Groundwater monitoring at the Otway project site, Australia

The Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway Project in the onshore Otway Basin, Victoria, is Australia’s first pilot project for the long term sequestration of CO2. The Otway Project has injected 65,445 tonnes of a mixed CO2-CH4 supercritical fluid (77 mol% CO2, 20 mol% CH4, 3 mol% of minor wet gases and N2) some 2000 m below the surface into the Waarre Formation, which is capped by the Belfast Mudstone regional seal. The site has been comprehensively characterised by a multidisciplinary team and the risk analysis has shown the likelihood of leakage out of the injection horizon–let alone to the land surface–to be exceedingly low. Nevertheless, the objectives of the CO2CRC through the Otway Project are not only to demonstrate safe CO2 injection, but also to develop new methodologies for monitoring and verification (M&V) of carbon storage that might apply to future commercial scale injection. At Otway, this involves M&V at the reservoir level and Assurance Monitoring, in the shallow subsurface (aquifers and soils) and the atmosphere. The groundwater monitoring system represents the most comprehensive system for monitoring freshwater in the vicinity of a CO2 storage demonstration to date. Monitoring the groundwater is of particular significance in demonstrating the ongoing integrity of natural resources to the general community.The first benchmark of any monitoring system is the establishment of a baseline from which to define natural variations in the system prior to injection. At Otway the natural baseline is complex due to the influence of the Port Campbell Limestone immediately below the soil zone. Since June 2006, groundwater levels and composition have been monitored at 21 bores completed in the unconfined Port Campbell Limestone aquifer, and 3 bores completed in the deeper confined Dilwyn aquifer. All monitoring wells are located within 10 km of the CRC-1 injection well. The groundwater program includes (i) biannual geochemical sampling to establish groundwater composition; (ii) monitoring of water levels to determine seasonal variations to formation water flow rate and direction; and (iii) headspace gas sampling of the Dilwyn aquifer to detect tracer compounds and CO2 content. This monitoring is necessary to establish the connectivity and fluid migration timescales of the fresh water aquifers and to understand the water-rock interactions and resulting fluid composition.The assurance monitoring team works closely with government agencies and landowners and provides data as required. Community engagement has been vital to the success of the program and considerable effort goes toward keeping landowners informed of our activities and minimizing disruption to their properties. To date, the groundwater component of the assurance monitoring program has not detected any perturbation in the baseline condition as a consequence of CO2 injection. It is important to note that this does not necessarily indicate containment; it does however provide assurance to the community and regulators that the natural resources have not been impacted by the CCS activities and can continue to be used safely.