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Charles Kerans1, Kirt Kempter1, Jason Rush1
(1) Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Abstract: Predictive model for Paleokarst Reservoir heterogeneity styles at high-frequency/composite-sequence boundaries

Paleokarst reservoirs represent one of the most complex and poorly understood carbonate reservoir styles. Predicting the size and distribution of paleokarst features is generally not possible using well data, and the small impedance contrast between host and collapse features makes seismic detection challenging. Improved prediction of reservoir development and heterogeneity styles in paleokarst systems is possible using outcrop data and unconformity rank on the basis of sequence stratigraphic hierarchical setting. A threefold classification, including karst developed at (1) high-frequency cycle boundaries, (2) high-frequency and composite-sequence boundaries, and (3) super-sequence or 2nd-order boundaries, allows key parameters to be emphasized. An example of a paired 3-D outcrop data set of paleokarst features associated with high-frequency/composite-sequence paleokarst and its reservoir equivalent with core, log, and 3-D seismic data is presented to highlight predictive aspects of this class of paleokarst reservoir.

Detailed mapping of paleokarst features from Leonardian and Guadalupian (Permian) outcrops in the Guadalupe and Sierra Diablo Ranges of West Texas includes size, dimension, and distribution relative to the shelf margin. In the case of the Leonardian (Abo) paleokarst system, 63 individual sinkholes and collapsed caves were mapped and analyzed in terms of timing of collapse and porosity evolution. A strong correlation between extent of karst profile and shelf-margin position is demonstrated. Application of this coastal paleokarst model to Kingdom Abo field of similar age in the subsurface of the Permian Basin allows delineation of the zone of paleokarst and helps explain the high variability in performance of producer wells.

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