One-way wave-equation migration for wide-angle propagation in anisotropic media

Abstract

Seismic depth migration is a major component in the search for hydrocarbons. As new prospects for oil and gas often are found in areas with challenging subsurface structures, more advanced methods to find and evaluate these prospects are needed. One-way wave-equation migration provides an appealing approach to be used to create an image of the subsurface.

The characteristics of wave propagation can be described through the dispersion relation, relating the vertical and horizontal phase-slowness. In the first part of this thesis, simple and accurate phase-slowness approximations valid for wide-angle propagation in a VTI media are derived.

Information from the subsurface might be increased by recording converted wave reflections in addition to pressure waves. The second part of this thesis provides the development of a set of new one-way propagators for imaging steeply dipping and complex structures using converted and pressure waves in a VTI medium.

Reliable amplitude information from one-way methods is useful as hydrocarbon indicators in structural imaging and for migration velocity analysis. In the third part of this thesis, a flux-normalized wavefield decomposition is used as a starting point to develop one-way propagators with improved amplitudes.

In new exploration areas, salt structures are important examples of subsurface complexity. This poses a challenge for one-way migration methods due to large velocity contrasts between salt and the surrounding sediments. A novel approach using one-way migration operators combined with a lateral windowing construction to limit the impact of errors introduced by large velocity contrasts is developed