Identification of a large Upper Cretaceous polygonal fault network in the Hammerfest basin: Implications on the reactivation of regional faulting and gas leakage dynamics, SW Barents Sea

Abstract

We use a high resolution 3D seismic dataset covering 970km2, over the Snøhvit and Albatross gas fields of the Hammerfest Basin in the Barents Sea, in order to investigate the basin fault architecture and identify potential fluid pathways of deeper thermogenic gas and fluids. A polygonal fault (PF) interval not previously published is described in the three non-connected blocks within Campanian sequences, which could imply a permeable complex network of pathways that facilitate the vertical migration of hydrocarbons along the fault planes. The dominant orientation of the PFs is similar to the main regional tectonic fault trend (EW), suggesting a tectonic influence upon the development of polygonal faults, although some individual PFs locally seem to develop orthogonally to regional 1st order tectonic faults. A lithologic control on the occurrence of PF patterns is evident as none are observed within calcareous low clay sediments. The PF networks present three main orientations: dominant ENE/WSW, secondary NNE/SSW and a minor NE/SW. Paleocene–Early Eocene Faults (PEEFs) prevail above the PF networks, with coinciding ENE/WSW fault strikes, interpreted as preferential reactivation of the PF systems. Numerous amplitude anomalies, linked to the escape of thermogenic fluids from the Jurassic reservoir were identified. We present a conceptual model where the 1st order reactivated faults and PEEFs acted as pathways for fluids from the deeper hydrocarbon reservoirs. The PEEFs are partially sealing with a lateral migration component. Interplay between the PFs, PEEFs and the 1st order reactivated faults focuses the fluids vertically along the polygonal fault traces creating a wider diffuse zone which form large gas cloud anomalies in the seismic data.