HR: 11:20h
AN: GC12A-05    [Abstracts]
TI: CO2 monitoring at the pilot-scale CO2 injection site in Nagaoka, Japan
AU: * Tanase, D
EM: sec549@enaa.or.jp
AF: Engineering Advancement Association of Japan (ENNA), 1-4-6 Nishi-Shinbashi, Minato-ku, Tokyo, 105-0003 Japan
AU: Xue, Z
GC12A-05 AF: Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto, 619-0292 Japan
AU: Watanabe, J
GC12A-05 AF: Geophysical Surveying Co., Ltd., 38 Kanda-Higashimatushita-cho, Chiyoda-ku, Tokyo, 101-0042 Japan
AU: Saito, H
GC12A-05 AF: OYO Corporation, 43 Miyukigaoka, Tsukuba, 305-0841 Japan
AB: A pilot-scale CO2 sequestration project supported by the Japanese Government (METI) has been conducted by Research Institute of Innovative Technology for the Earth (RITE) in co-operation with Engineering Advancement Association of Japan (ENAA). The test site is located at the South Nagaoka gas field operated by Teikoku Oil Co., Ltd. in Nagaoka city, Niigata Prefecture, 200 km north of Tokyo. The targeted layer for the CO2 injection is a thin permeable zone intercalated in a 60 m thick sandstone bed of early Pleistocene age, which lies about 1,100 m below the ground surface. One injection well (IW-1) and three observation wells (OB-2, -3, -4) were drilled at the site. The CO2 injection started on 7 July 2003 and ended on 11 January 2005 with the total injected amount of 10,400 tonnes within eighteen months. Purchased CO2 of 99.9 % pure was injected in the supercritical state at the rate of 20-40 tonnes per day. A series of time-lapse CO2 monitoring consisted of geophysical well logging and cross-well seismic tomography has been performed at the injection site and the results provide valuable insight into the CO2 movement in the sandstone reservoir. Time-lapse well loggings of induction, gamma ray, neutron and sonic were performed almost once a month to monitor CO2 breakthrough at the three observation wells. On 10 March 2004, a breakthrough was first detected at OB-2, 40 m apart from the injection well, after the cumulative injection of 4,000 tonnes. As an evidence of CO2 breakthrough changes appeared in results of sonic, induction and neutron logs. The sonic P-wave velocity decreased significantly up to 23% after the breakthrough, and then results of sonic logging showed the CO2-bearing zone getting wider during the injection of CO2. Differences appeared also in widths of CO2-bearing zone of induction and neutron logs. On 16 July 2004, another breakthrough of CO2 was detected at OB-4 of 60 m away from the injection well as changes in sonic and neutron logs. No sign of CO2 breakthrough has been confirmed at OB-3 of 120m from the injection well. The crosswell seismic tomography was conducted between OB-2 and OB-3 in a distance of 160 m to monitor the injected CO2. The baseline survey was conducted in February 2003 prior to the start of CO2 injection. The monitoring surveys were carried out four times in January, July, November 2004 and July 2005 after 3,200, 6,200, 8,900 and 10,400 tonnes of CO2 was injected, respectively. Difference tomograms obtained by subtracting each monitor velocity from the baseline velocity were generated. Each difference tomogram shows an outstanding area of velocity decrease around the injection well, indicating the distribution of injected CO2 within the sandstone reservoir. As the amount of injected CO2 increased, the low velocity zone expanded preferentially to the formation up-dip direction in the reservoir. The monitoring at Nagaoka will be continued till 2007 for more understanding of CO2 behaviors in the reservoir after the completion of the injection.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0915 Downhole methods
DE: 0935 Seismic methods (3025, 7294)
DE: 1600 GLOBAL CHANGE
SC: Global Climate Change [GC]
MN: Fall Meeting 2005