Present-day stress magnitudes in the Bowen-Surat Basin: implications for fluid flow through faults and fractures

Abstract

Stress magnitudes have been constrained at varying depths across 12 wells in the Bowen-Surat Basin, Eastern Australia. The vertical stress was measured at 21.42 –25.869 Mpa km-1. The minimum horizontal stress was measured using three extended leak-off tests, six leak-off tests and eight formation integrity tests ranging from 2.71 Mpa at 51 m to 66.69 Mpa at 2835 m. The maximum horizontal stress magnitudes were measured using frictional limits and hoop stress equations (sensu Kirsch 1898), ranging from 11.34 Mpa at 130 m to 148.71 Mpa at 2857 m. The stress magnitudes show a depth related trend changing from a reverse stress regime (ground level to ~500-600 m), into a dominant strike slip stress regime and transpressional stress regime (below ~500-600 m). The average SHmax stress orientation is shown in previous studies to rotate from NW-SE in the northern region of the basins to NE-SW in the southern regions of the basins. It is expected that conductive fractures which occur within 26° of the present day SHmax are open to fluid flow. Therefore the depth variable stress regime and rotating SHmax orientation exerts a large influence on the subsurface permeability of the two basins. Mapping this secondary permeability in the subsurface is vital to understanding fluid flow pathways in the subsurface and is vital for resource recovery.