Full Waveform Inversion

• Reduced dependence on very long offset: uses diving waves and reflections
• Delivers models with correct long wavelength information: avoids cycle-skipping artefacts
• Accurate deep velocity models: removes traditional migration isochrone artefacts
• No density model or hard model boundaries are required to generate reflections
• Cost-effective: reflected events can be used without solving two different wave-equations in the forward and backward propagation steps
• More accurate: unique wave equation implementation is superior to methods based on the first-order approximations and perturbation theory.  

The PGS FWI solution uses both diving waves (wavefronts continuously refracted upwards through the earth) and reflected waves to update the velocity model. The use of reflection information relaxes the traditional dependence of FWI upon very long offset acquisition. Background velocity model updates are completely separated from reflectivity information, thereby avoiding crosstalk artifacts in the output velocity model.

A proprietary dynamic warping correction avoids traditional cycle-skipping challenges, and the method does not depend upon an accurate starting model of velocity or any prior model of density. The PGS FWI solution is also extendable for multi-parameter updating, so that vertical velocity and epsilon are updated, and delta is fixed.

PGS has recently developed PGS Ultima, an evolution of FWI which yields models of both reflectivity and velocity.

Input model

FWI model

West of Shetland. Simple input model to FWI shown (left) and the updated FSB Vision FWI model (right). The resultant model is geologically conformable, resolving the vertical and lateral velocity variation in the image.