Analysis of crude petroleum oils using fluorescence spectroscopy.

Crude oil is defined as a mixture of hydrocarbons that existed in the liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities (joint American Petroleum Institute, American Association of Petroleum Geologists, and Society of Petroleum Engineers definition).1 Crude petroleum oils are complex mixtures of different compounds (mainly organic), which are obtained from an extensive range of different geological sources.2,3 Their physical appearance can vary from solid black tars to almost transparent liquids. In their natural state within an oilfield reservoir or entrapped within Hydrocarbon bearing Fluid Inclusions (HCFI), crude oils will also contain varying amounts of gasses (carbon dioxide, methane, etc.).4 This presents the analyst with considerable challenges when developing methods for the characterisation and analysis of crude oils.5 The non-contact, non-destructive, quantitative analysis of crude petroleum oils is a highly desirable objective for both research (e.g. study of microscopic HCFI) and industry (e.g. real-time assessment of oil production). Satisfying the needs of both macroscopic and microscopic applications is not straightforward, however, optical methods offer a convenient route to achieving these goals. Fluorescence spectroscopy is the best available optical technique, because it offers high sensitivity, good diagnostic potential, relatively simple instrumentation, and is perfectly suited to both microscopy and portable instrumentation