Flow Behaviour of Water-in-North Sea Acidic Crude Oil Emulsions and Preparation of Synthetic Reference Acidic Oils and Their Emulsions
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Two phase liquid-liquid flow is described as the concurrent flow of two immiscible liquids, encountered widely in the petroleum industry during the production and transportation of oil and water. Good estimations of rheological and pipeline flow behaviours of these fluids are very important for proper processing and flow assurance assessment. However, despite of their importance, liquid-liquid flow behaviours have not been investigated to the same extent as gas-liquid flows for crude oils. Experimental investigations on liquid-liquid flow in a pipeline are mainly based on binary synthetic oils and water. Models reported in the literature are generally based on the synthetic oil experiments supported by additional field tests. The prediction models are based on the following input bulk liquid properties for each phase: density, viscosity, and interfacial tension. However, crude oil systems contain interfacially active substances (resins and asphaltenes) that influence the formation and stability of droplets. Consequently, liquid-liquid flow behaviours of crude oil systems are generally different from synthetic oil systems even if both systems have similar density, viscosity, and interfacial tension values. The skilled chemist needs to be able to model the behaviour of crude oil wherever the need arises. In particular, it would be valuable to be able to model crude oil behaviour in a pipeline where it will be mixed with water. Whilst crude oil itself could be used, this obviously involves transportation of the crude oil to wherever it is needed. Also, crude oil is a noxious substance and is ideally avoided as there are issues with toxicity, volatility, storage, and so on. There is also the issue of laboratory safety. Consequently, it would be a great deal easier if the research petrochemical chemist had at his disposal a composition that mimicked the behaviour of crude oil which could be used for modelling crude oil behaviour and transport properties. This work was developed within the aims of the project “Multiphase Flow Assurance Centre (FACE)” and has been two folded with an attempt to investigate interfacial, rheological and pipeline flow properties of North Sea crude oils and their emulsions and prepare synthetic oils for mimicking the bulk, interfacial, and flow behaviours of acidic crude oils and their emulsions. The influence of dispersed phase volume fraction, temperature, shear rate, and flow rate on rheological and pipeline flow behaviours of North Sea acidic crude oil emulsions were investigated in Paper 1. Paper 2 investigates the influence of the pH on the pressure drop, pressure gradient, viscosity, droplet size, and droplet size distribution of water-in-North Sea acidic crude oil emulsions in pipelines. Paper 3 aims to investigate the effect of aqueous phase pH on the dynamic interfacial tension behaviours of acidic crude oils. The paper 3 also aims to the find suitable synthetic oils and interfacial active molecules for mimicking the initial, equilibrium, and dynamic interfacial behaviours of acidic crude oils at various pHs. In paper 4 (patent application) aims for the preparation and characterization of synthetic reference oils for the North Sea acidic crude oil emulsions. The motivation for this work was to prepare synthetic reference oils mimicking the flow behaviours such as pressure gradient, pressure drop, viscosity, Reynolds Number, friction factor, inversion point, and in-situ droplet size of water-in-North Sea acidic crude oils emulsions in pipelines. The motivation for the paper 5 was to systematically investigate the rheological and pipeline flow behaviours of water-in-North Sea heavy crude oil emulsions at different aqueous volume fractions, temperatures, shear rates, and flow rates.