Small Angle Neutron Scattering (SANS and V-SANS) Study of Asphaltene Aggregates in Crude Oil

Abstract

We report small angle neutron scattering (SANS) experiments on two crude oils. Analysis of the high-Q SANS region has probed the asphaltene aggregates in the nanometer length scale. We find that the radius of gyration decreases with increasing temperature. We show that SANS measurements on crude oils give similar aggregate sizes to those found from SANS measurements of asphaltenes redispersed in deuterated toluene. The combined use of SANS and V-SANS on crude oil samples has allowed the determination of the radius of gyration of large scale asphaltene aggregates of approximately 0.45 microm. This has been achieved by the fitting of Beaucage functions over two size regimes. Analysis of the fitted Beaucage functions at very low-Q has shown that the large scale aggregates are not simply made by aggregation of all the smaller nanoaggregates. Instead, they are two different aggregates coexisting.

A comprehensive study on mechanism of formation and techniques to diagnose asphaltene structure; molecular and aggregates: a review

“…Determination of the size and morphology of the aggregates has been the subject of many studies. So far, by applying the Schultz distribution function, Guinniur approximation, and Beaucage function, different morphologies including the monodisperse and polydisperse spheres, disc‐like particles, prolate ellipsoids, oblate cylinder, vesicles, and fractal shape have been suggested for the asphaltene aggregates . However, some studies reveal that a simple geometric model cannot represent the aggregate structure of asphaltene.…”

“…The results show that the fractal dimension depends on the source of asphaltene and the experimental conditions. The mean fractal dimension obtained for asphaltene aggregates can vary in the range between 1.5 and 3 …”

Fluorine tracers for the identification of molecular interaction with porous asphaltene aggregates in crude oil

“…In addition, they can have dramatic effects on the feasibility of oil exploitation itself when aggregation of asphaltenes leads to fouling and clogging of pipes at a drilling site. Under reservoir conditions, asphaltenes form small aggregates of several molecules, which can, for instance, be detected by X-ray and neutron scattering techniques [1][2][3]. The transition towards larger agglomerates that lead to precipitation, and possibly blockage of boreholes or pipelines in the course of time, is less well understood, but appears to be affected by temperature changes, shear and addition of non-solvents.…”

Aggregate structure analysis of Colombian heavy crude oil-derived asphaltenes using small angle X-ray scattering

“…Additionally, we proved the Asphaltenes nanoaggregates are fully formed in a solvent such as Toluene at concentrations similar to the previously reported "critical nanoaggregate concentration" (CNAC ~100 mg/L) (Andreatta, Bostrom, & Mullins, 2005) As we mentioned at the beginning of this section, the scattering curve for 1% Asphaltene solution is characterized by the appearance of a crossover between two successive power-law regimes which correspond to mass fractals. Evidence for succession of powerlaw regimes on Asphaltenic Systems from SANS data have been earlier reported (Headen, 2009). This type of scattering is commonly related with a complex multilevel structure, i.e.…”

“…Besides the size, establishing other parameters such as the shape, structural factors, and polydispersity of Asphaltenes is required to develop phase behavior models in order to predict the thermodynamic conditions where Asphaltene precipitation takes place. To quantitatively characterize these colloidal parameters, small-angle scattering techniques have been applied on Asphaltene systems as a function of thermodynamic conditions (Tanaka et al, 2003;Sheu, 2006;Headen, Boek, Stellbrink, & Scheven, 2009;Amundaraín, Chodakowski, Long, & Shaw, 2011).…”