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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: This paper reports the results of laboratory and field experiments of CO2 sequestration into the Ogachi hot dry rock(HDR; the temperature is 200 degree C) site, where a part of CO2 will be expected to be fixed as carbonates by interaction with rocks (Georeactor; Ca extraction from rocks and carbonate fixation). In 2007, CO2 dissolved water (river water with dry ice) was directly injected into OGC-2 (from September 2nd to 9th) and Run #2(from September 11th to 16th). Several tracers were also injected at the same time. Water samples are collected at the depth of ca. 800 m by a sampler (500 ml in volume) and monitored for their chemical and isotopic compositions. During the Run #2 experiment, river water was injected into OGC-1 at 2 days after injection of CO2 water into OGC-2. During the field experiments, dissolution or precipitation rates of calcite were determined by using a technique of ”in site analyses”. Calcite crystals covered with Ti rod or Au film is hold in a crystal cell and set in a crystal sonde. The crystal sonde is then put into OGC-2 and water samples at the certain depth is introduced into the sonde. After 1 hour, the sonde is recovered and the calcite crystal is observed by a newly developed phase shift interferometer to analyze the dissolution or precipitation rates of calcite from the reservoir fluids. The “in situ analyses” show that calcite precipitation was observed within 2 day after the injection. This supports the view that most of CO2 injected might be fixed as carbonate. [Copyright &y& Elsevier]