Geochemical, petrographical, and petrophysical evaluations of a heterogeneous, stratiform dolomite from a Barremian oil field, offshore Abu Dhabi (United Arab Emirates)

Kazuyuki Yamamoto, Gary Ottinger, Osama Al Zinati, Hideko Takayanagi, Koshi Yamamoto, Yasufumi Iryu

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

A stratiformdolomite is developed in the Barremian carbonates of offshore AbuDhabi,UnitedArab Emirates. Although the average thickness is only 1.1 m (3.6 ft), it is an important drilling target characterized by heterogeneous porosity-permeability values in the studied oil field. We discuss the origin and development of the dolomite based on geochemical, petrographical, and petrophysical evaluations using 81 cores recovered from the field. The d13C values of the dolomites are relatively high (>5‰), and 87Sr/86Sr mostly fall in the range of Barremian seawater. The thin stratiform geometry and the geochemical signatures of the dolomite suggest early dolomitization just below the seafloor that was driven by the diffusion of Mg2+ from the seawater on top of a shallow platform. Lateral changes in the degree of dolomitization seem to be controlled by the permeability of the precursors. Dolomitization progressed further in packstone precursors (higher permeability) than in wackestone precursors (lower permeability), which led to greater permeability improvement in the packstone by replacement of fine matrix with larger dolomite crystals. Subsequently, late burial dolomite cementation occurred during oil migration, which preferentially affected the higherpermeability early dolomite, and areally, it progressed more in the flank of the field because of the delayed oil charge there. Dolomite-to-dolomite recrystallization became dominant after the oil emplacement. The recrystallization has been continuing under current burial temperatures (>100°C [>212°F]), fully resetting d18O values and modifying the Fe and Mn concentrations of the dolomites, but has not significantly affected their petrography and petrophysics in the oil leg.

Original languageEnglish
Pages (from-to)129-152
Number of pages24
JournalAAPG Bulletin
Volume102
Issue number1
DOIs
Publication statusPublished - 2018 Jan

ASJC Scopus subject areas

  • Fuel Technology
  • Energy Engineering and Power Technology
  • Geology
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)

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