Date of this Version
Alkhardawi, I.A., 2014, Depositional Setting and Sequence Stratigraphy of Arab-D Reservoir in the Northern Rub Al Khali Basin, Saudi Arabia, M.Sc. thesis: Department of Earth and Atmospheric Sciences, University of Nebraska–Lincoln.
The Upper Jurassic Arab-D Formation, the world’s largest producing reservoir, has been thoroughly studied in most of the supergiant oil fields (i.e., Ghawar, Khurais and Qatif fields) of Saudi Arabia. This study comprises the first sedimentological and stratigraphic analysis of the Arab-D Reservoir in the northern Rub Al Khali basin, located 140 km southeast of the Ghawar Field. Cores from ten exploration wells were described and sampled for petrographic analysis. In each core, lithology, texture, porosity and permeability percentages, pore type, sedimentary structures, fossils, and other characteristics were logged. More than 200 thin sections were examined to aid in analysis of lithofacies, depositional environment, sequence stratigraphy and reservoir quality. Facies are arranged in shallowing upward cycles and divided into nine main lithofacies groups: 1) mudstone (outer ramp deposits); 2) skeletal/intraclastic packstone to floatstone (middle ramp deposits); 3) Stromatoporoid/peloidal wackestone-grain dominated packstone, floatstone and rudstone (platform margin reef shoals); 4 and 5) Cladocoropsis and Clypeina wackestone to mud dominated packstone (normal marine platform interior); 6 and 7) peloidal wackestone to grainstone and oolitic-grainstone (oolitic sand shoal); 8) Gastropod packstone to grainstone (restricted lagoon platform interior); and 9) chickenwire anhydrite (sabkha environment). In addition, dolomite, present as a diagenetic product, occurs as sheet-like beds throughout the Arab-D Reservoir. As seen elsewhere, the depositional succession records gradual shallowing, from outer ramp to sabhka environments. This pattern of long-term shallowing is overprinted by parasequence sets exhibiting progradational stacking patterns. The reservoir quality is highest in the upper portion of the sequence, where grainy lithofacies of oolitic sand shoal complexes and on the peritidal environments adjacent to the oolitic sand shoal. However, this high-quality interval is thinner in the north Rub Al Khali than in the nearby Ghawar Field due to the development of a large oolitic sand shoal setting and its subsequent progradation southward into the Rub Al Khali Basin. This study provides new insight into regional variations along the Arabian intra-shelf basin and the impact of these variations on the reservoir facies distribution and depositional setting. Results provide valuable insights for future exploration in this region.
Advisor: Tracy D. Frank