Abstract
Oil migrating into a water saturated reservoir is a drainage process while waterflooding an oil reservoir is a water imbibition process. Many factors affect drainage and imbibition rock properties including pore structure, rock surface properties (lithology) and their interactions with pore fluids (wettability), and fluids displacement processes. Difference in drainage and imbibition is significant and this difference should be considered, but is often neglected, in reservoir saturation monitoring (RSM).
In this study, fundamentals of rock properties and their interactions with oil and water were reviewed. In a specially designed laboratory special core analysis program, both drainage and imbibition rock properties were measured in the laboratory, at reservoir conditions, using reservoir rock samples, crude oil, and synthetic brine. Wettability was restored by aging the rock samples in crude oil at temperature. Pore structure was characterized by integrating capillary pressure and petrographic studies. Rock lithology was determined by X-ray diffraction measurements and thin section examinations. All laboratory measurements were integrated to better understand drainage and imbibition rock properties.
In applying the laboratory determined rock petrophysics to field RSM, time-lapse resistivity logs were used to identify the current dynamic water-oil contact (DWOC). Above this DWOC, drainage rock properties were used for log processing while below this contact imbibition rock properties were used. Field examples are shown to demonstrate the applications of drainage and imbibition petrophysics in evaluating waterflood sweep and identifying intervals for potential side-tracks.
