Recent Developments on the Elucidation of Colloidal Aspects of Asphaltenes and Their Relevance to Oilfield Problems

Abstract

Asphaltenes constitute the heavy petroleum fraction responsible for deposition events that may lead to reduced oil production, therefore of great interest for flow assurance. These molecules selfassemble in solutions leading to formation of aggregates that eventually grow towards precipitation and blockages in reservoirs and pipelines. Based on the Yen-Mullins aggregation model, two complementary scenarios are involved in asphaltenes phase behavior: one called thermodynamic, in which interacting molecules and other species can be assumed to be in equilibrium, and a second one, involving interacting colloidal particles, both being described by different theoretical frameworks. For the first, molecular interactions can explain the experimental observations or theoretical models. For the second stage, colloidal forces such as those described by Derjaguin, Landau, Verwey and Overbeek (DLVO) theory, steric particle stabilization and diffusion or reaction limited aggregation processes might control the process. Our evaluation is that this second approach is underrepresented in the current literature. For this reason, this review focuses on describing evidences for the presence of colloidal particles in crude oils obtained with different experimental techniques, drawing attention to this important attribute and we raise a few questions that we believe must be addressed in order to better understand the contributions from colloidal aspects.

Influence of High-Molecular n-Alkane Associates on Rheological Behavior of the Crude Oil Residue

“…However, it should be noted that real resin and asphaltene particles are much larger than theoretically predicted. 59,60 In the left corner of Figure 7, in the enlarged part of the spherical conglomerate image, worm-like structures are even visible, into which nanoaggregates of asphaltenes could be entailed. The fact of the presence of such agglomeration does not contradict the proposed model.…”

“…There are two approaches to describe the processes of flocculation and precipitation of asphaltenes. 59 The precipitation of dispersed molecular asphaltenes can be considered as a consequence of their low solubility in oil bulk. However, in the presence of asphaltene colloidal particles, flocculation is the result of disbalance in the interaction of particles.…”

“…They can be represented as spheres larger than 90 nm filled with randomly arranged cylindrical asphaltene associates having 2.5−5 nm in size. 59,60 Thus, the modern asphaltene aggregation structure is becoming more and more complicated, and the sizes of structural units are becoming larger. In particular, it was found that asphaltene nanoaggregates have a size of 2−5 nm.…”

Influence of Asphaltene Aggregation State on the Wax Crystallization Process and the Efficiency of EVA as a Wax Crystal Modifier: A Study Using Model Systems

“…Some authors propose the following growth: monomers → micelles → particles → precipitated. 38,39 Others proposed a growth system of molecule → nanoaggregate → clusters. 40 Several studies have shown that the wax crystallization process can be influenced by asphaltenes, 41−45 but there is no consensus on the underlying mechanism.…”

“…Such events are normally associated with variations in the temperature, pressure, and composition of the crude oil. ,− There are different studies proposing the growth system of the asphaltene structures. Some authors propose the following growth: monomers → micelles → particles → precipitated. , Others proposed a growth system of molecule → nanoaggregate → clusters …”