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Geoscience Conference & Exhibition
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The Sedimentary Architecture of a Prograding Platform Margin and Its Impact from Production Behavior - an Example from Giant Field “A” Abu Dhabi
(1) RDD, ADCO, Abu Dhabi, United Arab Emirates.
Giant Field “A” in Abu Dhabi produces from limestones of the Aptian Shu'aiba Fm with a complex platform margin architecture. Earlier analysis has revealed that after an initial stage of aggradation the platform prograded into the Bab basin with a prominent set of clinoforms. A southern platform interior area of aggradation was separated from the well defined northern clinoforms by a central platform margin belt with a less distinct seismic signature but a distinct production behavior.
Detailed seismic and core analysis has revealed that this margin actually represents another prograding clinform belt comprising a 3rd order depositional sequence, which originated during the late Highstand Systems Tract (HST) of the aggradational late Early Aptian platform phase. There is a distinct difference in composition and reservoir character between the sediments of the Transgressive Systems Tract (TST) and the HST. Property differences resulting from cementation at clinoform boundaries allow the detailed delineation of sedimentary features on depth converted seismic horizon slices. Clinoform packages are relatively steeply dipping with a depositional slope of up to 3 degrees. A distinct triangular feature along the progradation front is interpreted to represent a sediment point source such as a tidal delta draining sand flats on the platform top.
The location of the platform margin and possibly subsequent diagenetic alteration is profoundly influenced by a deep rooted fault system that became periodically reactivated.
Recognition of the architecture has had a profound impact on understanding production behavior in the field. Peripheral injected water advances more rapidly in heterogeneous platform interior sediments forming an areal water finger. The localized water advance is likely aided by fault planes. Its spread into the crestal parts of the field is retarded by a dense layer associated with a 3rd order maximum flooding surface and cementation along fault planes. The flood front in the central area is less advanced, and more even. Individual lower order clinoforms introduce a preferred directional flow behavior parallel to the platform margin further reducing the influx of water from the platform area.