Predicting Petrophysical Properties Based on Conformance between Diagenetic Products and Depositional Textures

Lucia, F. Jerry¹ (1) The University of Texas at Austin, Austin, TX

Carbonate reservoirs are a product of depositional and diagenetic processes and rock fabrics, which include the products of both processes, can be closely linked to petrophysical properties. There is considerable information on carbonate depositional facies that can be used to predict patterns of sedimentary fabrics. Predicting the spatial geometry of diagenetic products is more difficult because it often involves the transport of material by fluid flow, and we are poorly equipped to locate the source of the material or the direction of fluid flow. Therefore, the most successful method for predicting spatial distribution of diagenetic products is to relate them to depositional facies. Accuracy in predicting the 3-D distribution of diagenetic fabrics becomes a function of the conformance between diagenetic products and depositional textures.

The products of simple compaction, cementation, and grain dissolution have the highest conformance to depositional texture and are the most predictable. The pattern of dolostone beds formed by hypersaline reflux can be predicted using a prograding tidal-flat depositional model and a density flow model, resulting in some conformance to depositional models. However, predicting dolomite crystal size, which is critical to predicting flow properties, is more difficult and often has poor conformance to depositional textures. The products of late-formed dolostones generally have poor conformance to depositional textures because the flow of late dolomitizing water is typically controlled by touching-vug pore systems and because the hydrodynamics of the dolomitizing water is uncertain. Diagenetic processes that produce touching-vug pore systems typically have the least conformance between depositional textures and diagenetic products because their geometry is typically controlled by paleogroundwater systems.