Evaluation of measured and facies-based effective permeability and the significance for reservoir mapping and connectivity

This study addresses how reservoir-scale permeability models vary depending on the scale of investigation of the input permeability values. A common practice in reservoir modeling is to directly use permeability measurements from core-plugs or probe permeametry in petrophysical modeling. Three-dimensional permeability model cells are often several orders of magnitude larger than the scale of investigation (volume support) of the permeability measurement. This scale difference can produce unrealistic results in the permeability model which may not be representative of the reservoir heterogeneity.;To explore this issue, 3-D core lithofacies and permeability models of the Terry Formation in the Denver Basin, Colorado were created with permeability values measured using a mini-probe permeameter. These measured-permeability values were acquired by facies and lamina type and flow-based upscaling was used to generate effective-permeability values by facies. After upscaling, the range of permeability is reduced, and the average permeability is decreased by as much as 50%.;Using the original- and effective-permeability values, the significance of fine-scale permeability heterogeneity associated with lithofacies that exist below the resolution of reservoir model cells was investigated through comparative analysis of field-scale, 3-D permeability models and resulting static connectivity of permeability distributions. Statically connected reservoir volumes to producing wells defined by permeability cutoffs shows that for relatively lower permeability cutoffs, there is a distinct difference in connected volume between original- and effective-permeability models. In some cases, this difference is 50% lower for connectivity in the effective-permeability model. This is significant because it represents the reservoir volume connected to wells for potential production. As the permeability cutoff (reservoir definition) increases, static connectivity decreases and the differences between the original- and effective-permeability models is reduced. The differences between original- and effective-permeability values and models indicate why it is important to utilize scale-dependent, facies-based permeability values for reservoir mapping at the field scale.