Andreas Hannisdal

Emulsions of Heavy Crude Oils. I: Influence of Viscosity, Temperature, and Dilution

Twenty‐seven crude oils of different origin have been systematically analyzed with regard to viscosity, density, molecular weight, and SARA (saturates, aromatics, resins, asphaltenes) fractionation. Emulsion stability of water‐in‐oil emulsions of the different crude oil samples have been measured by the critical electric field technique (E‐critical). In addition, droplet size distributions for some of the water‐in‐oil emulsions have been determined by NMR self‐diffusion. Rheology measurements show that some of the crude oils have Bingham plastic type flow behavior at temperatures below 20°C, indicating content of waxes. Analysis of the critical electric field measurements shows that the E‐critical value depends on the applied electric field gradient. At low applied electric field gradients, the droplets are given more time to organize into water‐continuous bridges, resulting in a lower E‐critical value than when the applied electric field gradient is higher. The value of E‐critical also increases as the volume of the water phase decreases, due to the increased distances the droplets must move to form linear chains between the two electrodes. E‐critical measurements of emulsions of diluted crude oils show that, in general, the emulsion stability decreases with increased dilution of the oil phase. However, some systems show regions where the emulsion stability is independent of the dilution ratio or viscosity of the crude oil. Here the coalescence rate controls the level of emulsion stability. Viscosity and emulsion stability for water‐in‐oil emulsions were measured for the complete crude oil matrix (27 crude oils), and in general there is an increase of the emulsion stability as the viscosity increases. However, viscosity also correlates well with the SARA data of the crude oils. E‐critical shows a temperature dependence according to the Arrhenius law.

Viscoelastic Properties of Crude Oil Components at Oil‐Water Interfaces. 1. The Effect of Dilution

The dilational viscoelastic properties of diluted crude oil‐water interfaces have been studied using the oscillation drop method. The study focuses on the effect of altering aromaticity of the solvent and the concentration of the crude oil on the viscoelastic response of the crude oil‐water interface. Dynamic interfacial tension experiments (pendant drop), asphaltene aggregation state experiments (near‐infrared spectroscopy) and emulsion stability experiments (bottle test) have complemented the studies of interfacial rheological parameters in order to understand the mechanisms of film formation and emulsion stabilization. The overall w/o‐emulsion stability seemed to be determined by the aggregation state of asphaltenes in bulk and the reduced sedimentation rate of water droplets in concentrated systems. The storage E′ and loss E″moduli of the crude oil/water systems were determined with dilation rheology. At a perturbation frequency ω =0.1 Hz, the equilibrium storage and loss moduli passed through distinct maxima as a function of bulk concentration. The apparently low viscoelasticity of the interfaces in systems with high bulk concentration was probably caused by high diffusion flux of interfacially active components from bulk and was not entirely due to interactions within the adsorbed layers. Dilation experiments at other perturbation frequencies confirmed this phenomenon. Results have been discussed in connection with recent findings regarding the stabilization of water‐in‐oil emulsions.

Viscoelastic Properties of Crude Oil Components at Oil‐Water Interfaces. 2: Comparison of 30 Oils

The dilational properties of diluted (0.7 vol/vol in toluene) and undiluted crude oil‐water interfaces have been studied using the oscillation drop method with the objective of understanding the properties contributing to the overall stability of crude oil emulsions. The importance of working with undiluted crude oils instead of model systems when dilational properties of real oil‐water systems are going to be reproduced in the laboratory setting has been discussed. For such studies, molecular exchange mechanisms and the aggregation state of asphaltenes are too dependent on concentration to justify the use of model compounds, i.e. fractionated asphaltenes diluted in a solvent. As expected in the low frequency range (0.01–1 Hz), molecular exchange from the bulk oil phase strongly affected the measured dilational parameters. For the diluted crude oils, the frequency dependence of the dilational modulus increased with its magnitude. The systems that exhibited particularly low magnitude of the dilational modulus were of the heaviest crude oils in the sample set, whereas the systems with greatest dilational modulus were among the lightest crude oils. The overall characteristic time of relaxation of the crude oil‐water interfaces was in the range below 10 seconds. The undiluted crude oil‐water interfaces had similar interfacial properties as the diluted samples except for slightly reduced magnitude of the dilational modulus. The crude oil‐water interfaces appeared to be soluble, but some observations pointed to intrinsic rheological properties of the interfaces. Intrinsic elasticity and viscosity of the films should be studied outside the frequency range used here at low (ω∼0 Hz) and high (ω→500 Hz), respectively.

An Electrorheological Study on the Behavior of Water‐in‐Crude Oil Emulsions Under Influence of a DC Electric Field and Different Flow Conditions

The influence of an applied DC electric field on viscosity and droplet size distribution of different water‐in‐crude oil emulsions was monitored in order to investigate the induction of coalescence of the water droplets. The effects caused by the voltage imposition were studied by rheological analysis and the validity of the obtained results was discussed, comparing with the features of real electrocoalcscer systems. A low field NMR technique (CPMG NMR) and digital video microscopy (DVM) were used to elucidate the behavior of the emulsions. Experiments performed at low shear rate with increasing electric field magnitude showed an increase in viscosity until a critical value. ECRIT was reached. Thereafter coalescence occurred and viscosity decreased irreversibly below its initial value. The electrorheological behavior of the emulsions can be attributed to the organization (flocculation) of water droplets induced by the electric field, accompanied by an increase in viscosity. The structure breaks down as the shear rate is increased, leading to a decrease in viscosity. Experiments performed at high shear showed only a small decline in the viscosity. Although it was evident that coalescence took place, it did not involve the whole sample, because the electrodes were uncoated. As a direct consequence, the mean value of the droplet size within the emulsion did not change noticeably. Nonetheless this mean value was less recurrent and the formation of droplets of very large diameter occurred.

Solubility Parameters Based on IR and NIR Spectra: I. Correlation to Polar Solutes and Binary Systems

IR and NIR spectra were correlated to Hildebrand and Hansen solubility parameters through use of multivariate data analysis. PLS‐1 models were developed and used to predict solubility parameters for solvents, crude oils, and SARA fractions. PLS regression showed potential for good correlation of the solubility parameters with IR and NIR spectra. Principal component analysis of IR spectra showed that crude oils are grouped according to their relative contents of heavy components such as asphaltenes. PCA of IR spectra for SARA fractions resulted in obvious groupings of the respective fractions. Prediction of solubility parameters from IR spectra of polymers, crude oils, and SARA fractions gave values that are comparable to literature values. This study indicates that correlation of solubility parameters with IR and NIR spectra is possible. In turn, it may be possible to develop models that can predict the polarities of crude oils and crude oil fractions such as resins and asphaltenes.

Dehydration Efficiency of Water-in-Crude Oil Emulsions in Alternating Current Electrical Fields

The influence of several operational variables on the electrostatic separation of water-in-crude oil emulsions is investigated in a concentric cylinder rheometer equipped with an alternating current (AC) generator. Shear rate, temperature, emulsion water content, electric field strength, and application time are all found to play a role in the process. The droplet size distributions achieved across some of the experiments are acquired to give further support to the conclusions. Finally, the experimental results are compared to the theoretical expression for the electrocoalescence process and discussed.

Emulsions Stabilized by Indigenous Reservoir Particles: Influence of Chemical Additive

Interfacially active inorganic particles from the reservoir are often produced together with crude oil. These fines can have a tendency to accumulate at the water/oil interface and eventually stabilize w/o and o/w emulsions. The properties of the particles will change through interactions with indigenous crude oil components and also with added production chemicals. In this work focus has been towards a real system with particles sampled from the separator located on an installation on the Norwegian continental shelf. Stabilizing properties of different particle fraction has been studied (for both oil and water continuous emulsions). It is reported that the solids interact strongly with chemical additives. Silicon oil, used as foam inhibitor during production, adsorbs to the limestone particles and alters the properties of the fines dramatically.

Stability of Water/Crude Oil Systems Correlated to the Physicochemical Properties of the Oil Phase

A characterization of 30 crude oils has been performed to determine the relative level of influence that individual parameters have over the overall stability of w/o emulsions. The crude oils have been analyzed with respect to bulk and interfacial properties and the characteristics of their w/o emulsions. The parameters include compositional properties, acidity, spectroscopic signatures in the infrared and near‐infrared region, density, viscosity, molecular weight, interfacial tension, dilational relaxation, droplet size distribution, and stability to gravitationally and electrically induced separation. As expected, a strong covariance between several physicochemical properties was found. Near‐infrared spectroscopy proved to be an effective tool for crude oil analysis. In particular, we have showed the importance of the hydrodynamic resistance to electrically‐induced separation (static) in heavy crude oil‐water emulsions. A rough estimate of the drag forces and dielectrophoretic forces seemed to capture the difference between the 30 crude oils. Given enough time, water‐in‐heavy oil emulsions could be destabilized even at very low electric field magnitude (d.c.). When droplets approach each other in an inhomogeneous electric field, strong dielectrophoretic forces disintegrate the films and result in coalescence. The relative contribution from film stability to the overall emulsion stability may therefore be very different in a gravitational field compared to that in an electrical field.

Emulsions of Heavy Crude Oils. II. Viscous Responses and Their Influence on Emulsion Stability Measurements

The stability of 30 heavy crude oil emulsions was studied in a parallel-plate laboratory coalescer (DC field). Particularly, viscous responses and their influence on the emulsion stability measurements were investigated. In addition to highlighting previous results from the same experimental setup and discussing these based on recent experience, new results at different temperatures and volume fractions of water were presented. A new semi-empirical model for the characteristic time of the destabilization process was presented. The electrical forces were modelled with a point-dipole approximation and the hydrodynamic resistance to droplet transport was modelled with an empirical term including the logarithmic viscosity of the oil phase. The new model clearly performed much better than the previous model, particularly for very viscous crude oils. Studies of the performance of industrial electrocoalescers have showed that simple electrostatic theory can potentially explain complex separation phenomena when the resistance to the coalescence step is reduced by an efficient demulsifier. The ultimate goal is to build a model for both the laboratory setup and the industrial coalescer so that laboratory experiments can be used to predict the behavior of the industrial process.

On the nonsingle-site character of Bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride/MAO and Bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride/MAO: polymerization characteristics and mechanistic implications.

Ethene polymerization with bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride (1)/MAO and bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride (2)/MAO and ethene-co-1-hexene polymerization with 1/MAO are presented. The end group analysis of homopolymers reveals a pronounced dependence of the termination rate on temperature changes. In combination with the high molecular weights obtained, these results are in accord with theoretical predictions. Gel permeation chromatography, Fourier transform infrared, and 13C NMR analyses of copolymerization products from 1/MAO as a function of comonomer concentration at two different temperature series denote its tendency to form inhomogeneous polymer blends. Thermal analysis and fractionation results of one such blend indicate an inhomogeneity in the enchainment process and the existence of multiple active sites of differing geometry. These indications are further supported by AMBER force field and density functional theory studies of the catalyst precursors and the active site of 1/MAO. For this system, delta-agostic interactions for the stabilization of the zirconium cation are favored over beta-agostic interactions, which, in contrast to the situation in studies on bis-Cp systems, is a sparsely populated species. The gap in activation enthalphies for beta-hydride transfer and elimination is marginalized for these bulky zirconocenes, and conceptually new mechanisms for the isomerization of the vinyl end groups are discussed. Further, unexpected activation of the silicon-hydrogen bond within the ligand framework is observed with an activation enthalpy as low as 14 kcal/mol.