Remaining oil saturation established by waterflooding from maximum initial oil saturation was measured in Indiana limestone under four mixed-wet conditions established using different organic acids. The altered wettability is characterized by the advancing contact angle of the aqueous phase on a calcite substrate submerged in the oil phase, which ranged from θo = 50° to 150°. Remaining oil saturation decayed as a power of time for up to 55 pore volumes of water injected and then reached a constant value. The duration of oil production increased linearly with θo. In contrast, remaining oil saturation decreased and then increased with increasing θo within the range of experimental conditions, with optimal wettability for recovery shifting from θo = 110° to 135° as waterflood progressed.
This material includes work supported by a Society of Petrophysicists and Well Log Analysts (SPWLA) Foundation grant and a Aberdeen Formation Evaluation Society (AFES) scholarship. Magali Christensen was supported by the University of Aberdeen College of Physical Sciences studentship. The authors gratefully acknowledge Renaud Dufour (Max Planck Institute for Dynamics and Self-Organization) for the interfacial tension measurements, Amer Syed for his assistance in the design and assembly of the coreflood rigs, M.Sc. student Luca Romanello and undergraduate student Matthew P. Wilkie for density and viscosity measurements, Colin Taylor for the mercury injection porosimetry measurements, Corex (UK), Ltd. for allowing Luca Romanello access to their laboratory facilities during his work-based placement, and Roland Lenormand for his insightful comments and suggestions. The authors also thank the anonymous reviewers for their comments on the manuscript.