Rheological Properties of Gels Formed at the Oil–Water Interface by the Reaction between Tetrameric Acid and Calcium Ion under Flow Conditions and at the Batch Scale

The interfacial reaction between ARN tetrameric acid and Ca²⁺, which leads to the formation of calcium naphthenate deposits, was studied using a coaxial capillary device fitted to a profile analysis tensiometer. This device allows to continuously exchange the oil droplet subphase by a fresh ARN containing solution, thus mimicking the flow of oil as in an industrial separator. The effect of pH was first studied, and it was found that there was a formation of a cross-linking structure by the reaction between ARN and Ca²⁺ at pH comprised between 7 and 8. Then, the mechanism of growth of the interfacial gel was studied by determining the influence, on the interfacial shear rheology properties, of the exchange time and the contraction of the volume of the droplet. Two mechanisms can explain interfacial gel growth: formation of multilayers due to the constant input flow of ARN and coalescence between droplets reducing the interfacial area.