Maximum horizontal stress orientations in the Cooper Basin, Australia: implications for plate-scale tectonics and local stress sources

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.