Effect of Hydrodynamics and Fault Zone Heterogeneity from Membrane Seal
Capacity
Julian Strand1, Jim Underschultz1, Karsten Michael1, Brett Freeman2, and Graham Yielding2
1Petroleum Resources, CSIRO, Bentley, WA, Australia
2Badleys Geosciences Ltd, Spilsby, United Kingdom
The use of Shale-Gouge-Ratio (SGR) methods to predict across-fault seal
capacity relies on a calibration of the methodology against field examples. Existing calibrations have plotted across-fault pressure difference or buoyancy pressure against in situ SGR to define a fault-
seal
failure
envelope. Recent work on hydrodynamics and
seal
capacity has provided insight on fine-tuning the calibration methodologies that should in turn lead to improved fault
seal
capacity predictions. A situation not fully addressed, however, is the impact of fault zone heterogeneity on the hydrodynamic characteristics of a fault and thus the membrane
seal
capacity.
For a fault that defines a hydraulic head discontinuity at the reservoir scale, there exists a hydraulic head gradient or distribution within the fault-zone that is determined by the detailed permeability distribution within the fault zone. As a result, the capillary threshold pressure varies across the fault. When compared with the hydraulic head, the fault zone seal
capacity can be estimated at various locations within the fault zone. Theoretical examination of membrane
seal
capacity for various permeability distributions can be used to understand parameters that control the location of the critical leak point for a membrane fault
seal
. This can also be extended to examine possible up-fault leakage.
A range of permeability distributions are examined for a theoretical fault zone. Assuming a given across fault pressure difference in the aquifer, the internal fault zone seal
capacity is determined to demonstrate the various controls on a faults critical leak point.
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