6.4.2 Latrobe Valley and Otway Basin, Australia

The GEODISC-RISQUE approach (Quantitative Risk Assessment) has been used for several field cases in Australia, e.g. the Latrobe Valley located within the Gippsland Basin (Hooper et al., 2005) and the Otway Basin (Sharma and Cook, 2007). This semi-quantitative methodology relies on expert-panel analysis of hazardous events (i.e., risk events such as leakage from existing exploration and production wells or injection and monitoring wells, leakage from permeable zones in seals and regional-scale over-pressurisation, leakage from faults through seals and earthquake-induced fractures, leakage from exceeding the "spill point" of the storage site and incorrectly predicting the migration direction, loss of containment and event risks quotients), for which the likelihood, consequences, and timescale of occurrence of each is assessed (Hooper et al., 2005).

  1. The Quantitative Risk (QRA) carried out for the containment issue of the Latrobe Valley CO2 Storage Assessment (LVCSA) project. The context of the QRA for the studied site was defined, including injection timeframes, locations, and amounts; reservoirs and expected plume migration (including to existing wells and faults) and eventual traps (CSLF, 2009). The LVCSA risk process has provided strong indication that the Gippsland Basin can be safe and effective site for CO2 for thousands of years. A CO2 leakage rate of 1% over 1,000 years is commonly used as an acceptable level for storage assurance and the targeted reservoirs within the offshore Gippsland Basin are predicted to be below that level. The risk identified a number of issues and mitigation measures that will need to be addressed by project proponents. Several specific mitigation actions have already been factored into the costings for the project. The LVCSA indicates that all issues associated with proposed injection are manageable (Hooper et al., 2005).

  2. The CO2CRC's Otway Basin Pilot Project (OBPP) is located in Victoria. Risk areas have been identified through the project's risk process and an extensive monitoring and verification scheme has been proposed to address some of these issues. A Quantitative Risk Assessment (QRA) was performed using the RISQUE method. The process involves the use of expert panels to provide input into a quantitative risk analysis and management framework. The expert panel considered the data gathered since 2005 and the initial risk and updated the risk for the pilot project. Both the engineered system (wells) and the natural system (site geology, reservoir formation, overlying and underlying formations and groundwater flow regimes) were considered. The QRA can be modified as new data becomes available. At a planning confidence level of 80% it was seen that (a) no single risk events exceeded acceptable risk quotient, and (b) total risk event quotient was less than acceptable target (1% leakage over 1,000 years, thus a low risk). Major risks events are leakage from existing faults, and leakage from wells (in particular damage to cement) (CSLF, 2009; O'Brien, 2008).