ENHANCED OIL FLOW MODEL COUPLING FRACTAL ROUGHNESS AND HETEROGENEOUS WETTABILITY
Abstract
The oil flow behaviors in inorganic and organic nanopores are still unclear due to the effects of complex surface properties on boundary slip velocity and effective oil viscosity, such as surface roughness and various wettability. In this work, the oil flow enhancement factor and apparent permeability model are derived by coupling slip length and effective viscosity based on the no-slip Hagen–Poiseuille equation. The effects of the oil–wall molecular interactions, pore radius, fractal surface roughness and heterogeneous wettability are considered, and the heterogeneous wettability is caused by the trapped gas between rough elements. The results show that (1) the enhancement factor ranges from 10−1 to 108 with contact angle ranging from 0∘ to 180∘, and gradually tends to 1 with an increasing pore radius. Additionally, the flow enhancement factor and apparent permeability increase with an increasing contact angle; (2) The surface roughness can increase or decrease apparent contact angles of oil droplet on water-wetting or oil-wetting surface, respectively, and the increasing or decreasing value of contact angle increases with an increasing fractal dimension. Therefore, as rough fractal dimension increases, the enhancement factor and apparent permeability decrease in oil-wetting pores and increase in water-wetting pores; (3) With an increasing trapped gas content, because the surface becomes more oil-nonwetting that leads to the larger slip length and smaller effective viscosity, the enhancement factor and apparent permeability increase. This model has certain significance for the study of liquid flow behaviors in nanopores with rough surface and heterogeneous wettability, and can be used to fit the results measured by experiments by changing the fractal dimension and trapped liquid content.
