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A Revolution in Applied Petroleum Geochemistry Fostered by Diamondoids


Petroleum exploration is all about creating prospects that can yield new discoveries. While classical geochemical technologies; such as, standard biomarker analysis and correlation by isotopes of oils and oil fractions are extremely useful. They have already been available for more than three decades and been applied to most of the mature basins in the world. Therefore, classical analytical methods are unlikely to support new exploration ideas. Repeating the same analyses in the same basins time and time again will most likely not result in startlingly new play ideas or discoveries. Geochemical techniques based on diamondoids can provide the necessary crucial information to reach those objectives that were previously unattainable, filling mature basins with new exploratory opportunities.

Quantitative diamondoid analysis (QDA) is used for determining the maturity of any oil sample in both conventional and unconventional applications. The high degree of accuracy needed for application of this method is achieved by spiking the liquids with deuterated diamondoids before GCMS analysis. More recently, the ability to perform source correlations by using diamondoids has been developed. These correlation methods have an advantage over all others due to the thermal stability and recalcitrancy of diamondoids toward biodegradation. Thereby, all bitumen and oil samples (condensate, biodegraded oil, black oil) can be correlated by diamondoids. One method (called quantitative extended diamondoid analysis or QEDA) is based on quantitative analysis of large diamondoid molecules, eight compounds ranging from tetramantanes to pentamantanes to cyclohexamantane, which occurs in several isomeric structures that can be displayed in a similar fashion to biomarker fingerprints and ternary diagrams. A second approach is to measure the diamondoid carbon-isotope ratios. Application of these diamondoid technologies often reveals oil-source mixtures that have been consistently missed in all previous basin studies.

Compound specific isotope analysis of biomarkers (CSIA-B) is another revolutionary method. CSIA-B can be used for determining geological provenance and oil and extract correlations far exceeding the capability of biomarker analysis by GCMS. When employed in conjunction with diamondoids, CSIA-B leads to a better understanding of depositional environment and source facies relationships and helps to determine the components of oil mixtures.

Advantages of applying these methods to basin analysis in order to elucidate better basin models will be demonstrated by examples from Brazil, Alaska, the Middle East and elsewhere.