From Bureau of Economic Geology, The University of Texas at Austin (
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North Texas Geological Society Monthly Lunch Meeting, Wichita Falls, February 19, 2004

3D Modeling of Stratigraphically Controlled Petrophysical Variability in the South Wasson Clear Fork Reservoir

James W. Jennings, Jr., F. Jerry Lucia, and Stephen C. Ruppel


Petrophysical properties in Permian dolomitized shallow-water platform carbonate reservoirs of West Texas and New Mexico exhibit a high degree of spatial variability over a wide range of scales. These spatial variabilities are organized into rock-fabric flow units as much as 20 ft thick, which in turn compose the laterally continuous high-frequency cycles of a sequence-stratigraphic framework. Most of the petrophysical variability occurs at scales within the rock-fabric flow units and exhibits weak spatial correlations. The magnitude of this small-scale variability has important effects on reservoir injection and production rates. The larger scale heterogeneities are spatially controlled by the stratigraphy. These heterogeneities have a smaller variance and are easily obscured by the small-scale variability in data analysis; nevertheless, they exert a dominant control on large-scale sweep patterns in moderate mobility ratio displacements.

In this presentation we will outline a new approach for the construction of 3D reservoir flow simulation models with a superior representation of stratigraphically controlled petrophysical variability. Using the South Wasson Clear Fork reservoir as an example, and well logs as a primary source of subsurface data, we will illustrate a method of model construction that links high-resolution sequence-stratigraphic frameworks, porosity-permeability relationships from core data, outcrop-derived models of small-scale spatial statistics, and a practical approach to porosity-permeability scaleup. The resulting model exhibits stratification and stacking patterns typical of shallow-water platform carbonates in the Permian Basin and elsewhere, and it has a reduced requirement for arbitrary kv/kh modifications to inhibit cross-flow in waterflood simulations.