Organic geochemical analysis and comparison of oils, condensates and bitumens from the SW Barents Sea. Maturity, organic facies, biodegradation and migration assessment

• Main Author: Narvhus, Lars Jonas Jørgensen
• Format: Master Thesis
• Language: English
• Published: 2016
• Subjects: Barents Sea; Fid; Humps; Loppa; Norwegian Sea; Finnmark; Hammerfest; Hammerfest Basin; Johan Castberg
• Online Access: http://hdl.handle.net/10852/52336; http://urn.nb.no/URN:NBN:no-55558

The SW Barents Sea is a relatively unexplored area compared to the Northern North Sea and the Norwegian Sea. The area has undergone several events of upliftment and erosion making it very complex, with numerous source rocks capable of expelling petroleum. The upliftments are believed to have pushed the larger quantities of oil to basin margins and structural highs. In order to get a better understanding of the region nine oils and two condensates have been geochemically analyzed from the area. In addition, 15 shallow core samples from the Finnmark Platform and Norkapp Basin have also been extracted and analyzed. The geochemical analyzation methods used are TLC-FID, GC-FID and GC-MS. The derived information from these analyses was mainly focused on maturity and organic facies parameters, level of biodegradation and migration pathways. The core samples contain almost exclusively polar compounds, indicating severe biodegradation of the bitumen. Henceforth, elevated isoprenoid values relative to n-alkanes can be found in the shallower oil discoveries, where the lighter n-alkane fraction seems to be microbial degraded. Some of the deeper wells express elevated UCM “humps” but no other clear evidence of biodegradation. This could be related to an older biodegraded petroleum charge and a new charge masking the biodegradation. Mixing of hydrocarbon fractions can be seen in some of the oils based on the bimodal n-alkane signatures found in the GC-FID chromatograms. Moreover, conflicting maturity signatures based on the n-alkane distribution for some of the oils and condensates give a strong indication of mixed petroleums. This is in accordance with the conflicting maturity parameters for the saturated and aromatic biomarkers, and the medium-range biomarkers seen in many of the oils. Thus, suggesting a mixture of petroleums, where the former estimates maturities in the early oil window and the latter peak oil production maturities. All of the oils in the sample set appear to be influenced by two hydrocarbon charges, one lighter fraction (C15-) and a heavier black oil fraction (C15+). Two oil/condensate families can be discerned based on the ETR, C24-tetracyclic terpanes and bisnorhopane. The first family seems to originate from Jurassic and the second form a pre-Jurassic source. The pre-Jurassic discoveries are found on the Loppa High in Permian rocks and in the margins between the Hammerfest Basin and the Finnmark Platform, and are possibly of Paleozoic age. The Jurassic sourced discoveries can be found in the whole study area, with a lighter fraction in the center of the Hammerfest Basin and heavier remigrated oil in the margins and structural highs. The light fraction is believed to be live. The oil has probably remigrated due to Cenozoic upliftment. Profoundly geochemical similarities with the remigrated paleo-oil in the Hammerfest Basin and the discoveries in Johan Castberg could suggest a remigration of oil into the field.