Petroleum occurrences in the carbonate lithologies of the Gohta and Alta discoveries in the Barents Sea, Arctic Norway

Abstract

Investigation of petroleum inclusions in carbonate samples from the Senilix well in the Barents Sea reveals petroleum entrapment in Paleozoic carbonates at reservoir temperatures from as low as 87.3°C to more than 130°C. Using corrected bottom hole temperatures, this corresponds to depths of 2800–4100 m, compared to the present-day depth of these samples of only 1965.9–2020.5 m. The oil in the Gohta and Alta discoveries is concluded to be of either Lower Triassic or Paleozoic origin based on the isomer distribution of triaromatic dimethylcholesteroids (TA-DMC). A potential source-rock candidate is the Ørret Formation, which is the time-equivalent to the Ravnefjeld Formation in Greenland. These oils are of a different origin compared to oils in the nearby Skrugard (renamed to Johan Castberg) discovery which contain oil sourced from the Upper Jurassic Hekkingen Formation. Evidence is presented to suggest that the Gohta and Alta oils represent blends of petroleum expelled at maturities ranging from about 1.0% calculated vitrinite reflectance (Rc) to more than 1.3%Rc, and this corroborates the inferences made from the petroleum inclusions. This emerging play is significant to exploration in the karst developed on the Barents Shelf and the Bjarmeland Platform during the Permo-Carboniferous. Karst reservoirs have been linked to eustatic sea-level changes, and analogous karst reservoirs may be present elsewhere in the Circum-Arctic: for example, in the Sverdrup Basin.

Impact of growth faults on mixed siliciclastic‐carbonate‐evaporite deposits during rift climax and reorganisation—Billefjorden Trough, Svalbard, Norway

“…Palaeokarst systems are known to be controlled by pervious faults, fracture networks and bedding orientation (Palmer, 1991). In addition, the palaeokarst systems are targeted with a success in exploration of the Barents Shelf offshore Svalbard, for example, Gohta and Alta discoveries in Loppa High (Matapour et al., 2019; Sayago et al., 2012). The model presented in this study (Figure 8e) indicates simultaneous faulting and karstification and adds our understanding of palaeokarst formation in rift basins, as well as increase predictability of finding palaeokarrst features that might be considered as petroleum reservoir rocks.…”

Characterization of Upper Palaeozoic Organic‐rich Units in Svalbard: Implications for the Petroleum Systems of the Norwegian Barents Shelf

“…likely to be oil prone. It is noteworthy in this respect that Matapour and Karlsen (2017) and Matapour et al (2018), studying bitumen and oil at the Alta discovery on the Loppa High, recorded a marine Palaeozoic agespecific biomarker petroleum signature, suggesting that at least some of the petroleum at Alta/Gohta is of a Palaeozoic origin.…”

Influence of Pleistocene Glaciation on Petroleum Systems and Gas Hydrate Stability in the Olga Basin Region, Barents Sea

“…Upper Permian organic-rich argillaceous mudstones assigned to the Ørret Formation (Fig. 2) are oil-prone source rocks (Ehrenberg et al, 2001;Lerch et al, 2018;Matapour et al, 2019). During the Early-Middle Triassic, a large-scale progradational system developed in the Barents Sea (Riis et al, 2008;Lundschien et al, 2014) and thick sequences of clastic sediments, transported from provenance areas in the Urals foldbelt and western Siberia, were deposited in transgressive-regressive cycles (Faleide et al, 2010;Høy and Lundschien, 2011;Lundschien et al, 2014;Gilmullina et al, 2021;Gilmullina et al 2022).…”