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type     June, 2005

Vol 2 Chapter 29: Modeling of Near-Surface Leakage and Seepage of CO2 for Risk Characterization

Curtis M. Oldenburg and Andre A.J. Unger

Abstract: The injection of carbon dioxide (CO2) into deep geologic CO2 storage sites entails risk that CO2 will leak away from the primary storage formation and migrate upwards to the unsaturated zone from which it can seep out of the ground. We have developed a coupled modeling framework called T2CA for simulating CO2 leakage and seepage in the subsurface and in the atmospheric surface layer. The results of model simulations can be used to calculate the two key health, safety, and environmental (HSE) risk drivers, namely CO2 seepage flux and near-surface CO2 concentrations. Sensitivity studies for a subsurface system with a thick unsaturated zone show limited leakage attenuation resulting in correspondingly large CO2 concentrations in the shallow subsurface. Large CO2 concentrations in the shallow subsurface present a risk to plant and tree roots, and to humans and other animals in subsurface structures such as basements or utility vaults. Whereas CO2 concentrations in the subsurface can be high, surface-layer winds reduce CO2 concentrations to low levels for the fluxes investigated. We recommend more verification and case studies be carried out with T2CA, along with the development of extensions to handle additional scenarios such as calm conditions, topographic effects, and catastrophic surface-layer discharge events.

Carbon Dioxide Capture for Storage in Deep Geologic Formations – Results from the CO2 Capture Project Geologic Storage of Carbon Dioxide with Monitoring and Verification - Volume 2
Edited by:
Sally M. Benson, Lawrence Berkeley Laboratory, Berkeley, CA, USA

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