Despite the fact that most crude oils are dark coloured liquids, many are observed to be strongly fluorescent when illuminated with UV light. This fluorescence, which originates from the presence of aromatic compounds, is strongly influenced by chemical composition. This has led to the use of fluorescence techniques as tools for the characterisation and analysis of crude and refined oils. Various aspects of the fluorescence behaviour of oils (intensity, colour, wavelength distribution, and lifetime) have been correlated with factors such as
petroleum chemical composition and density (API gravity). Fluorescence based methods have several advantages, including: they are non-contact (e.g. can employ fibre optic probes for remote sensing), high sensitivity to the presence of aromatic hydrocarbons and easily miniaturised instrumentation. Fluorescence is often used to detect the presence of crude oil during drilling operations by observing the fluorescence of the cuttings.
However, there are possible interferences from mud additives or oil-based muds, and these need to be overcome to provide accurate results. In this article we outline the basics of petroleum fluorescence and discuss how a “Total Scanning Fluorescence” (TSF) method, developed in EniTecnologie, can be used to discriminate drilling additives from crude oils, and to quantify the API gravity (density) of crude oils.