Hydrocarbon potential of the Central Spitsbergen Basin

Abstract

Modern oil and gas exploration on Svalbard has not yet resulted in any commercial discoveries. Is this symptomatic of the area, or may new play concepts and improved exploration techniques change this picture? This is a key question regarding a remote exploration province where, as we judge it, the hydrocarbon potential has barely been tested successfully, despite the recent completion of a 14th wildcat. Post-Devonian sediments cover most of central Spitsbergen south of Isfjorden and east of the West Spitsbergen Orogenic Belt. The basic preconditions for a hydrocarbon discovery seem to be met in general: mature source, reservoir and cap rocks are known to exist and several closed structures have been mapped. Yet, based on tectonic style, basin filling and timing, the prospectivity of different exploration sub-provinces can be clearly discriminated between. Sub-province 1 -– West Spitsbergen Orogenic Belt: The eastern, thin-skinned part of the West Spitsbergen Orogenic Belt (Tertiary) has a limited hydrocarbon potential. Ramp anticlinal structuring within late Paleozoic-early Mesozoic carbonates and clastics produced closures, but strong cementation and tectonic fracturing have partly destroyed reservoir quality and cap rock properties. Sub-province 2 -– Central Spitsbergen Basin, west flank: The west flank and axial part of the Central Spitsbergen Basin foredeep also has a limited potential. Blind anticlinal closures in the late Mesozoic-Tertiary overlie deeper ramp anticlines or thrust duplexes, but with overall poor reservoir quality and cap rock properties. High thermal maturation indicates a gas prone area. Sub-province 3 -– Central Spitsbergen Basin east flank: Improved reservoir quality and maturation profile (north) eastwards are negated by a general lack of larger scale structuring along the east flank of the Central Spitsbergen Basin. Sub-province 4 -– Billefjorden Fault Zone, eastwards: Carboniferous extensional tectonics and fault block rotation produced large closures, and good quality source, reservoir and cap rocks are present in Carboniferous-Permian outcrops. However, thermal maturity varies from oil to gas maturation and reservoir quality is reduced with increasing subsurface depths. Ramp anticlines (Tertiary) above a Mesozoic decollement produce a second play. Oil prone source rocks are present, but structural closures are generally small and reservoir and cap rock properties become a problem. Further eastwards, less structuring reduces the general trap potential. One exception is along the Lomfjorden Fault Zone, where ramp anticlines are also present. Reservoir quality and source rock maturation seem favourable, but present shallow burial reduces the seal potential.