Sedimentology of Incised Channel-Fills and Their Associated Low Stand Deltaic Sediments, Late Permian Khuff Formation, Saudi Arabia

Muhittin Senalp, W. Allan King

Significant reserves of Arabian super light oil, condensate, and associated gas occur within non-marine, marginal marine, and marine sandstones of the Khuff Formation, Central Saudi Arabia. The sandstones of each depositional facies are unique in their sedimentologic characteristics.

A regional erosional surface with incised valleys developed on the paleoshelf due to a significant fall in sea level during the Late Permian time. During this time, uplift occurred in the source area, producing large amounts of fine to very coarse-grained sand. These sands were transported by incised channels across the shelf and were deposited as low stand deltaic wedges near or at the shelf break.

The deltaic sediments are composed of fine to very fine-grained turbidite sandstones in the lower part, and medium-grained cross-bedded sandstones of a distributary mouth bar in the upper part. The distributary mouth bar is cut by a distributary channel that has a conglomeratic base, fines upward into fine-grained sandstone and displays excellent reservoir qualities.

The base of the incised channels represent a sequence boundary. Red colored and rooted paleosoils were formed on the underlying marine sediments. During relative sea level rise, good quality reservoir sands were deposited by aggradation within the incised channels. Although there is a general transition in the size and the type of sediment fill, braided stream, estuarine and ebb-dominated tidal channels were clearly identified. Deposition within the channels terminated at the same time, and the area was covered by shallow marine limestones and marls during maximum sea level highstand.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995