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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Understanding Reservoir Heterogeneities of Upper Jurassic Carbonate Reservoirs and Its Critical Impact from Field Development, Offshore Abu Dhabi

Christoph T. Lehmann1; Khalil I. Hosani1; Mohamed Sayed Ibrahem1

(1) FDD (UDS), ADMA-OPCO, Abu Dhabi, United Arab Emirates.

A detailed reservoir characterization study was performed offshore Abu Dhabi in order to capture the key uncertainties for future field development. This study was performed on the Arab reservoirs and included detailed core description, sequence stratigraphic interpretation, conventional core analysis, and a rock typing study in an attempt to understand reservoir heterogeneities across the field and its impact on the field development plan which include a gas injection as the major development scheme.

The Arab Formation in Abu Dhabi is subdivided into 4 reservoir intervals (Arab A, B, C, and D) which coincide with third-order sequences. The fourth-order sequence stratigraphic framework represents the basis for the reservoir layering scheme. Reservoir facies distribution is controlled by fourth-order sequences superimposed on a large-scale shoaling upward trend. The Transgressive Systems Tract (TST) of the fourth-order sequences are dominated by off-ramp to fore-shoal deposit while Highstand Systems Tract (HST) are composed of progradational, peloidal shoal deposits. The reservoir rocks are limestones and reservoir quality is primarily controlled by facies (grain-dominated versus mud-dominated facies) and secondarily by diagenesis.

The Arab, A, B, and C are composed of mixed carbonates and evaporites. The carbonate reservoirs were deposited in sabkha/shallow lagoonal environment. The TST of the fourth-order sequences is dominated by shoal to back shoal deposits, while the HST are controlled by restricted shallow subtidal, intertidal and evaporate deposits. These facies are arranged in meter-scale peritidal and sabkha cycles. The reservoir is predominantly dolomite with the exception of the Arab C, which includes significant amount of limestones, which can vary between individual wells. Reservoir quality is strongly controlled by diagenetic processes such as dolomitization and anhydrite cementation.

This work has a major impact on the planning of the development wells and the type of gas injectors. The well distribution and completion has been changed to capture the heterogeneities of the reservoir and may lead to apply smart completion in order to achieve high sweep efficiency. In addition the heterogeneities also control the gas injection scheme for different reservoirs to avoid the early gas breakthrough. Therefore, understanding the complex architecture of the Arab reservoirs has a major impact on the development of these reservoirs.