There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest-southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

No abstract

SUMMARY Borehole breakouts and drilling‐induced tensile fractures (DITFs) were interpreted in 61 wells in the Cooper Basin indicating an average maximum horizontal stress orientation of 101°N. A total of 890 borehole breakouts and 608 DITFs were interpreted in the Cooper Basin. The approximately east–west maximum horizontal stress orientation is consistent over much of the basin, except in the Patchawarra Trough where maximum horizontal stress rotates to a northwest–southeast orientation. This rotation in maximum horizontal stress orientation is consistent with in situ stress data to the northwest of the Cooper Basin. The stress field in the Cooper Basin appears to mark the apex of a major horseshoe‐shaped rotation in maximum horizontal stress direction across central eastern Australia. Finite element modelling of the in situ stress field of the Indo–Australian Plate (IAP) using a range of plate‐scale tectonic forces is able to match the regional maximum horizontal stress orientation over most of Australia reasonably well, including the mean east–west maximum horizontal stress orientation in the Cooper Basin. However, plate boundary–scale modelling does not adequately match the horseshoe‐shaped stress rotation across central eastern Australia. The average east–west maximum horizontal stress orientation in the Cooper Basin indicates that stresses from tensional forces acting along the Tonga–Kermadec subduction zone are not transmitted into the interior of the Australian plate. The majority of the tensional forces associated with the Tonga–Kermadec subduction zone are most likely accommodated along the numerous spreading centres within the Lau–Havre backarc basin. A number of more localized stress anomalies have also been identified. These cannot be explained by plate‐scale tectonic forces and are possibly a result of geological structure and/or density contrasts locally perturbing the stress field.

No abstract