--> Geochemical Technologies to Characterize Heavy Oil and the Sources for Mixed Oil in Latin America

AAPG/SEG International Conference & Exhibition

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Geochemical Technologies to Characterize Heavy Oil and the Sources for Mixed Oil in Latin America

Abstract

Abstract

Advanced geochemical technologies (AGTs) are used to determine important features of oil provenance important to basin modeling. Such components as correlation of multiple sources in mixed oil and determination of reservoir charging and biodegradation history. Here we describe AGTs that see past the effects of biodegradation to the pristine oil from which it came, and to evaluate the composition of the oil in place. AGTs extended to either biodegraded or non-biodegraded oil provide the key to unraveling mixed-source oil that cannot be delineated by the classical geochemical methods. We will show applications of AGTs that determine those features in examples from Mexico, Brazil, Colombia and Venezuela.

Methods for Mixed-Oil Correlation and Heavy Oil Analysis: Diamondoids and compound specific isotope analysis (CSIA) head the list for correlation of all liquids. Diamondoids, virtually unaltered by biodegradation or high thermal maturity, provide the means to see beyond those altering effects. Likewise, carbon isotope ratios of complex molecules (e.g., biomarkers and diamondoids) by CSIA do not succumb to those circumstances.

For severely biodegraded heavy oil, pyrolysis of asphaltenes can yield the required compounds, including pristine biomarkers, diamondoids and even n-alkanes. Analysis of oil generated from asphaltenes resolves questions about oil mixtures for either biodegraded or non-biodegraded oil by releasing, preferentially, those components that migrated in the earliest charges to the reservoir. Those early oil components can often be obscured by biodegradation or covered up by later generated oil when another source enters the oil window. Thus, both the first and last generated oil can be correlated separately through different methods.

Detailed Heavy Oil History and Composition: The overall composition of heavy oil is described by high-temperature simulated distillation (HT-SimDis), which can be used to project Gravity from cuttings or oil-shows in field development, and to determine oil losses due to biodegradation. The history of charging for a heavy-oil reservoir, from earliest charge to most recent, is determined by biomarker acids analysis (BAA). The severity of biodegradation, up to five ranking levels mixed into a single oil sample can be determined by BAA. The different ranks represent the sequence of charges to the reservoir and their relative importance.