CO2 Fault Leakage of the Ladbroke Grove Gas Field: Establishing Potential Loss Rates for CO2 Geological Storage Risk Assessment

Maxwell N. Watson, CRC for Greenhouse Gas Technologies (CO2CRC), Australian School of Petroleum, The University of Adelaide, Adelaide, South Australia, 5005, Australia, phone: +61 8 8303 4295, fax: +61 8 8303 4345, mwatson@asp.adelaide.edu.au, Paul J. Lyon, Shell Internation Exploration and Production B.V, Kesslerpark 1, 2288 GS, Rijswijk (ZH), Netherlands, and Jürgen E. Streit, GeoMechanics Internation Inc (Asia Pacific), Level 3 Colonial House, 55 St George's Terrace, Perth, WA, 6000, Australia.

Achievability of long-term CO₂ containment can be assessed through risk and uncertainty analyses. These analyses would consider the occurrence and probability of possible containment loss mechanisms, such as leakage via a fault. Seepage rates from natural CO₂ accumulations with non-optimum fault seals are used to estimate potential leakage rates for risk and uncertainty analysis.

The Ladbroke Grove natural CO₂ accumulation in the Otway Basin, South Australia, demonstrates likely rates of natural fault leakage. The mineral marker laumontite indicates that the Ladbroke Grove CO₂ gas column was once nine metres thicker than present. Geomechanical modelling of the Ladbroke Grove Fault suggests a higher likelihood for fault reactivation along the NW-SE segment of the fault, resulting in a permeability pathway for gas to escape. Soil gas measurements at the surface suggest that the CO₂ has leaked up the NW-SE segment of the fault to surface, while the E-W segment of the fault has contained the CO₂. Flux data derived from this scenario and other examples throughout the world, suggests an estimated leakage range of 6 – 60 tonnes/yr should be applied to risk and uncertainty analyses for potential sites for CO₂ geological storage.

CO2 Sequestration – Concepts and Future Plans (EMD/DEG)
2006 AAPG International Conference and Exhibition, (November 5-8, 2006) Technical Program