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Origin and evolution of microporosity in packstones and grainstones in a Lower Cretaceous carbonate reservoir, United Arab Emirates

By
Daniel Morad
Daniel Morad
Department of Earth Sciences, University of Oslo, N-0316 Oslo, Norway
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Matteo Paganoni
Matteo Paganoni
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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Amena Al Harthi
Amena Al Harthi
School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, UK
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Sadoon Morad
Sadoon Morad
School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, UK
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Andrea Ceriani
Andrea Ceriani
School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, UK
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Howri Mansurbeg
Howri Mansurbeg
Department of Petroleum Geosciences, Soran University, Soran, Kurdistan Region, Iraq
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Aisha Al Suwaidi
Aisha Al Suwaidi
School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, UK
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Ihsan S. Al-Aasm
Ihsan S. Al-Aasm
Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada
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Stephen N. Ehrenberg
Stephen N. Ehrenberg
School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3FE, UK
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Published:
January 01, 2018

Abstract:

Microporosity in carbonate reservoirs is generated by the complex interplay between depositional and diagenetic processes. This petrographical, SEM, fluid-inclusion and isotopic study of a Lower Cretaceous carbonate reservoir, Abu Dhabi, UAE, revealed that: (1) micritization of ooids and skeletal fragments, which resulted in spheroidal (rounded) micrite, accounts for most microporosity in peloidal packstones and grainstones; and (2) transformation of spheroidal micrite into subhedral/euhedral micrite and microspar, known as aggrading neomorphism, could happen via precipitation of syntaxial calcite overgrowths around micrite (micro-overgrowths) and not only, as suggested previously in the literature, by recrystallization involving the dissolution (of micrite) and reprecipitation (of microspar). Precipitation of calcite cement around micrite (i.e. destruction of microporosity) is more extensive in the water zone than in the oil zone, which is possibly contributing to the lower porosity and permeability of the carbonate reservoir in the water zone. Similarity in bulk oxygen isotopic values of micritized packstones and grainstones in the water and oil zones (average δ18OV-PDB = −7.2‰ and −7.8‰, respectively) is attributed to: (1) a small difference in temperatures between the crest (oil zone) and the flanks (water zone); and (2) calcite precipitation around micrite occurred prior and subsequent to oil emplacement. Bulk carbon and strontium isotopic compositions of micritized packstones and grainstones in the water and oil zones (average δ13CV-PDB = +3.7‰ and average 87Sr/86Sr ratios = 0.707469) indicate that calcite cement was derived from marine porewaters and/or dissolution of the host limestones. The minimum formation temperatures of bulk micrite/microspar, which are inferred based on paragenetic relationships, fluid-inclusion microthermometry and oxygen isotope data, are around 58–78°C.

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Geological Society, London, Special Publications

Reservoir Quality of Clastic and Carbonate Rocks: Analysis, Modelling and Prediction

P. J. Armitage
P. J. Armitage
BP Upstream Technology, UK
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A. R. Butcher
A. R. Butcher
Geological Survey of Finland, Finland
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J.M. Churchill
J.M. Churchill
Shell UK Ltd, UK
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A.E. Csoma
A.E. Csoma
MOL Group Exploration, Hungary
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C. Hollis
C. Hollis
University of Manchester, UK
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R. H. Lander
R. H. Lander
Geocosm, USA
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J. E. Omma
J. E. Omma
Rocktype, UK
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R. H. Worden
R. H. Worden
University of Liverpool, UK
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The Geological Society of London
Volume
435
ISBN electronic:
9781786202901
Publication date:
January 01, 2018

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