Stress Orientation and Subsurface Natural Fractures Model Along the Rosedale Fault System, Gippsland Basin, Australia—Implications for Fault Related Fluid Migration Along Inverted Normal Fault Planes

Abstract

In the last two decades, petroleum exploration in the Gippsland Basin has moved away from mature Paleocene-Eocene (Upper Latrobe Group) plays located within wide ENE-trending anticlines in the Central Deep towards deeper, Cretaceous age targets (Lower Latrobe and Strzelecki Group) with more complex structural configurations along the basin bounding Rosedale Fault System (RFS). Whilst Upper Latrobe reservoirs show very good quality, deeper Lower Latrobe reservoirs will likely require stimulation of existing secondary permeability to be economically produced. Better understanding of natural fracture networks and their relation to in-situ stress is thus required to create conditions for optimal hydrocarbon production from deeper reservoir targets. We used five image logs from wells along the RFS where in-situ stress indicators (borehole breakouts BO and drilling induced fractures DITFs) and natural fractures have been identified. A total of 422 BO and 164 DITFs have been encountered, with combined lengths of 1070.5 and 193.5 m, respectively. A prominent rotation of stress orientation, from N140°W to ~80°E, observed along the northern basin margin, seems to be associated with the complex anastomosing geometry of the RFS. In the onshore region, where no such data have been available until now, in-situ stress seems to be in agreement with the regional N140°W maximum horizontal stress orientation derived from published earthquake focal mechanisms. Over 1500 fractures, both electrically conductive and resistive, have been detected in our study area, with the majority of them occurring in deeper Cretaceous sediments. High fracture intensity in the upthrown side of the RFS indicates its potential for current and/or paleo vertical fluid migration. Low angle (<30°) resistive fractures are also common, but their connectivity seems to be vertically limited and they probably do not contribute significantly to reservoir permeability. Seismic attributes calculated along the RFS helped us to generate a theoretical model of natural fracture evolution along the RFS that could be implemented for exploration or field development purposes. High consistency between seismically and well-determined fracture networks attests to the usefulness of combining such datasets to estimate fracture orientation and distribution during exploration and development projects.

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