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In this study, graphene oxide nanosheets (GONs) are introduced as a prospective candidate for enhanced oil recovery, so they were first synthesized and then fully characterized. Next, various suspensions were prepared to monitor the impacts of GONs and NaCl on the viscosity, interfacial tension (IFT), emulsification, wettability, and stability. The viscosity of the suspensions witnessed a 34% increase when their concentration was increased to 800 ppm. Mixing NaCl and 400 ppm GONs showed that the NaCl amount had a major effect on the viscosity. The viscosity rose steadily to 3 cSt by increasing NaCl to 30000 ppm but fluctuated at 40000 and 60000 ppm. Moreover, even though increments in the GON concentration decreased the IFT between oil and water to 19.4 mN/m, the IFT increased slightly from 400 ppm onward. GONs lessened the IFT as much as roughly 2.5 units by adding each 0.02 wt % NaCl to 400 ppm GONs. Besides, GONs made smaller and smaller emulsions when their concentrations rose from 100 to 400 and 800 ppm. Interestingly, 400 ppm GONs with 2 and 4 wt % NaCl produced oil-in-water emulsions of less than 10 μm. From contact-angle (CA) tests, it was found that GONs were amphiphilic and could not noticeably alter the wettability alone unless 2 wt % NaCl was added, and, consequently, CA varied from 13° to 75°. Also, the stability of GONs in an aqueous phase was immensely impressed by 4 and 6 wt % NaCl after 14 days but stable at 2 wt % NaCl. Last, in the micromodel flooding tests, the ultimate recovery achieved by nanofluid was 28% higher compared with brine. Wettability alteration and mobility improvement were obviously witnessed by flooding nanofluid into an oil-wet micromodel. The viscous fingering phenomenon could be decreased by increasing the breakthrough time from 55 to 98 min.

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We develop a comprehensive pore-network model for simulation of miscible displacements in laboratory-scale porous media. The goal is to study the effect of porescale heterogeneity, and in particular pore-size distribution and pore connectivity, as well as mobility ratio M on miscible displacements, and compute the effective longitudinal dispersion coefficient as a function of M. At the pore level the phenomenon is described by the convective-diffusion equation with a Taylor-Aris dispersion coefficient. Extensive simulations indicate the strong effect of the connectivity and broadness of the pore-size distribution on the efficiency of the displacement process. Moreover, the model enables us to compute the effective dispersion coefficient as a function of the mobility ratio of the two fluids that, to our knowledge, has not been calculated before. Simple generalization of the model will make it possible to study more complex related phenomena, and in particular injection of CO 2 into a pore space that contains saline water.