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Adrian Immenhauser1, Jeroen A.M. Kenter1, G. Della Porta1, I. Spillekom1, J.R. Bahamonde2
(1) VRIJE Universiteit Amsterdam, Amsterdam, Netherlands
(2) Oviedo University, Oviedo, Spain

Abstract: Contrast-comparison of Pennsylvanian platform cycles in the Precaspian subsurface (Tengiz) with outcrop analogs from N Spain

To develop a realistic reservoir model for the Pennsylvanian carbonate platform succession in Tengiz (Oksky to Bashkirian), age-equivalent outcrops of a platform in Asturias (N Spain) were investigated. The platform in Asturias was rotated in a near vertical position during Late Moscovian thrusting but remained intact. Both localities have comparable rhythmic shoaling cycles, 5 to 20 m thick, are flat lying, and border steep, high-rising margins.

In Asturias, a succession of three Moscovian shoaling cycles was analyzed. We mapped individual lithologic units on aerial photographs for a lateral distance of more than 2 km. Cycle composition indicates shoaling from open platform, normal marine algal boundstone and bioclastic grain-packstone (A facies), to restricted lagoonal, calpionellid-rich, fine-grained peloidal pack-grainstone (B facies), and finally, to coated grainstone with oncoids (C facies). Each sub-unit can be traced for the full width of the window studied; though some units show considerable variation in thickness. In addition, the platform show changes in morphology through time.

In Tengiz, shoaling cycles grade from open platform conditions to restricted shallow lagoonal facies for most of the cored succession. Assuming a lateral continuity of a typical 2.0 km well-spacing as observed in Asturias, cycles were identified in the recently drilled and fully cored T-220 well, and traced to nearby wells T-5050 and T-24 that have limited core control. The resulting pattern confirms that our results from Asturias may be used as input for a realistic platform reservoir model to simulate fluid and gas flow.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana