Sensitivity Analysis of FWI Applied to OVSP Synthetic Data for Fault Detection and Characterization in Crystalline Rock - Archive ouverte HAL Access content directly
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Sensitivity Analysis of FWI Applied to OVSP Synthetic Data for Fault Detection and Characterization in Crystalline Rock

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Abstract

In the present paper, we consider the context of Soultz-sous-Forêts geothermal site, revisiting well seismic data acquired in 2007. We will apply a full-wave inversion method on the 24 offset vertical seismic profiles in order to detect or image the heterogeneities and the faults in the granite geothermal reservoir. The main goal of this study is both to evaluate the application of a method already used in the oil&gas industry to geothermal purpose and if successful, to improve the knowledge of the fault network at the reservoir level. We recall that, in a crystalline context, the 3D geometry of the fracture/fault network in the granite around and between the wells is a critical issue in order to well constrain the fluid flow modelling in the reservoir and thus to help optimizing the geothermal production. The proposed full-wave inversion method (FWI) has already been conducted with success on offset VSP data (North Sea gas reservoir). However, such seismic imaging and characterization have been performed essentially in sedimentary contexts. Applying the FWI method to structures like faults in a crystalline environment is a real challenge. However, a previous study on these OVSP data has shown that waves scattered from the interaction of the incident seismic wave with the main faults is actually recorded at the receivers (3C geophones, P-to-S conversion for instance). Information is then present in the seismic data. The full-wave approach being more accurate than standard seismic processing methods, we expect an improvement of the knowledge of the reservoir structure, and particularly, of the main faults network. In the paper, we develop first the methodological aspects of the FWI. The main features are the multiscale approach using increasing frequency bands and spatial correlations, and that the rheology used to model the seismic wave propagation is realistic and accurate (elastic/viscoelastic and anisotropic in the sedimentary upper part of the model and viscoelastic in the granite reservoir). Thus, the physics of seismic wave propagation is correctly reproduced, allowing to extract more information from the seismic data. In addition, it allows to obtain several field parameters as the P-wave and S-wave velocities and others, depending on the case. As the computation costs are very high due to the accurate seismic full-wave modelling, we consider a 2.5D seismic wave propagation in the upper part of the model while both the field parameters and the propagation are fully 3D in the granite reservoir. In a second part, we recall the previous results obtained from standard methods (2013) and compare them to the results obtained from the FWI. Finally, we present the updated 3D fracture model.
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Dates and versions

hal-03682107 , version 1 (30-05-2022)

Identifiers

  • HAL Id : hal-03682107 , version 1

Cite

Christophe Barnes, Yassine Abdelfettah, Nicolas Cuenot, Éléonore Dalmais, Albert Genter. Sensitivity Analysis of FWI Applied to OVSP Synthetic Data for Fault Detection and Characterization in Crystalline Rock. World Geothermal Congress 2020+1, 2021, Reykjavik, Iceland. ⟨hal-03682107⟩
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