Adaptation of fluorescence excitation-emission micro-spectroscopy for characterization of single hydrocarbon fluid inclusions

Until now, fluorescence characteristics of hydrocarbon fluid inclusions have been limited in measurement by the requirement to use bandpass filters, dichroic mirrors and neutral density beamsplitters/quartz wedges in the optical light path. Measurements have generally been restricted to monitoring emission spectra from ca. 400 nm and above because the microscope arrangements have used fluorescence “cubes” optimized for specific excitation wavelengths such as the emission lines in the mercury spectrum. This has meant that only those lines can be used to excite an inclusion and recording of excitation spectra is not possible. Well established luminescence techniques of excitation-emission and synchronous excitation-emission spectroscopy have been expanded into the micro-scale domain by the use of a commercially available luminescence spectrometer adapted to a microscope via UV-transparent SuprasilR fiber optic cables. These techniques were developed to pursue non-destructive fingerprinting of individual hydrocarbon fluid inclusions by use of the quantitative parameters of optimum excitation wavelength and Stokesʹ shift. The technique of fluorescence excitation and emission micro-spectrometry (FLEEMS) has been tested on different hydrocarbon fluid inclusion samples from reservoir rocks of the Norwegian continental shelf and from a Norwegian on-shore hydrocarbon bearing diabase dyke. This new technology readily allows unique luminescence information to be extracted for discrimination of hydrocarbon fluid inclusions with visually identical fluorescence color and emission behavior in the visible region. Spectroscopic information in the range of 240–800 nm is accessible with a wavelength accuracy better than 0.25 nm and reproducibility better than 0.05 nm for both excitation and emission. Signal/noise ratios are higher than previously available for microscopic applications. This technology can readily be adapted to most brands of microscopes in a modular way without any irreversible microscope customization.