Abstract
Wettability alteration of near-wellbore region from liquid-wetting to gas-wetting has been known as a feasible method for eliminating condensate blockage in gas condensate reservoirs. In this research, the natural CaCO3 (Bio-Ca) nanoparticles containing chitin were used as environmentally friendly and cost-effective agents which can act as nanocomposite for wettability alteration. For this purpose, their performance was evaluated on wettability alteration of the gas/oil systems by conducting contact angle measurements and sand pack flooding tests. In addition, for evaluating the stability of nanofluids, zeta potential measurement was conducted. The Bio-Ca nanoparticles were produced using cuttlebone (Sepia Pharaonis) taken from the Persian Gulf. Also, silica nanoparticle was used as a scale for comparison of its performance with the newly synthesized nanoparticle. Four influencing factors including nanofluid concentration, gas flow rate, oil type, and nanoparticle type were investigated and the optimum conditions for improving oil recovery and gas/oil relative permeabilities were also obtained using Taguchi method. The values of zeta potential implied that both nanofluids are stable at the given pH. The results of the contact angle measurement indicated that the contact angles of condensate droplet raised from 0° to 105° after treating the rock surface by Bio-Ca nanofluid with a concentration of 0.05 wt. %. This is happened because of the increase in roughness with reduction of surface free energy of rock surface along with disjointing pressure mechanism. Analysis of variance showed the importance of considering the simultaneous effect of these parameters on oil recovery and relative permeabilities for wettability alteration purposes. Results show that the optimum conditions for increasing oil recovery using Bio-Ca nanoparticles include the nanofluid concentration of 0.05 wt. %, using normal heptane as a liquid phase, and a gas flow rate of 100 cc/min. Besides, for gas and oil relative permeability endpoints as a second response parameter, the most effective parameter is gas flow rate of 55 cc/min. Results of this work are confirmed that the Bio-Ca nanoparticles play a vital role in wettability alteration, which can alter the wettability of the medium from strongly oleophilic to oleophobic due to their biostructure.
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