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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