Effect of Sandstone Wetting Reversal Induced by Low Temperature Plasma on the Oil Droplet Scouring under Flowing Water.

The wettability of rocks in a reservoir has a great influence on the oil recovery factor in oilfield development. In the present study, we perform a comprehensive investigation to probe the effect of reservoir wettability on the displacement efficiency due to water flooding. First, we report that the wettability of the sandstones can be significantly improved by the Jet-type AP plasma equipment-it takes effect to make a hydrophobic surface become hydrophilic. Subsequently, the displacement efficiency is measured by the self-developed setup, where such factors as the flow field flushing time, the velocity of the flow field, and the volume of the oil droplet are surveyed as controllable variables. Moreover, the force analysis of oil droplets in the flow field is performed to explain the scouring mechanism, and the experimental results are in accordance with that based on the dimensional analysis. Next, the numerical simulation is carried out to explore the detailed information in the displacement process. The function curves of the displacement efficiency with respect to the control variables are given by numerical simulations, which are in excellent agreement with the experimental data. In addition, the numerical simulation demonstrates the deformation of the crushed oil droplets due to the shearing of the flow field, associated with the pressure alteration of fluid during the displacement process. These findings are beneficial to better understand the effect of reservoir wettability on the oil recovery, which also provides inspiration for the areas of microfluidics, diffusion of pollutants, microsensors, etc.