Application of New Seismic Attributes to Identify Karst- and Fracture-Related Compartmentalization: Permian San Andres Formation, Central Basin Platform, West Texas, U.S.A.

E. Charlotte Sullivan¹, Susan Nissen², Kurt J. Marfurt¹, and Charles. H. Blumentritt^1
1 University of Houston, Houston, TX
² Kansas Geological Survey, Lawrence, KS

Reservoirs in the Permian San Andres carbonates of the Central Basin Platform of West Texas produce from Guadalupian shallow water ramp lithofacies. This study focuses on a 3 mi X 5 mi (4.8X 8 km) area in the northern part of the Waddell San Andres field that is remarkable for exhibiting per well fluid production that is an order of magnitude greater than production in surrounding wells. Core from wells in the this high volume (HV) area contain anhydrite cemented breccias interpreted as paleocave facies developed during a time of falling water table, with progressive top-down cave formation and collapse. These karst breccias are overprinted by vuggy porosity due to anhydrite dissolution along open fractures. Cores from outside the HV area do not appear to have major karst overprint. Seismic sections indicate broken reflectors in the area of high fluid production. Volumetric curvature attributes identify ragged fracture zones and bowl shaped depressions, indicative of sinkholes, within the HV areas. Coherency attributes indicate localized areas of less coherent reflectors that coincide with two groups of HV wells, separated by a roughly 1 km wide area with more coherent reflectors and relatively low production. Tracer surveys within the HV area waterflood indicate the area of low production constitutes a field scale permeability barrier. We conclude, based on analysis of volumetric seismic attributes, calibrated by core, that the unusual production characteristics of this field and the location of field-scale permeability barriers are the result of localized, late stage fracturing and dissolution of anhydrite cement in a heterogeneous paleocave system.