Near-field Elastic Scattering of Rayleigh Waves - A Model for Interpreting Hydrocarbon Micro-tremors
A. Kazantsev, H. Chauris, P. Dublanchet and F. Huguet
Event name: 79th EAGE Conference and Exhibition 2017
Session: Diffraction Modelling and Imaging
Publication date: 12 June 2017
Info: Extended abstract, PDF ( 681.75Kb )
Price: € 20
Spectral amplitude effects of hydrocarbon reservoirs in passive seismic data gave rise to growing interest since the early 2000s. The use of spectral anomalies in the ambient noise would allow for applications in reservoir monitoring and exploration. Several successful field experiments were reported in literature. However, to our knowledge, no general agreement on the nature of these anomalies has yet been met, which remains an obstacle to a quantitative interpretation. With an aim of testing the simplest mechanism possible, we propose a purely elastic model of the Rayleigh wave fundamental mode scattered by a reservoir-like inclusion in the sub-surface. The frequency-dependent penetration depth of surface waves is indeed able to generate selective spectral effects. This property is well known in global seismology. Using both semi-analytical and numerical approaches, we retrieve a positive spectral anomaly vertically above the inclusion, on the vertical component of a Rayleigh wave generated by a distant source. Both the frequency of the anomaly and its strength decrease with the depth of the inclusion. For small elastic contrasts (-10%), the magnitude of the computed anomaly remains below what was reported from field experiments, meaning that extra complexity might have to be added to the model.