Abstract
The objective of My thesis concerns the acoustic and seismic properties of unconsolidated formations. This topic is poorly known, from the surface -of one hand- because the physical of unconsolidated environments is still poorly understood, and in the well on the other hand where these environments are not mechanically stable. Therefore any downhole measure requests the installation of a casing and taking measurements through this casing. In my thesis, these measurements were used for the geological storage of CO2, and then in the landslide. In this context, measures have been carried out on sites Maguelone and Svelvik for the geological storage of CO2, and in the Lodeve site for landslides.The Maguelone experimental site (France) has been the subject of surface and downhole geophysical monitoring of gas injection experiments in a shallow subsurface clastic reservoir. In particular, vertical seismic profiles (VSP) and downhole SONIC logs (through PVC liners) were recorded in two holes located within meters of the gas injection hole, before, during and after a series of gas injections. VSP first-arrival times were obtained by picking, and interpreted in terms of seismic velocity models. The sonic data, once compared to other logs and core petrophysical measurements, have been processed and analyzed in terms of velocities and amplitudes. Before injection. The comparison of seismic velocities and amplitude between experiments for a single hole brings out the impact of gas injection on the elastic properties of the porous clastic sediments at the injection site, suggesting an increase in gas saturation in front of the sandy and gravel-rich layers. . In all, time-lapse VSP and sonic logging through PVC provide a means to detect and monitor gas injection and storage in geological reservoirs, leading to a view on subsurface dynamics over time. The objective of the CO2FieldLab project (Svelvik site_ Norway) was to demonstrate that adequate monitoring methods can be deployed to document potential leaks of CO2 from subsurface reservoirs. For this, a shallow injection experiment through permeable sediment was designed and conducted at Svelvik (Norway) in September 2011. The goal was to produce a CO2 leak in order to assess the relative sensitivity of several geochemical and geophysical CO2 monitoring tools. This study highlighted the potential of acoustic methods for shallow monitoring and detecting of the CO2 storage and migration. In each of the study sites, the series of techniques have been successfully used to monitor CO2 storage and migration in the shallow reservoirs, these techniques combine geophysical and geochemical approaches On the Lodeve site, my work focused on the well logging analyzes especially the ultrasonic images obtained 20 meter only of the hole in the deformation zone un active landslide in the region. A slight elastic deformation oval of the hole was demonstrated both the distance and amplitude images. Using the methodology traditionally used for the analysis of the breakouts, we have noted that the ovalisation direction corresponds to the direction of slope of the hillside affected by slipping, traversed by the well between 60 and 70 meters of depth, the interval were the image ultrasonic recorded.