Formation of calcium naphthenate in water/oil systems, naphthenic acid chemistry and emulsion stability

Abstract

In recent years the production of crude oils with high amounts of naphthenic acids has increased. Certain problems are related to this type of crudes and a better understanding of the chemistry of the naphthenic acids is therefore of interest.

Synthetic model naphthenic acids, as well as commercial mixtures and crude oil naphthenic acids have been utilized to study the chemistry of naphthenic acids. Partitioning of naphthenic acids between oil and water and the dissociation equilibria in water have been studied in addition to their interfacial tension and micellisation behaviour.

A method for studying the precipitation of calcium naphthenate particles by means of near infrared spectroscopy was presented. It was shown that the method gives information about the induction period and about the rate of reaction for particle growth. Solubility products can also be estimated.

Near infrared spectroscopy were also utilized to study the ability of naphthenic acids and other amphiphiles to disintegrate asphaltene particles. It was shown that the structure of the naphthenic acids is important and that a commercial mixture of different surfactants had the best disintegration effect. The technique is applicable for screening the efficiency of various additives as disaggregation chemicals.

Emulsion stability was studied by means of Langmuir technique, critical electric field and bottle tests. The Langmuir study showed that the presence of Ca2+-ions at elevated pH gave rise to stable naphthenate monolayers. Oil/water emulsions stabilized with different carboxylic acids were investigated at different pH-levels and water-contents. It was demonstrated that water/oil emulsions could be stabilized by a combination of multilayer (D-phase) and asphaltene particles. Critical electric field was used to determine the emulsion stability of these systems and it was shown that a combination of 60% asphaltene particles and 40% D-phase gave the stablest w/o-emulsions. This investigation verifies the importance of D-phase stabilization in combination with asphaltene particles in systems with acidic heavy crude oil (including bitumen) and water.