STRATIGRAPHY AND DIAGENESIS OF THE THAMAMA-B RESERVOIR ZONE AND ITS SURROUNDING DENSE ZONES IN ABU DHABI OILFIELDS AND EQUIVALENT OMAN OUTCROPS

S. N. Ehrenberg ¹*, J. E. Neilson ², E. Gomez-Rivas ³, N. H. Oxtoby ⁴, I.S.A.J. Jayachandran ⁵, Q. Adlan ⁶ and V. C. Vahrenkamp ⁷

¹ Ehrenberg Geoconsulting, Sandnes, Norway.

² School of Geosciences, University of Aberdeen, King’s College, Aberdeen AB24 3UE.

³ Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Martí i Franquès s/n, 08028, Barcelona, Spain.

⁴ retired, 41 Oaken Lane, Claygate, Surrey KT10 0RG.

⁵ Texas A & M University, College Station, Texas, USA.

⁶ Research Centre for Geological Resources, National Research and Innovation Agency (BRIN), Bandung, Indonesia.

⁷ Energy Research and Petroleum Engineering, Ali I. Al-Naimi Petroleum Engineering Research Center, King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia.

* author for correspondence, e-mail: 111sne@gmail.com

We review published studies characterizing the Thamama-B reservoir zone in the upper Kharaib Formation (late Barremian) in Abu Dhabi oilfields and at outcrops in Oman. Available data for oxygen and carbon isotope compositions, fluid inclusion measurements, cement abundance and formation water composition are interpreted in terms of a paragenetic model for the Thamama-B in field F in Abu Dhabi where the interval is deeply buried. The present synthesis provides a useful basis for understanding and predicting reservoir quality in static models and undrilled prospects, as well as for planning promising directions for further research. The goals of this study were to summarize the geologic setting and petrology of the Thamama-B reservoir and its surrounding dense zones, and to examine how sedimentology, stratigraphy and diagenesis have interacted to control porosity and permeability. Results that may have useful applications for similar microporous limestone reservoirs in general include:

- the depositional environments and stratigraphy of the subject strata;

- a model for how porosity variations result mainly from calcite cementation sourced from stylolites, with little dependence on lithofacies other than the localization of chemical compaction by depositional clay linked to sequence stratigraphy;

- the use of solidity (rock thickness with porosity removed) as a check on porosity creation by burial dissolution;

- observations linking high-permeability streaks with storm lag beds and fractures;

- the concept of strata being gradually buried through a relatively static salinity-stratified water column;

- integration of conventional and clumped stable-isotope data with petrologic observations to constrain the timing of porosity evolution.

Key words: microporous carbonates, reservoir quality, diagenesis, sequence stratigraphy, isotope geochemistry.

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