Geochemical study on reservoir and source rock asphaltenes and their significance for hydrocarbon generation vorgelegt von Diplom-Geologe Eric Lehne von der Fakultät VI – Planen Bauen Umwelt der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften - Dr. rer. nat. – genehmigte Dissertation Promtionsausschuss: Vorsitzender: Prof. Dr. Ugur Yaramanci Berichter: Prof. Dr. Brian Horsfield Berichter: Prof. Dr. Wilhelm Dominik Tag der wissenschaftlichen Aussprache: 09. Oktober 2007 Berlin 2008 D 83 Abstract 3 ___________________________________________________________________________ Abstract Non-isothermal open system pyrolysis - gas chromatography and bulk petroleum generation experiments were performed on type II-S petroleum asphaltenes, source rock asphaltenes and related source rock kerogens to evaluate petroleum composition and generation timing. The results show that despite the traditionally assumed similarities between petroleum asphaltenes and their related kerogens, significant differences in petroleum generation timing and composition occur, at least for the studied type II-S petroleum system. Petroleum asphaltenes and source rock asphaltenes are less stable and show tighter petroleum formation windows than kerogens when extrapolated to geological heating rates. However, no obvious structural links were found that could directly explain the observed reactivity differences from bulk kinetic measurements. But, the amount of organic sulphur is not proportional to the reactivity of petroleum generation from asphaltenes at lower thermal stress. More likely is, that kerogens and asphaltenes posses different positions and types of sulphur bonds resulting in cracking of covalent bonds at different levels of thermal stress. Source rock asphaltenes, related kerogen, and oil asphaltene pyrolysates show major structural differences and differ in aromaticity and organic sulphur content. Highest aromaticity was found in pyrolysates of source rocks asphaltenes, medium from kerogens, and lowest aromaticity in pyrolysates formed from petroleum asphaltenes. In addition, the highest organic sulphur content was identified in kerogen pyrolysates, whereas pyrolysates of both types of asphaltenes do not show a major difference in the content of organic sulphur. Based on the n-alkyl chain length distribution the kerogen pyrolysates predict the field of the paraffinic-naphtenic-aromatic low-wax oil generating facies. Pyrolysates of both asphaltene types plot at a triple point predicting P-N-A low and high wax, as well as paraffinic oil generating facies. These predictions however do not correlate with the asphaltic natural oils found in this petroleum system. The pyrolysates from both types of asphaltenes, as well from Abstract 4 ___________________________________________________________________________ kerogens show differences such as alkane / alkene ratios, xylene distributions, and toluene/ xylenes ratios, which can be attributed to different concentrations of precursors within the asphaltene and kerogen macromolecules. Micro-scale sealed vessel pyrolysis (MSSV) experiments were applied on reservoir asphaltenes from a sulphur-rich sequence from Southern Italy in order to compare their petroleum and gas generation characteristics, in terms of primary and secondary gas generation, as well as the compositional kinetic prediction of determining the actual products that will be released from the asphaltene under specific geologic conditions.. The outcoming results were compared to MSSV products formed from an immature source rock kerogen of the same petroleum system in terms of chemical structural differences, as well as differences in gas formation, isotopic composition of products and compositional kinetics. The detailed compositional information from non-isothermal MSSV pyrolysis indicate that hydrocarbons formed from the oil asphaltenes show lower aromaticity and lower content of organic sulphur than products from source rock kerogen. Primary gas and secondary gas kinetics evaluated on petroleum asphaltene products result in similar geological prediction as gas formation from the source rock kerogen. Nevertheless, the GOR of product formed from the asphaltenes is much lower than that formed from the kerogen. Carbon isotopes measured on gas formed from these different types of asphaltenes and the kerogen reveal that differences are most probably related to different maturities and gas generating precursor structures. The C6+ oil like kinetics and geological predictions are nearly identical for hydrocarbons formed from the oil asphaltene and the kerogen. The simulation experiments using MSSV-pyrolysis illustrated that compositional features of hydrocarbons formed from asphaltenes are very similar to compositional feature found for natural petroleum. This was especially the case of n-C6-14, n- C15+, aromatic compounds and NSO like compounds. For that reason a compositional kinetic Abstract 5 ___________________________________________________________________________ model for C6+ formation was build up for the asphaltenes from the Italian petroleum system, which reflects the major characteristics of oils formed in this area. Asphaltenes from reservoir oils, source rock bitumen and the kerogen of related source rocks of the Duvernay Formation (WCSB) have been studied in order to compare their petroleum generation characteristics. Open system bulk petroleum pyrolysis for bulk kinetic evaluation and geological extrapolation and pyrolysis GC experiments for petroleum compositional characterisation were applied in order to evaluate the reliability of petroleum asphaltenes in source rock evaluation studies in which a potential source rock sample is not available. Kinetic parameters and resulting geological extrapolations of petroleum formation calculated on immature source rock kerogens and asphaltenes fit exactly to corresponding parameters measured on asphaltenes precipitated on low mature oils. In contrast molecular characteristics such as aromaticity and the amount of alkylated thiophenes reveal highest values in source rock asphaltenes, while oil asphaltenes demonstrate lowest aromaticity. Source rock kerogens seem to represent an intermediate between both types of asphaltenes at low levels of maturity. Interestingly the molecular ratios observed in products formed from oil asphaltenes fit exactly to those observed in natural oils and support the application of petroleum asphaltenes to predict petroleum formation and especially petroleum compositional characteristics. Further on, reservoir asphaltenes isolated from crude oils from Nigeria onshore were investigated in terms of bulk kinetic parameters, structural moieties, such as aromaticity and n-alkyl chain length distribution obtained from open-system pyrolysis, as well as hydrocarbon generation characteristics based on MSSV pyrolysis. Bulk kinetic measurements on oil asphaltenes predict peak hydrocarbon generation for geological temperatures of 145°C. This predicted temperature correlates with hydrocarbon generation for example in the western part of the Anambra Basin in Nigeria onshore. The n-alkyl-chain distribution of investigated Nigerian oil asphaltene pyrolysates predicts the facies generating high-wax P-N-A-oils or Abstract 6 ___________________________________________________________________________ paraffinic oils. The changes for facies recognition based on the n-alkyl chain length distribution of asphaltene pyrolysates correlates with facies changes due to variations of terrestrial input obtained from biomarker parameters of related crude oils. Hydrocarbons formed from the Nigerian reservoir asphaltene show a strong heating rate dependency for the n-alky-chain length distribution and for the generation of aromatic hydrocarbons, like alkylbenzenes and alkylphenols. Compositional kinetic parameters of oil and gas formation obtained from oil asphaltene pyrolysates show high values together with the early potential for the generation of gas, which may support that the original source rock of these oils correspond to a type II/III organic matter. The simulation experiments using MSSV-pyrolysis illustrated that compositional features of hydrocarbons formed from Nigerian asphaltenes are very similar to compositional feature found for natural petroleum. For that reason a compositional kinetic model for C6+ formation was build up for the asphaltenes from Nigeria onshore. This model reflects the major characteristics of NSO lean oils formed in this delta system. Acknowledgment 7 ___________________________________________________________________________ Acknowledgment This study is part of the Industry Partnership Programme “Asphaltenes as geochemical markers” at the GFZ-Potsdam. I am grateful to the companies Shell, ENI-Agip, Norsk Hydro, Statoil and ConocoPhillips for financial support. Very special thanks to Dr. Volker Dieckmann for supervising this thesis and for managing the IPP-project. As well I gratefully acknowledge Professor Dr. Brian Horsfield for suggestions and support during my time at the GFZ-Potsdam. Thanks for analytical support to the technical stuff Cornelia Karger, Kristin Günther, Michael Gabriel, and Anke Sobotta at the GFZ-Potsdam, section 4.3, especially to Ferdinand Perssen for assistance during the pyrolysis experiments. I thank also Dr. Rolando di Primio for his suggestions concerning asphaltenes, and Dr. Heinz Wilkes for constructive comments regarding biomarkers. Also I would like to thank my friends and colleagues