Predictions of Water-in-crude Oil Emulsion Stability From Chromatographic Data

Abstract

Abstract Following a recent method which aims to characterize solvents in terms of given solute-solvent molecular interactions, a general solvation linear free energy relationship (LSER) equation was devised by Abraham and used in gas chromatography with crude oils as stationary phases to calculate molecular interaction. terms According to these terms and to information relatedto the bottle test, a new decision model has been set up to predict the stability of water-in-crude oil emulsions. It requires two discriminant functions taking into account two interaction terms characterizing hydrogen bonds and polar interactions. Of the 24 crude oils selected from miscellaneous geographical and geological origins 80% were correctly classified in three categories related to emulsion stability. Therefore, this model permits us to estimate the stability of water-in-crude oil emulsions and provides knowledge, which can be used in the selection of optimal conditions for the oil recovery process. Introduction In the petroleum industry, emulsions of oil and water are one of the many problems encountered. These emulsions have widespread occurrence in petroleum recovery and they may be desirable or undesirable(l). So the evaluation of the stability of emulsion systems and the selection of optimal conditions for the oil recovery process must be closely scrutinized. Most of the crude oil emulsions formed in the oil field are of the water-in-oil type. They vary from one field to another and many scientific disciplines are involved in their study and treatment, but the fundamental explanation of this phenomenon is now well known. Emulsions are normally prepared by shaking two immiscible liquids like oil and water and usually some kind ofemulsifying agent has to be added to stabilize the product. Small droplets are then produced and the stability of these droplets depends upon a number of factors: the ratio of the phase volume, the mechanical shear forces, some physical parameters and the chemical composition. If the three first factors are fixed, then emulsion stability could be approached from different sides of the chemical composition. Regarding the molecules in a crude oil, two types of them could be distinguished to explain bulk viscosity properties and interfacial properties. Conventional analytical techniques and classical methods as separative, spectrometric, and statistical tools(2, 3) have been applied to correlate chemical composition of crude oils and their properties or behaviour in production(l, 4–6). But crude oils are very complex mixtures and chemical composition analysis is limited. Moreover, the importance of the amount of some chemical species in explaining the crude oils behaviour is different from one crude oil to another. So it seems to be more interesting to study molecular interactions rather than the chemical composition(7–9). To be more precise, the process of emulsification is governed by surface forces(l) which depends upon intermolecular forces. These forces have been classified in non specific forces (Keesom, Debye, and London) usually known as van der Waals forces and specific forces or hydrogen bonding.