Asphaltenes and Asphaltene model compounds: Adsorption, Desorption and Interfacial Rheology.

Abstract

There are numerous problems encountered during extraction, production, transportation and refining of crude oil. Most of these problems are typically oil-specific, meaning that they depend upon the source of the oil, and sometimes they are reservoir-specific, meaning that they depend on the stage of extraction (primary, secondary or enhanced recovery). Nevertheless, a great part of the problems are related to the indigenous surface-active species such as asphaltenes, naphthenates and resins. The definition of asphaltenes rather than being a single molecule is instead based on a solubility class. This means that they are polydisperse in nature which leads to differences in properties and composition. Asphaltenes are responsible for stabilizing water-in-oil emulsions by forming a mechanically strong gel at the interface that prevents droplet coalescence. Asphaltenes are also known to precipitate and under certain conditions (pressure, temperature, composition) form deposit layers which could lead to plug formation. All this issues generate deficits in flow assurance and evidently, increases in the operational costs. Two strategies might be implemented to further advance in the understanding of the mechanisms involved in asphaltene adsorption onto various interfaces (liquid-liquid or solidliquid). (i) Fractionation or (ii) model compounds. The first strategy explores the different sub-fractions that are obtained at different solvent/precipitant ratios using indigenous asphaltenes. The second strategy is to design a molecule, or group of molecules with defined functionalities that mimic the main known asphaltene properties, for instance self-association in solution and interfacial behavior. In this thesis, the different publications were aimed to study and explore possible solutions to the several problems stated. In the first and second publications, adsorption and desorption aspects of asphaltenes and demulsifiers at the liquid-liquid interface were explored. Furthermore, interactions between asphaltenes and demulsifiers were studied via interfacial tension measurements and interfacial dilatational rheology. The results shed light on the mechanisms involved during chemical demulsification of water-in-crude oil emulsions. In the third publication, rheology and sorption aspects of asphaltene model compounds at the liquidliquid interface were studied. The main goal of this publication was to establish the interfacial properties inherent to asphaltenes captured by a set of asphaltene model compounds developed at the Ugelstad laboratory. Similarly, in the fourth publication adsorption of asphaltenes and asphaltene model compounds onto the solid-liquid surface was studied. In this study, the determination of the adsorption enthalpy via microcalorimetry allowed to elucidate the type of bond and the driving force for adsorption onto surfaces of different nature. With these publications, a complete study at the liquid-liquid interface and the solid-liquid surface was developed for asphaltenes and asphaltene model compounds. This provides a fundamental framework for model systems that can be used to understand the behavior in real applications.