Abstract
A large number of core-flooding and micromodel experiments have examined the potential of nanoparticles to increase oil recovery. The mechanism of enhanced oil recovery using nanoparticles (nanoparticles-EOR) is still unclear. Nanoparticles may aid enhanced oil recovery because they may alter rock wettability and possibly reduce oil-water interfacial tension (IFT). The effect of nanoparticles on the oil-water IFT is controversial, as some have found that nanoparticles reduce IFT and others have illustrated that they have no significant effect. Nanoparticles' attachment at the oil-water interface, which causes IFT reduction is complex and bulk fluids properties (water and oil) directly affect their self-assembly. Fully understanding the driving forces causing self-assembly of nanoparticles at the oil-water interface and its controlling parameters are crucial for determining the effect of nanoparticles on IFT.In this research, by investigating the controlling parameters of nanoparticle attachment at the interface (bulk suspension properties including the concentration of nanoparticles, concentration of HCl, salinity, size and charge of nanoparticles, and operating conditions i.e. temperature and pressure), and coupling them with nanoparticles' stability in solution, the conditions under which silica nanoparticles can reduce oil-water interfacial tension are experimentally investigated. The results reveal that by appropriately designing the operating conditions, H+-protected silica nanoparticles can reduce the oil-water IFT. The maximum reduction of the oil-water IFT was obtained for 0.20 wt% silica nanoparticles in a solution containing 0.025 wt% HCl and 0.15 wt% nanoparticles in 0.0076 wt% HCl, where the IFT was reduced from 23.56 ± 0.36 mN/m to 12.81 ± 0.77 mN/m and from 22.61 ± 0.41 mN/m to 14.01 ± 0.87 mN/m, respectively. However, the minimum IFT reduction occurs when the surface energy reduction due to the adsorption of nanoparticles is minimal, i.e. the chance of nanoparticles to desorb from the interface due to thermal fluctuations is high, and nanoparticles' aggregation on the bulk surface is initiating.
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