Chapter 6.3 - Geophysical monitoring at the Nagaoka pilot-scale CO2 injection site in Japan

Abstract

Monitoring of injected CO2 at geological storage sites is necessary to ensure that the injected CO2 remains in the target formation. This chapter presents the CO2 monitoring results obtained from the pilot-scale injection test at Nagaoka, Japan. At the Nagaoka site, CO2 injection started in July 2003 and ended in January 2005, with 10.4kt of CO2 injected into a sandstone aquifer at a depth of 1100m. It is the first CO2 storage project in Japan, aimed to demonstrate the safety and efficacy of CO2 geological storage in Japan with its complicated geology. A comprehensive monitoring program, including continuous pressure measurement, time-lapse multicomponent well logging, cross-well seismic tomography and three-dimensional (3D) seismic survey, was carried out at the injection site. One injection well (IW-1) and three observation wells (OB-2, OB-3, OB-4) were drilled at the site. Pressure measurements were performed at the bottom hole of IW-1 and the reservoir depth of OB-4 for the safe operation of CO2 injection. Time-lapse well logging was carried out to detect breakthrough of injected CO2 at the three observation wells and the breakthrough times were subsequently used to help calibrate the geological and reservoir model. Further information on CO2 migration in 2D cross-section within the target layer was obtained by cross-well seismic tomography. The time-lapse 3D seismic survey was a challenge for CO2 monitoring at the small-scale injection site. Lessons learned from the Nagaoka project including design of the monitoring program and selection of monitoring technology for CO2 storage projects are summarized.