TABLE OF CONTENTS Wettability is the term used to describe the relative adhesion of two fluids to a solid surface. In a porous medium containing two or more immiscible fluids, wettability is a measure of the preferential tendency of one of the fluids to wet (spread or adhere to) the surface. In a water-wet brine-oil-rock system, water will occupy the smaller pores and wet the major portion of the surfaces in the larger pores. In areas of high oil saturation, the oil rests on a film of water spread over the surface. If the rock surface is preferentially water-wet and the rock is saturated with oil, water will imbibe into the smaller pores, displacing oil from the core when the system is in contact with water.
If the rock surface is preferentially oil-wet, even though it may be saturated with water, the core will imbibe oil into the smaller pores, displacing water from the core when it is contacted with water. Thus, a core saturated with oil iswater-wet ifit will imbibe water and, conversely, a core saturated with water is oil-wet if it will imbibe oil. Actually, the wettability of a system can range from strongly water-wet to strongly oil-wet depending on the brine-oil interactions with the rock surface. If no preference is shown by the rock to either fluid, the system is said to exhibit neutral wettability or intermediate wettability, a condition that one might visualize as being equally wet by both fluids (50%/50% wettability).
Other descriptive terms have evolved from...
