Palaeo-carbonate seep structures above an oil reservoir, Gryphon Field, Tertiary, North Sea

A. Mazzini, Davide Duranti, R. Jonk, John Parnell, Bryan Thomas Cronin, Andrew Hurst

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Petrographic and geochemical analyses performed on a North Sea core from the Gryphon Field reveal the presence of palaeo-degassing features surrounded by injected sandstones in the Eocene interval. The injected sandstones are oil-stained and poorly cemented by carbonate and quartz. O-18 isotope analyses indicate that carbonate cementation occurred during shallow burial (likely less than about 300 m). Depleted C-13 (around -30parts per thousand V-PDB) carbonate cement suggests that bicarbonate was derived from the microbial oxidation of oil and gas. Late quartz overgrowths enclose oil present in the injected units. The tubular degassing conduits are composed of zoned cements and have delta(18)O and delta(13)C isotope values similar to the injected sandstones, indicating that oil and gas seepage induced the precipitation of authigenic carbonate in the shallow subsurface. Oil inclusions in inter- and intra-crystal cement sites in both injected sandstones and degassing conduits indicate that oil seepage was an ongoing feature at shallow burial. A proposed model involves oil and gas seepage and the formation of the degassing conduits, followed by a sand injection phase. It seems likely that oil and gas continued to leak towards the seabed by exploiting the network of permeable injected sandstones and the horizons of porous degassing features.

Original languageEnglish
Pages (from-to)323-339
Number of pages16
JournalGeo-Marine Letters
Volume23
Issue number3-4
DOIs
Publication statusPublished - 2003

Keywords

  • AUTHIGENIC CARBONATES
  • COLD-SEEPS
  • ACCRETIONARY PRISM
  • MEDITERRANEAN SEA
  • FLUID INCLUSIONS
  • SUBDUCTION ZONE
  • INJECTED SANDS
  • METHANE
  • CEMENT
  • SEDIMENTARY

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