The current situation of monitoring technology for CO2underground storage is reviewed. Projects of CO2 injection into saline aquifer are picked out, and technologies applied on each project are classified.
Vertical seismic profiling (VSP) method has some advantages over other methods for monitoring CO2 underground storage:
Less leakage risk and cost of drilling comparing to seismic tomography since it requires only single borehole that could be a leakage pass.
Less attenuation of a transmitted signal, and less noisy optimal environment comparing to surface seismic method since geophones are installed in a borehole.
The results of experimental study of VSP application and validity for CO2 monitoring in the Japanese first pilot test site located in Nagaoka Japan are shown. Zero offset VSP measurements were carried out in the monitoring borehole where CO2 breakthrough had been observed with time-lapse logging. Basic data prosessing such as up and down wavefield separation and corridor stacking was applied to the VSP data, and VSP seismogram was obtained. The processed VSP seismograms are in good agreement with the synthetic seismograms calculated from an acoustic impedance model based on the logging data. The difference of amplitude between the synthetic seismograms from logging data before CO2 injection and VSP data after injection is very clear at the depth CO2 trapped.
These results indicate a possibility that VSP method would be a valid technology to detect CO2plume extent if it is applied before injection and repeated survey after injection.