Fault architecture in the Port Campbell Embayment, Otway Basin (Vic, Australia)

  • McMahon, C. (Speaker)
  • Roberts, J. (Contributor)
  • Shipton, Z. (Contributor)
  • Eric Tenthorey (Contributor)
  • Andrew Feitz (Contributor)
  • Stephen Gallagher (Contributor)
  • Rohit Soman (Contributor)
  • Gareth Johnson (Speaker)

Activity: Talk or presentation typesOral presentation


The potential for fluid movement along fault zones has implications for the measurement, monitoring, and verification (MMV) of subsurface technologies such as geological carbon storage. Predicting fluid flow pathways in the shallow part of the overburden of a storage site will be crucial to design effective MMV systems. However, the architecture of faults at shallow depths is less well understood than fault architecture at reservoir depths, and consequently the effect of shallow faults on fluid flow is far less well understood.

In early 2024, a novel field trial injection will be conducted at the CO2CRC Otway International Test Centre (OITC), in southern Victoria, Australia. A small volume of CO2 (~10 t) will be injected into the Brumbys Fault and monitored to provide data on the transport of CO2 in the shallow subsurface. The 1.2km long Brumbys Fault is hosted in the Miocene Port Campbell Limestone (PCL) carbonate sequence that crops out across southern Victoria. The Brumbys fault has been interpreted as a strike-slip fault, due to its near-vertical dip (~80° as imaged on 3D seismic data), small throw (2-4m), and favorable orientation to the present-day stress (striking 170°, ~30° from the maximum horizontal stress direction of 142°). However, there are no convincing surface markers that could indicate horizontal displacement. Given uncertainty in the magnitude of the stress near the surface, all possible fault kinematics can (and have been) interpreted in the region. To reduce the uncertainty regarding the fault kinematics, we attempt to reconcile the styles of faulting observed in nearby field exposures with observations made at the OITC and the stress regime in the region. This is important for defining the fault architecture within the borehole and understanding the potential implications for future injection experiments at the OITC.

We synthesise core logs, field observations and geochemical data to suggest possible faulting mechanisms. Observations of the Brumbys-1 core show a diffuse fault zone with no clear core/damage zone and a deformation style dominated by particulate flow. Field data from a 45km section of costal outcrops are compared to data from the inland Kurdeez Quarry and core from the OITC wells. The location and type of faulting varies: eastern coastal areas host reverse faulting, western coastal areas have no faults, and inland areas lack evidence of faulting. Geochemical analysis suggests there is no compositional difference in the inland and coastal PCL inland that could explain different structural responses to the same stress. We speculate that coastal reverse faulting may be due to broad regional folding, localised where the PCL thins out. In contrast the OITC is closer to volcanic centres that were active during deposition, so it is possible that the strike slip faulting may have been initiated by volcanic related deformation or seismicity. We discuss these mechanisms and potential implications for shallow subsurface fluid flow and future injection experiments at the OITC.
Period10 Jan 2024
Event titleTectonic Studies Group
Event typeConference
Conference number2024
LocationSt.Andrews, United KingdomShow on map
Degree of RecognitionInternational


  • Faults
  • Fluid flow