Workshop Description

In the last two decades, full waveform inversion (FWI) has become a standard high resolution imaging tool in the exploration scale imaging workflow. One of the main difficulty practitioners conventionally face when applying FWI to field data is related to the cycle skipping issue: to prevent the convergence towards a non-informative local minimum of the misfit function, one has to resort on sufficiently high quality low frequency data and initial model, as well as a dedicated data-oriented hierarchical workflow. This well known issue, related to the non-convexity of the misfit function, has been the motivation of a wide variety of methods all along the last two decades. The purpose of this workshop is to propose a state-of-the art regarding cycle skipping in the industry. Beyond a review of existing strategies proposed to mitigate/overcome cycle skipping issues, we would like to discuss in depth in which contexts the cycle skipping is still an issue(which arrivals? which geological environments? which physical model for wave propagation?),what is applied in practice to mitigate it, and how this could be extended in the frame of elastic FWI.

The workshop could be structured as follow:

1. State of the art of cycle skipping in the exploration scale industry: in which context do we observe cycle skipping? What are the origins of cycle skipping? Are we concerned only about cycle skipping on diving waves? What is the impact of cycle skipping on later arrivals?
2. What is done in practice: improving starting models (high resolution tomography), hierarchical approaches (frequency sweep, combined with offset and time windowing i.e. layer stripping approach)
3. What are the new tools proposed to mitigate cycle skipping, and how do they apply to field data? We will review in particular extension methods (either model extension i.e. migration velocity analysis or data extension i.e. wave field reconstruction inversion, source extension, adaptive waveform inversion), as well as misfit function modifications (instantaneous phase and envelope, nonlinear transform of the data, optimal transport distances)
4. Cycle skipping free approaches versus more physics? Can it help mitigating elastic effects when doing acoustic FWI? How does it apply in the frame of elastic FWI?

1. How cycle skipping is dealt with in practice: better initial models, data processing
2. Model space extension, data-space extension, misfit function modifications: what is used?What is not? Why?
3. How cycle skipping is to be considered in the perspective of high resolution and/or elastic FWI?

Researchers interested in seismic imaging and full waveform inversion

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Workshop Programme