Investigation of the role of chemical composition on the weathering and emulsification behaviour of North Sea crude oil

Abstract

The exploration, production, transportation and refining of petroleum often pose great technical and environmental challenges to the oil and gas industry. It is therefore extremely important to reliably predict and control fluid behaviour, in order to optimize production cost and for purposes of potential environmental pollution in the oil and gas operational activities. The investigations in this work focuses upon North Sea crude oils. In view of the fact that the North Sea crude oils are derived from the same source rock (Kimmeridge), they would be expected to have the same chemistry, but however, they tend to behave differently. The objectives of the research were to develop a better understanding of the effect of temperature and time on evaporation rate and its role in modifying the rate of weathering of North Sea crude oils on seawater. In this research, the chemistry of the oils was investigated to see the relationship to their emulsification behaviour. In the first part of this thesis, the weathering behaviour of four North Sea crude oils were investigated, in particular the evaporation, using a novel evaporation method. It was observed that the rate of evaporation varied between the North Sea oils. Evaporation of emulsified oil differed to unemulsified oil. North Sea crude oils of different states of weathering were emulsified and their viscosities and water contents measured. The four oils produced emulsion types of different viscosities and states of stability. The effects of degree of weathering of oils on emulsion states were assessed. The chemistry of the four North Sea crudes was investigated using a range of analytical techniques. The oils were fractionated by SARA analysis to produce saturates, aliphatic, resins and asphaltene fractions, prior to chemical analyses, using a range of analytical techniques (The crude oils were fractionated and the fractions analyzed for their chemical compositions). The compositions of the four crude oils differed to one another. From these analyses, a number of parameters were selected to characterize the oils. These were polarity, aromaticity and alkyl side chain. These data were used in a modeling study. The asphaltenes from the North Sea crudes investigated were substituted into both synthetic and model oils to study the effect on emulsification. It was observed that the asphaltenes had an effect on the emulsification behaviour. The behavior of modeled asphaltene structures based on the chemical characterization data was found to correlate with the emulsification behavior of the North Sea crudes investigated