Hydrocarbon fluid inclusion fluorescence: A review

Abstract

Geological fluid inclusions are small voids that can contain a variety of liquids which are often found in natural minerals and rocks. Typically they are less than 10 micrometres in size that host fossil fluids which existed when the minerals grew or healed after fracture. Of particular interest to the petroleum industry are inclusions that contain hydrocarbon fluids, which originated from petroleum that once migrated through the rocks before becoming trapped. These hydrocarbon-bearing fluid inclusions (HCFI) are useful for learning about the processes, fluid compositions, temperatures and pressure conditions in geologic systems such as the migration of hydrocarbon fluids in petroleum basins. The accurate characterisation of the petroleum fluid entrapped in inclusions presents the analyst with considerable challenges. HCFI samples are very valuable (usually obtained from core drilling) and thus a non-contact, non-destructive, analytical method is required. The small size of HCFI necessitates the use of microscopy based techniques while spectroscopic methods are needed to characterise the chemical composition. Fluorescence based methods offer the best combination of high sensitivity, diagnostic potential, and relatively uncomplicated instrumentation. It is the fluorescence of HCFI and the spectroscopic methods employed for their analysis which is the focus of this review. Specific sections focus on the description of HCFI, petroleum fluorescence, and microscopic techniques. The review and discussion focuses primarily on advances and studies reported in the literature from 1980 s onwards, and outlines some of the issues that need to be addressed to make fluorescence methods more reproducible and quantitative for HCFI analysis.