摘要
This study investigated the mechanisms and performance of SiO2 nanofluid for enhanced oil recovery (EOR) in low-permeability cores. Three-phase contact angles for quartz/oil/brine systems were measured, and the microscopic imbibition characteristics of nanofluids in a capillary were observed through visualization experiments. In addition, the effects of the adsorption of the nanoparticles on the oil–water relative permeability was studied using core displacement tests. Furthermore, a total of 11 core flooding tests were performed, and the effects of injection parameters, such as nanoparticle concentration, injection rate, and injection scheme, on the oil recovery were investigated. Wettability alterations were observed among quartz/oil/brine systems that contributed to higher displacement efficiencies in microscopic imbibition tests. Relative permeability measurements showed that, upon the adsorption of the nanoparticles, the irreducible water saturation and oil-phase relative permeability increased whereas the water-phase relative permeability decreased. Moreover, nanoparticles tended to adhere to the pore surface of the rock, which significantly changed the wettability of cores to strongly water-wet conditions. Nanofluid displacement tests showed that additional 4.48–10.33% increments in the oil recovery can be obtained compared to conventional waterflooding. With increasing nanoparticle concentration, the viscosity and asphaltene content of the produced oil gradually decreased. The results showed that the optimum nanoparticle concentration was 10 ppm, whereas further a increase in the injected nanoparticle concentration could plug the pore throats, resulting in a slight decrease in tertiary oil recovery. The effects of nanofluid imbibition on the recovery were more significant at lower injection rates, leading to higher recoveries. Furthermore, it was found that cyclic nanofluid injection can provide higher tertiary oil recovery than a continuous nanofluid injection scheme.
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