Interrelationship of Wettability, Initial Water Saturation, Aging Time, and Oil Recovery by Spontaneous Imbibition and Waterflooding

TLDR

Wettability in crude oil/brine/rock systems influences oil recovery through complex interactions. The study varied initial water saturation and aging time to create different wettabilities in Prudhoe Bay crude oil/brine/rock systems, quantified water wetness with an Amott index, pseudowork, and contact angle, and measured spontaneous imbibition and waterflood curves for each state. Imbibition rate and water wetness declined with longer aging and lower initial water saturation, while breakthrough and final oil recoveries from waterflooding rose as water wetness decreased, with correlations between wetness and recovery presented.

Abstract

Summary 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 Sandstone was varied by systematic change in initial water saturation and length of aging time at reservoir temperature (88°C). All displacement tests were run at ambient temperature. Various degrees of water wetness were achieved and quantified by a modified Amott wettability index to water, the relative pseudowork of imbibition, and a newly defined apparent advancing dynamic contact angle. Pairs of spontaneous imbibition (oil recovery by spontaneous imbibition of water) and waterflood (oil recovery vs. pore volumes of water injected) curves were measured for each of the induced wetting states. Several trends were observed. Imbibition rate, and hence, water wetness, decreased with increase in aging time and with decrease in initial water saturation. Breakthrough recoveries and final oil recovery by waterflooding increased with decrease in water wetness. Correlations between water wetness and oil recovery by waterflooding and spontaneous imbibition are presented.