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Novel Technologies for Unraveling the Charge History of Multiply-Sourced Petroleum Systems

J. M. (Mike) Moldowan1,2, David Zinniker1, Jeremy Dahl2, Shaun Moldowan1, and Geoffrey Bott3
¹Biomarker Technologies, Inc., Rohnert Park, CA, USA
²Stanford University, Stanford, CA, USA
³GB Scientific, Inc., So. Lake Tahoe, CA, USA

Lower Paleozoic petroleum systems require application of advanced geochemical technology to delineate all the hydrocarbon sources and de-convolve the mixtures. Problems commonly faced by geochemists include (1) working with highly mature liquids, (2) understanding gas origin and generation, and (3) differentiating oil families that manifest only subtle compositional differences. Multiple sources are common but determining mixedoil accumulations is difficult, yet extremely important. Application of advanced geochemical analyses can unravel such mixtures.

Here we describe a cocktail of currently underutilized technologies novel geochemical methods that present new avenues to unravel complex petroleum systems of all types. Traditional or classical geochemical methods repeated time and time again over the last two or three decades have not provided the answers that await the application of these novel methods.

Diamondoids are small, thermally stable cage-like hydrocarbons in petroleum, in which the carbon-to-carbon bonding network is equivalent to that of diamond. They possess great stability and increase systematically from the end of the oil window, from about Ro = 1.1%, until well into the dry gas window, to about Ro = 4%. The three available diamondoid application methods are essential for Lower Paleozoic basin studies: (1) the diamondoidbiomarker method to estimate extent of oil cracking and mixing of cracked and non-cracked liquids, (2) compound specific isotope analysis of diamondoids (CSIA-D) for source correlation of non-cracked oil and source rocks with cracked (i.e., condensate) liquids, and (3) quantitative extended diamondoid analysis (QEDA) for similar correlation to CSIA-D, albeit, a diamondoid-fingerprinting method similar to biomarkers, but extending into the gas window.

When biomarkers are present CSIA of biomarkers (CSIA-B) combines classical biomarker information with that of isotopes for a unique 2-dimensional approach. Sources generating oil types with similar biomarker fingerprints can often be differentiated by CSIAB. Combining CSIA-B with CSIA-D and QEDA is ideal for unraveling petroleum mixtures. Unlike biomarker fingerprinting, these methods do not succumb to difficulties in interpretation caused by advanced maturity and biodegradation. Additional information from age-related biomarkers can be added to the applications-cocktail for the Lower Paleozoic. It is often important to distinguish Mesozoic from Paleozoic oil and a variety of methods present themselves, based on: highly branched isoprenoids, triterpane molecules, C26-steranes and various dinosteroid-related compounds. Now, terrestrial plant compounds (diterpanes) fingerprinted by GC-MS-MS offer a new level of source and age-specificity not available from algal biomarkers. This may be due to the rampant evolution of terrestrial flora during the Paleozoic, during which time major evolutionary trends for algae were less evident.

The advanced technologies briefly described here will be illustrated by examples from worldwide Paleozoic basins, including Tarim, Sichuan, Williston, Arabian, N. Africa and W. Africa.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013