The role of stratigraphic juxtaposition for seal integrity in proven CO fault-bound traps of the Southern North Sea

G. Yielding, N. Lykakis, John Underhill

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Exploration well 50/26b-6 in the UK Southern North Sea discovered a trap containing a gas-bearing Rotliegend Group (Leman Sandstone Formation) reservoir which was a major surprise at the time of drilling in that its gas composition was approximately 50% CO (with 9% N2 and the remainder methane). Christened the 'Fizzy Discovery', the accumulation was appraised by well 50/26b-8. Subsequently, another CO-rich discovery (Oak) was made along-strike in nearby block 54/1b. Column heights at the well locations are of the order of a few tens of metres, but at the Fizzy Discovery the column height at the trap crest is estimated to be over 200 m. Interpretation of a high fidelity PSTM 3D seismic dataset has been constrained by 33 exploration wells allowing fault geometries and stratigraphic offsets to be determined with confidence. Despite late-stage (Late Cretaceous) structural inversion, the net boundary-fault offset is sufficient in both the Fizzy and Oak discoveries to almost breach the Zechstein Group evaporite super-seal, and the CO-bearing Rotliegend Group in the footwall is now juxtaposed against hanging wall sediments of the uppermost Zechstein Group. Hence, these Zechstein Group units evidently act as a robust long-term side-seal for the carbon dioxide column. The Fizzy and Oak accumulations are noteworthy in providing a natural demonstration of top seal and fault side-seal integrity for carbon dioxide in a subsurface reservoir, that has remained intact over a geological timescale in what is otherwise a prolific methane-rich reservoir play fairway.
Original languageEnglish
Pages (from-to)193-203
Number of pages11
JournalPetroleum Geoscience
Volume17
Issue number2
DOIs
Publication statusPublished - 1 May 2011

Keywords / Materials (for Non-textual outputs)

  • Allan diagram
  • Carbon storage
  • Fault seal
  • Rotliegend group
  • Southern north sea
  • Stratigraphic juxtaposition
  • Zechstein group evaporites

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