Insights Into the Tectonic Stress History and Regional 4-D Natural Fracture Distribution in the Australian Cooper Basin Using Etchecopar's Calcite Twin Stress Inversion Technique, 2-D/3-D Seismic Interpretation and Natural Fracture Data From Image Logs and Core

Abstract

Knowledge of natural fractures has two principal uses: to predict subsurface fluid flow through optimally oriented fractures relative to the present day stress regime, and as a tool to predict the stress orientation and regime of tectonic events affecting a given area. The fundamental principles of rock failure form the basis of this methodology. Six systematically appearing natural fracture sets were interpreted from 27 borehole image logs across the South Australian portion of the Cooper Basin. The interpreted natural fracture sets indicate that at least 4 individual tectonic events have contributed to the development of natural fractures with successive periods of flexural relaxation likely occurring post major shortening tectonic events. Our results also provide insights into the likely paleo stress orientations of the four main tectonic events. We believe the development of high angle NE-SW and SE-NW striking conjugate fracture sets are related to frequent post compressional ‘sag’ periods, or flexural relaxation, along pre-existing structural lineaments. These high angle fractures sets show evidence to suggest that they are more likely to reactivate under the present day stress regime, and as such should be preferentially hunted to identify natural fracture ‘sweet spots’. Future research aims to constrain the orientations and magnitudes of tectonic events affecting the Cooper Basin through the integration of Etchecopar's Calcite Twin Stress Inversion Technique (CSIT) with our natural fracture data conclusions.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015