(135e) Water Composition and Its Effect on the Wettability of Carbonate Surfaces

Laboratory tests show that salinity and ion type impact the recovery of crude oil from carbonate rocks subjected to water injection. Increased recovery has been noted upon reducing total salinity as well as modification of the type of divalent ions in carbonate rock/brine/oil systems. In this work, we study carbonate wettability using outcrop and reservoir limestones, classic crude-oil adhesion tests on smooth calcite surfaces, fluid-fluid and fluid solid interfacial tension, as well as zeta potential measurements. X-ray Computed Tomography (CT) imaging indeed confirms that salinity and ion type influence the distribution and amount of oil and water in limestone. DLVO (Derjaguin, Landau, Verwey and Overbeek) theory of surface forces, using the measured zeta potentials, provides a means to rationalize observations of recovery and crude-oil adhesion to solids. Although crude-oil rock interacations are important, the often overlooked water-solid surfaces are important to understanding the wettability evolution of carbonate surfaces.