Core-and-Log Signature of High-Resolution Sequence-and-Cycle Stratigraphy of Permian Khuff Reservoir: Implications for Reservoir Characterization and Development, Ghawar Field, Saudi Arabia

Raed K. Al Dukhayyil, Ghazi A. Al Eid, and Aus A. Al Tawil
Saudi Aramco, Dhahran, Saudi Arabia

The Permo-Triassic Khuff carbonates were deposited during a major marine transgression on the Arabian Plate at the terminal Paleozoic to form a huge, east-facing, arid ramp. The Khuff is made up of four subsurface members, stratigraphically D and C of Permian age, and B and A of Triassic age. Three high-frequency sequences make up the Permian 270 foot Khuff C carbonate interval. The lower sequence, Khuff C1 (KC1), consists of up to seven mappable upward shallowing cycles, where the flood of each cycle is made up of storm influenced fore-shoal and shoal facies commonly shallowing up into restricted carbonate mudstone and capped by lower-intertidal facies.

Khuff C Sequence 2 (KC2) is marked by a flooding surface at the top of KC1 with storm influenced fore-shoal grainstone/packstone facies capped by dolo-mudstone restricted facies. The middle cycle of KC2 is a thicker (38 foot) symmetric cycle with intensely burrowed shallow sub-tidal pellet packstone deepening to dominantly open marine lime-mudstone shallowing up to sand-flat low angle cross-bedded to burrowed peloid packstone. The upper cycle of KC2 is made up of shallow sub-tidal embayment lime-mudstone shallowing up to a breccciated Paleosol easily recognized in cores and on wireline logs.

Khuff C Sequence 3 (KC3) is made up of two transgressive peri-tidal cycles of lagoonal dolomudstone capped by crinkly laminated to mud-cracked dolomudstone tidal flat facies. This is overlain by a back-stepping cycle-set of grainstone with their distal bryzoan lime-mudstone equivalent. The High Stand Systems Tract (HST) of KC3 is marked by shallow sub-tidal sand flat facies prograding over distal open marine lime-mudstone. KC3 is marked at the top by a Ghawar-wide paleosol.