| A petroleum system can be classified only as speculative (?) or hypothetical (.) by geological and/or geophysical inference. Geochemical correlation is needed for a petroleum system to be termed known (!). To better define the petroleum systems on the North Slope of Alaska, the oil cracking, mixing, and correlation studies were accomplished by biomarkers and diamondoids in Chapter One of this dissertation.;Biomarkers are complex molecular fossils derived from biochemicals, particularly lipids, in once-living organisms. Biomarkers can provide information on the age, source rock lithology, the organic matter in the source rock, environmental conditions during its deposition and burial, the thermal maturity experienced by rock and oil, and the degree of oil biodegradation. Because biomarkers can be measured in both oils and source rock extracts, the distributions of biomarkers can be used to correlate oil and oil or oil and source rock.;Diamondoids are small, thermally stable, cage-like hydrocarbons in petroleum. Due to high thermal stability, diamondoids resist oil cracking and become more concentrated, while biomarkers crack and decrease in concentration. Therefore, the extent of oil cracking can be investigated by comparing both diamondoid and biomarker concentrations. Furthermore, mixtures of high- and low-maturity oil can be identified when concentrations of both biomarkers and diamondoids are high. The compound-specific isotope analysis of diamondoids (CSIAD) analyses were used to correlate the high-maturity components, while biomarkers, especially those providing information on the age of the source rock, were used to correlate the lower-maturity components.;Forty-one crude oil samples from the North Slope of Alaska have variable diamondoid and biomarker concentrations, which indicate different extents of oil cracking. Some of the samples are mixtures of high- and low-maturity components because they contain high concentrations of both diamondoids and biomarkers.;The North Slope oils in this study were grouped according to their related source rock formations into Triassic Shublik Formation, Jurassic Kingak Shale, Lower Cretaceous pebble shale and Hue/GRZ, and Tertiary Canning Formation. Two Lisburne-designated oils were determined to be generated from Shublik source rock in this study. Four oil samples collected from wells located to the North of the Barrow Arch show unique biomarker characteristics, but biomarker parameters indicate that they were generated from a clay-rich equivalent of the calcareous Shublik Formation from North of the Barrow Arch.;Molecular geochemistry was also applied to environmental studies (e.g., oil spills in the open ocean). Petroleum enters the ocean from both natural oil seeps and oil spills every year. The fate of spilled oil in the ocean and the biodegradation rate of oil were investigated through molecular geochemistry, including biomarkers and non-biomarkers.;In Chapter Two, oil biodegradation in the open ocean was simulated in the laboratory. Chemostats were newly invented and fabricated to incorporate features that could simulate open ocean conditions for refreshing water, agitation, temperature and other factors. Oil compositional changes were observed by gas chromatography coupled with flame ionization detection (GC-FID). Gas Chromatography coupled with mass spectrometry (GC-MS) helped to detect changes in the biomarkers and polycyclic aromatic hydrocarbons (PAHs) in the oil.;The work in Chapter Two summarized the various factors influencing biodegradation of oil after it was spilled into the marine environment. Significant factors controlling oil compositional changes include (1) air flow, (2) oil amount, (3) stirring rate, (4) bacterial compositions in the seawater itself, (5) temperature, and (6) nutrients. Some other factors, such as seawater flow rate and water-washing of the oil, do not exhibit important effects on oil biodegradation rates. The mean halftimes of selected hydrocarbon compounds in the oil were estimated by equations derived from the measured compositional changes. Phylogenetic and qPCR studies helped to identify which bacteria in the seawater play important roles in the biodegradation of oil components (n-alkanes, isoprenoids, and the UCM). Some genera of microorganisms were more effective in degrading different fractions of oil. Alcanivorax and Legionella were proven to play important roles in biodegradation of n-alkanes and isoprenoids. Organisms in the genera Oceanobacter kriegii/Thalassolituus oleivorans could also be alkane-degraders. |
