Thomas Birchall (UNIS/UiO), Kim Senger (UNIS), M. Hornum (UNIS/Univ. Copenhagen), Snorre Olaussen (UNIS) and Alvar Braathen (UNIS/UiO) are the authors of the accepted article “Underpressure in the northern Barents shelf: Causes and implications for hydrocarbon exploration” to appear in the November edition of the journal American Association of Petroleum Geologists Bulletin. A preprint of the article is available in the ARCEx intranet. Please note that the figures are missing in the preprint.
The underexplored Barents shelf petroleum province is a globally unique example where naturally occurring underpressure is observed offshore and onshore. In the offshore parts of the northern Barents shelf minor underpressure (up to 23 bar subhydrostatic) is observed in the fault-bounded Mesozoic reservoirs of the Fingerdjupet subbasin. More severe (50 bar subhydrostatic), though irregular, occurrences of underpressure are encountered in the Triassic intervals of the neighboring Greater Hoop area. The abnormal pressures extend to the onshore archipelago of Svalbard, where pressures exceeding 60 bar below hydrostatic were encountered during drilling for a carbon dioxide sequestration project. In Svalbard, reservoir pressures were constantly monitored over three years, providing an insight into the reservoir behavior at unique timescales. The low permeability (< 2 md) reservoir in Svalbard is exposed some 15 km to the north of the drill site. Quantitative analysis with the apparent lack of a regional lateral seal, suggest a geologically recent origin of underpressure. There is evidence that the underpressure extends into the top seal which provides further indication to the likely cause of underpressure. Similarly to many global occurrences of underpressure in petroleum provinces, the Barents shelf has undergone severe uplift, most recently due to deglaciation. Well data, outcrop observations and isotope data combined with the areas geological history indicate that glacial loading, unloading and erosion, potentially with the aid of natural fractures, is the likely dominant underpressure generating mechanism.
Birchall, Thomas; Senger, Kim; Hornum, M.; Olaussen, Snorre & Braathen, Alvar (2020). Underpressure in the northern Barents shelf: Causes and implications for hydrocarbon exploration. American Association of Petroleum Geologists Bulletin, vol. 104, no. 11, November 2020. ISSN 0149-1423. doi: 10.1306/02272019146. [intranet]