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Al-Dakhil, Raid K.1, Ghazi A. Al-Eid1, Aus A. Al-Tawil1, Rick R. Davis1, Shoaib M. Rawasia1
(1) Saudi Aramco, Dhahran, Saudi Arabia

ABSTRACT: High Resolution Sequence Stratigraphy of Permo-Triassic Khuff Carbonate Reservoirs, Ghawar Field, Saudi Arabia – A Field-Scale Characterization Study

The Permo-Carboniferous Khuff Formation contains some of the major gas reservoirs in Saudi Arabia. In Ghawar Field, Permian Khuff C carbonates contain three, reservoir bearing high-resolution sequences. The Triassic Khuff A and B Carbonates, each, are made up of one reservoir bearing sequence. Anhydrite/dolomite coastal successions formed thick, intra-formational seals, between Khuff C & B, and Khuff B & A, during long-term HST (3rd/2nd order ?) and extreme climatic aridity.
Exposure surfaces mark sequence and cycle-set boundaries during low-stand of base-level, with corresponding gamma-ray log signatures allowed mapping high resolution (4th order?) sequences, onlap geometry of the TST, and prograding geometry of the HST in 5000 meters of core in 50 wells, and on wire line logs in 200 wells.
Glacio-eustacy during the Permo-Triassic are transitional from ice-house to green-house times, resulted in moderate amplitude sea-level fluctuations, giving rise to regionally mappable, high-resolution sequences, their component systems tracts, and cycle sets. This controlled vertical partitioning of reservoir facies. The active Ghawar structure during the Permian, lead to lateral partitioning of these facies from proximal on the crest to distal on the flanks. Subtle highs and saddles along the crest; furthered such partitioning. Reservoir facies formed in retrograding oolitic shoal belts of the late TST (Khuff A, B, & C) and the prograding shallow subtidal burrowed HST facies of high resolution sequences (Khuff C only). This high resolution stratigraphy allowed very precise mapping of facies down to the cycle-set level (3 meters) at the scale of the Ghawar Field.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004