Extending interpretations of natural fractures from the wellbore using 3D attributes: The Carnarvon Basin, Australia

Abstract

Natural fractures can be identified in wellbores using electric resistivity image logs; however, the challenge of predicting fracture orientations, densities, and probable contribution to subsurface fluid flow away from the wellbore remains. Regional interpretations of fracture sets are generally confined to areas featuring an extensive reservoir analog outcrop. We have made use of extensive data sets available in Western Australia’s Northern Carnarvon Basin to map subsurface natural fractures, contributing to a regional understanding of fracture sets that can be applied to broader parts of the basin. The Northern Carnarvon Basin is composed of distinct structural domains that have experienced differing tectonic histories. Interpretation of regional fractures was achieved through an integrated approach, incorporating electric resistivity image logs from 52 Carnarvon Basin wells and seismic attribute analysis of two 3D seismic data sets: Bonaventure_3D ([Formula: see text]) and HC_93_3D ([Formula: see text]). Integration of these two data sets allows for a regionally extensive identification of natural fractures away from well control. Fractures of differing age and character are identified within the basin: Outboard areas are dominated by fractures likely to be open to fluid flow that are parallel to subparallel to the approximately east–west present-day maximum horizontal stress, providing possible flow conduits between potential damage zones identified alongside the north–northeast/south–southwest-striking faults that constitute the major structural trend of the basin, and inboard areas dominated by northeast–southwest to north–northeast/south–southeast fractures formed in fault damage-zones alongside normal, and inverted-normal, faults at those orientations. Finally, fractures observed in wells from the Rankin Platform and Dampier Subbasin occur at neither of these orientations; rather, they closely parallel the strikes of local faults. Additionally, variation is seen in fracture strikes due to isotropic present-day stress magnitudes. This methodology extends fracture interpretations from the wellbore and throughout the region of interest, constituting a regional understanding of fracture sets that can be applied to broader parts of the basin.