Line-Tension-Based Modification of Young's Equation for Rock/Oil/Brine Systems

Abstract

Summary The two-century-old Young's equation has been widely used in petroleum engineering to depict the reservoir wettability in terms of contact angle, which is a function of surface free energies of the system. For solid/liquid/vapor (S/L/V) systems, Young's equation has been modified in the recent literature to include a line-tension term. This modification was sought to accommodate the imbalance of intermolecular forces experienced by the three-phase confluence zone. Also, Young's equation does not account for the vertical component of liquid/vapor surface tension. The present study aims to experimentally investigate the applicability of the line-tension-based modification of Young's equation to solid/liquid/liquid (rock/ oil/brine) (S/L/L) systems of interest to the petroleum industry. Both the ambient- and reservoir-condition optical cells were used, with stock-tank and live oil, respectively, to determine the drop-size dependence of dynamic contact angle subtended by the oil/brine interface with the rock surface. The experimental data were correlated with the modified Young's equation to determine the magnitude of line tension for different rock/oil/brine systems. To the best of our knowledge, this is the first attempt to apply the modified Young's equation to rock/oil/brine systems and to measure line tension for a rock/live-crude-oil/brine system at reservoir conditions of pressure and temperature. The measured line tension for S/L/L systems, while being positive and of the same order of magnitude as in S/L/V systems, correlates well with the water-advancing contact angle and the adhesion number, a ratio of adhesion force to capillary force. This experimental study indicates that the extent of deviation from Young's equation exhibited by rock/oil/brine systems may be directly related to the rock/oil adhesion interaction. This study reinforces the need to include the rock/oil adhesion force in our consideration of rock/fluid interactions, wettability, and their impact on enhanced-oil-recovery (EOR)/improved-oil-recovery (IOR) processes.