Time-Resolved Fluorescence Microspectroscopy for Characterizing Crude Oils in Bulk and Hydrocarbon-Bearing Fluid Inclusions

Abstract

Abstract:Time-resolved fluorescence data was collected from a series of 23 bulk crude petroleum oils and 6 microscopic Hydrocarbon-bearing Fluid Inclusions (HCFI). The data was collected using a Diode Laser Fluorescence Lifetime Microscope (DLFLM) over the 460-700 nm spectral range using a 405 nm excitation source. The correlation between intensity averaged lifetimes (τ ) and chemical and physical parameters was examined with a view to developing a quantitative model for predicting the gross chemical composition of hydrocarbon liquids trapped in HCFI. It was found that τ is nonlinearly correlated with the measured polar and corrected alkane concentrations, and that oils can be classified on this basis. However, these correlations all show a large degree of scatter, preventing accurate quantitative prediction of gross chemical composition of the oils. Other parameters such as API gravity and, asphaltene, aromatic, and sulphur concentrations do not correlate well with τ measurements. Individual HCFI were analysed using the DLFLM and time resolved fluorescence measurements were compared with τ data from the bulk oils. This enabled the fluid within the inclusions to be classified as either low alkane/high polar or high alkane/low polar. Within the high alkane/low polar group, it was possible to clearly discriminate HCFI from different locales and to see differences in the trapped hydrocarbon fluids from a single geological source. This methodology offers an alternative method for classifying the hydrocarbon content of HCFI, and observing small variations in the trapped fluid composition, that is less sensitive to fluctuations in the measurement method than fluorescence intensity based methods.

Frequency Domain Fluorescence Lifetime Study of Crude Petroleum Oils

“…The fact that there are very large numbers of interacting fluorophores produces very complex decay behaviour. In previous work from this laboratory [9][10][11][12][13][14] the intensity averaged lifetime calculated from a multiple discrete lifetime model was used. However, it should be noted that while this model is not an accurate descriptor of the emitting species, it had utility in describing general trends in the photophysics of crude oils.…”

“…All measurements were made in triplicate at room This is the author version of the paper: Frequency Domain Fluorescence Lifetime Study of Crude Petroleum Oils. P. Owens, A.G. [12,14].…”

“…Previous studies in our laboratory using Time Correlated Single Photon Counting (TCSPC) methods have shown that one can correlate various aspects of oil composition with lifetime changes [9][10][11][12][13][14]. Unfortunately, these studies also showed that accurate quantitative measurements were not possible using intensity averaged lifetimes calculated from TCSPC data.…”

Simulation of the fluorescence evolution of “live” oils from kerogens in a diamond anvil cell: Application to inclusion oils in terms of maturity and source

“…Lo, 1987;Diessel and Gammidge, 1998;Han et al, 1999;Tyson, 2006;Chang et al, 2008). It is widely recognized that increasing the excitation wavelength may affect fluorescence properties resulting in changes in the resulting fluorescence emission bands, Stokes' shifts, fluorescence lifetimes, and quantum yields (Wang et al, 1994;Downare and Mullins, 1995;Kihle, 1995;Lakowicz, 1999;Ryder et al, 2004).…”

“…During the past 20 years, analytical methods have seen great improvement, providing for better determination of the composition, source, and maturity of inclusion oils. Some of these advanced techniques include synchronous excitation-emission micro-luminescence spectroscopy (Kihle, 1993(Kihle, , 1995Musgrave et al, 1994;Ryder, 2004;Abbas et al, 2006), and time-resolved fluorescence microspectroscopy (Ryder, 2002;Ryder et al, 2002Ryder et al, , 2004. Currently, fluorescence spectroscopy has become an effective and non-destructive tool for supplementing molecular analysis using chromatography (Pang et al, 1998;Jones and Macleod, 2000;George et al, 2001;Li and Parnell, 2003;Dutkiewicz et al, 2007).…”