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High-Resolution Sequence Stratigraphy and Reservoir Characterization of Upper Thamama (Lower Cretaceous) Reservoirs of a Giant Abu Dhabi Oil Field, United Arab Emirates

Christian J. Strohmenger1, L. Jim Weber2, Ahmed Ghani1, Khalil Al-Mehsin3, Omar Al-Jeelani1, Abdulla Al-Mansoori1, Taha Al-Dayyani1, Lee Vaughan2, Sameer A. Khan4, and John C. Mitchell2
1 Abu Dhabi Company for Onshore Oil Operations (ADCO), Abu Dhabi, United Arab Emirates
2 ExxonMobil Exploration Company (EMEC), Houston, TX
3 Abu Dhabi National Oil Company (ADNOC), Abu Dhabi, United Arab Emirates
4 ExxonMobil Upstream Research Company (URC), Houston, TX

Important hydrocarbon accumulations occur in platform carbonates of the Lower Cretaceous Kharaib (Barremian and Early Aptian) and Shuaiba (Aptian) formations (Upper Thamama Group) of Abu Dhabi. The Kharaib and Lower Shuaiba formations contain three reservoir units separated by three low porosity and permeability dense zones. Core and well-log data of a giant oil field of Abu Dhabi, as well as outcrop data from Wadi Rahabah (Ras Al-Khaimah)were used to establish a sequence startigraphic framework and a lithofacies scheme; applicable to all three reservoir units and the three dense zones.

The Lower and Upper Kharaib Reservoir Units as well as the Upper Dense Zone are part of the late transgressive sequence set of a second-order supersequence, built by two third-order composite sequences. The overlying Lower Shuaiba Reservoir Unit belongs to the late transgressive sequence set and the early highstand sequence set of this second-order supersequence and is built by one third-order composite sequence. The three third-order composite sequences are composed of nineteen fourth-order parasequence sets that show predominantly aggradational and progradational stacking patterns.

On the basis of faunal content, texture, sedimentary structures, and lithologic composition, thirteen reservoir lithofacies and eight non-reservoir (dense) lithofacies are identified from core and outcrop data. Depositional environments of reservoir units range from lower ramp to shoal crest to near back shoal open platform deposits. Dense zones were deposited in a restricted shallow lagoonal setting.

Outcrop analogues of subsurface reservoirs allow for a detailed investigation of facies architecture and structure of carbonate bodies. Integration of subsurface and outcrop data leads to more insightful and realistic geological models of subsurface stratigraphy.