Field-Wide Variations of Wettability

Abstract Core laboratory results are used to describe the variations of wettability Index and residual oil saturation to water within an oil-bearing consolidated reservoir. Core sampling is carried out to cover a large range of permeability ( from 1 mD to 1600 mD) and height above the initial water-oil contact (from 4 m to 175 m). The following experimental data are available: Twenty-six drainage and imbibition capillary pressure curves are measured at reservoir conditions, using reservoir fluids and both water-wet and oil-wet semi permeable membranes.Quantitative mineralogy and pore geometry by combined SEM and image analysis. Both bulk and pore wall mineralogy is available on some samples. Typical mixed-wet imbibition capillary pressure curves are obtained. Experimental results illustrate strong trends between the amount of spontaneous imbibition, the wettability Index to water and the residual oil saturation on one hand and both the structural position and the permeability of samples on the other hand. Relationships with pore wall mineralogy are rather weak. The combined effects of structural position and permeability on wettability result in unusual variations of the forced imbibition capillary pressure curve within the reservoir. The plateau of the Pc curve is weakly dependent on permeability. A new way to extrapolate forced water/oil imbibition Pc curves is proposed.