Minipermeameter-Based Study of Permeability Trends in Channel Sand Bodies (1)

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Permeability is the single most important factor influencing fluid flow in reservoirs. To map the distribution of this property in three dimensions, we did outcrop studies with a minipermeameter. Ribbon-like distributary channel sand bodies exposed along the Yorkshire coast of England were selected as study objects. Results show a close connection between depositional facies and permeability in the ribbon channels, as witnessed by the five facies-related permeability classes. Semivariogram analyses and correlation of permeability profiles indicate that permeability measurements tend to be unrelated at distances exceeding 2-3 m. Thus, the detailed permeability patterns seen in these distributary channel sand bodies in well bores may be significantly different from the perm ability distributions in the vicinity of the well. The short permeability correlation length implies that at the macroscale or facies level, flow units are expected to be strongly lenticular. Models of the spatial flow-unit distribution in this sand body type should mimic such a pattern. By using a scaling-up procedure, the complex macroscale pattern could be used to generate models of the gross permeability distribution in ribbon-like channel sand bodies at less refined averaging scales. In the active fills of ribbon-like channel sand bodies, the classical upward decrease in permeability was rarely seen. The zones with highest permeability were mostly present in the central to uppermost parts of these sand bodies. These trends, along with the lensoid shape of the permeability class zones, should be maintained in detailed modelings and simulations of this type of reservoir sand body. Clay content, grain size, and stratification type seem to be the factors most strongly influencing permeability in the investigated sand bodies.