Technical de-risking of a demonstration CCUS project for final investment decision in Australia

CO2CRC is developing subsurface monitoring technologies which can significantly reduce the cost and environmental footprint compared to traditional 4D surface seismic. These can be applicable to both hydrocarbon production and CO2 injection projects. These methodologies involve continuous seismic monitoring using well-based distributed acoustic sensors and pressure tomography. CO2CRC’s Otway Stage 3 Project is aiming to validate these techniques while injecting 15 000 t of CO2 into the Paaratte Formation in the Otway basin and monitoring the plume using an array of six wells. The main technical risks for subsurface monitoring are migration of the plume outside of the survey area and lack of communication between the wells. Moreover, given some amount of CO2 is already in the injection formation (from CO2CRC Otway Stage 2C Project), it is required to understand the chance of the new plume merging with the existing plume and the possible timeframe. This paper summarises the workflow followed to de-risk the project and optimise the injection and monitoring wells location to reduce the abovementioned risk factors. As a result of the de-risking process, by changing different parameters and mitigating some of the risks, we gained a high degree of confidence that the CO2 plume will stay within the survey area and that the chance of pressure communication between the wells was increased. A thorough sensitivity analysis was also performed to understand the influence of each parameter on the plume speed. This process provided a higher confidence to decision makers to make a final AU$45 million investment decision.