Petroleum-bearing fluid inclusions are small encapsulations of oil and gas that offer
an invaluable opportunity to better constrain the evolution of petroleum systems.
Insights into palaeo fluid compositions complement observations on present day fluid
compositions, which represent only the end-point of complex cumulative processes throughout
basin history. In this contribution, we review a wide range of approaches used to
extract geochemical information from petroleum inclusions, and how these can be used
to better constrain petroleum systems. These techniques can be grouped into optical,
spectrographic and thermometric non-destructive methods, or destructive chemical analyses
of bulk samples or individual inclusions.Typically optical methods documenting the
distribution and visual properties of petroleum inclusions are used to provide petrographic
context for subsequent specialised geochemical analyses of petroleum inclusions. Additional
non-destructive techniques such as Raman spectroscopy can then be applied to provide
some further insights into the composition of the trapped fluids, although the complex
nature of petroleum generally requires direct access to the fluid for a more complete
understanding of geochemical aspects. A variety of destructive techniques have been
developed, initially to analyse bulk samples released by mechanical crushing and more
recently through ablation type techniques that allow the composition of individual
inclusions to be characterised.Screening geochemical techniques that utilise mechanical
crushing of bulk samples to analyse petroleum inclusions using mass spectrometry without
prior chromatographic separation have become routine analyses. Other geochemical techniques
more geared towards detailed molecular information such as biomarkers utilise chromatographic
separation prior to mass spectrometry. Evaluation of the isotopic composition of petroleum
inclusions is also possible for both bulk samples and compound specific analyses.The
use of lasers to open individual inclusions allows the released contents to be analysed
by thermal extraction-gas chromatography-mass spectrometry (GC-MS), or mass spectrometric
mapping of minerals using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS),
a surface-sensitive analytical method that uses ion beams to ablate into minerals.The
continued evolution of techniques to analyse the incredibly small volume of hydrocarbons
trapped within fluid inclusions has progressed to a point where there is little that
can be done to evaluate a live oil or gas sample that cannot be achieved for a fluid
inclusion sample. The full power for tracing petroleum systems is, however, only realised
where there is an effective integration of fluid inclusion data with a more conventional
approach to petroleum systems analysis. (C) 2019 Elsevier Ltd. All rights reserved.
