Search
17. Geophysical methods to detect CO2 migration pathways in the shallow subsurface
 
This project aims to study how the combination of geophysical methods could
  • better define the pathways of the leaking gas at shallow depths (from the surface down to a few tens of meters);
  • characterise the eventual points of leakage in the shallow subsurface structures and possibly at the surface; this can be used for site selection, location and design of the surface monitoring arrays, and risk management;
  • detect CO2 unambiguously at depth and eventually be used in the future as a permanent monitoring system.
 
In this study, different monitoring methods were evaluated over a site where natural, thermo-metamorphically produced CO2 finds its way to the surface (Latera caldera, Italy).
The study area clearly shows a change in vegetation at the locations where CO2 (and H2S) is reaching the surface. Different geophysical monitoring techniques have been deployed: 2D reflection seismics, 2D refraction seismics, Multi channel analysis of surface waves (MASW), ground penetrating radar (GPR), micro-gravity, 2D and 3D geo-electrical measurements, Self Potential (SP) and electro-magnetic (EM31, EM34 and TDEM) measurements. Furthermore both soil gas and gas flux measurements were performed in a dense grid over the study area to “ground-truth” the geophysical results.
 
In general, a good correlation between the different methods and the presence of CO2 was observed. The observed fault on the seismic data appear to correspond to the preferred migration pathways of CO2. A repeat survey of different methods (electrical resistivity tomography, EM and 2D seismics) was carried out to investigate repeatability aspects. Possible seasonal changes affecting the CO2 fluxes are still to be investigated.
 
 
Snapshot of the 3D integrated data model of the Latera site showing the superposition of different methods.
Snapshot of the 3D integrated data model of the Latera site showing the superposition of different methods:
(A) Measured gas fluxes (purple peaks); (B) Electrical Resistivity Tomography (ERT); (C) seismic profiles; (D) Integrated interpretation of the different methods showing a major fault (golden surface).
 
 
For more information please contact: Hubert Fabriol at Bureau de Recherches Geologiques et Minieres