Harald Kallevik

Our current understanding of water-in-crude oil emulsions.: Recent characterization techniques and high pressure performance

Abstract Stable water-in-oil emulsions may form during the production of crude oil, as co-produced water is mixed with the oil from reservoir to separation facilities. Such emulsions introduce technical challenges, as they must be resolved to provide the specified product quality. Asphaltenes and resins indigenous to the oil are acknowledged as the most important components in respect to stabilization of the interface against coalescence. Fine solids may also contribute to the stabilization, as may the presence of naphthenic acids. Combined, this creates a complex picture of several contributing mechanisms, and it is established that the pressure conditions will influence the behavior of active components and the properties of the interface. In order to successfully mitigate the problems of stable emulsions, a thorough knowledge of component properties, behavior, interactions and effect on water/oil interfacial properties must be developed for pressures ranging from ambient to high. This review seeks to bring to light recent findings related to these topics.

Water-in-crude oil emulsion stability studied by critical electric field measurements. Correlation to physico-chemical parameters and near-infrared spectroscopy

Twenty-one crude oils and condensates of different origins have been thoroughly characterised including SARA (saturates, aromatics, resins, asphaltenes) data, interfacial elasticity, total acid number (TAN), density, viscosity, interfacial tension (IFT) and molecular weight. In addition all samples have been characterised by near-infrared (NIR) spectroscopy. A cell was developed to measure emulsion stability at applied electric fields. The cell produces values of stability of crude oil/water emulsions in a fast and simple manner. Emulsions of the 21 crude samples at different water cuts have been characterised by the electric field technique. The emulsion stability data have been correlated with both the physico-chemical data and NIR spectra. Asphaltene content and aggregation state, in addition to interfacial elasticity, are shown to be important contributions to emulsion stability as defined above. NIR spectra are shown to be informative with regard to emulsion stability.

The Role of Asphaltenes in Stabilizing Water-in-Crude Oil Emulsions

Stable water-in-oil emulsions may form during the production of crude oil, as coproduced water is mixed with the oil from reservoir to separation facilities. Such emulsions introduce technical challenges, as they must be resolved to provide the specified product quality. Asphaltenes and resins indigenous to the oil are acknowledged as the most important components in respect to stabilization of the interface against coalescence. Fine solids may also contribute to the stabilization, as may the presence of naphthenic acids. The combination of these components creates a complex picture of several contributing mechanisms to the stability of water-in-oil emulsions. It is also established that the pressure conditions will influence the behavior of active components and the properties of the interface. In order to successfully mitigate the problems of stable emulsions, a thorough knowledge of component properties, behavior, interactions, and effect on water/oil interfacial properties must be developed for pressures ranging from ambient to high. This chapter seeks to bring to light recent findings related to these topics. The theoretical and experimental impacts to create a better understanding of association phenomena and molecular interaction in oil-based systems are of recent date. One can say that these needs significantly emerge from the crude oil industry where a lot of problems of practical nature are closely related to colloid chemistry. In this chapter, we will concentrate on a description of water-in-crude oil (or model oil) emulsions and topics related to these. The coproduction of water and crude oil in the form of an emulsion is highly undesirable from a process and product quality point of view. When the crude oil is processed from the well head to the manifold, there is usually a substantial pressure reduction with a pressure gradient over chokes and valves where the

Crude Oil Model Emulsion Characterised by means of Near Infrared Spectroscopy and Multivariate Techniques

Abstract Water-in-oil emulsions are investigated by means of multivariate analysis of near infrared (NIR) spectroscopic profiles in the range 1100 — 2250 nm. The oil phase is a paraffin-diluted crude oil from the Norwegian Continental Shelf. The influence of water absorption and light scattering of the water droplets are shown to be strong. Despite the strong influence of the water phase, the NIR technique is still capable of predicting the composition of the investigated oil phase.

A New Procedure for Direct Precipitation and Fractionation of Asphaltenes from Crude Oil

A new precipitation and fractionation procedure was established where asphaltenes were precipitated successively by stepwise addition of pentane. The first fraction was obtained by mixing 3∶1 volumes of n‐pentane/crude oil followed by filtration. The following fractions were obtained by addition of more pentane to the crude oil with filtration between each step. Four fractions were precipitated with this procedure giving fractions based on a pentane‐to‐crude oil ratio of 3∶1, 10∶1, 15∶1, and 20∶1. Near infrared light at 1,600 nm was used to detect precipitation of asphaltenes in solutions of heptane and toluene. The asphaltenes precipitated showed an increasing solubility in heptane/toluene mixtures from the first precipitate to the last one. Interfacial tension was determined using the pendant drop technique. These measurements showed that the 10∶1 intermediate fraction exhibited a considerable reduction of the interfacial tension between toluene and water compared to the other fractions. Obviously the surface activity varies very much (almost by a factor of 2) between the different solubility classes within the asphaltene family. This may have large technical consequences within crude oil production and processing.

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.

Chemical Influence on the Formation, Agglomeration, and Natural Transportability of Gas Hydrates. A Multivariate Component Analysis

Abstract This study has focused on chemical components in two paraffinic oil phases, expected to have an influence on the properties of gas hydrates regarding formation, agglomeration, and natural transportability. Crude oil, toluene, wax, and naphtenic acids were selected for this purpose. Two paraffinic phases were used; n‐decane and Exxsol D‐80, the latter containing surface active material. The experiments were performed in a sapphire PVT‐cell. The use of experimental design and multivariate data analysis facilitates identification of the important chemical components. Interfacial tension measurements towards de‐ionised water were performed on the paraffinic solutions to gain more information on the interfacial phenomena.