Abstract

A workflow for generating internally consistent sets of saturation functions from capillary pressure and relative permeability data for use in numeric reservoir simulation is described. This workflow was implemented in software that was developed to facilitate the filtering and grouping of these data using a variety of screening criteria. Such implementation ensures the application of consistent practices, based on the physics of multiphase displacement in porous media, when developing relative permeability and capillary pressure models. The data are reviewed to confirm that they are of acceptable quality prior to use in saturation function development. The workflow described here conforms to the displacement categories defined in the simulation model, e.g. families of reservoir facies. In addition to grouping and analyzing SCAL data (capillary pressure, relative permeability, wettability) for a specific reservoir, the software can access a larger database that contains all available SCAL data. The database also provides convenient access to analog data for reservoirs in which sufficient SCAL data have not been generated. To our knowledge, such a systematic method for the development of consistent capillary pressure and relative permeability saturation functions based on families of reservoir facies for simulation has not been presented in the literature.

Saturation endpoints are first established by analyzing the appropriate capillary pressure data (e.g., primary drainage Pc for Swir, primary imbibition water-oil Pc for Sorw, primary drainage gas-oil Pc for Sorg, etc.). This analysis involves fitting the data to a consistent constitutive equation that contains the saturation endpoint as a regression parameter. The resulting models should be compared to any available field data to ensure consistency (e.g., primary drainage Pc vs. calibrated log Sw(z)). Once the saturation endpoints have been established, the grouped relative permeability data are analyzed, starting with the bounding water-oil primary drainage data. After defining the bounding primary drainage curves, the primary imbibition krow-krw curves can be developed. Individual imbibition krow-krw tests generally correspond to unique imbibition scanning curves rather than the bounding primary imbibition curve, suggesting the measured imbibition curves be scaled to the bounding primary drainage kro curve to ensure consistency. Secondary drainage kro-krwo data, if available, are similarly scaled. Three-phase gas-oil primary drainage krog-krg and primary imbibition kro-krgo data are treated in an analogous manner. This process is applied to each group of capillary pressure and relative permeability data. Experience has shown that this approach properly represents the displacement physics, facilitating accurate reservoir performance predicitions and history matches.

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