Improving interpretation of complex subsalt structures by integrated modelling. An example from the Barents Sea

Abstract

The geological evolution of the Barents Sea is very complex, due different styles of deformation at different times it passed through. The Barents Sea developed through compressional tectonics during Ediacaran Timanian orogeny, followed by the Caledonian orogeny in Ordovician-Early Devonian and Uralian orogeny. The Barents Sea is underlain by Caledonian nappes with a general trend of NW-SE according to a recent aeromagnetic and marine gravity surveys. The post Caledonian deformation was followed by a series of faulting in Late-Devonian, mid Late Carboniferous, Late Permian, Middle Jurassic and Late Cretaceous which resulted in formation of rift basins (Tromsø, Bjørnøya, Nordkapp, Fingerdjupet, Maud and Ottar) and fault bound highs (Loppa and Norsel), with a general trend of NE-SW. The extensional tectonics was also responsible for triggering salt diapirism in Nordkapp Basin during Early Triassic. The mobilised salt has a negative impact on conventional seismic due to its properties (high reflectivity, rogues surface) and complex geometry in the subsurface, and leads to limited application of seismic reflection method in salt basins. Low density and diamagnetic nature of salt gives potential field data an ability to discriminate and map salt bodies with respect to surrounding host rock. The non - uniqueness of the model derived from potential field data is constrained by seismic interpreted horizons and calibrated with borehole measurement. The model was constructed by combining geological information, well long data and seismic data as constraints. The resulted model agrees with previous studies, although some of the aspects of the salt in Nordkapp Basin (cap rock and detached salt) was not covered by the model. While most of the salt in Nordkapp Basin was extruded as diapir, the model suggests that there still considerable amount of salt in the Nordkapp Basin which was not fully mobilised owing to competent overlying strata. Filtering of the potential field data has shown that the salt are surrounded by magnetic high lineaments, proving the control of regional tectonics over the salt formation, distribution and mobilisation.