A monitoring framework for assessing underground migration and containment of carbon dioxide sequestered in an onshore aquifer

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Abstract Monitoring is essential to assess whether sequestered carbon dioxide (CO 2 ) behaves as expected and whether unexpected migration or leakage occurs. A variety of monitoring techniques have been proposed and examined. Although those techniques provide useful information, such as CO 2 migration and distribution, individual information yields only limited insight into CO 2 behavior in geological reservoirs. To deepen our understanding of migration and containment of sequestered CO 2 , a monitoring framework must be established to comprehend the individual sources of information. This paper describes the monitoring framework that was applied to a test field of CO 2 sequestration conducted at an onshore site in Nagaoka, Japan. The target aquifer was the early Pleistocene sandstone bed, around 60m thick and 1,100 m below the ground surface. During the 550-day injection period, around 10,000 tonnes of CO 2 were sequestered. Three monitoring wells were completed around an injection well and several monitoring schemes, including pressure and temperature measurements, well logging, crosswell tomography, in-situ fluid sampling, were applied. Based on the monitoring results, meso-scale as well as macro-scale migration is examined and discussed. This study addresses monitoring issues in an integrated framework, with emphasis on the importance of comprehensive analyses, since they can bridge the gap between the individual monitoring results.