Novel Technologies for De-convolving Petroleum Mixtures

Moldowan, John M.¹; Moldowan, Shaun M.; Dahl, Jeremy; Zinniker, David; and Bott, Geoffrey
¹[email protected]

Accurately assessing the source or sources of petroleum liquids in reservoirs is critical to identifying and modeling important resource plays, migration pathways, migration barriers, and the overall history of basin fluids. Correctly identified petroleum mixtures can point toward multiple source rocks, multiple maturity contributions such as condensate from deep and black oil from shallow, and multiple charge pulses to an oilfield from one or more source rocks.

In the basins of Latin America multiple source formations account for many large oil accumulations. The contribution of a deep source is often missed because its fluids lack biomarkers. Thus, biomarker analysis of a deep source-shallow source mixture will reveal only the shallow source. Mixtures of two oil-window liquids can best be delineated by biomarker isotope ratios together with diamondoid source parameters. Here we demonstrate how biomarker and diamondoid isotope ratio analysis (CSIA) and fingerprints of extended diamondoids are used to de-convolve all types of oil mixtures and semi-quantitatively determine the sources.

Both laboratory-mixed and naturally-occurring oil mixtures are presented to illustrate the use of these novel technologies. Late Cretaceous-Tertiary (Oligocene) oil mixtures from Northern South America (Venezuela and Colombia) and parameters to distinguish four source families that occur together in South Atlantic marginal basins will be described in detail.

Key source-discriminant parameters include isotopic ratios of individual diamondoid hydrocarbons and distributional differences in higher diamondoids (tetra-, penta- and cyclohexa-mantanes). Source-controlled differences in diamondoids are unperturbed by the effects of even the most extreme biodegradation or maturation, such as oil-to-gas cracking. As such diamondoids are effective for delineation of all mixture types.

Biomarker isotopes are shown to be more discriminant than biomarker fingerprints and not subject to post-generative processes. Biomarkers, which are correlated to paleo-environment and paleo-flora, provide the link to specific source rocks to complete the correlation of mixtures. Together parameters based on biomarker and diamondoid isotopes and extended diamondoid fingerprints provide the most effective and universal way to identify and unravel any and all mixed-oil accumulations.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013