Igor N. Evdokimov

Assembly of asphaltene molecular aggregates as studied by near-UV/visible spectroscopy: I. Structure of the absorbance spectrum

Abstract The aim of this paper is to provide new data on the properties of molecular aggregation in toluene solutions of crude oils and of solid asphaltenes. The shape of the optical absorption spectrum was found to be sensitive to the details of asphaltene aggregation processes. In dilute solutions, these processes are apparently determined by the net concentrations of asphaltenes; other oil constituents play a secondary role. Our experimental data indicate that molecular solutions of asphaltenes are possible only for concentrations below 1 mg/l. With increasing asphaltene content, more and more complex molecular aggregates are formed. In particular, asphaltene dimers evidently are the predominant species in the range of 5–15 mg/l, while stable “nanocrystallites” (dimer pairs) are predominant at concentrations ≈90 mg/l. Aggregates at higher concentrations may be viewed as assemblies of such “crystallites”. The observed gradual aggregation process is distinct from conventional micellisation phenomena with step-like changes at critical micelle concentrations (CMCs).

Assembly of asphaltene molecular aggregates as studied by near-UV/visible spectroscopy: II. Concentration dependencies of absorptivities

Abstract The properties of molecular aggregation in toluene solutions of a crude oil and solid asphaltenes are determined almost solely by the concentration of asphaltenes, as shown by absorptivity measurements at 315–750 nm. From non-monotonic concentration dependencies of absorptivities, it is concluded that asphaltene monomers are abundant in solutions with asphaltene concentrations below 1–5 mg/l, while molecular aggregates are effectively formed above 20–25 mg/l. The most stable oligomers are a dimer and a dimer pair (Yens “nanocrystallite” [NC]). Nanocrystallites act as building blocks for more complex aggregates at asphaltene concentrations exceeding 90–100 mg/l. These optical absorption results are supported by studies of Rayleigh scattering in asphaltene solutions.

Initial stages of asphaltene aggregation in dilute crude oil solutions: studies of viscosity and NMR relaxation☆ ☆

In crude oil – toluene solutions dynam ic viscosity  and spin-spin relaxation time T2 were measured as functions of asphaltene concentration C in the range of 10300 mg/l. The results were supplemented by studies of optical absorption. Extrema in the measured concentration dependencies are attributed to a transient predominance of specific asphaltene aggregates – from dimers to stacked molecular nanoclusters (MNCs) of four monomers. The strikingly non-ideal properties of solutions with C below 150-170 mg/l are attributed to the strong interactions between asphaltene species. At higher C the solution properties are evidently determined by the weaker interacting MNCs and the concentration effects are closer to those in ideal fluid mixtures. The observed re-entrant (T2) behaviour in asphaltene solutions hypothetically has the same origin as in supercooled or demixing molecular systems, where anomalous structural and dynamical features are often explained by emerging heterogeneity due to transient spontaneous clustering.

Rheological evidence of structural phase transitions in asphaltene-containing petroleum fluids

Abstract The aim of this paper is to provide data on the rheological/structural properties of “synthetic oils,” composed of light hydrocarbons (toluene) and a heavy fraction, containing asphaltenes (vacuum residue, VR). Samples with asphaltene concentrations 20–85 g/l have been studied at temperatures 0–60 °C and shear rates up to 1500 s−1. The non-Newtonian flow curves were approximated by the Bingham and the Herschel–Bulkley models to determine the apparent yield stress and the shear-rate exponent as functions of the asphaltene concentration and the temperature. Sharp variations of these parameters were attributed to formation/destruction of extended ordered structures in asphaltene colloid suspensions. Structural changes were observed in the temperature range 20–30 °C, particularly important for industrial processes of reservoir development and pipeline transportation. A molecular model of the observed macroscopic effects takes into account possible first-order structural phase transitions in the nanometer-size resin/asphaltene colloid microparticles.

On a new method of observing defects annealing in crystals

Abstract A simple convenient method based on the use of ion impact phenomena is proposed for studying the kinetics of the annealing of defects.

Emerging Petroleum-Oriented Nanotechnologies for Reservoir Engineering

This research principally differs from other works as (for the first time with respect to petroleum resources) it utilizes nanotechnological methods, approaches and models devised for other industrial applications (e.g. for microelectronics and biotechnology). The specifics of petroleum were accounted for by development of new experimental techniques, particularly sensitive to properties of petroleum nanocolloids.

On the Nature of UV/Vis Absorption Spectra of Asphaltenes

Abstract New experimental data show that previously reported UV/vis spectra of asphaltenes/crude oils may have been strongly distorted by artifacts, affecting not only quantitative parameters (spectras slopes), but also qualitative features (a presence of strong UV peaks). In a popular revised “amorphous semiconductor” (AS) model, the properties of UV/vis spectra are defined by population distribution of higher aromatics. This interpretation is obviously incompatible with the newly observed concentration effects in toluene solutions. Possibly, some specific features of UV/vis absorbance in asphaltenes/crude oils may be better described by the traditional AS model, taking into account the distribution of defects in chromophore carriers, e.g., nanosized carbonaceous species of the graphene family.

Proper surface channelling of low energy argon ions incident on a nickel (110) crystal

Abstract The scattering behaviour of 6 keV argon ions from a nickel (110) surface has been investigated for specular reflection under grazing incidence conditions. The occurrence of an anomalously high energy loss has been confirmed and the transition from chain scattering at large scattering angles to a distinctly different type of scattering at small angles has been investigated. The characteristics of the low angle scattering phenomena, which dominate the observed spectra at scattering angles below about 18° may be explained in terms of a surface hyperchannelling model in which the incident ions are confined to move within the shallow “potential valleys” between two atomic rows in the surface. The critical angle for occurrence of this phenomena which is distinctly different from surface semichannelling has been evaluated with Lindhards standard string potential. The experimentally measured critical angles are in good agreement with the calculated ones.

Simplified models for surface hyperchannelling

Abstract Experimental and detailed, three-dimensional computer simulation studies of the scattering of low energy argon ions incident at grazing angles onto a nickel single crystal have shown that under certain, well defined conditions, surface hyperchannelling dominates the reflection process. The applicability of simple computer simulation models to the study of this type of scattering has been investigated by comparing the results obtained using a “summation of binary collisions” model and a continuous string model with both the experimental observations and the three dimensional model calculations. It has been shown that all the major features of the phenomenon can be reproduced in a qualitative way using the simple models and that the continuous string represents a good approximation to the “real” crystal over a wide range of angles. The saving in computer time compared with the more complex model make it practicable to use the simple models to calculate cross-sections and overall scattering intensit...

Morphological Transformations of Native Petroleum Emulsions. I. Viscosity Studies

Emulsions of water in as-recovered native crude oils of diverse geographical origin evidently possess some common morphological features. At low volume fractions varphi of water, the viscosity behavior of emulsions is governed by the presence of flocculated clusters of water droplets, whereas characteristic tight gels, composed of visually monodisperse small droplets, are responsible for the viscosity anomaly at varphi approximately 0.4-0.5. Once formed, small-droplet gel domains apparently retain their structural integrity at higher varphi, incorporating/stabilizing new portions of water as larger-sized droplets. The maximum hold-up of disperse water evidently is the close-packing limit of varphi approximately 0.74. At higher water contents (up to varphi approximately 0.83), no inversion to O/W morphology takes place, but additional water emerges as a separate phase. The onset of stratified flow (W/O emulsion gel + free water) is the cause of the observed viscosity decrease, contrary to the conventional interpretation of the viscosity maximum as a reliable indicator of the emulsion inversion point.