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ABSTRACT: Structural Controls on Reservoir Distribution, Southeast Turkey

V. Ottensman, J. Reed, G. Cushing, P. Dagget, S. Aytuna

The middle Cretaceous Mardin Formation produces oil from several fields along a 200-mi stretch of the Zagros fold and thrust belt in southeastern Turkey. Extensive well control along this productive trend combined with seismic data and field observations, provides the opportunity to analyze the tectonic and stratigraphic evolution of the middle Cretaceous passive margin of the northern Arabian shelf.

Regional isopach mapping of Cretaceous and Tertiary units, coupled with regional gravity data, indicates that the northern Arabian shelf is cut by normal and reverse faults which form horsts, grabens, and half-grabens across the margin. Limited seismic data tied with wells allows recognition of such structures on a smaller scale. The reverse and normal faults have a complex history of reactivation. These reactivated structures influenced the (1) sedimentation patterns in the middle Cretaceous, (2) erosional level of the Turonian unconformity, (3) distribution of organic-rich source facies developed on the Turonian unconformity, and (4) later compressional structures.

The Mardin Formation was deposited in relatively quiet water on a moderately restricted carbonate shelf. Facies are dominated by mudstones and wackestones with grainstones occurring predominantly on fault-bounded highs as a result of localized shoaling conditions. Deposition ended in the Turonian with a regional unconformity, and continued uplift of horst blocks occurred through the Turonian and may be the result of a migrating peripheral bulge associated with the onset of the Late Cretaceous compressional event. These structural highs were the site of preferentially deeper erosion and dolomitization of the Mardin Formation on the Turonian unconformity surface.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990