Micro- and macroscopic experiments on self-adaptive mobility control and displacement efficiency of carbon-based composite nanofluid for enhanced oil recovery

Abstract

Reservoir heterogeneity, unfavorable water–oil mobility ratio, and high oil-water interface energy are primary constraints impeding macroscopic sweep and microscopic oil displacement efficiencies of water flooding reservoirs. Nanofluid's unique interface and small-scale effects offer significant potential in solving the low-universal problem of water flooding reservoir recovery. In the study, systematic micro- and macroscopic experiments, including microscopic visualization, core flooding, and nuclear magnetic resonance online flooding experiments, to reveal unique self-adaptive mobility control and superior displacement efficiency of amphiphilic graphene oxide (GOC)-based composite nanofluid. The results indicate that GOC nanosheets exert negative curvature at the oil-water interface, forming water-in-oil Pickering emulsion thermodynamically. These Pickering emulsions exhibit remarkable properties, with up to 90% internal phase volume and higher viscosity than oil across a broad water saturation, signifying GOC's self-adaptive mobility control in porous media. Furthermore, the Jiamin effect and in-situ thickening characteristics from the emulsion's micro-size compensate porous media heterogeneity, significantly improving the GOC nanofluid's macroscopic sweep efficiency. Moreover, a slight surfactant addition to the nanofluid further reduces oil-water interfacial tension to 10⁻² mN/m and regulates the rock surface's hydrophilic wettability, notably improving microscopic oil displacement efficiency. Therefore, the remaining oil and residual oil after brine flooding have been effectively utilized and efficiently displaced. The composite nanofluid with 0.3–0.7 pore volumes enhances oil recovery by 15.8%–37.7% after ultimate brine flooding. Moreover, carbon-based nanomaterials' synthesis is eco-friendly, and both carbon-based composite nanofluid preparation and the injection process are simple. These advantages show nanotechnology's excellent industrial application potential in improving oil recovery efficiency.