An Integrated Approach to Reservoir Characterization of the Upper Jurrasic Arab Formation, Onshore Abu Dhabi, UAE

By

 Stephen Lokier¹, Jürgen Grötsch², Reyad Khassawneh², Erik van der Weerd², Shehadeh Masalmeh², Johan van Dorp², Gordon Coy¹

(1) Badley Ashton and Associates Ltd, Lincolnshire, United Kingdom (2) ADNOC/Shell Sour Gas Team, N/A,

 Detailed sedimentological description and interpretation of recently acquired data from four cored wells was integrated to produce a new sequence stratigraphic, sedimentological and diagenetic model for the Manifa, Hith, Arab-ABC, Arab-D and Upper Diyab Formations. Six distinct palaeoenvironments were identified during the study; a supratidal sabkha setting with localised salinas, an intertidal environment, a low-energy sub-tidal setting, a high-energy inner ramp environment, a moderate-energy mid-ramp setting, and a low-energy outer ramp setting.

Correlation within a sequence stratigraphic framework has constrained the distribution of these palaeoenvironments across the field and has established that this is a complex reservoir controlled by fourth order aggradational and progradational cycles composed of fifth order shallowing-upward cycles. Appraisal drilling results have confirmed that well productivity in the Arab ABC is predominantly controlled by the development of thin permeable dolomite streaks associated with these fifth-order shallowing-upward cycles. An overall progradational geometry towards the east-northeast has been established.

Diagenetic modification of the sediments, by processes such as syndepositional dolomitization, displacive anhydrite formation, non-ferroan calcite burial cementation, and leaching, prohibited the establishment of a direct relationship between primary depositional facies and rock properties, therefore a rock-type scheme was established to encompass all lithostratigraphic units. Standard core-analysis data acquisition and attribution of saturation functions to the static and dynamic model were performed on a cell-by-cell basis using these established rock types. Upscaling was performed with an emphasis on preserving the cyclicity and thin increased-permeability streaks in the dynamic model. The series of extracted dynamic simulation models allowed definition of the development requirements of the reservoir.