Interrelationship of wettability, initial water saturation, aging time, and oil recovery by spontaneous imbibition and waterflooding

Previous studies of crude oil/brine/rock (COBR) and related systems showed that wettability and its effect on oil recovery depend on numerous complex interactions. In the present work, the wettability of COBR systems prepared using Prudhoe Bay crude oil, a synthetic formation brine, and Berea Sandst one was varied by systematic change in initial water saturation and length of aging time at reservoir temperature (88 degreesC). All displacement test s were run at ambient temperature. Various degrees of water wetness were ac hieved and quantified by a modified Amott wettability index to water, the r elative pseudowork of imbibition, and a newly defined apparent advancing dy namic contact angle. Pairs of spontaneous imbibition (oil recovery by spontaneous imbibition of water) and waterflood (oil recovery vs. pore volumes of water injected) cur ves were measured for each of the induced wetting states. Several trends we re observed. Imbibition rate, and hence, water wetness, decreased with incr ease in aging time and with decrease in initial water saturation. Breakthro ugh recoveries and final oil recovery by waterflooding increased with decre ase in water wetness. Correlations between water wetness and oil recovery b y waterflooding and spontaneous imbibition are presented.