Silica or limestone porous materials in contact with pure hydrocarbon liquids are strongly hydrophilic. When naturally occurring surface active materials are present in the liquid, they are adsorbed at the solid surface, rendering it less hydrophilic. If the concentration of such material is sufficient, the oil-water-matrix contact angle can be significantly greater than zero. The effect of increasing temperature in such a system will usually be to shift the adsorption equilibrium causing desorption of surface active material and a decrease in contact angle.
A simple geometrical model of a porous medium is used to approximate the effect of variation in wettability, as characterized by the oil-water-matrix contact angle, on imbibition relative permeability. Based on this model and other considerations, we conclude that the following trends will occur in a series of isothermal water floods with temperature increasing;
oil-water-matrix contact angle decreases to zero;
residual oil saturation decreases;
the ratio krw/kro at a fixed water saturation can increase for materials with a low residual oil saturation such as unconsolidated sands;
the ratio krw/kro at a fixed water saturation decreases for materials with a high residual oil saturation such as consolidated sands.
Experimental observations of these conclusions are reported in the literature.
A method is presented for the correction of imbibition relative permeability curves to compensate for changes in temperature, based on the model developed.