The aim of this project is to develop a low-cost monitoring system, to be used continuously during and after the CO2 injection phase, in order to get information on the interaction between fluids and rock formations (where those fluids migrate by strong pressure gradients) and a prompt alert for possible migration of CO2 through the cap-rock and to the overburden.

Test of the cable-less system near Ketzin.

 

The system combines surface and borehole or buried arrays of 3C geophones that enable the recording of some limited active seismic sources, as well as the continuous recording of micro-seismicity, that may be generated by the re-distribution of stresses due to the CO2 injection.

 

The deep borehole measurements guarantee the detection and accurate location of even tiny micro-seismic events, while the high number of surface stations enables the identification of points of highest energy emission in the subsurface. The same low cost cable-less recorders used continuously for micro-seismicity, may be used, from time to time, to survey limited “key” parts of the area where extensive and by far more costly 3D seismic surveys are repeated generally at intervals of 2-3 years.

 

By comparing these results it is possible to detect changes in the seismic signal characteristics (amplitude and frequency of P wavelets, Vp/Vs ratio, etc.) that may be indicative of changes in fluid content, related to CO2 migration. Moreover, in this methodology, the detailed seismic velocity fields are of great importance and, hence, they are determined by tomographic techniques.

 

 

For more information please contact: Giuliana Rossi at Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS