4D seismics, gas-hydrates detection and overpressure prediction as a combined methodology for application to CO2 sequestration

Remote-sensing techniques such as seismic surveys proved to be capable to monitor CO2 in the subsurface. In this work, we show how the combination of an inversion method, such as 3D seismic tomography, and poro-elastic seismic modeling are powerful tools in analyzing the subtle changes in seismic properties bound to fluid movements after CO2 injection. Through the 3D seismic tomography, it is possible to know the 3D P-and S-wave velocity field versus depth, essential to evaluate the fluid content, type and saturation, and the geopressure conditions. For this purpose we use a poroelastic model based on the generalized Gassmann equation and an effective pressure law. Field examples of time-lapse analysis, free-gas and gas-hydrate evaluation and detection of overpressure conditions are used to illustrate the procedure, in view of the extension of these techniques to CO2 storage problems.