Residual oil saturation under mixed-wet conditions: a direct comparison between Indiana limestone and its microfluidic analogue

We present laboratory measurements of residual oil saturation established by secondary waterflood in packed beds of crushed calcite assembled in a microfluidic channel under mixed-wet conditions. The measurements are compared with analogous measurements in Indiana limestone cores using the same test fluids and comparable injection rates. The wettability is characterized by the advancing contact angle of the flood water on a mineralogically representative substrate submerged in the oil phase, which ranged from θa = 90° to 160°. While residual oil saturation is larger in the microfluidic analogue than the limestone cores over the full range of θa considered presently, its dependence on θa is qualitatively similar for both media and is well described by a concave-up quadratic function. Maximum recovery occurs at moderately oil-wet conditions of θa = 130° in Indiana limestone and 120° in its microfluidic analogue. These findings demonstrate that salient features of oil/brine flow through O(10)cm-long cores are conserved in two-dimensional microfluidic models under conditions considered presently.