Role of Naphthenic Acids in Emulsion Tightness for a Low-Total-Acid-Number (TAN)/High-Asphaltenes Oil

Abstract

The emulsion stabilizing properties of a low-total-acid-number (TAN) crude oil, which had initially been attributed to asphaltenes and calcite precipitation, were re-analyzed with regard to the role of organic acids. Despite high asphaltenes content, this crude oil exhibits features classically observed with acidic oils, such as the increase in emulsion stability upon pressure decrease/pH increase or the poor efficiency of demulsifiers. The potential for a significant role of organic acids was confirmed by the high interfacial activity of indigenous acids, as extracted from the crude oil by means of an ion-exchange resin. This was further addressed analyzing the molecular chemistry of the interfacial layer and its rheology. The interfacial material was found to be composed of a mixture of asphaltenes and organic acids. These acids exhibit a wide range of structures (mono- versus dicarboxylic, fatty versus naphthenic and benzoic) and molecular weights (from 200 to 700 g/mol), contrary to the medium molecular weight fatty monocarboxylic acids that are generally believed to cause “soap emulsions”. The interfacial rheology is indicative of a 2D gel, with an assumed glass transition temperature of approximately 40 °C. In conclusion, this study shows that a co-precipitation of asphaltenes and organic acids can promote the build up of a very cohesive interface. The disruption of this interface not only requires the drainage of individual molecules but also a collective yield of the gel. This paper is part one of two: it confronts physical and chemical data, the latter being further detailed in an associated paper.

Rhamnolipids Produced by Indigenous Acinetobacter junii from Petroleum Reservoir and its Potential in Enhanced Oil Recovery

“…The importance of oxygenated polar compounds as interfacial active components in crude oil is widely acknowledged as one of the primary causes of emulsion stability in crude oil mixtures (Acevedo et al, 1999; Pauchard et al, 2008). Oxygenated polar compounds also play an important role in wettability alteration.…”

Oilfield metal naphthenate formation and mitigation measures: a review

“…Serang field sludge was reported to be composed of 70% paraffins and iso-paraffins (C 14 -C 28 ), 20% (C 28 -C 30 ) carboxylate salts and < 5% inorganic material (Gallup et al 2002). Large carboxylic acids with molecular weight up to 700 g/mol have been reported (Pauchard et al 2009). Serious challenges arise in the field from sludge formation because of reduced storage capacity, restricted flow of petroleum due to constrictions arising from solid loading in subsea lines, risers and in separation vessels especially after treatment, and poor oil/water separation (Turner and Smith 2005).…”

“…A study by Pauchard et al (2009) identified asphaltene-naphthenic acid interactions modulated by pH and acid structure as the main factor responsible for changes in interfacial behaviour of naphthenic acids and emulsion stability of a low-TAN crude oil. Asphaltenes are inhibitive to CaN formation.…”

Modelling approach for multi-criteria decision-making selection process for artificial lift systems in crude oil production

“…Different authors have discussed the surface-active character of oils to combined effects of the presence of carboxylic acids and asphaltenes in crude oils. Accordingly, these carboxylic acids and the asphaltenes perform a synergic effect, resulting in emulsion stabilization [19,42]. Thus, one possibility is that the aggregates formed between these species are the emulsion stabilizing materials.…”