Case study: trapping mechanisms at the pilot-scale CO₂ injection site, Nagaoka, Japan

In this paper, we present the results of geophysical and geochemical observations at the Nagaoka site, where the first Japanese project on CO₂ geological storage is currently underway. We collected formation water and rock samples from the reservoir, and conducted laboratory experiments to investigate the seismic wave response and geochemical reactions due to the CO₂ injection under simulated in situ conditions. The results of time-lapse crosswell seismic tomography indicate an area of P-wave velocity decrease due to CO₂ saturation, and the CO₂-bearing zone near the injection well expanded clearly along the formation up dip direction during CO₂ injection. The presence of CO₂ was also identified by induction, sonic and neutron logging at the observation wells. The results of geochemical reactions demonstrated the potential of reservoir sandstones at the Nagaoka site for the effective solubility, ionic, and mineral trapping of CO₂.