The age of the source rock and its source facies for the migrated oil in rock samples from Novaya Zemlya

• Main Author: Kúld, Ingi Thór Hallgrimson
• Other Authors: Dag A.Karlsen
• Format: Master Thesis
• Language: English
• Published: 2009
• Subjects: petroleum geologi geofysikk kildebergart Novaya Zemlya alders spesifiserte biomarkører geokjemi; VDP::450; Barents Sea; Fid; Holtedahl; Novaya Zemlya
• Online Access: http://hdl.handle.net/10852/12655; http://urn.nb.no/URN:NBN:no-22635

In this work I have in detailed tried to determine the age of the source rock that is responsible for petroleum impregnation in onshore samples from Novaya Zemlya. I have worked with a selected set of 6 samples. Pilot investigations of nearly 90 year old rock samples of Devonian to Carboniferous age, sampled by Professor Olaf Holtedahl in 1921 from the archipelago of Novaya Zemlya, which spans on a regional scale some 500 km, has shown that several rock samples were impregnated with migrated bitumen, i.e. oil of surprisingly uniform maturity and organic facies in particular when bearing in mind the large lateral distances. While these samples were originally sampled for fossils, I found irrefutable proof of hydrocarbon migration episodes. The TOC and HI values of in-situ organic matter of the samples today reflect deep burial and overmature conditions, with values mostly in the range of 1-4.5 % of TOC and HI values in as low as 1–6. I conclude that the source rock potential of these rocks show a paleopotential realized possibly already during the Ural-Novaya Zemlya – Permian Orogeny. Yet, extracts in the range of 0.37-2.83 mg/rock show on Iatroscan typically 48-70 % saturated hydrocarbons, 4-14 % aromatic hydrocarbons and 15-47 % polar compounds (resins plus asphaltenes). GC-FID data show normal alkanes and “Unresolved Complex Mixture” (UCM) which reflects several migration episodes of oil into the “burned out carbonaceous/silty lithologies” with intermittent periods of biodegradation, and most likely water washing cf. low contents of aromatic hydrocarbons. Inferred source rock facies from GC-FID and GC-MS data reflect that the source rock is likely to be a marine shale with some influence of land plant derived organic matter, i.e. containing mainly kerogen type II, but with some type III. Land derived organic material is indicated by the occurrences of oleanane and heavy δ13C stable carbon isotope ratios. The unknown hydrocarbon source rock is therefore suggested to be a distal, predominantly marine shale with organic matter of marine/planktonic origin deposited under anoxic to dysoxic conditions. Maturity inferences made from GC-MS data suggest expulsion at maturities corresponding to the early oil window, this is based on terpane maturity parameter vs. the calculated vitrinite reflectivity and sterane maturity parameters. There are also evidences for a late, non-biodegraded condensate migration event. The age of the source rock for the migrated petroleum was attempted determined by several age-specific biomarkers from the data obtained by the GC-MS and GC-MS-MS analysing methods. The biomarkers used in this study were; oleanane index (OI), C28/C29 ratio, 24-nordiacholestane ratio (NDR), 24-norcholestane ratio (NCR) and dinosterane ratio. These age-specific biomarkers from different biota, angiosperm land plants and marine algae, have been shown to be advantageous in constraining the geologic age of a petroleum source. The biomarker data based on a number of age-specific biomarkers, both individually and especially when used together, suggests strongly that a Cretaceous or even younger source rock i.e. Tertiary, must be considered in the eastern Barents Sea and possibly also in the Kara Seas region. These results are based on the occurrences of oleanane and the high C28/C29, 24-nordiacholestane and 24-norcholestane ratios, all indicating Cretaceous to Tertiary source rock ages. The existence of a source rock of Cretaceous or Tertiary age, as suggested by the biomarker data in this study, may add new potential ideas concerning petroleum systems in the Barents and Kara Seas, ideas which may help in future petroleum exploration in the area.