Shallow gas accumulation in glacigenic sedimentary formation of the mid-Norwegian margin north of Storegga slide (Helland Hansen 3D cube)

Abstract

My master thesis concentrates on the distribution of gas accumulation to infer vertical fluid migration in sedimentary formations of Eocene-Oligocene (Brygge Formation) and Pliocene-Pleistocene (Naust Formation) in the mid-Norwegian margin at the Helland Hansen Arch, north of the Storegga slide. The seismic interpretation is based on “Helland Hansen 3D cube SH9602”. The N-S oriented Helland Hansen Arch (HHA) has a hydrocarbon potential where both tectonic and thermal subsidence has played a role in forming hydrocarbon traps. The oozes and debris flow deposit seal off the vertical migrating fluids allowing them to accumulate along the HHA. At the crest of HHA seismic bright spots are delineated by using acoustic attributes. The area beneath the bright spots shows the depletion of higher frequencies due to absorption of seismic energy. Beneath the bright spot vertical fluid migration features appear as disturbed and distorted wipe-out seismic zone and velocity sags (push down). The vertical fluid migration features occur along major faults and are identified by the low coherency values on variance attribute maps. Gas accumulation zones are extensively disturbed by faulting along the eastern flanks of HHA where polygonal faults provide routes for vertical gas migration. The polygonal faults were reactivated by sediment loading from submarine slides. Pipe structures provide further pathways for vertical gas migration from reactivated polygonal faults. The presence of gas in the glacigenic sedimentary formation of Naust A and U unit is identified by the distinct reduction of P-wave velocities.