Study of a deep geothermal reservoir using ambient seismic noise correlation

This work focuses on the application of the ambient seismic noise correlation technique for the characterization and monitoring of deep geothermal reservoirs near Rittershoffen (ECOGI) and Soultz-sous-Forets (GEIE-EMC). The strong spatial and temporal variability of the noise sources in the period range 0.2-7 s limits the reconstruction of the Green's functions. This results in significant errors in the velocity models. Two approaches are proposed to overcome the spatial nonuniformity of the noise and to improve the quality of the velocity models. Besides that, the temporal variability of the noise sources is a limiting factor for monitoring purposes. We estimate that the speed variations should be larger than 0.1% to 1% to be detected by the available networks. This threshold was not reached at Rittershoffen during the drillings or the stimulations. However, a change of the diffracting properties of the medium was observed following a hydraulic stimulation. The methods developed in this work could be applied to dense seismic networks. (author)