Oil Recovery by Spontaneous Imbibition from Weakly Water-Wet Rocks

Spontaneous imbibition is of special importance to oil recovery from fractured reservoirs. Laboratory measurements of volume of liquid imbibed versus time are often used in the prediction of oil recovery. Imbibition measurements also provide a useful approach to the complex problem of characterizing the wetting properties of porous media. Correlation of a large body of data for imbibition of brine into porous media initially saturated with refined oil was achieved through a semi-empirical scaling group which includes permeability, porosity, interfacial tension, oil and brine viscosity, and the size, shape and boundary conditions of the sample. The objective of the present study was to test this correlation for samples of different geometry for spontaneous imbibition under weakly water-wet conditions established by adsorption from crude oil with initial water saturation ranging from 14% to 31%. After establishing initial water saturations, the wettability of thirty-two core samples was changed to weakly water-wet by aging in an asphaltic crude oil at elevated temperature. Initial water saturation had a dominant effect on rate of oil recovery. Times for imbibition decreased by about 2 to 4 orders of magnitude with decrease in initial water saturation. Results for cores with the same initial water saturation but of different size and shape (cylindrical, annular, and rectangular) and boundary conditions (given by sealing off part of the rock surface with epoxy resin) were closely correlated. The presence of epoxy resin during aging in crude oil enhanced the decrease in water-wetness attained for cores and crude oil alone. The contribution to oil recovery by gravity segregation at very weakly water-wet conditions is addressed.