7. Spatial/Time-lapse Data Management
Time-lapse CO2 Monitor Logging in the First Pilot-scale CO2 Sequestration Site in Japan
Ziqiu Xue(1), Daiji Tanase(2) and Jiro Watanabe(3)
(1) Research Institute of Innovative for the Earth (RITE), Japan. (2) Engineering Advancement Association of Japan (ENAA), Japan. (3) Geophysical Surveying Co., Ltd., Japan.
Abstract
The first Japanese pilot-scale CO2 sequestration project has been undertaken in an onshore saline aquifer, near Nagaoka in Niigata prefecture, and time-lapse well logs were carried out in observation wells to detect the arrival of injected CO2 and to evaluate CO2 saturation in the reservoir. CO2 was injected into a thin permeable zone at the depth of 1110 m at a rate of 20–40 tonnes per day. The total amount of injected CO2 was 10 400 tonnes, during the injection period from July 2003 to January 2005. The pilot-scale demonstration allowed an improved understanding of the CO2 movement in a porous sandstone reservoir, by conducting time-lapse geophysical well logs at three observation wells. Comparison between neutron well logging before and after the insertion of fibreglass casing in observation well OB-2 showed good agreement within the target formation, and the higher concentration of shale volume in the reservoir results in a bigger difference between the two well logging results. CO2 breakthrough was identified by induction, sonic, and neutron logs. By sonic logging, we confirmed P-wave velocity reduction that agreed fairly well with a laboratory measurement on drilled core samples from the Nagaoka site. We successfully matched the history changes of sonic P-wave velocity and estimated CO2 saturation after breakthrough in two observation wells out of three. The sonic-velocity history matching result suggested that the sweep efficiency was about 40%. Small effects of CO2 saturation on resistivity resulted in small changes in induction logs when the reservoir was partially saturated. We also found that CO2 saturation in the CO2-bearing zone responded to suspension of CO2 injection.
Last modified: Sat May 13 01:06:43 2006