Fluid flow and faulting along the northern margin of the Loppa High

Abstract

The Barents Sea is a large epicontinental sea and petroliferous basin, which is fairly unexplored compared to other regions of the Norwegian Continental Shelf (NCS). The structural configuration of the SW Barents Sea is characterized by a complex mosaic of structural highs, platforms and basins, reflecting the interplay between multiple tectonic phases. Late Cenozoic glacially induced subsidence and uplift, and extensive differential erosion, may have had a major impact on the petroleum systems in the area, causing a reconfiguration of the fluid flow systems by gas expansion, oil-spill, migration and remigration of hydrocarbons into the shallower subsurface. Subsequent accumulations of shallow gas may represent significant drilling hazards, potential commercial hydrocarbon resources or be indicative of deeper prospective reservoirs, and are as such important exploration targets. Identification and analysis of fluid flow indications and their relationship to the structural development and denudation history of the Loppa High will provide a better insight to the controlling mechanisms of fluid flow systems on both a local and regional scale.

Seismic interpretation, spatial visualization and analysis of 2D and 3D data from the northern margin of the Loppa High have revealed numerous fluid flow indications such as leaking faults, gas chimneys, shallow gas accumulations and buried and exposed depressions. The complex structural development of the Loppa High has led to the development of several sets of faults, which have been classified as deep-seated Permian, vertically extensive Permian-Triassic and shallow Triassic. The larger-scale structural geology of the study area encompasses narrow grabens and extensive horsts, believed to reflect Carboniferous-Permian rifting, extensional faulting related to the proto-Atlantic rift system and later rifting events associated with the opening of the Norwegian-Greenland Sea. The numerous faults identified may constitute a larger network of potential fluid conduits, connecting deeper reservoirs with shallower, suggesting a structural control on the fluid flow systems in the study area. Gas chimneys and high-amplitude anomalies occurring at several levels within the subsurface strata, and the presence of both buried and exposed seabed depressions, testifies to vertical and lateral migration from deeper source rock intervals, gas accumulations along faults and URU, and episodes of potential gas release at the seabed. Observations and results largely correspond to similar studies carried out in the SW Barents Sea region, supporting the theory that fluid flow systems in the area are at least partially structurally controlled and that the distribution of fluid flow systems may have been altered by Late Cenozoic tectonic readjustments through extensive uplift and erosion.