The interaction of structure and sedimentary process controlling deposition of the Upper Jurassic Brae Formation Conglomerate, Block 16/17, North Sea

Abstract

Block 16/17 is located in the UK Sector of the South Viking Graben adjacent to the Fladen Ground Spur. The block has yielded four major oil fields to date, and the principal reservoir is the Upper Jurassic Brae Formation. Relative uplift of the basin margin associated with the onset of a major extensional phase during the Oxfordian, and related seismic activity, generated gravity and turbidity flows which deposited coarse submarine conglomerates at the base of the graben boundary fault scarp. The distribution of these deposits has been controlled in part by the presence of transfer faults which cross-cut the graben boundary fault system. Transfer faults reflect the older structural grain of the area, which was mainly Caledonide and Tornquist. Detailed interpretation of a 3D seismic dataset has identified locations for possible submarine fan feeder channels. These are interpreted to be ‘canyon-like’ features located high on the terrace and closely controlled by major transfer faults. Such structural channelling has produced ‘shadow zones’, which are areas relatively starved of coarse clastic input in the basin. The geometry of the graben boundary footwall varies along-strike, and has influenced the lithofacies associations within the Brae Formation.