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Rediscovering The Arab-D Reservoir


The Arab-D reservoir is composed of highly porous and permeable carbonate strata, which in large structural closures form super giant oil fields. Arab-D deposition was on a broad, arid, storm-dominated carbonate ramp that prograded into the Arabian intra-shelf basin. The Arabian intra-shelf basin contained three sub-basins: (1) North Ghawar; (2) Rub’ Al Khali; and (3) Jafurah. Rimthan Arch separated the Arabian and Gotnia intra-shelf basins, while Qatar Arch separated the Arabian and UAE intra-shelf basins. Access ways connected these intra-shelf basins and provided normal marine circulation. Nine lithofacies were identified in the upper Arab-D: (1) oolitic grain-dominated packstone and grainstone; (2) skeletal-peloidal grain-dominated packstone and grainstone; (3) Thaumatoporella-Clypeina wackestone and packstone; (4) Cladocoropsis packstone and grainstone (floatstone and rudstone); (5) stromatoporoid wackestone and packstone (floatstone and rudstone); (6) intraclast floatstone and rudstone; (7) oncolite rudstone; (8) pelletal-skeletal mud-dominated packstone; and (9) wackestone and mudstone. These lithofacies were deposited in: (1) inner ramp; (2) ramp crest shoal; (3) middle ramp; (4) outer ramp; and (5) basinal depositional settings. Following deposition of Arab-D carbonate strata, relative sea level fell and subaerially exposed paleo-highs upon the carbonate ramp. Fault readjustment of some structures created subtle uplift. These two events caused the Arabian intra-shelf basin to become restricted and deposit the Arab-D evaporite in a regional salina. Utilizing all of this information Arab-D lithofacies were regionally mapped, utilizing outcrops, cores, well cuttings, and open-hole well logs, from Kuwait to the Rub’ Al Khali and from central Arabia to the Arabian Gulf. The goal of this study was to identify potential Arab-D stratigraphic traps. The vertical seal for this stratigraphic trap play relies on the overlying Arab-D evaporite. The lateral seal relies on the transition from porous, grain-rich lithofacies into nonporous, mud-rich lithofacies. Results of this study identified several potential Arab-D stratigraphic trap fairways.