Tore Skodvin

STABILITY OF WATER-IN-CRUDE OIL EMULSIONS: ROLE PLAYED BY THE STATE OF SOLVATION OF ASPHALTENES AND BY WAXES

Abstract The stability of water-in-crude oil (or model crude oil) emulsions was determined by means of separation/sedimentation tests and high voltage destabilization tests. First the impact of the state of solvation of asphaltencs on their ability to stabilize emulsions were studied. Secondly, we analyzed the role of naturally occurring waxes in the stabilization of emulsions. Finally, the emulsion stability when both asphaltenes and waxes are involved was investigated.

Dielectric Spectroscopy and Emulsions. A Theoretical and Experimental Approach

ABSTRACT The theoretical interpretation of experimental data from the previous papers (1,2) are extended with the purpose to demonstrate the possibilities of a qualitative characterisation of flocculated emulsions by means of dielectric spectroscopy. Both low and high frequency limits of dielectric spectra are analysed, which is an extension of our previous paper (1) where only low frequency values were interpreted. Attention is paid to the emulsion stability with regard to flocculation in a dielectric spectrum. The influence of salt concentration inside the aqueous droplets in the dispersed phase is interpreted. The theoretical interpretation is based on a generalised model of the flocculated state, where floes are characterised not only by their shapes, but also by their volumes. The information of floe properties obtained by means of dielectric spectroscopy, and different hydrodynamic estimations characterising the flocculation process is compared and correlations are established.

DIELECTRIC PROPERTIES OF W/O EMULSIONS UNDER FLOW

ABSTRACT Water-in-oil model emulsions with various amounts of the aqueous phase, i.e. 24 to 74 % by volume and with 4% NaCl, have been characterized by means of time domain dielectric measurements in the frequency region 50 MHz to 2 GHz. The measurements were carried out in a flow loop which made it possible to do the characterization of the emulsions both under flow and at rest. The flowing emulsions show in general lower static permittivities than the corresponding emulsions at rest. The dielectric data are explained by models involving a flocculation of the aqueous droplets. The result indicate just a small deviation from sphericity of the formed floes.

Optical monitoring of low-field magnetophoretic separation of particles

We describe the design and testing of a low-cost optical sensor for monitoring separation of magnetic micro and nanoparticles in low magnetic field gradients. The sample is placed in a vertically aligned test tube, where the magnetic field gradient and the gravitational field are both in the same direction, such that the magnetophoretic velocity can be calibrated against a known value. We describe methods for extracting the magnetophoretic velocity using two different theoretical approaches, one based on linear interpolation and another based on fitting to a physical theory implementing a time-dependent version of Beers law. We discuss strengths and weaknesses of the two approaches. We show that the sensor can be used to detect particle aggregation in polymer solutions. We also show that the magnetic field gradient may alter the size distribution of the aggregates, which is detected as larger intensity fluctuations and nonlinear response.

Dielectric spectroscopy on W/O emulsions under influence of shear forces

The dielectric properties of concentrated w/o-emulsions have been investigated, both at rest and during shear. The volume fraction water ranged from 0.50 to 0.95. The time domain dielectric spectroscopy techniques (TDS) was used to record the dielectric spectra, which covered the frequency region from 25 MHz to 2 GHz. In order to simultaneously record rheological and dielectric data a modified viscometer of the coaxial cylinder type was applied.A close connection between the viscosity and the dielectric properties of w/o emulsions is demonstrated. The very large effects of shear both on the static permittivity and the dielectric relaxation time for the emulsion can partially be ascribed to the degree of flocculation in the system. At high shear rates, at which the emulsions are expected to have a low degree of flocculation, the observed dielectric properties differ from those expected from a theoretical model for spherical emulsion droplets.

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.

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.

Characterization of carbon black modified by maleic acid

We present here a method for modifying the surface of carbon black (CB) using a simple heat treatment in the presence of a carboxylic acid as well as water or ethylene glycol as a solvent. CB was mixed with maleic acid and either water or ethylene glycol, and heated at 250°C. Unlike the traditional surface modification processes which use heat treatment of carbon with mineral acids the present modification method using a carboxylic acid proved to be simple and time efficient. CB from two different vendors was used, and the modified samples were characterized by TGA, BET surface area measurement, XRD, particle size and zeta potential measurements, and FTIR. It was found that several material properties, including thermal stability and surface area, of the modified CB are significantly altered relative to the parental carbon samples. This method provides a rapid and simple route to tailor new materials with desired properties.

A time domain dielectric spectroscopy study of some model emulsions and liquid margarines

Abstract A dielectric study, using time domain spectroscopy, of model water-in-triglyceride emulsions with and without added NACl in the frequency interval 10 MHz to 10 GHz is reported. It is shown that the static permittivities can be explained from a model permitting a slight flocculation of the aqueous droplets. The relaxation times were interpreted by means of a Maxwell—Wagner—Sillars mechanism which was verified by the salinity dependence. The experimental findings in the model systems were also reproduced in samples of real liquid margarines.

Colloid chemistry and modern instrumentation in offshore petroleum production and transport

A summary of the central problems of a colloidal chemical nature in offshore crude oil production and transport is presented. It is concluded that emulsified systems, mainly water/oil, are of high importance. Under North Sea conditions these emulsions will become increasingly important with the ageing of fields in production and with the exploitation of new marginal fields. Spectroscopic techniques applied to characterize emulsified systems are also presented.