Michal Nemcok¹, Andreas Henk², Rodney A. Gayer³, Sara Vandycke³, Tanya M. Hathaway³

(1) Energy and Geoscience Institute, University of Utah, Salt Lake City, UT
(2) Geological Institute, Wurzburg University, Germany
(3) Cardiff University, United Kingdom

ABSTRACT: Strike-Slip Fault Bridge Fluid Pumping Mechanism: Insights from Field-Based Paleostress Analysis and Numerical Modeling

Paper presents a finite-element study of stress perturbation in evolving compressive and extensional strike-slip fault bridges. Results are compared with a fracture study of a compressive bridge at St. Donats, UK. Horizontally interbedded mudstone and bioclastic calcilutite at St. Donats have a distinct permeability anisotropy, retained even after fracturing, that favors lateral fluid flow and causes the elevation term in the hydraulic head equation to vanish. Therefore, the mean stress perturbation patterns can be used to interpret fluid flow, between mean stress maxima and mean stress minima. The stress patterns, defined by modeling, are reestablished by each stress buildup preceding the rupturation of the boundary faults throughout the development stages of a strike-slip fault bridge. The influence of mean stress anomalies on the amount of flow postfailure is dependent on the size of the anomalies and the distance between them, provided that the connecting fault aperture and permeability remain constant. Fault reactivation and new fault generation within an evolving bridge is a process consisting of multiple successive events that retains the storage capacity of the bridge. Rupture and sealing of the main bounding-faults is a step-wise process that opens and closes fluid conduits between areas with different pressures.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado