Full waveform inversion of seismic data: Investigating the Earth for high-resolution velocities and more...
Honorary Lecturer 2014 - Europe

Laurent Sirgue
Total
Pau, France

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Summary

The principles of full waveform inversion (FWI) have been established for about 30 years. This approach aims at finding an Earth model that explains the seismic data. This is achieved by estimating the physical properties of the subsurface (Vp, Vs, density, attenuation, anisotropic parameters, etc.) within an inverse problem that aims at minimizing the difference between seismic data acquired in the field and predicted data modeled in a computer. The ultimate goal of FWI is therefore very ambitious as this multiparameter inversion is a highly nonlinear and ill-posed problem. In addition, it requires accurate and efficient modeling of the wave equation which makes it challenging to apply to real, industrial-scale, 3D problems.

In recent years, rapid improvement of supercomputers and breakthroughs in numerical computations of various forms of the wave equation allowed the academic community and the seismic industry to apply this technique in 3D.

Initial applications of 3D FWI made the assumption of acoustic-wave propagation, thus ignoring viscoelastic effects and mainly focusing on the recovery of a single parameter: acoustic velocity (Vp).

While the recovery of this unique Earth model parameter seems to fall short of the stated ambition of FWI, it is at the heart of prestack depth imaging commonly used by the seismic industry. In order to obtain an image in depth, a velocity model must be estimated prior to performing prestack depth migration (PSDM) which produces the final image for geologic interpretation.

The process of velocity model building is a critical stage of this workflow and is conventionally performed using ray-based reflection-tomography techniques. Velocity models derived by such methods are typically low-resolution and are used only for PSDM.

In this presentation, I will first review the basic theory of FWI. I will then define, by means of illustrative synthetic examples, the key parameters that play a role in the success of FWI (data and model requirements). This will lead to the understanding of why FWI has enjoyed its most success in the recovery of shallow velocity anomalies.

I will continue by showing real data examples that demonstrate the potential of FWI to generate high-resolution velocity models which may improve the images produced by PSDM. Because of the highly detailed nature of the velocity field produced from FWI, it also contains valuable information that can be used directly for geologic interpretation. I shall finally discuss ongoing research and the evolution of FWI across the academic and industrial communities.

This lecture is intended for a large audience and no background knowledge about FWI is needed.

Biography

Laurent Sirgue

Laurent Sirgue joined Total France in 2009 as a geophysicist. He has been conducting research on the topic of full waveform inversion (FWI) for nearly 15 years.

Laurent received a BSc in physics from Versailles University in 1995 and an MSc in geophysics from the University of Strasbourg in 1997. He joined CGG in 1998 as a research geophysicist. In 1999, CGG sponsored Laurent's 16-month National Service, which took him to Queen's University, Kingston, Canada, where he worked with Gerhard Pratt on FWI.

In 2003, Laurent received his PhD from the University of Paris-sud XI. His dissertation research also focused on FWI. CGG sponsored Laurent's doctoral research in collaboration with Professor Pratt. As a postdoctoral researcher at Total (Pau, France), Laurent conducted research on reservoir characterization. In 2004, he joined the depth-imaging group at BP America where his work focused mainly on FWI.

Laurent has received a number of awards for his research including Honorable Mention for Best Paper in Geophysics in 2004 and the 2010 Bonarelli Award for best oral presentation at the EAGE Annual Conference.

Schedule

Date Location Hosts
13 December 2014 Paris, France Institut de Physique du Globe de Paris
3 February 2014 Trondheim, Norway Norwegian Univ of Sci & Tech Geophys Soc
4 February 2014 Stavanger, Norway Statoil
6 February 2014 Oslo, Norway Oslo Society of Exploration Geophysicists (OSEG)
24 February 2014 Edinburgh, United Kingdom Univ of Edinburgh Geophysical Society
24 February 2014 Edinburgh, United Kingdom Heriot-Watt University Geophysical Society
25 February 2014 Leeds, United Kingdom University of Leeds Geophysical Society
26 February 2014 Sunbury, United Kingdom BP Sunbury
27 February 2014 London, United Kingdom Imperial College Geophysical Society
17 March 2014 Novosibirsk, Russia University of Novosibirsk Geophysical Society
20 March 2014 Moscow, Russia Gubkin Russian State University of Oil & Gas
21 March 2014 Nizhny Novgorod, Russia The Institute of Applied Physics Geophysical Society
31 March 2014 Uppsala, Sweden Uppsala University Geophysical Society
1 April 2014 Copenhagen, Denmark Maersk Oil
3 April 2014 Massy, France CGG
4 April 2014 Paris, France GEP- AFTP, Total
10 April 2014 Pau, France Total
28 April 2014 Krakow, Poland AGH Univ. of Sci. & Tech. Geophysical Society
29 April 2014 Warsaw, Poland Polish Academy of Sciences
30 April 2014 Zurich, Switzerland Student Association of Geophysicists at ETH
15 May 2014 Rijswijk, Netherlands Shell - Begins at 9:30 a.m. (local CEST time)
19 May 2014 Pisa, Italy University of Pisa Geophysical Society
21 May 2014 San Donato Milanese, Italy EAGE-SEG Italian Section
22 May 2014 Trieste, Italy University of Trieste Geophysical Society
26 May 2014 Torino, Italy Politecnico di Torino Geophysical Society

SEG Honorary Lecturers
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