Harald Førdedal

Crude oil emulsions in high electric fields as studied by dielectric spectroscopy. Influence of interaction between commercial and indigenous surfactants

The behaviour of different types of water-in-oil emulsions in high electric fields as investigated by means of time-domain dielectric spectroscopy (TDS) is reported. The studied emulsions include true crude-oil-based ones as well as model systems stabilised by indigenous crude oil fractions or, alternatively, by commercial nonionic surfactants. It is seen that the developed TDS equipment gives a good quantitative measure of the emulsion stability. The emulsion stability in crude oil systems can be modelled by the separated asphaltene fraction as far as coalescence is considered. Although the resin fraction might be even more interfacially active than the asphaltenes, it cannot alone stabilise the w/o emulsions. The importance of the interplay between the asphaltenes and resins is clearly revealed. When commercial surfactants (ethoxylated nonyl phenols, NP-EO or monoalkyl sorbitan esters) are combined with the separated crude oil fractions, different levels of compatibility are displayed. The addition of a tetraoxyethylene nonyl phenol ether (NP-4), for instance, completely destabilises the original emulsion, although a high level of interfacial activity is retained in the system.

COMPLEX PERMITTIVITY OF CRUDE OILS AND SOLUTIONS OF HEAVY CRUDE OIL FRACTIONS

ABSTRACT Dielectric spectroscopy is considered as an interesting method for determination quality parameters like density, viscosity and interfacial properties of petroleum fluids. In this paper are the mechanisms important for the dielectric properties of crude oils studied for development of new charaterising methods.

Lipoamino acid association in the system Nα-lauroyl-l-arginine methyl ester—1-pentanol—water as studied by dielectric spectroscopy

Abstract The system N α -lauroyl arginine methyl ester— 1-pentanol—water has been investigated by means of dielectric spectroscopy according to the time-domain method in the frequency range 20 MHz–2 GHz. The relaxation time τ in the liquid crystalline phase (D) and in the solution phase (L) is attributed to a Maxwell—Wagner—Sillars mechanism. The distribution of Cl − ions between different parts of the electric double layer will cause changes in τ. The level of the static permittivity ϵ s is determined from different geometries of the aggregates in the solution phase. The phase transition D → L could be accurately determined by means of dielectric relaxation measurements.

EMULSIONS CHARACTERIZED BY MEANS OF TIME DOMAIN DIELECTRIC MEASUREMENTS (TDS). TECHNICAL APPLICATIONS

ABSTRACT The authors have in previous contributions determined dielectric properties of W/O-emulsions by applying the Time Domain Dielectric Spectroscopy technique. The main findings are summarized here. The influence of droplet shape and flocculation on the dielectric parameters characteristic of the emulsions is discussed. A technique developed for a dielectric investigation of electrically induced coalescence is demonstrated, together with experimental results from surveys on emulsions stabilized both by commercial and natural surfactants.

Asphaltene and Resin Stabilized Crude Oil Emulsions

Asphaltenes can have crucial impact on several stages of production of crude oils. First of all, asphaltenes can precipitate in the well or in the formation and cause severe formation damage, and in the worst case the well might be shut down. Second, asphaltenes cause problems if they deposit on the steel walls in the production line. They can also be transported along the production line and accumulate in separators or in other fluid processing units.

A dielectric spectroscopy study of the system tetraoxy ethylene dodecylether (C12EO4)/water/copper nitrate/cyclohexane

Abstract The system tetraoxyethylene dodecylether (C 12 EO 4 )/water/cyclohexane was investigated with and without Cu(NO 3 ) 2 by dielectric spectroscopy. Addition of Cu(NO 2 ) 2 to the lamellar liquid crystal induced a dielectric dispersion. The location and magnitude of this dispersion were dependent on the ionic diffusion in the aqueous channels. In the W/O microemulsion phase, only the elongated aggregates containing Cu(NO 3 ) 2 showed a dielectric dispersion. All the effects observed could be explained by the fact that Cu(NO 3 ) 2 behaved as an ordinary electrolyte; no indication of small particle formation or other associations was observed.

GAS HYDRATE FORMATION IN COLLOIDAL MATRICES

ABSTRACT The hydrocarbon rich phase (L2) of the system trichlorofluoromethane CCl3F / water (electrolyte) / nonionic surfactant has been investigated by means of NMR self-diffusion measurements, and dielectric spectroscopy. The dielectric spectra were recorded between 50 MHz and 5 GHz and fitted to a Cole-Cole model function with an additional Debye term. The main relaxation was due to a polarization inside the aqueous droplets (Maxwell-Wagner-Sillars relaxation). The NMR self-diffusion data display a low molecular self-diffusion for both water and surfactant over a broad interval consistent with a droplet structure. However at the highest CCl3F concentrations the rapid diffusion of the nonionic surfactant reveals that the aqueous droplets are most likely stabilized by means of gas hydrates at the w/o microemulsion interface.

Interactions between drugs and nonionic lamellar liquid crystals as studied by dielectric spectroscopy and phase equilibria

Abstract Dielectric properties of nonionic lamellar liquid crystals with and without electrolytes and pharmaceutical drugs are reported in the frequency range 40 MHz to 2 GHz. In the aqueous C 12 EO 3 lamellae sodium chloride and pilocarpine chloride both give rise to a dielectric dispersion. The nonionic chloramphenicol is completely incorporated into the interfacial region or imbedded into the hydrocarbon part of the model membrane, without giving rise to any dispersion. With added ionic surfactants the membrane surface becomes charged and all systems show a dielectric dispersion. Qualitatively, the findings can be explained by means of counterion behavior at the membrane surface (surface diffusion) or freely diffusing counterions in the aqueous layer. When the lamellar liquid crystalline phase is melted the dielectric dispersions vanish.