Source dependence of fluorescence characteristics and aromatic, biomarker maturity parameters evaluated by artificial maturation.
Date Issued
2010
Date
2010
Author(s)
Chang, Ying-Ju
Abstract
The fluorescence spectroscopy has been widely used to estimate compositions, sources, and maturities of “live” oils during the time of entrapment. In the present study, we investigate the bulk fluorescence response of kerogens and macerals from various depositional environments that the objective was to characterize their average fluorescence properties before and during oil generation, with special emphasis on the fluorescence intensity variation as a function of organic species, time, and temperature. The experiments were conducted using the Diamond Anvil Cell (DAC) pyrolysis technique, which enables the measurement of the fluorescence spectra of newly generated “live” oils during maturation experiments. This study aimed to directly address the maturity dependence of fluorescence color variation observed in natural hydrocarbon inclusions, and the effect of source types on the evolutional trend. The fluorescence spectra of oils generated from all studied kerogens exhibit progressive blue-shift of peak wavelengths (λmax) and red/green quotients (I650/I500) upon increasing maturity, suggesting that the fluorescent colors of crude and inclusion oils are both maturity- and source-dependent, and therefore cannot be used as universal maturity indicators.
The initial fluorescence intensities for bulk kerogens (Finitial) under ambient conditions are correlated with their hydrogen index (HI). The Finitial of these kerogens can be correlated with the maximum fluorescence (Fmax) of their generative oils, and may provide some insight into their oil generation potential. Liptinite separated from humic coals exhibits both higher Finitial and Fmax, consistent with their higher oil-generation potential than vitrinite and fusinite (inertinite). Fmax of separated vitrinites show a positive correlation with their maturities below 1.2 %Ro and a negative correlation at higher maturity, implying the decline of their oil generation potentials at high maturity. The present study has demonstrated that the fluorescence of bulk kerogens at elevated temperatures before or during organic transformation can be used to characterize organic matter.
In addition, oils generated from isolated kerogens under confined pyrolysis were characterized by GC-MS for the distributions of aliphatic and aromatic hydrocarbons and biomarkers for studying source dependability of some conventional organic maturity parameters. Normal alkane distribution in oils from different kerogens exhibit distinct preference in carbon number and predominance in specific compounds. The carbon preference index (CPI) and odd-even predominance (OEP) ratios tend to approach to 1 with increasing maturity. The methylphenanthrene ratios (MPR) are suitable for high maturity indication. The methylphenanthrene index (MPI1 and MPI3) from GR kerogen and two marine kerogens show better correlation than terrestrial kerogens. Source dependence of these methylphenanthrene maturity parameters was observed. The MDR ratios (i.e. 4-MDBT/1-MDBT) for two marine kerogens follow oppose trends, suggesting high source-dependence. Two trimethylnaphthalene parameters, TNR-2 and TMNr, exhibit good correlation with maturity for most kerogens, but the MNR, DNR-1, and TNR-1 ratios for GR kerogen are suitable only for indicating maturity higher than 1.0 %Ro. Pr/n-C17 and Ph/n-C18 ratios decrease with increasing maturity but show distinct trends for different kerogens. The pristane/phytane (Pr/Ph) and [(Pr/C17)/(Ph/C18)] ratios in oils from three major kerogen types vary barely with maturity but are discernible in diverse organic types, implying good source indication. The contents of bicyclic sequiterpanes in oils vary with their sources but their relative concentration changes significantly with maturity as a result of neo-formation and/or secondary cracking; the drimane/homodrimane ratio in Green-River oil increases progressively with maturity whereas the eudesmane/drimane ratio in the terrestrial oils decreases with maturity.
Subjects
fluorescence
aromatic
biomarker
source rock
SDGs
Type
thesis
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