To evaluate the feasibility of "Smart Water" injection, reproducing representative initial wettability in laboratory experiments is essential. Experimental studies have confirmed that adsorption of polar organic components from crude oil to the rock surface is a main contributor in establishing initial wettability. This study intends to examine the effect rock surface accessibility, by altering the initial water saturation (Swi), has on the adsorption efficiency of polar components in carbonates.
The adsorption study of polar components was performed by flooding several pore volumes of crude oil through outcrop Stevns Klint carbonate cores at different Swi. To observe the amount of adsorbed polar components, the acid and base numbers of the effluent were examined regularly using titration. Core wettability was thereafter investigated by spontaneous imbibition, forced imbibition and by the chromatographic wettability test.
The study illustrated the importance of the acidic components in the crude oil on wettability alteration in carbonates. It was observed that 1) increased adsorption to the pore surface of acidic polar components lead to less water-wet conditions. 2) The adsorption process occurs immediately as the oil contacts the porous media, having the highest rate of adsorption during the first pore volumes of injection. 3) Increasing the surface accessibility for polar components by reducing the initial water saturation has strong influence on the initial wettability. 4) Adsorption of acidic components is more pronounced than that of basic components.
Aging of cores has for a long time been regarded as the primary method for establishing initial wettability in the laboratory. This study demonstrates that the adsorption of polar components occurs almost instantly, and that aging is not necessary to obtain mixed wettability.