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Sequence Stratigraphy of the Subsurface Late Jurassic Arab-D Reservoir, Hawiyah and Harmaliyah Fields, Saudi Arabia

Al-Temimi, Khalaf O.*1; Read, J. Fred 2
(1) Saudi Aramco, Dhahran, Saudi Arabia. (2) Geosciences, Virginia Tech, Blacksburg, VA.

The Late Jurassic Arab-D reservoir and Arab-D anhydrite were studied in the Hawiyah and Harmaliyah fields located in the Eastern Province of Saudi Arabia. The Jubaila-Arab-D interval is a shallowing upward succession of two composite sequences, with up to nine higher frequency sequences in the Arab-D. Both fields have similar parasequences, typically 3-5 meters thick. Facies in ascending order include: deeper, hardground-capped lime mudstone, wackestone and intraclastic rudstone; fine packstone forebank apron, and extensive stromatoporoid banks; Cladocoropsis peloid packstone/ grainstone/floatstone; fine algal packstone/wackestone; peloid packstone/grainstone, nearshore ooid/mollusk grainstone/packstone, rare peritidal laminites, and evaporites.

Each sequence records a progressive upward-shallowing of facies. The lower units are dominated by deeper (below to within storm-wave base), open marine facies. The upper units are characterized by shallow water, typically high-energy facies (within a fairweather wave base) that show effects of increasing hypersalinity and restriction upsection.

Between the two fields, the facies, parasequences, and vertical stacking of facies are very similar. Together with regional isopach maps, this suggests that the Arab-D reservoirs of these two fields may represent part of a single carbonate ramp, at least in their upper part, although the present structures were probably formed at the locations of syndepositional subtle highs. Across the fields, the stromatoporoid facies thicken and climb toward the east, the Cladocoropsis facies appear earlier in the west, and climb to the east, and the ooid grainstone facies thin to the east. Also, the two lowest evaporites in the Arab-D anhydrite become thinner and pinch out toward the east, whereas the Arab-D anhydrite overall thickens westward. This suggests at least locally, subtle progradation to the east-northeast.

The scarcity of exposure surfaces with caliche in the Arab-D reflects the relatively high subsidence rate (~6 cm/k.y.) relative to the small sea level oscillations that formed the succession. The grain-rich Arab-D reservoir contrasts with mud-rich cyclic facies of many large greenhouse ramps, which produce lower quality reservoirs.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain