--> Abstract: Sequence Stratigraphic Framework, Paleogeography, and Exploration Potential of the Early Jurassic Marrat Formation, Saudi Arabia, by David Z. Tang, Paul Lawrence, Abdel Fattah M. Bakhiet, Arthur E. Gregory, Wenbin Tan, Abdelghayoum Ahmed, and Bradford Macurda; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Sequence Stratigraphic Framework, Paleogeography, and Exploration Potential of the Early Jurassic Marrat Formation, Saudi Arabia

David Z. Tang1; Paul Lawrence1; Abdel Fattah M. Bakhiet1; Arthur E. Gregory1; Wenbin Tan1; Abdelghayoum Ahmed1; Bradford Macurda2

(1) Exploration Resource Assessment, Saudi Aramco, Dhahran, Saudi Arabia.

(2) The Energists, Houston, TX.

The Early Jurassic Marrat carbonate play has emerged as an increasingly important Jurassic exploration target in the Partitioned Neutral Zone (PNZ), Kuwait, and Saudi Arabia. The Marrat Formation is unconformably underlain by late Triassic Minjur Formation clastics and overlain unconformably by the middle Jurassic “Dhruma Shale”. This formation comprises a composite third order sequence with the Lower, Middle and Upper Marrat each comprising fourth order sequences.

The Lower Marrat consists of mixed clastics and carbonates with anhydritic interbeds. It is the earliest basin-fill in response to an early Jurassic marine transgression that flooded the Arabian platform from the northeast, progressively onlapping onto the Qatar Arch and the Arabian Shield. The Lower Marrat was deposited in a very shallow and relatively low energy environment with limited accommodation space. Grainier carbonates are confined predominantly to the northern onshore and offshore areas. Overlying the Lower Marrat carbonates is the “Lower Marrat Shale”, which thickens to the southwest and thins substantially to the northeast, suggesting a possible siliciclastic influx from the Arabian Shield. The top of the Lower Marrat was locally eroded and marks a fourth order sequence boundary. Renewed flooding and moderately increased accommodation space during the Middle Marrat resulted in a major transgression and maximum flooding onto the platform with widespread carbonate deposition. A shoaling complex and backshoal flats, with mixed skeletal grainstones-packstones, were developed as aggrading and generally northeasterly prograding highstand systems in the northeast onshore and offshore areas. Latest Middle Marrat sediments are mostly anhydrites, which provide an excellent marker and top seal for the Middle Marrat across the region. The Upper Marrat consists of shaley carbonates and thinly intercalated anhydrites, particularly in southerly and westerly more restricted areas, indicating overall inner shelf and lagoonal environments. The post-Marrat subaerial unconformity has been identified in the subsurface through well-log correlations and is evident in a recently cored shallow well in an outcrop south of Riyadh.

Exploration opportunities for the Marrat play have been assessed through integrating the reservoir fairways, source rocks and seals. Targeting Marrat carbonate reservoirs in undrilled structural and stratigraphic traps could add significant additional hydrocarbon reserves.