Spontaneous imbibition of water by crude oil/brine/rock systems

This paper reports on the effect of brine composition, crude oil type, and aging conditions on wettability measured by rate of spontaneous inhibition of water that has been investigated for Berea sandstone. Brines were formulated with sodium and calcium chloride. Two crude oil samples, Moutray from West Texas and ST-86, a North Sea crude oil, were employed. Changes in wettability caused by Moutray crude were sensitive to brine composition; water-wetness decreased as the calcium chloride concentration increased. For cores aged with ST-86, wettability was much less influenced by brine composition. Aging temperature and initial water saturation were dominant variables with respect to the wettability change induced by a given crude oil. Wettability with respect to water decreased as aging temperature increased. Decrease in initial water saturation resulted in a shift towards oil-wetness. Oil recovery by waterflooding for weakly water-wet systems was high compared to that for strongly water-wet systems.