Consistent laboratory studies of the effect of wettability on fluid displacement in core flood experiments have long been hampered by the lack of cores with well defined, reproducible wetting states, other than strongly water or oil wet. There is ample evidence that wettability is an important factor in determining the outcome of core floods. Wetting can be altered using organic reactants, however the wetting state produced may not be representative of realistic wetting conditions. In this study, the control of wetting using crude oils at various aging conditions is explored.

Berea core plugs, saturated with brine, were flushed with crude oil and aged at a set temperature ranging from 22-90°C. Two crude oils were used, one from West Texas and the other from the North Sea. After aging, the crude oil was displaced by mineral oil and wettability was assessed using a variation of the Amott imbibition test. The procedure was developed for testing the effect of drilling mud filtrates on wettability for a range of wetting conditions.

Variables which affected the wettability index were often interdependent. They included the crude oil, the temperature at which the cores were aged with the oil, the initial water saturation, the aging time, and the volume of crude oil with which the core was flushed. Cores with wettability from strongly water-wet to neutrally wet could be produced by varying the conditions of crude oil exposure. Aging temperature and initial water saturation have predominant influence on the wettability induced by a given crude oil. However, all of the factors mentioned above must be considered in order to reproduce the state of wetting from one core plug to another. Stability of the altered wetting states was found to be reasonable for tests in which the cores were stored for two months in mineral oil.

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