2, SiO2 and CNT nanofluids containing fluorochemicals, for enhanced gas recovery

Wettability alteration of near-wellbore region in gas condensate reservoirs by chemical stimulation is known to be an effective method for decreasing liquid accumulation and increasing the fluid mobility that results in improving the well's deliverability. This paper reports on liquid-repellency of TiO2, SiO2 and CNT nanostructures, applied for wettability alteration of carbonate reservoir rock. The characterization of nanoparticles synthesized via sol gel process was evaluated by SEM, FTIR, XRD and TEM analyses. It was observed that the liquid drop of water or n-decane imbibed instantly into the liquid-wetting untreated rock. The contact angle of water droplet on the rocks aged in nanofluids containing each of these rough nanoparticles in alcoholic medium changed significantly from 0 degrees to 161 degrees, 164 degrees and 163 degrees, respectively. It was supported by self-cleaning properties while the wetting behavior of n-decane was remained unchanged. In order to add oil repellency feature to the existing nanofluids as well, low surface energy agents like PTFE, Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane and 2, 2, 2-Trifluoroethanol were added selectively to the solutions. The wettability of n-decane droplet on the rocks treated with these TiO2, SiO2 and CNT nanofluids increased from 0 degrees to 144 degrees, 151 degrees and 147 degrees, respectively. SEM images verify adsorption of nanoparticles on the rock and the roughness of nano-textured surfaces. Surface chemical composition of the treated carbonate rocks with nanofluids was determined by EDX analysis. The alteration of rock wettability to gas-wetness state was also confirmed by imbibition test. Moreover, thermal stability of nanofluids at 160 degrees C were quite appropriate to be used practically. (C) 2015 Elsevier B.V. All rights reserved.