TECTONIC MODELING OF THE MIDDLE JURASSIC SYNRIFT STRATIGRAPHY IN THE OSEBERG-BRAGE AREA, NORTHERN VIKING GRABEN

A finite difference model, allowing for episodic movements along diffe rent faults, is used to examine the effect of tectonics on the stratig raphic signature in the Oseberg-Brage area in the northern Viking Grab en. Constraints are provided by local exploration and production well data and 3-D seismic coverage, and a regional depth-converted seismic line. In the modelling, we focus on the influence of varying rates of fault movement on stratigraphic signatures such as upflank unconformit ies and changes in layer thickness. We couple the basinwide features o f the northern Viking Graben with the fault-block-scale features of th e Oseberg-Brage area by using parameter constraints derived by large-s cale modelling as input for the local-scale model. In addition, subsid ence patterns resulting from the basinwide model were used as backgrou nd subsidence fbr the fault block model of the Oseberg-Brage area. The model results indicate that the alternating activation of different f aults with varying extension rates can cause stratigraphic features su ch as unconformities, condensation and onlap/offlap patterns. Onlap oc curs during periods of low extension rates. An increase in extension r ate along a fault causes footwall uplift, resulting in condensation or upflank erosion yielding unconformities. This influence can also affe ct sub-basins further away from the fault. Downdip layer thickening re flects the local tilting of fault blocks. The coupling of the local an d regional scales turns out to be essential in explaining the stratigr aphy of the Oseberg-Brage area: basinward and, notably, updip layer th ickening as observed on some of the fault blocks can only be explained by activity of the boundary fault on the opposing, western margin of the northern Viking Graben.