The Inclusion of Two-Phase Fault Rock Properties into Upscaled Models: A Novel Flow-Based Geometrical Upscaling Approach
Authors: Islam M. S. , Manzocchi T. 
Published: October 2017

This paper presents an innovative method for inclusion of two-phase fault rock properties into upscaled flow simulation models. Faults are generally represented in conventional full-field flow simulation models of clastic reservoirs as 2D planar surfaces. Often, however, faults are structurally complex 3D zones containing numerous fault segments each accommodating a portion of the total fault displacement and associated with particular single-phase (absolute permeability and thickness) and two-phase (relative permeability and capillary pressure) fault rock properties. Ignoring this structural and petrophysical complexity of 3D fault zones may impart considerable inaccuracy on the predictive performance of the upscaled simulation model. Therefore, this study has developed a flow-based geometrical upscaling method capable of representing the geometrical and saturation-dependent flow properties of realistic fault zones at the resolution of a conventional full-field simulation model.

Geometrical upscaling is the process of calculating transmissibilities for tortuous flow paths through a 3D fault zone, and representing these as appropriate neighbor and non-neighbor connection properties in a conventional upscaled model. In flow-based geometrical upscaling, all transmissibilities associated with an individual cell adjacent to the fault are calculated using a high resolution flow model in which the geometrical and petrophysical heterogeneities of the complex fault are included explicitly. Running each model with different fractional flows of oil and water results in saturation dependent upscaled pseudo relative permeability curves for each across-fault or up-fault flow path out of the cell in question, and repeating for all cells allows representation of the two-phase properties for the entire fault zone structure.

This study has been performed to account for the effects of two-phase fault rock properties as well as sub-seismic fault zone structure in reservoir flow simulation modeling. Flow results of a high resolution truth model are compared with those of the upscaled model to test the accuracy of the method. The results show that the two-phase flow-based geometrical upscaling method is a very promising method for representing two-phase fault rock properties associated with fault zone structure.

In the recent years, it has become popular to represent single-phase fault rock properties as fault transmissibility multipliers. The effects of two-phase fault rock properties and 3D fault zone structure are widely recognized to be potentially significant in reservoir management studies, but their inclusion into production flow simulation models is technically very challenging. The newly developed two-phase flow-based geometrical upscaling method accounts rigorously for both effects and is applicable at a full-field scale. The value of the method is highlighted through application to a compartmentalized reservoir model in which the two-phase fault rock properties are more influential on production than the single-phase ones.