The Law of Effective Stress has found wide application in structural geology, rock mechanics and petroleum geology. The commonly used form of this law relies on an assumption of isotropic porosity. The porosity in and around fluid-saturated fault zones is likely to be dominated by tectonically induced cracks of various shapes and sizes. Previously published field and laboratory data show that these cracks occur in distinct patterns of preferred orientation, and that these patterns vary around the fault zone. This paper uses the more general form of the Law of Effective Stress which incorporates anisotropic poroelasticity to model the geomechanical response of fault zones surrounded by patterns of oriented cracks. Predictions of fault stability in response to fluid pressure changes are shown to depend on both the nature (or symmetry) of the crack pattern and the orientation of the crack patterns with respect to the in situ stress. More complete data on the porosity of natural fault zones will enable more accurate predictions of fault stability in the subsurface.
|Title of host publication||Faulting, Fracturing and Igneous Intrusion in the Earth's Crust|
|Editors||David Healy, Rob Butler, Zoe Shipton, Rick Sibson|
|Publisher||Geological Society of London|
|Number of pages||14|
|Publication status||Published - 2012|
The author thanks the following people for discussion: D. Dewhurst (CSIRO Perth); B. Gurevich (Curtin University, Perth); R. Hillis (DET CRC, Adelaide); G. Lloyd (University of Leeds); P. Ruelland (Total); P. Schutjens (Shell); Z. Shipton (Strathclyde University); C. Wibberley (Total). The comments of three reviewers (I. Main and 2 anonymous) also helped to clarify the arguments made in this paper. This work has been part-funded by a NERC New Investigator award NE/I001743/1, which is gratefully acknowledged.