摘要：

Concentrations of biomarkers remaining in straight-run refinery products of crude oil feedstock are mainly controlled by relative volatility. Thermal cracking exerts a second-order control on biomarker compositions of these products. Factors controlling biomarker concentrations and distributions in processed materials are more complex and include volatility, thermal stability, generation from heavier precursors, and the effects of catalysts and hydrogen pressure. Differential volatility of compounds within each biomarker class and sharp temperature gradients defining each distillation cut complicate interpretation of source- and maturation-dependent biomarker parameters used by petroleum exploration geochemists. For example, conventional biomarker parameters could be interpreted to indicate that the residuum is unrelated to and less mature than the feedstock. Partitioning of biomarkers by volatility among distillation cuts affects the compound ratios used for assessment of thermal maturity where the numerator and denominator consist of early- and late-eluting biomarkers, respectively. For example, the residuum, which is enriched in the least volatile biomarkers, shows diasterane/sterane, tricyclic terpane/17alpha(H)-hopane, and triaromatic steroid TA-(I)/TA(I+II) ratios indicating lower maturity than the feedstock. The residuum also shows lower sterane isomerization ratios than the feedstock, possibly due to release of epimers showing the immature stereochemical configuration (e.g., 20R) from heavier precursors during cracking. Hydrocracked products lack mono- and triaromatic steroids due to their destruction at high temperatures and hydrogen pressures. Increased sterane concentrations in the hydrocracker product could be due to their generation from bound precursors in the feedstock. Source- and maturity-related biomarker parameters for hydrocracker product and TKN feed (gas oil feed for the hydrocracker) are nearly identical. Hydrofining of vacuum gas oil does not significantly alter the concentrations or distributions of terpanes, except Tm [17alpha(H)-22,29,30-trisnorhopane]. Tm appears less stable to hydrofining than other terpanes. Sterane and aromatic steroid concentrations generally decrease during hydrofining without changes in distribution, except the diamonoaromatic steroids. Fluid catalytic cracking reduces the amounts of most biomarkers without changing their distributions significantly. Fluid catalytic cracking product lacks monoaromatic steroids. Medium coker gas oil is highly volatile and lacks biomarkers, except C19 and C20 tricyclic terpanes. Coking of residuum severely reduces and alters distributions of biomarkers. High concentrations of Tm, 5alpha,14alpha,17alpha(H)-27-norcholestane 20R, and other compounds indicate generation from heavier precursors. Heavy coker gas oil lacks monoaromatic steroids, probably due to low concentrations in the residuum and subsequent destruction during coking.

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