Context
Seismic imaging offers a unique way of finely characterising the subsurface by sending waves from the surface. In the context of CO2 injection and storage, the subsurface properties vary over time. It is therefore essential to repeat the acquisition and to analyse any modifications. However, 4D dense acquisitions (repeated 3D imaging over time) are not affordable for economic reasons.
Based on an initial 3D image, SpotLight Earth has developed a strategy for deploying a few sources and receivers at optimal locations to detect the evolution of the CO2 plume within the subsurface. This makes it possible to repeat the acquisition monthly, for example, rather than every two years for the standard approach. This is an important factor for controlling the integrity of the reservoir and for preventing any CO2 leakage towards the surface.
Currently, the analysis of such sparse acquisition data sets is based on reflected waves only, i.e. waves propagating from the source to some elastic contrast, being reflected at some elastic contrasts only once, and reaching the surface. However, real wave propagation is much more complex. We can potentially consider diffractions, refractions, diving waves, maybe surface waves, ... as far as these waves are influenced by the modifications of the subsurface. Currently, these other waves are simply ignored.
Main objectives
The main objectives of the project are
- Study the sensitivity of different types of waves to some elastic changes, both in terms of both kinematics (time delays) and dynamics (amplitude modifications);
- Propose a strategy to map the changes (recorded by the waves at the surface in the time domain) to some subsurface locations (i.e. construct partial images to locate the changes in depth);
- Assess uncertainties (Bayesian context) on the modifications of the subsurface images by considering different sources of uncertainties, while respecting a priori information;
- Design an optimal acquisition geometry to capture the changes and to discriminate between different scenarios; take into account operational constraints;
- Validate on real data sets;
- Play a central role in the collaboration between Mines Paris, SpotLight Earth and clients who provide the real data sets.
The PhD student will benefit from existing numerical modelling tools to investigate the potential of different types of waves for monitoring the subsurface. He/she will develop a specific imaging tool, considering sparse data and a specific data type.
Contacts and Places of Work
Pr. Hervé Chauris
Mines Paris - PSL Research University
35 rue Saint-Honoré
77305 Fontainebleau Cedex, France
Dr. Nour Mikhael
SpotLight Earth
37 rue du Saule Trapu, 91300 Massy, France
References
Al Khatib, H., Boubaker, Y., and Morgan, E. (2021). Breaking the seismic 4D ‘image’ paradigm of seismic monitoring. First Break, 39(9):85–91. Number: 9
Al Khatib, H. and Morgan, E. (2025). Trigger Seismic CCS surveillance: Not to image, but to know when to image. First Break, 43(10):27–91.
Chauris, H. (2019). Full Waveform Inversion, in Seismic Imaging, a practical approach , J-L. Mari and M. Mendes (Eds.), EDP Sciences, chapter 5, 23 p., ISBN (ebook): 978-2-7598-2351-2, doi:10.1051/978-2-7598-2351-2.c007
Chauris, H. and E., Cocher (2017), From migration to inversion velocity analysis, Geophysics 82(3): S207–S223, doi:10.1190/GEO2016-0359.1
Cotton, J., É. Forgues and H. Chauris (2018), Time-lapse velocity analysis – application to onshore continuous reservoir monitoring, Geophysics 83(3): B105–B117, doi:10.1190/geo2017-0014.1
El Khoury, C., A. Kazantsev and H. Chauris (2024), The influence of an anticline structure on ambient noise spectral anomalies at an underground gas storage, 237: 1061–1078 Geophysical Journal International, doi:10.1093/gji/ggae089
Fachtony, F.A., R. Brossier, B. Boddupalli, B. Dupuy, L. Metivier and A. Romdhane (2025). CO2 monitoring at sleipner field using reflection oriented Full Waveform Inversion - part 1: baseline reconstruction. Geophysical Journal International, 241(2):1226-1242, https://doi.org/10.1093/gji/ggaf097
Fachtony, F.A,, R. Brossier, B. Boddupalli, B. Dupuy, L. Metivier and A. Romdhane (2025). CO2 monitoring at Sleipner field using reflection oriented Full Waveform Inversion: part 2 - 4d investigation. Geophysical Journal International, 242(1):ggaf185, http://dx.doi.org/10.1093/gji/ggaf185
