Present-Day State-of-Stress of Southeast Australia

Abstract

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry.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.

3D seismic analysis of complex faulting patterns above the Snapper Field, Gippsland Basin: implications for CO2storage

“…The present-day stress tensor in the Snapper Field is likely to be consistent with regional observations in the Gippsland Basin and suggests transitional conditions between strike-slip and reverse fault stress regimes (S Hmax D 41 MPa km À1 >> S v D 21 MPa km À1 »S hmin D 20 MPa km 1 ; Table 2) (Nelson & Hillis 2005;Nelson et al 2006;van Ruth et al 2006). The orientation of maximum horizontal stress in the Snapper Field is assumed to be »150 N, based on projection (Table 2).…”

Fault seal analysis in ‘branched’ fault traps, eastern Gippsland Basin

“…The parameters that follow form the input to modelling the ∆P for the 62 faults being considered (mostly 'branched' faults). A S Hmax , S hmin and S V of 42, 20 and 21 MPa/km, respectively, are used based on Nelson et al (2006). A pore pressure of 10 MPa/km is used to calculate the effective stress.…”

Quantifying Neogene plate-boundary controlled uplift and deformation of the southern Australian margin

“…South Australia; Hillis et al 1995) to c. 1378N in the eastern Otway Basin (i.e. Victoria; Nelson et al 2006;Vidal-Gilbert et al 2010;Fig. 2).…”

“…Using an extensive dataset of stress measurements, based mainly on wells from the Port Campbell Embayment and Shipwreck Trough, Nelson et al (2006) concluded that the present-day stress regime is strike-slip (approaching reverse). Leak-off pressure test and extended leak-off pressure test data reported by Nelson et al (2006) indicate an increase in the magnitude of S Hmin from the western to eastern Otway Basin, indicating that the eastern part of the basin is approaching a reverse stress regime (Nelson et al 2006).…”

“…Using an extensive dataset of stress measurements, based mainly on wells from the Port Campbell Embayment and Shipwreck Trough, Nelson et al (2006) concluded that the present-day stress regime is strike-slip (approaching reverse). Leak-off pressure test and extended leak-off pressure test data reported by Nelson et al (2006) indicate an increase in the magnitude of S Hmin from the western to eastern Otway Basin, indicating that the eastern part of the basin is approaching a reverse stress regime (Nelson et al 2006). However, in a study of the stress regime at a CO 2 storage site in the Port Campbell Embayment, Bérard et al (2008) constrained a normal stress regime; this is less consistent with the geological evidence for neotectonic reverse faulting and compressional deformation in this region (Nelson et al 2006).…”