Effect of wettability on crude oil recovery using microfluidics*

Surface wettability plays an essential role in drop impact dynamics, microfluidic emulsion dynamics, slip flow for drag reduction, fluid-fluid displacement in various technological applications. Targeting enhanced oil recovery applications, we experimentally investigate the effect of porous networks' wettability on the invasion morphology and sweep efficiency of viscous oil displaced by different salinity floods using microfluidics. Two different microfluidic models are employed, namely a uniform network of homogeneous pore arrangement and a rock network mimicking a sandstone structure.  Systematical experiments (of the same flood-pairs) are carried out in both hydrophilic and hydrophobic chips for comparison. The results show that regardless of flood type or wettability, oil recovery is lowered by approximately 20 – 40% in the rock-like porous media compared to the uniform one.  We also find that the hydrophilic microfluidic rock has a remarkable increase in oil recovery by ≈ 30%, compared to the hydrophobic case. In addition, we observe a more pronounced lateral growth of displacing pattern of the aqueous flood when the surface is hydrophilic. Finally, by incorporating the contact angle into analysis, we quantitatively explain the increasing factor in both recovery rate and finger width for the hydrophilic vs. hydrophobic rock-liked porous networks.