Aleksandr P. Losev

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.

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.

Thixotropy in Native Petroleum Emulsions

Native water in crude oil emulsions, stabilized by indigenous surfactants, exhibit both positive thixotropy (PT) and negative thixotropy (NT) in Couette flow. PT is associated with microscopic processes, local break-up of droplet clusters in emulsions with low and moderate volume fractions of water φ, or fracturing of emulsion-gels with φ > 0.7. The latter process involves the coalescence of water droplets along a fracture plain, which results in vorticity banding of emulsion flow. NT reflects evolution of the macroscopic radial banding in flow of emulsions with 0.18 < φ < 0.58 and is dictated by the displacement of the interface between the sheared and unsheared regions.

Common Features of “Rag” Layers in Water-in-Crude Oil Emulsions with Different Stability. Possible Presence of Spontaneous Emulsification

Aging W/O emulsions with various stabilities brake into “rags” – fragments with uneven shapes. Individual “rags” combine into a separate “rag” layer below supernatant oil. In the “rag” material, the continuous oil phase is enriched in heavy constituents, while the disperse phase contains two populations of water drops. Larger drops are formed by mechanical dispersion during emulsification, as indicated by their log-normal number size distributions. Smaller droplets possess exponential number size distributions, indicating a possibility of their spontaneous nucleation. The latter conclusion is supported by microscopic observation of spontaneous appearance of small droplets at a stationary oil–water interface. GRAPHICAL ABSTRACT

Settling Properties and Fractal Dimensions of Aggregated Water Emulsions in Native Crude Oils

In as-prepared emulsions with volume fractions of water φ < 0.18, clusters of ca. 30 water droplets are basic structural units. In course of settling, these clusters form transient percolation aggregates with fractal dimension DF ≈ 2.38, and the final structure of the sediment is a tight emulsion gel with packing density of 0.74. In emulsions with φ > 0.29, the basic structural units are individual water droplets which form percolation aggregates with DF ≈ 2.60. The final structure of the respective sediment is a less tight emulsion gel with packing density of 0.64. In emulsions with 0.18 < φ < 0.29, settling kinetics is characterized by both fractal dimensions.