The first attempt to correlate the migrated bitumen from the Helgeland Basin cores to Devonian source rocks and oils from the UK Orcadian Basin - Is there a Devonian Orcadian type basin offshore Norway?
A key focus of this thesis is if migrated bitumen from Lower to Middle Jurassic and Cretaceous age sandstones in the 6609/11-1, 6610/7-1 and the 6609/5-1 wells in the Helgeland Basin might originate from Devonian source rock strata. For a possible comparison of source rock facies has nine outcrop samples collected from the Orkneys been used alongside with the Beatrice oil from Moray Firth as references of the lacustrine Middle Devonian organofacies present in the Orcadian Basin, Also, oils from the Judy Field and the Embla Field were included in this investigation as their geochemical signature differs from the typical Kimmeridge derived oils on the Norwegian Shelf, which in this study is represented by the NSO-1 oil i.e. oil from the Oseberg Field. Analytical methods i.e. GC-FID and GC-MS were used to generate characterization parameters used for indicating the maturity and also the type of organofacies of bitumen samples and the oil samples. In addition, TOC and Rock-Eval analysis were performed on the source rock samples for assessing the quality i.e. the kerogen type and the generative potential, and also for obtaining additional maturity information. Based on the TOC and Rock-Eval analysis, the HI of the five highest quality source rocks samples is in the range of 313 mg HC/g TOC to 397 mg/ HC/g TOC and those values corresponds to type II kerogen and the overall generative potential of the same five samples is categorized as good to very good, i.e. the TOC values in the range of 1.48wt.% to 2.79wt.%. The four other samples scores lower in both quality and/or generative potential. Of the nine source rock samples in total, only one scores below the minimum criteria for being categorized as a source rock, i.e. a TOC value of at least 0.5wt%. All the three wells i.e. 6609/11-1, 6610/7-1 and 6609/5-1 from which the bitumen bitumen samples studied in this thesis were isolated show evidence of having received migrating oils from a source rock that correlates with the geochemistry of the lacustrine Middle Devonian source rocks of the general Orcadian Basin source rock facies. In particular is the positive identification of β-carotane in the 6609/11-1, 6610/7-1 and 6609/5-1 wells of the highest interest as this biomarker is a type component for the Devonian lacustrine systems. It is thus concluded that there are Devonian source rock systems present in the Helgeland Basin which are of sufficient magnitude to generate and migrate oil into the studied sandstones which are of Early to Middle Jurassic and Cretaceous age. In addition to oil from the likely Middle Devonian source rock, well 6609/11-1 also contains migrated oil from a terrestrially derived source rock and the upper section in well 6610/7-1 (depth 2661m to 2668.5m) and also well 6609/5-1 contains migrated bitumen (oil) which is clearly sourced form a marine derived source, i.e. the Late Jurassic Kimmeridge equivalent. The bitumen samples in the lower section of well 6610/7-1 (depth 2713.8 to 2715m) bears no resemblance of influence from lacustrine Middle Devonian source rocks, but are interpreted to have been sourced mainly from terrestrially derived source rocks, and there is also indications for co-sourcing from the Late Jurassic Kimmeridge equivalent source rocks. Furthermore, oils representing the Embla Field, the Judy Field and the Oseberg Field, are interpreted to have been mixed in the reservoir with petroleum from a lacustrine Middle Devonian source rock equivalent. Also this is totally new information as such has never been described, and it is inferred that such palaeo-oil must have escaped from the Oseberg Field reservoir and the Judy Field reservoirs long before the arrival of the present oil charges. It is thus inferred that also in the drainage areas of Oseberg, Embla and Judy are the Devonian basins which have generated oil. Concerning the maturity, the source rock bitumen samples from the Orkneys are considered marginally mature, and the Helgeland Basin bitumen samples, the Judy oil, the Beatrice oil and the Oseberg oil are considered to be at maturity levels which corresponds to the middle of the oil window. The Embla oil is highly mature, with a maturity level corresponding to the later part of the oil window. The maturity from the lowest to the highest is as follows: The source rock bitumen samples from the Orkneys - NSO-1 (Oseberg) - Beatrice - 6609/11-1 - Judy - 6610/7-1 upper section - 6610/7-1 lower section - 6609/5-1 - Embla.