Ambient noise spectral amplitude distortions above heterogeneities : feasability study for multi-fluid reservoir exploration and monitoring

Abstract : This PhD work investigates the possible elastic mechanisms behind the ambient noise amplification above multi-phase fluid reservoirs. Three datasets are analysed above different reservoirs. The observed spectral signature is different in the gas storage and geothermal contexts. A non-supervised algorithm for amplitude spectrum classification is developed, allowing to extract and map the relevant attributes of a multi-phase fluid presence. As a first modelling step, a wavefield characterisation methodology is applied to determine the composition of the ambient noise. It reveals the presence of strong Rayleigh overtones. Numerical 2D elastic modelling is used to simulate the propagation of overtones across a reservoir within a realistic geological structure. The modelled reservoir response is too small compared to the real data. However, the small amplitude perturbations arising in the numerical simulations are successfully inverted for the position of the reservoir, in simple background models. The developed method could in theory be used for imaging small time-lapse amplitude variations (monitoring), despite the obstacles remaining to be overcome before a real-data application. Neither visco-elastic nor 3D effects are adressed. Thus this work does not exclude the possibility of strong reservoir-specific spectral anomalies.
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Alexandre Kazantsev. Ambient noise spectral amplitude distortions above heterogeneities : feasability study for multi-fluid reservoir exploration and monitoring. Geophysics [physics.geo-ph]. PSL Research University, 2018. English. ⟨NNT : 2018PSLEM075⟩. ⟨tel-02143918⟩

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