THE ZECHSTEIN Z2 HAUPTDOLOMIT PLATFORM IN THE SOUTHERN UK MID NORTH SEA HIGH AND ITS ASSOCIATED PETROLEUM PLAYS, POTENTIAL AND PROSPECTIVITY

Peter Browning-Stamp ^*+, Carlo Caldarelli ^*, Graham Heard ^*, James Ryan ^* and James Hendry ^#

^* Horizon Energy Partners Limited, London, UK

^# Iapetus Geoscience Limited, Dublin, Ireland

⁺ Correspondence: peter.browning-stamp@horizonenergyglobal.co.uk

The Mid North Sea High (MNSH) region represents one of the least explored areas for the Late Permian Zechstein Hauptdolomit play in the Southern Permian Basin although some of the first offshore wells drilled in the UK were located here. In other parts of the basin such as onshore Poland, the Hauptdolomit Formation (“Hauptdolomit”) is an active and attractive exploration target, with oil and gas production from commercial-sized fields. In the UK, the play has been overshadowed by drilling campaigns in areas to the south of the MNSH which tested plays in the underlying Rotliegend and Carboniferous successions. However, with these areas now in decline, there is increased exploration interest in the Hauptdolomit in the MNSH region, particularly since 2019 when 3D seismic data were acquired and the first hydrocarbon discovery was made at Ossian (well 42/04-01/1Z). Geochemical data from the latter discovery have pointed to the presence of a prolific petroleum system with the potential for Hauptdolomit reservoirs to be charged both by Zechstein-generated oils and Carboniferous condensate/gas. With regard to hydrocarbon migration and preservation in the southern MNSH, a detailed evaluation of the effects of the Mid Miocene Unconformity has allowed for a greater understanding of the main factors controlling hydrocarbon preservation and remigration. Reservoir characterization of the Hauptdolomit play has been achieved by integrating petrographic microfacies analyses, core data and petrophysical interpretations. The most important factors controlling reservoir quality are the presence and extent of anhydrite cementation and the presence of high energy shoal facies. Thicker and coarser grained shoal facies are expected to occur along the yet-to-be explored Orchard platform margin where numerous prospects have been mapped and refined using recently acquired 3D seismic data.

Key words: Hauptdolomit, Mid North Sea High, UKCS, Zechstein Supergroup, Permian, North Sea, Southern Permian Basin, Z2 cycle, carbonate platform, reservoir rock.

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