Phase Inversion, Stability and Destabilization of Model and Crude Oil Water-in-Oil Emulsions

Abstract

The demand for crude oils has constantly been increasing forcing the industry to exploit heavier crude oils. These oils are more difficult to produce and transport than classical light oils, this leads the oil industry to improve their processes. The production of oil also implies the formation of water-in-crude oil emulsions. The presence of dispersed water causes an increase of the viscosity and corrosion problems in the equipment that induce the production difficulties. This doctoral work has been part of the JIP-1 project “Increased Energy Savings in Waterin- Oil Separation Through Advanced Fundamental Emulsion Paradigms” funded by the Research Council of Norway (NFR) and an industrial consortium. The goal of this thesis is to study the phase inversion mechanisms of emulsions and develop new protocols to study emulsion destabilization. In a previous doctoral work,a it was shown that phase inversion of water-in-crude oil emulsions can occur in a pipe line when the water fraction is high enough. This causes a drastic decrease of the viscosity, which can be used to obtain an easier separation of both phases and an easier transportation. Phase inversion is therefore of interest and must be studied to gain a better knowledge of this phenomenon. One should employ techniques which can provide a higher level of detail, and low field NMR is a good candidate to achieve that purpose. In paper I two new low field NMR-based methods for tracking and studying phase inversion have been developed. The first method is able to monitor the phase inversion of an emulsion under continuous stirring conditions. The second provides the quantity of total water and the contribution of the emulsified water, which helps to identify double emulsion formation during the inversion process. These methods have been validated after being compared to classical techniques such conductivity measurements and optical microscopy. The phase inversion mechanisms were then studied in paper III by combining NMR surface relaxivity measurements, IFT measurements and dilational rheology. It is shown a change in interaction between surfactants when passing through a phase inversion. With the new developed methods validated in paper I, phase inversion has been studied in more relevant industrial systems such water-in-crude oil emulsions. It has been shown that model corrosion inhibitors can cause a phase inversion of crude oil emulsions, which might be of interest for economic and practical reasons. Due to regulation constraints, demulsifiers used in the Norwegian Continental Shelf must be more and more environmentally friendly. Consequently, a new low field NMR based protocol was used to compare new generation of environmentally friendly demulsifiers with already commercial demulsifiers (classified as red according to Norwegian legislation) in paper II. The low field NMR has been shown to be a very effective tool to study emulsion destabilization and provide information about demulsification mechanisms. The new generation of chemicals showed a lower efficiency than commercially available demulsifiers at low concentrations. The rheological properties of dense packed layers (DPLs) were studied in paper IV. These layers are commonly formed during gravitational separation processes but there is a lack of information regarding their fundamental properties which are important for further separation of oil/water. In this study model DPL were formed using asphaltenes dissolved in xylene. It is shown that asphaltene stabilized DPLs contained between 70 and 80 vol. % of dispersed phase and exhibit similar rheological properties as weak gels.