The measurement of static physico-chemical properties of oil-water interfaces provides a useful method of indicating where problem emulsion stability areas arise for water-in-crude oil emulsions and the effectiveness of chemical demulsifiers in resolving these problems. The paper in-cludes a discussion of interfacial tension, interfacial shear viscosity and interfacial film compressibility, particularly as applied to complex crude oil systems, and deals with the modification of these properties on the addition of a chemical demulsifier. Introduction Stable water-in-crude oil emulsions occur at many stages during the production and processing of much of the world's oil. The breaking of these emulsions, frequently by the a ddition of a chemical demulsifier, is an essential step. Factors that affect the stability of such emulsions, and the role played by the demulsifier in destabilizing them, are of paramount importance. Little experimental information exists for complex crude oil systems. It has been suggested"' that the structu-ral mechanical properties of the natural crude oil emul-sifiers in the interfacial layer surrounding the drop are important. This layer provides a resistance to coalescence in the final stage of emulsion breaking. The chemical de-mulsifier is thought to destabilize the emulsion by causing a disintegration of this layer at the interface. This work supports that viewpoint.Static physicochemical properties of crude oil/water interfaces have been evaluated over a variety of conditions and correlations with emulsion stability, particularly those TABLE 1. Dissolved salt influence on interfacial tension -Murban crude oil aqueous pha se Interfacial Tension (mNm-1) at 25'C Aqueous Phase pH 2 min 10 min 30 min Equilibrium encountered during oil production and processes, have been sought.Thus, the relevance of oil/water interfacial tension to emulsion formation and stability has been investigated. The influence of interfacial shear viscosity (and visco-elasticity) on the coagulation stage of emulsion resolution has been examined. Also, the resistance of interfacial films to expansion/compression has been studied and the effect on c:oalescence elucidated. Finally, modification of these physicochemical interfacial properties on the addi-tion of a chemical demulsifier has been investigated, with a view to determining the additive's ability to destabilize such emulsions. Interfacial Tension Oil/water interfacial tension changes were measured by the method outlined in reference (2). Previous work"I has shown that interfacial tension lowering alone is n ot an emulsion stabilizing factor. Table 1 shows the influence of various dissolved salts on y o/w of Ninian crude oil/ water interfaces. These systems have widely different emulsion !;tabilities at 25'C, yet the interfacial tension values are hardly different. Mass Transport As well as adsorption of surfactants at the interface, mass transport of water-soluble crude oil components across the oil/wtter interface will also influence the measured y o/@w lolver...

This spectroscopic and thermodynamic study of aqueous dimethyl sulphoxide (DMSO) suggests that the properties of the system are dominated by direct component interaction. Maximum interaction occurs in the region of 0.35 mole fraction (DMSO) and '' enhancement of water structure " by added solute is absent, except perhaps at very low concentration, cO.01 mole fraction. The excess enthalpy HE, is compared with literature values.

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Introduction This paper reviews the developments in the measurement of interfacial shear viscosities. A laboratory approach has involved the use of a biconical bob tension pendulum viscometer. The problems encountered in its use are explained, the special characteristics related to interfacial behaviour are detailed, and the relevance of the method to emulsion stability and enhanced oil recovery processes are discussed. Introduction Measurements of liquid/liquid and liquid/air interfacial shear viscosities have found relevance in such diverse studies as molecular interactions in polymer systems(1), transport processes(2), foam stability(3), emulsion stability(4) and displacement mechanism in enhanced oil recovery processes(5). Over the past few years, there have been significant developments in the measurement of interfacial shear viscosities(6–14). In many of these instances, a theoretical hydrodynamic analysis of the flow patterns in the neighbourhood of the liquid interfaces is presented. However, with very exceptions, these new approaches still possess shortcomings when applied to crude oil/water systems. In particular, it is a difficult task to design practical surface viscometers capable of giving interfacial flows with constant shear rates. Thus, the investigation of non-Newtonian interfacial flows is plagued by interpretation problems(8). Most approaches assume a Newtonian film behaviour. Hedge and Slattery(15) have proposed a method whereby the non-Newtonian character, frequently encountered with crude oil systems, can be estimated from a study of the complete velocity profile across the channel of a viscous viscometer. However, this technique, as well as others that rely on centre-line velocity measurements using PTFE markers, become extremely difficult when dealing with one liquid which is opaque (eg. crude oil). Wasan et. al.(13) have proposed a modified approach for the study of crude oil/water interfaces based on the canal viscometer of Mannhehner and Schechter(16). Here they propose the measurement of the centre-line velocity in the canal at the crude oil/ air interface when the canal contains only crude oil. They then set up a crude oil/water interface in the canal and remeasure the centre-line viscosity at the crude oil/air interface. These two results are then mathematically treated to reveal the crude oil/water interfacial viscosity. In view of the special difficulties encountered with crude oil, one approach that has been used in this laboratory(4,5,17,18) has been to make use of a biconial bob torsion pendulum viscometer. Although it has been pointed out that such a (Equation in Full Paper) device fails in the region of low interfacial viscosity(8), it is very effective for measuring high surface viscosities. It is the belief of the authors that only high interfacial viscosities are of practical significance in crude oil/water systems. The instrument provides a suitable approach for their measurement. The use of this apparatus, however, poses some problems (see Figure 1 and appendix). One must especially ensure that a reliable torque transmission property of the interface is measured. In particular, three problems are frequently encountered, viz:Does slip occur at the extremities of the interfacial annulus (i.e. at the bicone bob or at the glass container wall)?

Direct measurement has been made of the forces acting during immiscible displacement in a capillary system of model geometry. The aim of this study is to obtain better understanding of the microscopic displacement mechanism, and to determine how these processes may be characterized in terms of the interfacial properties of the system. The parameters measured include the interfacial tension, the wettability and the interfacial rheology. A range of crude oil/aqueous phase systems representing a range of interfacial rheological characteristics has been examined. The implications of the various interfacial characteristics for immiscible displacement during oil recovery are discussed. Introduction The development and optimization of chemical Enhanced Oil Recovery (EOR) systems is based on our understanding of the mechanisms by which oil is displaced from a porous matrix, and of the parameters which control those mechanisms. Better insight into the displacement processes is required than is afforded by "black box" experiments such as displacement tests in sand packs. It is therefore necessary to carry out laboratory experiments concerned with specified system parameters, and to link the results of these experiments with displacement tests. The most commonly applied measurement used in this way is of interfacial tension, which is linked to displacement tests via intuitive conceptual models of the displacement process. In the development of EOR systems based on waterflooding, the generation of a very low interfacial tension is often considered to be of paramount importance(1.2). However, it is also recognized that a system with a low interfacial tension is not by itself certain of success as the basis of an EOR process(3,4). Hence, the measurement of an equilibrium (or steady-state) interfacial tension is a valuable screening test, but other parameters are also relevant to the dynamic process of oil recovery. This paper focusses attention on these dynamic processes. Its scope is limited to consideration of the local microscopic immiscible displacement mechanisms in capillary-size pores; thus, interfacial properties dominate the over-all system behaviour. The use of model capillary systems is widely reported in the literature. Blake, Everett and Haynes(5) have previously pointed out that immiscible displacement in even a single cylindrical capillary is associated with radial flow near the interface, so that a dynamic interfacial tension will apply. Blake et al.(5) reported measurements of displacement rate as a function of dynamic contact angle and pressure gradient for pure oil/water systems in a single cylindrical glass capillary. Capillaries of the same geometry were used by Hansen and Toong(6), who reported displacement phenomena other than the piston-like mode. Templeton(7) described the break-up of a crude oil/water interface during displacement in a single capillary, and confirmed the applicability of Poiseuille's law in micron-size capillaries. The potential importance of hydrodynamic effects in the interfacial region and the paucity of information concerning them has been highlighted by Dussan(8), who emphasized the importance of this topic in understanding surfactant behaviour. None of the above studies were able to give an instantaneous measurement of displacement pressure, and hence they were unable to examine the effects of changes in capillary geometry.