A log correlation of the Rotliegend of the northern Cleaver Bank High: the search for controls on reservoir sand distribution

Abstract

Gamma ray log correlations of some 50 Open File wells were used to investigate the distribution and relative age of aeolian Leman Sandstone developments across the northern Cleaver Bank High. The correlations led to a sequence stratigraphic interpretation based on a depositional record of climatically forced fluctuations in the level of the Silverpit Formation playa lake system. This confirmed the widely reported diachroneity of the Leman Sandstone and identified the onlapped Base Permian palaeotopography and climatically forced, generally positive, changes in the water budget of the Silverpit Lake as the chief controls on aeolian sand distribution. However, a ‘1/f n ’ power law distribution of changes in water budget is preferred to the idea of strictly cyclic climatic control. On this basis, the transgression of the northern Cleaver Bank High and the occurrence of aeolian and lacustrine end-member facies within depositional sequences of uniform thickness can be understood. Interval isochores were used to derive palaeotopographic maps of the Base Permian. Taken in conjunction with the observed facies of the onlapping depositional sequences, the maps locate under-explored basal aeolian Leman Sandstone play fairways.