Enhancing the Sedimentological Understanding within the Arab Formation (Upper Jurassic), Abu Dhabi - Constraining the Future Reservoir Model Build
Neil Bishop, Jon Gant, Meriem Bertouche and Andrea James
Correlation and prediction of facies and reservoir quality variability/heterogeneity within shallow carbonate ramp deposits of the Arab Formation in an Abu Dhabi offshore field has previously proved challenging. This study, focuses on the results of an integrated sedimentology and reservoir quality assessment of the Arab Formation. Specific focus has been placed on detailing depositional architecture, within which variations in reservoir properties have been identified. Dunham-based lithofacies have been used to characterise c. 6,800 ft of the Arab Formation, members A to D, in 20 partially cored wells. These sub-bed/bed-scale lithofacies are grouped into a series of lithofacies associations based on genetically related textures, sedimentary structures, and allochem assemblages to provide an understanding on the depositional evolution of the Arabian Platform in this offshore location. Assessing vertical and lateral stacking patterns of these lithofacies and lithofacies associations, and also using core to log calibration of key surfaces, has allowed for a revision of ADMA's layering scheme and the development of a sequence-stratigraphic framework. This was carried out initially within cored wells before extrapolation into uncored wells. This framework captures a hierarchal scale of eleven fourth-order cycles over three third-order cycles, each marking a transgressive and regressive event developed over the formation-scale shallowing-upwards trend, in which to better understand the lateral facies variability. In addition, three ‘type’ logs have been identified that capture broad changes in gamma ray and neutron/density log responses across the field, thought to represent discrete sedimentological domains as a potential tool for future application in extrapolation of the framework. Within this sequence stratigraphic framework, facies trend maps were produced, using GIS software, for each of the fourth-order cycles that provide a time average understanding of the lateral facies variability across the field. These maps are generated from the interrogation of thickness data of lithofacies associations from both cored and uncored intervals, applying percentage ‘cut-off’ values to this data, along with sedimentological principles. The resulting GIS shape data provides important constraints on geobody geometry and lateral facies development for the update of the static geological model.
Garrick, K, Davies, Q, Al-Menhali, H, Al-Tamimi, I, Bishop, N, Gant, J, Bertouche, M, James, A and Deville de Periere, M. (2014) Enhancing the Sedimentological Understanding within the Arab Formation (Upper Jurassic), Abu Dhabi - Constraining the Future Reservoir Model Build. Paper presented at the AAPG International Conference and Exhibition, Istanbul, 14-17th September, 2014
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