Effectiveness of three fingerprinting techniques to correlate oil seeps: Biomarkers, Diamondoids, and Multi-elemental Analysis

• DOI: https://doi.org/10.22533/at.ed.153112401079

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• Abstract: Seeped oil-to-source correlation requires sophisticated geochemical fingerprinting techniques and an understanding of their limitations. Through the past several decades, studies have used EOM composition, biomarkers, diamondoids, and multi-elemental analyses to correlate oils in reservoir studies; yet only EOM composition and biomarkers are routinely used to correlate seeped oils. Thus, in the current study, seven seeped oils (Soxhlet-extracted, mainly Type III (terrestrial origin) and Type II/III (mixed) of organic matter in the source rock, API values = 35 - 40°) from a single basin (consisting of five Blocks: A, B, D, E, and F) and EOM from a background sample (from Block C) were analyzed using the aforementioned techniques and data therein was correlated to investigate the utility of these as advanced geochemical seep hunting tools. The extracted oils (from Blocks A, B, D, and E) varied between light condensates and black oils. Variations on the seeped oils may be attributed to oil fractionation, thermal maturation, chemical interactions during the upward migration of hydrocarbons, and / or biodegradation. Biomarkers results confirmed a Tertiary to Late Cretaceous Type III, low hydrogen kerogen source, and Type II/III consisting of high 18a(H)-oleanane (average Ol/H30=0.50), Gammacerane, a high (C29)/(C28+C27) sterane ratio, and low abundance of C30 steranes. Diamondoid analysis complemented these findings by targeting light hydrocarbon compounds, which are biodegraded in areas of passive or microseepage. High adamantane:diamantane ratios were consistently observed across the basin's seeped oil extracts, suggestive of light condensate oil. According to the results, diamondoids are a better indicator of maturity than biomarker parameters, especially for biodegraded hydrocarbons. The study also helped to find relation among elements, which could be of interest in correlating oils from similar/different sources when looking at seeps. Lastly, a logical workflow strategy is provided that can be used to determine which fingerprinting techniques are merited for seeped oil samples.