Diagenesis and Fluid System Evolution of the Khuff Formation Outcrop Analogues, Northern United Arab Emirates

Fontana, Simone ¹; Nader, Fadi H.²; Morad, Sadoon ³; Ceriani, Andrea ¹; Al-Aasm, Ihsan S.³
(1) Dipartimento di Scienze della Terra e dell'Ambiente, University of Pavia, Pavia, Italy. (2) Ministry of Water and Energy, Beirut, Lebanon. (3) The Petroleum Institute, Abu Dhabi, United Arab Emirates.

The Permo-Triassic rock successions of the northern United Arab Emirates (UAE) are partly correlatable with the Khuff Formation, which is one of the most important carbonate reservoir in the Middle East. Reservoir properties of this formation are significantly determined by the original depositional facies and the diagenetic evolution. We have, therefore, constrained the distribution of diagenetic alterations within the context of depositional facies and stratigraphy of the succession.

Excellent outcrops of the Bih, Hagil and Ghail formations, which represent analogues for the third order cycles KS5 to KS1 of the Khuff Formation, as well as the Middle and Upper Triassic Milaha and Ghalilah formations were studied. An integrated approach including fieldwork, petrography, geochemistry, fluid inclusions and basin modelling was used in order to comprehend the diagenetic history and its relation with the sequence-stratigraphic architecture as well as with the regional-structural geological setting.

Porosity is higher in pack/grainstones of the Bih Formation than in mud/wackestones of the Hagil and Ghail formations. The overall paragenesis includes early diagenetic replacive dolomitization of the carbonate sediments, which might have occurred in a sabkha/reflux system by evaporated seawater. This event was followed by mesogenetic/burial precipitation of dolomite, quartz and calcite in vugs and fractures. Such late diagenetic fracturing and associated cementation are also accompanied with partial recrystallization of the host dolostone, mainly in the vicinity of fault-controlled fractured/brecciated zones. Isotopic and microthermometric analyses suggest the involvement of highly saline (20-23% NaCl eq.) and hot (150-220°C) diagenetic fluids, which have presumably originated from deep parts of the basin and circulated along faults and fractures through the entire Permo-Triassic succession. The hydrothermal fluid flow was presumably triggered by the tectonic compression caused by the Zagros orogeny, which affected the Musandam Peninsula particularly during Oligocene and Miocene epochs. The interaction between stratigraphic intervals affected by diagenesis at the regional scale (e.g. sabkha/reflux dolomitization) and fracture-related diagenesis linked to the Zagros orogeny, resulted in a complicated reservoir compartmentalization that hinders exploration efforts. This contribution attempts to understand such processes and their impacts on reservoir heterogeneities.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.