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Rediscovering the Arab-D Reservoir: The Search for Stratigraphic Traps


The Arab-D Member of the Arab Formation and upper Jubaila Formation comprise the largest reservoir in the world, Ghawar field, and other Arab-D super giant reservoirs. 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. Arab-D lithofacies were regionally mapped by utilizing cores and well cuttings from Kuwait to the Rub’ Al Khali and from outcrops in central Arabia to the Arabian Gulf, with the goal to identify Arab-D stratigraphic traps. The vertical seal relies on the overlying Arab-D evaporite, whereas the transition from porous, grain-rich lithofacies to nonporous, mud-rich lithofacies forms the lateral seal. 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 the Arab-D carbonate, relative sea level fell and briefly subaerially exposed paleohighs of the carbonate ramp. Fault readjustment of some structures created subtle uplift. These events caused the Arabian intra-shelf basin to become restricted, leading to deposition of the Arab-D evaporite in a regional salina.