The evolution of the dowsing graben system: Implications for petroleum prospectivity in the UK Southern North Sea

Ross J. Grant, John R. Underhill, Jaume Hernández-Casado, Rachel J. Jamieson, Ryan M. Williams

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Upper Permian (Zechstein Supergroup) evaporites have a major control on structural styles and prospectivity in the UK Southern North Sea (SNS). They form the regional super-seal for the main Rotliegend Group (Leman Sandstone Formation) reservoir play fairway immediately beneath. The evaporites have highly variable thicknesses due to the syndepositional basin architecture, differential loading and post-depositional deformation through diapirism and salt withdrawal. The halokinetic activity leads to touchdown (welding) of the supra-salt section onto the sub-salt strata and the development of narrow (up to 15 km-wide) graben systems. The interpretation and depth conversion of well-calibrated, highquality, 3D post-stack time-migrated (PSTM) seismic data along the southwestern margin of the basin show that a NW–SEstriking elongate extensional Dowsing Graben System transects the area. The graben is defined by a series of large, overlapping, en echelon listric growth faults, with oblique secondary planar faults, which sole-out on two main (deep and shallow) décollement levels in the Zechstein Supergroup and the Middle Triassic Röt Halite Member. Whilst its initial formation was related to Mesozoic extension, the graben system also displays a contractional overprint resulting from regional compression and structural inversion during the Cenozoic. Detailed mapping of the Zechstein Supergroup has revealed that the evolution of the extensional system was influenced by the ESE–WNW-striking anhydrite–carbonate Zechstein shelf-margin. The occurrence of variable-thickness, low-velocity sediments within the graben impacts seismic imaging and depth conversion, leading to prospective structures being overlooked; something that has implications for prospectivity in the SNS and other evaporite basins where similar graben occur.

Original languageEnglish
Article numberpetgeo2018-064
JournalPetroleum Geoscience
Volume27
Issue number1
Early online date16 Dec 2019
DOIs
Publication statusPublished - Feb 2021

ASJC Scopus subject areas

  • Fuel Technology
  • Geology
  • Geochemistry and Petrology
  • Economic Geology
  • Earth and Planetary Sciences (miscellaneous)

Fingerprint

Dive into the research topics of 'The evolution of the dowsing graben system: Implications for petroleum prospectivity in the UK Southern North Sea'. Together they form a unique fingerprint.

Cite this