Saudi Arabian Silurian and Devonian Sequence Stratigraphy, Paleogeography and Play Concepts

By

Michael L. Hulver¹, Riyadh A. Rahmani¹, Patrick M. Rutty², Ronald J. Steel³, Robert S. Johnson², Randall G. Demaree²

(1) Saudi Aramco, Dhahran, Saudi Arabia (2) Saudi Aramco, (3) University of Wyoming, Laramie, WY

 A third-order sequence stratigraphic model of the Silurian and Devonian systems in Saudi Arabia has been constructed, using detailed sedimentologic, lithostratigraphic and biostratigraphic data from 50 wells and approximately 10000 feet of core from the Kingdom’s Paleozoic basins. Eight third-order sequences were identified and correlated from the base of the Silurian Qusaiba Member to the Devonian Jubah Formation. Six depositional systems tracts were recognized in the section: offshore marine highstand, offshore marine lowstand, offshore marine transgressive, tide-dominated transgressive, fluvial-deltaic forced regressive, and wave-dominated forced regressive.

Mapping of the systems tracts highlighted several key features: 1) the ongoing influence of Infra-Cambrian basins on Silurian and Devonian paleogeography; 2) a clear second-order basinward progradation of the shoreline during the Devonian; 3) a persistent clastic depocenter on the eastern side of Ghawar; 4) development in the northwest of a broad shelf with local carbonate sedimentation; and 5) periodic Devonian exposure of the Qatar arch, which - along with the stable east edge of Ghawar and the Niban arch to the south - formed a recurrent embayment in which were deposited restricted marine facies, including the reservoir units of the Jauf Formation.

In light of this new sequence stratigraphic interpretation, analysis of trap elements has enabled better risk assessment of various existing play types, and has helped identify new play concepts.