Reservoir Characterization Research LaboratoryCarbonate Reservoirs

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Characterization of a carbonate reservoir for fluid flow simulation is a highly complicated task. What is clear is that the end product must be a three-dimensional numerical image of petrophysical properties: porosity, fluid saturation, permeability, and relative permeability. The principal problems are (1) determining petrophysical values to be imaged and (2) distributing petrophysical values in space. Petrophysical properties are determined by measurements on core and outcrop material, by calculations using wireline log data, and by well tests and tracers. Methods of distributing the petrophysical values usually involve a combination of geologic and statistical modeling.

This report emphasizes wireline log calculations and geologic modeling using a rock-fabric approach developed in outcrop studies (Lucia and others, 1992; Senger and others, 1993; Kerans and others, 1994). The approach is to construct a detailed chronostratigraphic framework using sequences of geologic features that are related to water depth and to fill the framework with petrophysical attributes using relationships between rock-fabric and petrophysical properties. Geologic and petrophysical studies of the San Andres Formation in Lawyer Canyon, Algerita Escarpment, Guadalupe Mountains of New Mexico, suggest that (1) petrophysical properties are near-randomly distributed within rock-fabric facies; (2) rock-fabric facies are systematically stacked within high-frequency cycles (HFC's); (3) rock-fabric facies can have significantly different petrophysical properties; (4) vertical changes in properties can be abrupt, whereas lateral changes are gradual; and (5) thin, discontinuous, tight mudstone beds are effective vertical barriers to fluid flow. These findings have been applied to a detailed reservoir characterization study of two sections of the Seminole San Andres Unit operated by Amerada Hess Corporation.


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