The Otway Shallow Fault Project is a field demonstration that aims to better understand CO2 migration in faults, by injecting a small amount of CO2 into a shallow fault under highly controlled conditions to image the CO2 migration behaviour and reservoir response. This experiment enables critical capabilities in the accurate representation of fluid flow in shallow faults to be developed and transferred to deeper faults.
The previous appraisal work answered key questions regarding the rock-fluid mechanics, subsurface structure through seismic and rock coring and groundwater quality. Numerical simulations of potential CO2 were completed to assess the pathways and behaviour of the plume during and after the injection. Two bore holes, Brumbys-1 and Brumbys-2 were drilled in the previous phase to underpin the appraisal phase.
In preparation for the operation phase, where CO2 injection operation occurs, two new boreholes Brumbys-3 and 4 are drilled. The wells are completed with fibre optics and pressure gauges outside the casing. A gravel pack is installed at the targeted injection interval of ~65 – 75 m depth in the injection well. Both wells are armed with fibre optics cables to record Distributed Acoustic (DAS), Temperature (DTS) and Strain (DSS) sensing.
The experiment would provide an opportunity to demonstrate high-resolution, semi-continuous, combined reverse Vertical Seismic Profile (VSP) and Distributed Strain Sensing (DSS) monitoring of CO2 movement near and along a fault. In preparation for the injection phase in Q1 of 2024, a water pump test was completed to understand the injectivity of the injection well (Brumbys-3), pressure and hydraulic communication between the wells and to update the reservoir model with the collected data.
The behaviour of a small amount of gaseous CO2 is different from the larger plume in the dense phase. Significant efforts were dedicated to modelling the likely behaviour of the CO2 plume around the Brumbys fault. The previous forward-modelled scenarios are updated with the outcome of the water injection test. Parallels are also drawn from experimental sand box models of the injection scenario to demonstrate the likely behaviour of the CO2 during and after injection. The findings of the updated models are key in adjusting the planned monitoring solutions to enable effective imagining and detection of the injected CO2.