An Integrated Seismic Facies Analysis: Shu’aiba Formation, Southern Rub’ Al-Khali

An environment of deposition (EOD) map for the lower 3rd of the Early Cretaceous Shu’aiba Formation was made on the basis of observations from 2D and 3D seismic and a priori knowledge of the depositional system. An integrated workflow specific to this Shu’aiba interval was used and included integration of (1) seismic observations; (2) relevant geologic observations; and (3) ranking of key points from the literature.

Seismic observations were posted as a seismic facies ribbon map. This ribbon map provided a starting point for combining other relevant observations such as input from conventional play analysis. Conventional play elements included relevant time structures, isochrons, and seismic attributes. From these combined observations, a secondary map, called here a “blob map” was produced. These “blobs” were captured as a series of polygons. Relevant attributes were assigned to particular polygons. For example, mounded seismic geometries were deemed highly significant — with respect to what was known about the Shu’aiba — and polygons highlighting these features were designated as “mounded.”

Geologic observations suggested that the Shu’aiba is best characterized as a low-angle ramp. On this basis, a low-angle ramp model was selected to link seismic observations with interpreted EODs. The various polygons were assigned likely EODs according to probabilities starting, with polygons where knowledge or confidence about their EOD was highest.

Literature and core studies were used to guide the interpretations. On this basis, polygons designated “mounded” (an observation) were assigned a second designation “isolated buildup” (an interpretation). The remaining polygons were treated in a similar fashion resulting in an EOD map for the lower third of the Shu’aiba over a large area of the southern Rub’ Al-Khali basin.

The EOD map highlights areas with significant reservoir potential, thus allowing predrill predictions of reservoir quality and evaluation of the potential for the Shu’aiba/Bab basin system to charge the reservoirs. For example, this analysis has (1) identified basin-centered Lithocodium mounds as likely stratigraphic traps; (2) greatly expanded the low-angle ramp and carbonate shoal play fairway; and (3) shown that the basin margin is more complicated than suggested by previous work.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California