Petroleum-related hydrocarbons in deep and subsurface sediments from South-Western Barents Sea

Abstract

Havforskningsinstituttets institusjonelle arkiv Brage IMR - Institutional repository of the Institute of Marine Research b r a g e i m rDette er forfatters siste versjon av den fagfellevurderte artikkelen, vanligvis omtalt som postprint. I Brage IMR er denne artikkelen ikke publisert med forlagets layout fordi forlaget ikke tillater dette. Du finner lenke til forlagets versjon i Brage-posten. Det anbefales at referanser til artikkelen hentes fra forlagets side. Ved lenking til artikkelen skal det lenkes til post i Brage IMR, ikke direkte til pdf-fil.This is the author's last version of the article after peer review and is not the publisher's version, usually referred to as postprint. You will find a link to the publisher's version in Brage IMR. It is recommended that you obtain the references from the publisher's site.Linking to the article should be to the Brage-record, not directly to the pdf-file. AbstractSubsurface sediments from a pockmark area in South-Western Barents Sea have been earlier found to contain elevated levels of petroleum-related polycyclic aromatic hydrocarbons. This work describes a comprehensive analysis of various biomarkers, including the highly sourcespecific hopanes, in a 4.5 m long gravity core from the same area, together with subsurface sediment samples from other areas in the region without pockmarks present ("background samples"). A clear difference between the pockmark gravity core and the background sediment cores was found, both with regard to genesis and the level of transformation of organic matter. A number of indicator parameters, such as methylphenanthrene index (MPI-1), point towards a significantly higher maturity of hydrocarbons in the pockmark core throughout its length as compared to the other sampled locations. Higher contents of microbial hopanoids (hopenes) may indicate the former presence of petroleum. These findings confirm the hypothesis of a natural hydrocarbon source in the deeper strata present in the studied location with pockmarks.

Tracing the origin of thermogenic hydrocarbon signals in pockmarks from the southwestern Barents Sea

“…Additionally, a similar distribution of the hopanoic compounds (see Fig. 5 Our conclusions are in contrast to the interpretations of Boitsov et al (2011), who also investigated a pockmark area in the SW Barents Sea (approx. 50-100 km distance to our study area).…”

“…Such a seepage scenario of thermogenic hydrocarbons through the pockmark system cannot be concluded from our data. Nevertheless, the pockmark area investigated by Boitsov et al (2011) was very close to the Goliat oil field, which might explain the different findings between the two studies.…”

“…Together with thermogenic gas, these hydrocarbons might have migrated to the seafloor (Hood et al, 2002;Logan et al, 2009;Thrasher et al, 1996); thus, forming the pockmark structures (Hvoslef et al, 1996). Boitsov et al (2011) reported that petroleum leakage pulses might have occurred in pockmarks in the south western Barents Sea. To identify the potential seepage of oil, the pockmark sediments can be analyzed for specific petroleumderived thermogenically generated biomolecules, such as n-alkanes, hopanoids and steranes.…”

The MAREANO programme – A full coverage mapping of the Norwegian off-shore benthic environment and fauna

“…In areas with very soft sediment a multicorer can also be deployed. Following laboratory analysis of the sediment cores, these multicorer data are used to map the occurrence of pollutants at different depths in the sediment, reflecting the environmental status at different points in time (Boitsov et al 2011(Boitsov et al , 2013.…”

Hydrocarbon plumbing systems above the Snøhvit gas field: Structural control and implications for thermogenic methane leakage in the Hammerfest Basin, SW Barents Sea

“…In the formation of gas hydrate, thermogenic methane content may range from 27-97 mol% while biogenic methane generally contains over 99% methane (Kvenvolden, 1995). Since the total organic carbon (TOC) content of the late Weichselian glaciomarine sediments is lower than 2% (Boitsov et al, 2011) and this amount would be too low to produce biogenic methane that could explain the observed seabed pockmarks (Solheim and Elverhøi, 1985), a deeper thermogenic source of gas must be present.…”