Wettability effects in thermal recovery operations

Do the three-phase oil-water-rock systems remain unaltered in wettability or do they become more strongly water- or oil-wet when the reservoir temperature is increased during thermal recovery operations? The published Literature provides an affirmative support to each of the three possible answers to this question. Should we let this controversy continue or is it time to put together different pieces of the puzzle to reach at least a semblance of a solution? The latter is the purpose of this paper. This paper aims to shed more light on the controversy surrounding the effect of temperature on wettability by bringing together the various schools of thought on this subject under a simple mechanistic explanation involving an interrelationship between the spreading behavior in solid-liquid-liquid (SLL) systems and the liquid-liquid interfacial tension, and thin wetting film stability considerations. This paper extends the Zisman-type correlation between contact angles and surface tension in solid-liquid-vapor (SLV) systems to the SLL systems. The success achieved in establishing such a correlation in this study is of practical significance in that it shows a way of identifying crucial wettability changes that may occur in secondary and tertiary recovery processes through simple laboratory experiments involving interfacial tension and contact-angle measurements. This would help in recovery process selection and optimization. The paper also describes a technique, which was discovered during the course of this experimental study, to prevent adverse wettability shifts in thermal operations. The technique involves in-situ deposition of small quantities of calcium carbonate (scale) particles near the wellbore region to maintain a strongly water-wet region of high relative permeability to crude oil. Encouraging results from an Alberta field test of this technology are also presented.