The Wettability Alteration In Oil Reservoir And Its Effect On Porous Flow Process

In this paper, the classification, characteristic and mechanisms of the wettability alteration in oil reservoir have been discussed. And its effects on the process of porous flow and its application in tertiary oil recovery project have been studied in details.Accordingly, the changes of wettability in reservoir contain the changing process from water-wet to oil-wet, or from oil-wet to water-wet, or form liquid-wet to gas-wet, which are dominated by the wetting agents, the surface of rock particles and the conditions in porous media, etc.Relating experiments showed that the static adsorptive power of the chemical on oil sand surface is 6-15 mg.g~-1, while the dynamic adsorptive power on natural core is 0.81 mg.g~-1.The adsorptive images of the wettability alteration agents were examined under Atomic Force Microscopy. The result showed that there is strong appetency between the wettability alteration agents and oil or oil-wet surface, and as a result, the adsorptive power on oil-wet surface is more than on water-wet surface.By measuring Contact-angels in which Dynamic Contact-angel Analyzer and Washburn method were used, the best formulation can change the contact angle from 93° to 60°.Here, adhesion work factor (E), interfacial tension factor (Eδ) and wettability factor (Eθ) were firstly introduced, and determinant criterion of wettability alteration agents was presented. The analysis proved that wettability alteration agents can be selected by the wettability factor.The relative permeability experiments showed irreducible oil was reduced by 10% by the wettability alteration agents, and the cross-point relative permeability moves to right, and the core converts to water-wet.In microcosmic flooding experiments, the oil film became thinner, the residualoil was peeled off, and the oil was prevented re-adhering to sand surface. Then oil recovery was enhanced. In addition, the wettability alteration agents are contributable to spontaneous imbibition.Both the shop experiment and field test showed that the wettability alteration agents have the ability to reduce the injection pressure and enhance oil recovery.