80th EAGE Conference & Exhibition 2018
Opportunities presented by the energy transition
Seismic Imaging with Ray and Waves - Where do we stand? Part I: Velocity Estimation
Sunday 10 June 2018
|Title:||Seismic Imaging with Ray and Waves - Where do we stand? Part I: Velocity Estimation|
|Convenors:||P. Hardy (Total)
I. Jones (IONGEO)
G. Lambaré (CGG)
In the last decade, full wave methods have captured much attention in the research community. Numerous bodies of work have addressed those methods driven by the great promise of deriving high resolution volumes of subsurface properties using the entire seismic wave-field. However, ray methods are still widely used today. In fact, ray methods still make up most of our 3D seismic imaging project workflows, with Kirchhoff/beam migrations and tomography as the two principal components. Two main reasons explain this: ray methods are fast and robust whereas full wave methods still have technical challenges to resolve. Nowadays the two approaches are commonly used in conjunction to provide the best of both worlds.
Ray-based method limitations are well known theoretically: since rays are predicated on the high frequency asymptotic approximation of seismic wave propagation, they tend to be unstable (thus not well suited) in the presence of sharp, localised velocity contrasts. Ray based tomography also requires the extraction of kinematic attributes of usable (primary) seismic events from prestack gathers. It is said that those aspects cause instability in general, and limit ray based methods to the determination of low resolution velocity models. However significant progress has been made in recent years to overcome these limitations. Ray propagation can be made more robust, leading to more regular illumination, and efficient volumetric auto-pickers can now produce dense and reliable kinematic information without requiring parametric fitting. Some implementations of ray based tomography can handle very complex models and resolve velocity up to 15Hz!
FWI methods have made significant progress over the same period. New schemes have emerged to address the cycle skipping problem; new approaches have been proposed to work with more data such as primary and/or multiples reflected events, and work with more parameters in so-called multiparametric inversions. Various new reformulations of the objective function have been proposed to stabilize and accelerate the inversion process.
Successive step changes in both ray and wave based method formulation, or in parts of their workflow have therefore pushed the limits of their resolving power, and ongoing developments continue to have a significant impact. This workshop aims to illustrate practical and theoretical innovations that improve on the quality and resolution of the velocity images estimated with ray and/or wave based methods.
Who should attend
Researchers interested in seismic imaging and seismic velocities.