Controls on and Consequences of Upper Permian Carbonate Platform Margin Palaeomorphology in the Southern North Sea

Abstract

Interpretation of 1484 km² of high-quality overlapping three-dimensional (3D) time-migrated seismic datasets in the Quadrant 47 area of the UK Southern North Sea has revealed in forensic detail the palaeomorphology of a deeply buried (Upper Permian) Zechstein Group (Z2 Cycle) carbonate shelf margin. The shelf edge is imaged clearly at a sub-regional scale enabling the mapping of a hitherto unrecognized spectacular series of corrugated embayments and promontories which locally have a relief in excess of 200 m. Petrophysical well-log and core data have been used to devise facies models then when combined with 3D seismic data permit a detailed understanding of the Zechstein shelf-edge geology to be determined along a 40 km segment. Strong lateral and vertical variations in velocity between anhydrite, dolomite and halite within the Zechstein Supergroup has long been recognized to cause seismic imaging and depth conversion uncertainty and are the main issues and challenges when interpreting and understanding seismic data in the region. We demonstrate that the mapping of the Zechstein shelf edge in conjunction with new velocity models affords a more accurate delineation of the basin margin geometry in both the time and depth domains leading to enhanced identification and delineation of the prospective Rotliegend Group reservoirs that lie below. The study provides not only important new insights into the nature of the south-western margin of the Southern Permian Basin but a new-found basis for interpreting the basin's ancient (buried) shelf-margin physiography. The results also have significant implications for future petroleum exploration in an area which has been off-radar for some time. The improved insight into the Zechstein margin has led to the identification of the Juliet field trap in UKCS block 47/14b along the periphery of the gas basin. This discovery, which has recently begun development, proves that the Upper Palaeozoic play fairway is more extensive along the Southern Permian Basin margin than many had previously thought. It is anticipated that this work may help extend the life of this mature yet prolific gas province by delineating further potential traps and new plays.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016