The Sedimentology and Sequence Stratigraphy of the Arab D Reservoir from a Giant Eastern Province Field, Saudi Arabia
Alnazghah, Mahmoud H.*1; Kerans, Charles 2; Smith, Langhorne B.3
(1) Reservoir Characterization Department, Saudi Aramco, Dhahran, Saudi Arabia. (2) John A. and Katherine G. Jackson School of Geosciences, Department of Geological Sciences, University of Texas at Austin, Austin, TX. (3) Reservoir Characterization Group, New York State Museum, Albany, NY.
Carbonates of the Late Jurassic Arab D Member in Saudi Arabia host some of the world’s largest hydrocarbon reservoirs including Ghawar, the world’s largest oil field, and the supergiant Khurais field. This study of the Arab D reservoir from a field immediately to the north of Ghawar, provides one of the first approaches to a modern sequence analysis of this producing interval and suggests that porosity zonation, and ultimately flow unit architecture, may be substantially different from the models currently in use. The Arab D of the Arabian Plate is a carbonate ramp system of exceedingly low angle (<1°), that developed during a low eustatic amplitude greenhouse setting.
Combined macroscopic and petrographic data analysis allowed recognition of nine depositional lithofacies: 1) spiculitic wackestone, 2) Planolites-burrowed wackestone, 3) bioturbated skeletal-peloidal packstone, 4) pelletal packstone, 5) peloidal-skeletal grain-dominated packstone, 6) peloidal-skeletal grainstone, 7) skeletal-ooid grainstone, 8) cryptalgal laminites and 9) anhydrite. These depositional facies are used to define three lithofacies tracts, from deep to shallow, across the ramp profile. These include: 1) low energy sub-storm wave base lithofacies types 1 and 2, that suggest disaerobic tendencies, 2) high energy within fair-weather wave-base ramp-crest or mid-ramp facies association including foreshore and upper shoreface oolitic and skeletal grainstones and 3) back-barrier tidal flats consisting of cryptalgal laminites, sabkha-type anhydrites, and salina-type anhydrites.
The Arab D composite sequence is made up of four-stacked high frequency sequences (HFS). S1, S2, and S3 represent carbonate sequences topped by the evaporites of the youngest HFS, S4. The basal HFS S1 is highly asymmetric, dominated by the HST deposits of low energy sub-storm wave base origin. The overlying HFS S2 records a major differentiation of facies along the structure, with grainy facies dominating in the north and muddy facies in the south. Its maximum flooding zone is interpreted to represent that of the composite Arab-D sequence. The HFS S3 records a major south-westward progradation of the high energy grainy facies along the entire structure. The overlying evaporites of HFS S4 record a major restriction of the entire platform, corresponding to the latest highstand deposits of the Arab D composite sequence.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain