Interfacial Films of Calcium Naphthenate: Influence of Polycardanol Structures

Abstract

Calcium naphthenate deposition is a well-known challenge in South America oil fields. This type of scale results from the interfacial reaction of a specific naphthenic acids group with the divalent metal ions, more precisely Ca 2+ , found in produced water. To avoid/minimize precipitation of these solids, we have been used certain chemicals, while different chemicals acted by different mechanisms. In this work, amphiphilic macromolecules were produced by cardanol polyaddition (PCA) and polycondensation (PCC), characterized by Fourier transform infrared spectroscopy, 1 H NMR, and size exclusion chromatography (SEC), and evaluated regarding their influence on the calcium naphthenate interfacial film formation, using model systems, by rheology tests. Naphthenic acids with a high concentration of tetra-protic naphthenic acids (ARNs) were extracted from an indigenous calcium naphthenate deposit and used to prepare model systems containing 25 mg/L of acids in toluene. Interfacial tension measurements of the model systems were also carried out. The results show that the mechanism of delaying film formation of calcium naphthenates is more related to the molar mass and structure of the additive than to its ability in reducing interfacial tension. The polymer structure must allow sharing the interface with naphthenic acids, which is achieved by PCA but not by PCC, disturbing the interaction between naphthenic acids and calcium ions.