420,000 year assessment of fault leakage rates shows geological carbon storage is secure

• Published in: Scientific reports Vol. 9; no. 1; p. 769
• Main Authors: Miocic, Johannes M., Gilfillan, Stuart M. V., Frank, Norbert, Schroeder-Ritzrau, Andrea, Burnside, Neil M., Haszeldine, R. Stuart
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25.01.2019; Nature Publishing Group
• Subjects: 704/106/694/682; 704/172/4081; 704/2151/213; 704/2151/562; Atmosphere; Calcium carbonate; Carbon dioxide; Climate change; Deposits; Fault lines; Geology; Humanities and Social Sciences; Leakage; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-36974-0

Carbon capture and storage (CCS) technology is routinely cited as a cost effective tool for climate change mitigation. CCS can directly reduce industrial CO 2 emissions and is essential for the retention of CO 2 extracted from the atmosphere. To be effective as a climate change mitigation tool, CO 2 must be securely retained for 10,000 years (10 ka) with a leakage rate of below 0.01% per year of the total amount of CO 2  injected. Migration of CO 2 back to the atmosphere via leakage through geological faults is a potential high impact risk to CO 2 storage integrity. Here, we calculate for the first time natural leakage rates from a 420 ka paleo-record of CO 2 leakage above a naturally occurring, faulted, CO 2 reservoir in Arizona, USA. Surface travertine (CaCO 3 ) deposits provide evidence of vertical CO 2 leakage linked to known faults. U-Th dating of travertine deposits shows leakage varies along a single fault and that individual seeps have lifespans of up to 200 ka. Whilst the total volumes of CO 2 required to form the travertine deposits are high, time-averaged leakage equates to a linear rate of less than 0.01%/yr. Hence, even this natural geological storage site, which would be deemed to be of too high risk to be selected for engineered geologic storage, is adequate to store CO 2 for climate mitigation purposes.