PETROPHYSICAL CHARACTERIZATION OF, AND FLUID FLOW MODELING THROUGH, FAULT ZONES IN SANDSTONE: NEW INSIGHTS

This presentation is part of an on-going effort to improve representation of fault zones in fluid flow simulation models using data from an analogue paleo-reservoir in the Aztec sandstone outcropping widely across the Valley of Fire State Park, Nevada. The premise is that slip surfaces are important components of fault zones, and there fore, they require a more careful structural and petrophysical characterization. Generally, most fault zone permeability studies assume slip surfaces as continuous features that enhance fault-parallel flow in accordance with the parallel plate representation. However, our field observations and laboratory analyses suggest that slip surfaces are highly heterogeneous features that are subjected to diagenetic and cataclastic alteration. As a result, petrophysical properties of slip surfaces such as porosity, permeability and connectivity vary throughout the fault evolution. We studied geometric, temporal, textural and mineralogical aspects of slip surfaces and the adjacent fault rock to better represent fault zones in fluid flow models.

Results of this study are subsequently used in permeability upscaling of fault zone blocks and are compared with previous fluid flow modeling results using the same blocks in which permeability of the slip surfaces was assumed to be constant and was estimated by a parallel plate model. We conclude that representation of slip surfaces make a significant impact on the upscaled permeability depending on the continuity and connectivity of the slip surfaces with respect to the block size used for upscaling.