Controls on fluid-flow systems in the Loppa High, SW Barents Sea

Abstract

The SW Barents Sea is a large hydrocarbon-prone epicontinental Sea comprised of a complex mosaic of deep sedimentary basins and structural highs. Uplift and erosion have been affecting the area on a large scale since the Cenozoic and have had a major impact on the petroleum systems in the area, resulting in spillage of hydrocarbons. The origin of the hydrocarbons are from deep source rocks, which have leaked or migrated into the shallow subsurface, forming gas hydrates and shallow gas accumulations, often accumlated in extensional fault blocks and the flanks of basins. This makes the Loppa High, bound by major faults complexes and basins on all sides, a potential target for hydrocarbon exploration. The distribution of fluid flow systems may improve our understanding of the sedimentary basins in the area. Numerous fluid flow features (e.g. fluid leakage along faults, gas chimneys, amplitude anomalies, pockmarks), and their relationship to tectonic elements and geological history have therefore been analyzed from 3D/2D seismic data. The faults in the area are divided into deep-seated faults and shallow faults, based on their vertical extent and the strata they are confined in. The deep-seated faults were probably initiated during the Permian - Early Triassic rifting and/or the Kimmerian tectonic phase in the Middle – Late Jurassic when the Atlantic rifting propagated northwards. The shallow faults are most likely the result from tectonic readjustments related to the opening of the Norwegian-Greenland Sea, in Late Cretaceous – Paleocene. This event and multiple glacial cycles resulted in multiple episodes of reactivation. Fluid migration from deeper reservoirs is evidenced by nine large gas chimneys, representing excellent migration pathways for gas. High amplitude anomalies within the Torsk Formation most likely represent accumulations of free gas below a sealing layer of gas hydrates. The occurrence of shallow gas is also probably controlled by the Opal A to Opal CT transition zone. Free gas accumulations are also represented along the URU as the unconformity may act as an impermeable barrier. Fluid expulsion events have led to the formation of circular to sub-circular depressions (pockmarks) on the seafloor. The fluid flow features occur mainly above major deep-seated faults, suggesting that the faults and occurrence of mature source rocks control the fluid flow in the area.