Understanding present-day stress in the onshore Canning Basin of Western Australia

The Ordovician to Cretaceous Canning Basin of Western Australia is an underexplored prospective onshore petroleum basin with proven petroleum systems currently producing on a small-scale. The Canning Basin has recently become a site of interest for unconventional hydrocarbon exploration, with several formations within deeper basin depocentres being investigated for resources and estimates that suggest it may have the largest shale gas potential in Australia. Modern petroleum resource evaluation generally depends on an understanding of both local and regional stresses, which are a primary control over the formation and propagation of induced fractures. Presently, there are significant gaps in our understanding of these factors within the Canning Basin. This study characterises the regional stress regime of the onshore Canning Basin and presents detailed models of present-day stress within the subsurface. These allow for the identification of significant stress heterogeneities and natural barriers to fracture propagation. Wireline data interpretation reveals a variable present-day state of stress in the Canning Basin. An approximately NE-SW regional present-day maximum horizontal stress orientation is interpreted from observed wellbore failure in image logs, in broad agreement with both the Australian Stress Map and previously published earthquake focal mechanism data. One-dimensional mechanical earth models constructed for intervals from 15 Canning Basin petroleum wells highlight the relationship between lithology and stress. This study describes significant changes in stress within and between lithological units due to the existence of discrete mechanical units, forming numerous inter- and intra- formational stress boundaries likely to act as natural barriers to fracture propagation, particularly within units currently targeted for their unconventional resource potential. Broadly, a strike-slip faulting stress regime is interpreted through the basin, however, when analysed in detail there are three distinct stress zones identified.: 1) a transitional reverse- to strike-slip faulting stress regime in the top ~1 km of the basin, 2) a strike-slip faulting stress regime from ~1 km to ~3.0 km depth, and 3) a transitional strike-slip to normal faulting regime at depths greater than ~3.0 km. This study is a component of the Australian Government’s Exploring for the Future (EFTF) initiative, which is focused on gathering new data and information about the resource potential concealed beneath the surface across northern Australia. Appeared online in the Australian Journal of Earth Sciences 17 Feb 2021