Post-Injection monitoring of stored CO2 at the Nagaoka pilot site: 5 years time-lapse well logging results

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.