Potential for subtle traps in the Permian Rotliegend of the UK Southern North Sea

Abstract

The Permian, Rotliegend Group of the UK Southern North Sea is shown to consist of periodic, cyclic stratal packages which can be used to aid regional correlation in the zone of playa–erg interaction colloquially known as the Rotliegend Feather Edge. In this area, the depositional topography controls the sedimentary facies, with a concentration of aeolian sandstone deposition in the topographic depressions, especially in the lee of hills. These units onlap the contemporaneous intra-basinal and marginal highs. The palaeotopographic lows rapidly became infilled, with later lacustrine deposition occurring over a smoother surface. This allowed the deposition of finer-grained lake deposits over the sands. Prediction of the palaeotopography is key to understanding potential reservoir distribution and seal juxtaposition within the Rotliegend. This paper demonstrates how pre-Permian subcrop maps, Bouguer anomaly maps and the Rotliegend isopach can be used to reconstruct this palaeotopography. Two areas are studied which demonstrate some of the subtleties of the model. The southern Quadrant 42–43 area had a palaeotopography with gentle gradients and a number of subtle intrabasinal highs that allowed for isolated reservoirs overlain by shales with high sealing potential. In contrast, the northern Quadrant 49 area, contained only intra-basinal relief, with high palaeotopographic gradients. Aeolian sediments banked up against this barrier and no intra-Rotliegend seal was deposited over these sands.