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Novel Geochemical Technologies Reveal Everything You Wanted to Know About Heavy Oil

Abstract

Novel technologies have been developed to determine reservoir charging history, to quantify biodegradation history, to correlate severely biodegraded oil and determine multiple co-sources. All of these factors are important to design correct petroleum system models. Here we describe new technologies to see past the effects of biodegradation to the pristine oil from which it came. Biomarker acids were analyzed in a sequence of oil samples to calibrate their appearance and disappearance at various levels of biodegradation severity. This technique allows the quantitative estimation of the fraction of an oil sample that has reached each of five levels of biodegradation. The combined totality of those fractions comprises the biodegradation profile of the oil. Single-rank biodegradation scales usually provide only the biodegradation level of the freshest charge to the reservoir; whereas, biomarker acids analysis provides a history of multiple charging events along with their subsequent biodegradation to different levels and their relative importance to the composition of the entire oil sample. The important tools for oil-source correlation of non-biodegraded oil are biomarkers and diamondoids. Biomarkers are altered and lost during biodegradation becoming less reliable. Diamondoids survive providing one type of reliable technology for correlation. However, diamondoid correlations are empirical and less detailed than biomarkers, and many heavy oil reservoirs are charged by multiple source rocks requiring additional technologies to be applied. Asphaltenes are a storehouse of molecules that have been protected from biodegradation, but they are rarely used because of difficulties in their analysis. We found that biomarkers and diamondoids released from asphaltenes by hydrous pyrolysis can be used to determine sources of severely biodegraded oil. Isotopic analysis of the biomarkers and diamondoids and the fingerprints of diamondoids can delineate the oil sources over the charging history of heavy oil reservoirs. This novel technique compares analysis of the non-biodegraded oil components, diamondoids in particular, with isotopic analysis of the components released from the asphaltenes. Knowledge of all the heavy oil sources opens a window for basin modelers to identify deeper prospects and less biodegraded reserves of lighter oil.