High-resolution 3D-seismic data indicate focussed fluid migration pathways above polygonal fault systems of the mid-Norwegian margin

Abstract

Seismic attribute analysis and interpretation of high-resolution 3D-and 2D-seismic data reveal focussed fluid flow processes through the gas hydrate stability zone (GHSZ) at the northern flank of the giant Storegga Slide. Diffusive fluid migration predominantly starts from a widespread polygonal fault system in fine-grained sediments of the Miocene Kai Formation. The overlying 600-700 m thick Plio-Pleistocene Naust Formation shows spatially related soft-sediment deformation and overlying fluid conduits. A low relief antiform structure connects to an overlying 250 m high, 300 m wide and 3 km elongated columnar zone, where seismic signatures suggest self-enhanced permeability, i.e. natural hydraulic fracturing. "Push-down" effects create an elongated depression caused by increased gas accumulations where a cluster of vertical cylindrical acoustic pipe structures originates. These pipe clusters pierce the GHSZ and indicate focussed fluid flow pathways originating from potentially overpressured sediments. High seismic reflection amplitudes at the seafloor above the pipe structures may indicate pockmarks with authigenic carbonates and/or gas hydrates. The observed objects and seismic features presented are not stand-alone indicators for fluid flow, but a joint perspective illustrates that they are vertically tied together providing new insights to the effects of focussed fluid flow.

First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea

“…Physical sampling of shallow gas hydrates was first reported in 2006 [52], though the Nyegga gas hydrates have long been studied "geophysically" [53][54][55]. It is notable that a shallow geotechnical borehole, 6404/5 GB1, penetrated the BSR during a drilling campaign in 1997.…”

“…Hustoft et al [55] illustrate a series of porous and permeable zones suitable for hydrate formation. A quick estimate suggest that this "reservoir" accounts for approximately 50% of the area of interest.…”

Norwegian margin outer shelf cracking: a consequence of climate-induced gas hydrate dissociation?

“…It is an area where numerous seeps have been documented (e.g. Hovland 2009), and we thus know that gas migration has occurred or takes place continuously in permeable or hydro-fractured layers of sediments (Hustoft et al 2007;Hustoft et al 2009a, b). More than 400 pockmarks that are connected to chimneys (columnar disturbances of parallel-bedded deposits) were identified in the Nyegga pockmark field (Hustoft et al 2009b).…”

Seismic Expression of Polygonal Faults and Its Impact on Fluid Flow Migration for Gas Hydrates Formation in Deep Water of the South China Sea

“…However, the polygonal faults may provide an additional pathway for the fluid flow, and the relationship has also been documented in the Lower Congo Basin [25], Norway continental margin [26,27], and Scotian slope of the eastern Canada continental margin [28].…”

“…The relationship between the polygonal fault and gas hydrate has been discussed on the continental margin of Norway, the Lower Congo basin, and the Scotian margin of the east coast of Canada [23,24,26]. On the mid-Norwegian margin, the polygonal fault system is located in the fine-grained hemipelagic sediments of the Kai formation, showing that fluid flow related to polygonal fault in this area is an ongoing process since the early Miocene in the mid-Norwegian [26,27].…”