New Insights into Regional Correlation and Sedimentology, Arab Formation (Upper Jurassic), Offshore Abu Dhabi

Correlation uncertainties within the Arab Formation reservoirs of the Ghasha-Bu Tini field were resolved with a combined biostratigraphic and lithostratigraphic study. A chronostratigraphic framework was established based on the type and reference localities elsewhere on the Arabian Peninsula. Construction of a regional biozonation scheme for the entire Arab Formation resulted in a downward shift of the Arab C-D unit boundary by approximately 100 feet in the field, which was reconcilable with a lithological change from anhydrite to dense limestone at that stratigraphic horizon. As a result of the modified Arab C-D boundary, younger boundaries in the Arab Formation were adjusted. These secondary adjustments were assisted by the identification of lithological markers such as thrombolitic horizons, charophytic bands and distinctive anhydrite layers. These horizons were constrained (in a broad sense) by the new biozonation scheme. Ghasha-4 is introduced as a candidate reference well for the Arab Formation of western Abu Dhabi and could be used to adjust reservoir boundaries in other fields. In this manner, not only could regional consistency be ensured, but further insights in exploration could be gained. Evidence for the occurrence of subaqueous sulphate deposits is discussed. Subaqueous anhydrites comprising palisades of subvertically orientated nodules exist at all levels within the upper Arab Formation, but the case is made for thicker, nodular anhydrites interbedded with subtidal stromatolites also having formed subaqueously.