AAPG Annual Convention and Exhibition

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The Importance of Petrophysical Stratification on Fluid-Flow Behavior in Carbonate Reservoirs


Although carbonate reservoirs are notorious for their complexity and heterogeneity at multiple scales, the single most important feature controlling fluid flow in many cases is simple stratification. Petrophysical stratification can exist at many scales, but the scale that is most important for reservoir behavior is typically the scale that can be correlated between wells. One purpose of this presentation will be to reemphasize the importance of this simple layer-cake view of carbonate heterogeneity. Of course many carbonates have a great deal of heterogeneity in complex spatial arrangements. The layer-cake model is an oversimplification of that complexity. Nevertheless, the additional variability often occurs at smaller scales within the correlatable units creating fluid-flow effects that can be captured with relatively simple effective properties. The main impact of these smaller-scale heterogeneities is that they create difficulties for identification, quantification, and modeling of the more-important larger-scale stratification. In this presentation the importance of petrophysical stratification will be illustrated with fluid-flow models. Then some typical ways in which small-scale variability interferes with adequate modeling of stratification will be described. Finally, some simple strategies to overcome the distraction of small-scale variability and construct better models of stratification will be summarized.