The static and dynamic behaviour of large faults as seals and conduits to aqueous and petroleum fluid flow at geological time-scales: Observations from the Beryl Embayment, UK North Sea

Abstract

Faults play an important role in controlling flow and retention of aqueous and petroleum fluids from overpressured basin centres (“kitchens”) to basin flanks. The Beryl Kitchen is a deep overpressured basin in the Beryl Embayment on the flanks of the Viking Graben in the UK northern North Sea and provides a data rich laboratory allowing these processes to be studied in detail. In this study we combine the results of detailed structural mapping, constrained by broadband seismic and abundant well control, with reservoir pressure data and hydrocarbon geochemistry. We use the data to demonstrate how the bounding faults of the Beryl Kitchen have acted as significant capillary seals, even with abundant porous and permeable reservoir juxtaposition across the key faults. The fault plane seals allowed the baffled escape of aqueous fluids, creating fault-bounded pressure compartments, while trapping significant hydrocarbon columns at the boundary between overpressured and normally pressured reservoirs. We demonstrate how the behaviour of some of these faults has evolved with progressive burial and increasing source rock maturity in the deepest parts of the basin. On the flanks of the Beryl Kitchen these processes have resulted in the preservation of hydrocarbon accumulations with unexpectedly tall columns and an unintuitive distribution of hydrocarbon water contacts in adjacent fault blocks. These accumulations provide valuable exploration analogues for the evaluation of the hydrocarbon potential of fault bound structures at the margins of overpressured basins.