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Abstract: Monitoring is the major challenge in CO2 geological sequestration. At the first Japanese pilot CO2 injection site (Nagaoka), CO2 was injected into a thin permeable zone at a depth of 1100 m and the total amount of injected CO2 was 10,400 tons during the injection period from July 2003 to January 2005. After ceasing of CO2 injection, well loggings which mainly consist of neutron logging, sonic logging and induction logging have been continued for 5 years. The Nagaoka site may provide the first field data set of post-injection monitoring and essential information on long-term CO2 behaviour in a saline aquifer. In this paper reports the results of formation pressure, well logging and fluid sampling aiming to improve understanding of CO2 long term behaviour in the reservoir. The results of time-laps well logging provide the evidences of the solubility trap and residual trap in progress at Nagaoka, suggesting CO2 is stored safely in a complex sandstone reservoir. [Copyright &y& Elsevier]

Abstract: Monitoring is essential to assess whether sequestered carbon dioxide (CO2) 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 CO2 migration and distribution, individual information yields only limited insight into CO2 behavior in geological reservoirs. To deepen our understanding of migration and containment of sequestered CO2, 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 CO2 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 CO2 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. [Copyright &y& Elsevier]