Iradj Rahimian

Influence of the crude oil resin/asphaltene ratio on the stability of oil/water emulsions

Abstract During the production of crude oil, water/oil emulsions are formed. They are stabilized by asphaltenes and resins which are colloidally dispersed in the crude oil. Asphaltenes consist mainly of polar heterocompounds. It is known that they decrease the interfacial tension between oil and water and form stable interfacial films. Both effects favour the formation and stabilization of emulsions. Crude oil resins consist mainly of hydrocarbons. Their interfacial activity is less than that of asphaltenes, and they are known to peptize the asphaltenes. Their influence on the formation and stability of emulsions in the presence of asphaltenes is, however, not well understood. This study investigates the influence of resins from different crude oils as well as of different resin/asphaltene ratios dissolved in decahydronaphthaline as model system on • colloidal stability of model oils • interfacial tension between model oil and distilled water • stability of emulsions formed from model oils and brine • effectiveness of demulsifiers • viscosity and droplet size distribution of emulsions It was found that (1) the influence of resins in the presence of asphaltenes on the properties of emulsions is independent of the origin of the resins, i.e. of the oil, from which they are obtained, and (2) high resin/asphaltene ratios decrease the emulsion stability.

Thermodynamics and mechanis of stabilization and precipitation of petroleum colloids

Abstract The influences of different factors on the stability of colloid disperse crude oil systems are investigated by determining the flocculation points. The results are discussed on the base of theory of regular solutions considering the influence of solvation on the kinetics of chemical processes in liquid phases. Analogy to the behavior of polymer solutions was found. Differences result from the micelle structure of colloid particles. The criterion of metastability using nonpolar precipitants is defined by the Flory-Huggins interaction parameter. Using polar precipitants, the polar interactions and the solvation of asphalt require to use the Hansen solubility parameter to interpret the results. The influences of conditions of precipitation and of surfactants are discussed also.

Theoretical and practical approach to the selection of asphaltene dispersing agents

Abstract To evaluate the interaction forces between asphaltenes and amphiphilic compounds influencing the colloid stability of crude oils during the production, transport and processing, the cohesion energy parameters according to Hansen are used. Calculating the cohesion energy parameters of different homologous series, it was found that a stabilising effect can be expected if the dispersion interactions of amphiphilic compounds correspond with that of asphaltenes and the hydrogen bonds are in the region of 10 [MJ m−3]0.5. Flocculation point determination and thermogravimetric analysis were used to verify this experimentally.

EFFECT OF ASPHALTENE AND RESINS ON THE STABILITY OF WATER-IN-WAXY OIL EMULSIONS

ABSTRACT Asphaltene, resins and paraffin waxes, their mutual interactions and their influence on the stability of water-in-oil emulsions have been studied. 20 wt % paraffin wax dissolved in decalin was used to model the waxy crude oil. Asphaltene and resins separated from a crude oil were used to stabilize the water-in-oil emulsions. Synthetic formation water was utilized as the aqueous phase of the emulsion. The emulsion stability increased with increasing the concentration of asphaltene with a subsequent decrease in the average particle size distribution of the emulsion. Resins alone are not capable of stabilizing the emulsion, however, in the presence of asphaltene they form very stable emulsions. Dynamic viscosity and pour point measurements provided evidence for resins-paraffin waxes interactions. Asphaltene in the form of solid aggregates form suitable nuclei for the wax crystallites to build over with a mechanism similar to that of paraffin wax crystal-modifiers. As asphaltene are polar in nature they are derived at the oil/water interface which was proved by the ability of asphaltene to reduce oil/water interfacial tension. Consequently, nucleation of the wax crystallites by asphaltene and resins at the interface will add to the thickness of the oil-water interfacial film and hence increase the stability of the emulsion.

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. I. EXPERIMENTAL DETERMINATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was investigated in the pressure range from 1 to 300 bar and at temperatures of 55, 75, and 100°C. Methane was employed as gas component, and i-octane was used as precipitant. The onset of flocculation was determined with a light intensity meter. Three crude oils of different provenance were chosen for the investigations. The crude oils were stabilized in a rotary evaporator at 50 mbar and 180°C, and a part of stabilized products were mixed with different amounts of n-octane or methylcyclohexane. The dependence of the onset of flocculation on the pressure is analogous for all products. The required volume of i-octane decreases strongly with pressure up to 100 bar. Above 100 bar the influence of the pressure diminishes. This dependence corresponds with the solubility of methane in crude oil products. The amount of light hydrocarbons determines the position of the pressure dependence of the onset of flocculation. Without the addition of i-octane, the onset of flocculation could not be ascertained. The observed kinetics of flocculation depends on the asphaltene content as well as on the pressure. The influence of dispersing agents was also examined.

THE COLLOIDAL STABILITY OF CRUDE OILS AND CRUDE OIL RESIDUES

A crude oil and three residues of the crude oil processing were investigated by determination of flocculation points of both the product solutions and the original products. Diverse analytical methods were used for characterizing products and their fractions. The evaluation of results was performed by the theory of regular solutions and its extension by Hansen. It was found, that the colloidal disperse phase shows a behaviour similar to that of polymer solutions. The conditions of the destabilization of the colloids can be defined by the critical Flory-Huggins interaction parameter. The solvation and the low soluble part of the asphaltenes have the greatest influence on the colloidal stability. The lowest stability is found for the visbreaking residue. The influence of the crude oil distillation on the colloidal stability is not significant.

Hydrodenitrogenation of Aleksinac shale oil distillates in a pilot trickle-bed reactor

Abstract Hydrodenitrogenation (HDN) of the Aleksinac shale oil distillates was studied in a pilot trickle-bed reactor at 340–435°C, 8.0 MPa, 1–4.57 h−1 liquid hourly space velocity (LHSV) and 500 cm3 (STP) of H2/cm3 oil. The commercial Co  Mo Al 2 O 3 and Ni  Mo Al 2 O 3 presulfided catalysts were evaluated for the HDN of three different shale oil distillates. The initial HDN catalyst deactivation was followed using a linear catalyst deactivation model. The Ni  Mo Al 2 O 3 catalyst showed somewhat higher initial HDN activity and lower initial deactivation rate than the Co  Mo Al 2 O 3 catalyst for the first 30–45 h on shale oil feedstock. Nitriles in shale oil first undergo HDN reaction at mild operating conditions, much faster than five- and six-membered nitrogen heterocyclic compounds. The overall HDN kinetics of refractive nitrogen in shale oil was analyzed using a modified pseudo-first-order behavior. The on-line measured hydrogen consumption was in the range 200–300 cm3 (STP)/cm3 for HDN > 80% regardless of the catalyst type and feedstock.

Pyrolysis of oil shale in a microretorting unit

With the aim of investigating the dependence of shale oil composition on pyrolysis conditions (temperature and time), a laboratory microretorting unit was constructed which enabled experiments to be conducted under isothermal conditions with ~ 20 g of oil shale, and allowed the collection of four to six fractions of shale oil. The details of the microretorting unit are presented, as well as the results of preliminary investigations. The composition of shale oil and gas produced by pyrolysing Aleksinac oil shale under isothermal conditions (420–520 °C) was determined using column and gas chromatography, 13C n.m.r. spectroscopy and elemental analysis. The results showed that a pyrolysis temperature between 450 and 480 °C gave the highest quantity of aliphatics and the lowest quantity of aromatics in the product.

ORGANIC PRECIPITATES IN OIL PRODUCTION OF A VENEZUELAN OIL FIELD

A very light crude oil is being produced in an oil field in Venezuela. Such oils are susceptible to asphaltene precipitation as the reservoir pressure decreases during production. An asphaltene deposit has been found in the tubing of one of the wells and in the bottom sediment of the tanks on site. Dead oil samples from the well head of seven different producers in the field were analyzed by three different companies. The laboratory results covering the following aspects of different solvents show significant differences: asphaltene content, asphaltene/resin ratio, molecular mass of the precipitated asphaltenes, flocculation point, Vanadium/nickel ratio, precipitated asphaltenes, and the Hildebrand parameter. Using different consistency checks and establishing correlations among the results, the analysis of one lab is strongly favored against the others. The analytical results are discussed in detail, including the correlation between asphaltenes and the well situation regarding perforation depth and the phase behavior of the produced oil.