Discovering and Quantifying Oil Mixtures for Correct Petroleum Systems Modeling

Abstract

Petroleum accumulations with multiple sources are often mis-assigned to one source, when only standard geochemical approaches are applied. Determination of the component sources of such mixtures is even more rarely achieved or verified. Here we present a smorgasbord of geochemical analyses that can both identify the occurrence of mixed oil and determine its component sources. Diamondoids provide universally applicable technologies for maturity and correlation, because they are resistant to biodegradation, unaffected by maturation and present in all crude petroleum. Mixtures of cracked oil with non-cracked oil, usually from a deep and shallow source, respectively, can be determined by quantitative diamondoid analysis (QDA). Source correlation by diamondoids comes from compound specific isotope analysis of diamondoid (CSIA-D) and fingerprinting of large diamondoid molecules called quantitative extended diamondoid analysis (QEDA). CSIA-D and QEDA are the most source-specific methods to correlate cracked-oil either in mixtures with non-cracked oil or as condensates. In any case, very mature and very biodegraded oils lack biomarkers that could otherwise be used for correlation. When the samples are not badly altered by maturity or biodegradation, CSIA of biomarkers (CSIA-B) is the method of choice in combination with diamondoid methods for correlation of mixed oil. Biomarkers are taxon-specific and dependent and depositional environments determine isotope ratios. Thus, CSIA-B is a powerful method for correlation with the source rock and understanding provenance of the oil. Isotope ratios vary linearly between depositional environments and can simply be averaged to quantitatively determine the co-sources of non-altered oil. 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 Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014