Abstract Hydrocarbon exploration in the North Sea Basin has revealed a multitude of focused fluid conduits, which manifest in seismic data as pipe or chimney structures that in some instances are connected to underlying hydrocarbon reservoirs. 3D seismic data from the eastern margin of the East Shetland Platform reveal the presence of more than 450 focused fluid conduits. Most of these initiate at the Base Tertiary Unconformity and cross-cut the overlying sediments. The focused fluid conduits correlate with intra-platform basin structures beneath the Base Tertiary Unconformity and with permeable sediment lobes, channels and deltaic units in the overlying Paleocene to Eocene successions, which include known hydrocarbon reservoirs (e.g. Bressay, Bentley, Skipper or Piper). Clusters of pipes associated with other channels and deltaic units may indicate the presence of additional prospects at the eastern margin of the East Shetland Platform. Our study highlights the potential of using seismically imaged focused fluid system analyses in hydrocarbon exploration in platform areas on both sides of the Viking Graben and other frontier areas as they reveal the presence of working hydrocarbon charge pathways.

Abstract Thick Paleozoic successions are buried under the Greater East Shetland Platform (ESP) and Mid North Sea High (MNSH), two large underexplored platform regions flanking the structural depocentres of the North Sea. Here, newly acquired broadband seismic data are interpreted to provide a novel assessment of the regional tectonostratigraphic evolution and its influence on hydrocarbon prospectivity. Numerous working reservoir units are present over these two frontier areas, together with large Paleozoic traps. Hydrocarbon charge occurs either via a likely maximum 30–40 km lateral migration from the Jurassic/Carboniferous basinal source kitchens or, possibly, via vertical/lateral migration from deeper Devono-Carboniferous source intervals. The two regions underwent a largely similar evolution, consisting of at least eight successive switch-overs between regional compression/uplift and extension/subsidence in the last 420 myr. However, on the Greater MNSH, the lack of significant Permo-Triassic rifting probably resulted in too little subsidence for the lower Carboniferous interval to reach sufficient burial depth for gas maturation. Seep and fluid escape data suggest a working ‘deep’ source in the Greater ESP. Here, the presence of localized Permo-Triassic intra-platform grabens and half-grabens provided sufficient subsidence for the oil-prone middle Devonian unit to eventually enter the oil maturation window and faults provide easy conduits for the upwards migration of oil.

Abstract 2D and 3D seismic data from the mid-Norwegian margin show that polygonal fault systems are widespread within the fine-grained, Miocene sediments of the Kai Formation that overlie the Mesozoic/Early Cenozoic rift basins. Outcropping polygonal faults show that de-watering and development of polygonal faults commenced shortly after burial. On the other hand, the polygonal fault system's stratigraphic setting, upward decreasing fault throw and the association with fluid flow features that are attributed to de-watering of the polygonal fault systems shows that polygonal faulting and fluid expulsion is an ongoing process since Miocene times.