Shear-wave velocity structure derived from seismic ambient noise recorded by a small reservoir monitoring network

Reservoir monitoring is essential to guarantee safe operations for all activities involving the production and injection of fluids into the subsurface, such as hydrocarbon production, gas storage and the exploitation of geothermal reservoirs. For this purpose, microseismic monitoring networks are operated in real time in order to identify and locate any possible seismic events in the vicinity of the reservoir. The goal of this study is to investigate whether the large amount of ambient seismic noise recorded by seismic reservoir monitoring networks can be used to infer a one-dimensional shear-wave velocity profile representative of the area covered by the network. Shear-wave velocities are generally difficult to characterize and constrain, yet they are key to precisely locate seismic events. The adopted workflow consists of three steps: first, the cross-correlation functions between all station pairs are retrieved, using 1 year of continuous data; second, the average group- and phase velocity dispersion curves are extracted; third, a joint group and phase velocity inversion is done. For validation, the obtained average shear-wave velocity profile is compared with a regional model of the area as well as with local shear-wave velocity measurements from a sonic log.