A study of the Lower Cretaceous Åsgard Formation in the South Viking Graben, North Sea
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The Åsgard Formation of Lower Cretaceous age in the South Viking Graben represents a formation of great interest in petroleum exploration in the North Sea, but is poorly understood. The area of study is in the North Sea; west of the Utsira High and east of the Crawford Spur. Many wells exist in the area, but not all wells penetrate the Lower Cretaceous strata. There exist some publications on the formation in the Viking Graben area, but most of these are focused around the northern part of the Viking Graben, the Sogn Graben and the Agat discovery. This leaves this formation poorly known in the central and southern part of the Viking Graben area. In this work, available 3D seismic and well data are used for mapping the Åsgard Formation and predicting the deposition and extent of the possible Åsgard sands. The sedimentation of the Lower Cretaceous was controlled by the inherited fault-bounded structural highs and deep basins that were a product of the rifting that happened in Late Jurassic. During periods of sea-level fall these structural highs developed into local sediment sources, as clastic sediments were derived from the highs and transported into the deep-marine basins by slumping and mass-flow processes. There has been a potential for transport of sand from both east and west; the sand derived from the Crawford Spur has been transported over the terraces and deposited in submarine fans in the basin, while the sediments derived from the Utsira High have been locally deposited in fans on terraces west of the high. The available data suggest that most of the sands have been sourced and transported from the west. The well coverage is better to the west of the study area than in the east, this makes the reliance in the interpretation better for a potential transport from west than for the east. The possibility of finding large amounts of sand is highest in the middle part of the basin where the strong amplitude features are found, on the Top Åsgard reflector, but there is little evidence from the well data for the transportation of sands further out into the basin.