--> New Approaches on Source Rock Analysis to Improve Hydrocarbon System Analysis — Optical Kerogen Analysis of Organic Rich Mesozoic Shales (Germany, Chile)

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New Approaches on Source Rock Analysis to Improve Hydrocarbon System Analysis — Optical Kerogen Analysis of Organic Rich Mesozoic Shales (Germany, Chile)

Abstract

Kerogen composition of organic rich rocks is a crucial parameter for the analysis of the source rock potential, which is a major input to hydrocarbon system analysis. Commonly geochemical techniques are used (Rock Eval, TOC, biomarker) to analyse quantity and quality of potential source units. But geochemical analysis, all based on bulk rock analysis, is partially misleading, due to highly complex mixtures of different kerogen types with different maturation and degradation within the total kerogen, not seen in geochemistry. In opposite Optical Kerogen Analysis provides high resolution data sets, identifying kerogen mixture and quantifying the different kerogen types within the total kerogen. This leads to highly enhanced analysis of the source rock potential, which can change the hydrocarbon system model completely. The aim of the present study is to combine classic geochemical and new optical workflows, to severely increase the evaluation of hydrocarbon systems and decrease the risk of failure in exploration. The focus is on Optical Kerogen Analysis, providing highly detailed data sets on composition, degradation and maturation of the kerogen, combined with geochemical analysis (TOC, Rock Eval). Organic rich shales and marlstones were studied from the lower Jurassic in Germany (including Toarcian Posidonia-Shale) and the lower Cretaceous of central Chile (western end of Neuquen basin). Beside several similarities the studied organic rich units show certain differences in geochemical and optical kerogen analysis, showing the significant influence of maturation and degradation on bulk kerogen types. Special attention is given to amorphous organic matter (AOM), which is very common in organic rich units, but highly complex regarding its hydrocarbon potential due to its ambiguous origin. Commonly AOM is considered as highly degraded algal and bacterial remains and is classified as highly oil-prone kerogen type I. All samples from this study are strongly dominated by AOM. But due to the highly varying origin of AOM identified in this study, the hydrocarbon potential of the studied black shales differs strongly too. Results show also, that the high TOC values, indicating a highly prolific play, are partially highly dominated by unproductive kerogen, diminishing dramatically the prosperity of the play. Therefore the combination of different chemical and optical workflows is highly recommended to improve hydrocarbon system analysis and reduce exploration risk.