Contact angle measurements and wetting behavior of inner surfaces of pipelines exposed to heavy crude oil and water

The technology of oil flow in pipelines assisted by its confinement within an annular aqueous section, known as core-flow, has emerged as a viable alternative for the transportation of heavy crude oils. The lubricating effect of the aqueous film leads to reduced equivalent viscosities and, hence, low energy consumption. One of the possible problems associated with this technique is the gradual accumulation of oil on the inner pipeline surfaces, requiring the use of cleaning procedures. This work is aimed at investigating the roles of the oil polar components on the wetting of such surfaces by crude oils through contact angle measurements in systems containing heavy oil/aqueous phase/metallic surfaces. Asphaltenes and naphthenic acids were removed from the crude oil, respectively, by flocculation with alkanes and by washing with alkaline solution. As model metallic surfaces, commercial and galvanized steel were used; and the studied aqueous phases comprised pure water, 1% sodium chloride and sodium meta-silicate solutions. Static contact angles were determined via the placement of an oil droplet under the metallic surface in the presence of an aqueous phase. These measurements revealed small influence of the nature of the metallic surfaces on the observed wettability. Significant effects, however, were observed depending on the presence of asphaltenes and naphthenic acids, whose removal reduced the contact angles from an oil-wet behavior (angles above 145 degrees) to a water-wet situation, with angles smaller than 45 degrees and 80 degrees, respectively. Experiments carried out with aqueous phases containing 1% sodium meta-silicate and sodium chloride revealed contact angles smaller than 60 degrees in most cases, confirming their suitability for the prevention of oil deposition onto these surfaces. Moreover, this study confirms that measurements of static contact angles are useful for screening of formulations and surfaces used in oil transportation prior to flow tests. (c) 2005 Elsevier B.V. All rights reserved.