Analysis of Seismic Ambient Noise Spectral Anomalies above Fluid Reservoirs

Strong spectral amplification of the vertical component in seismic ambient noise is commonly observed on sites located above hydrocarbon reservoirs. If well understood, these anomalies could have a potential for fluid reservoir exploration or monitoring. Under purely elastic modeling, the nature of these anomalies was mainly explained by the geological structure more than the fluid reservoir itself. Analysis on real dataset of ambient noise measurements shows that surface waves, mainly fundamental mode, seem to be the main contributors to the anomaly. This work further explores the Rayleigh wave fundamental mode interaction with an anticline structure a typical geological trap for a hydrocarbon reservoir. We propose an approximate semi-analytical surface wave approach for modelling the spectral anomalies. It is based on the contribution of 1D local solutions, and it allows to run a larger number of simulations to finally provide a general law linking the anticline geometrical and elastic parameters to the anticline-induced spectral anomaly for the case of the fundamental mode of Rayleigh waves.