The non-contact, non-destructive, analysis of crude petroleum oils is required, in particular for the characterisation of Petroleum-bearing Fluid Inclusions (PFI). Petroleum oils are fluorescent because of the presence of polycyclic aromatic hydrocarbons and other fluorophores. The wide range of fluorophores in crude oils produces very broad absorption and fluorescence emission bands. The shape and temporal behaviour of the fluorescence emission is dependent on oil composition (API gravity, aromatic-, sulphur-, and asphaltene concentration) and therefore fluorescence can form the basis of a characterisation method. The fluorescence lifetimes of crude oils, measured using different excitation wavelengths and at various emission wavelengths, also depends on these compositional factors.1,2 Examples of quantitative models for estimating API gravity and aromatic concentration, based on fluorescence lifetime data obtained with 380 nm LED excitation, will be presented. In particular, the influence of sulphur concentration on fluorescence lifetime will be discussed.
Currently we are developing a range of time-resolved instrumentation for the analysis of PFIs and bulk petroleum oils. The instrumentation is based around compact 400 nm pulsed and modulated laser diodes. A microscope based system has been built for PFI analysis using both fluorescence lifetime and Time-Resolved Emission Spectra (TRES).3 Preliminary TRES and lifetime data from a series of North Sea crude oils, and their relationship to chemical composition will be presented. The development of quantitative methods for oil characterisation based on this data using multivariate analysis, is also discussed.
1) Characterization of crude oils using fluorescence lifetime data. A. G. Ryder, T. J. Glynn, M. Feely, A.J.G. Barwise. Spectrochim. Acta (A), 58, 1025-1038, (2002).
2) Quantitative analysis of crude oils by fluorescence lifetime and steady state measurements using 380 nm excitation. A.G. Ryder, Appl. Spectrosc., 56, 107-116, (2002).
3) A compact violet diode laser based fluorescence lifetime microscope. A. G. Ryder, T. J. Glynn, M. Przyjalgowski, B. Szczupak. J. Fluor. (In press 2002).