Anisotropic depth migration of converted wave data, inversion of multicomponent data to estimate elastic parameters at the seafloor and one-dimensional data-driven inversion

Abstract

The increasing demand for oil and gas in the world today drives the need for new and improved methods for identifying hydrocarbon prospects. The petroleum industry uses information about the subsurface in the exploration and production of oil and gas. The industry's tendency to explore deeper waters and more geologically complex areas requires reliable and more robust methods for extracting such information.

This thesis illustrates possible strategies for using seismic reflection data in the inversion for subsurface earth properties. One strategy which is the traditional approach in seismic is to consider inversion as a stepwise procedure consisting of a model-driven global reflectivity imaging process (migration) followed by target-related elastic inversion of the reflectivity information into earth property parameters.

In this thesis a method describing wave equation prestack depth migration of converted wave data in anisotropic media is presented. The migration is accomplished by numerical wavefield extrapolation in the frequency-space domain using precomputed space-variant fillter operators. Imaging is performed by crosscorrelating the source wavefield with the data wavefield at each depth level. Data examples demonstrate good dip response and correct kinematic behavior and illustrate the method's ability to handle complex multi-layer models with a relatively high degree of anisotropy.

By considering seismic inversion as a stepwise approach, this thesis also presents a method for inversion of reflection information into medium parameters. The method provides estimation of density and P-wave and S-wave velocities at the seafloor by inversion of the acoustic-elastic PP reflection coefficient estimated at the seafloor. The PP reflection coefficient is calculated in the frequency-slowness domain from seafloor measurements of the pressure and the vertical component of the particle velocity. The algorithm gives estimates of seafloor parameters in good agreement with the true model parameters.

Another strategy for using seismic data in the inversion for subsurface earth properties is to perform inversion as a data-driven procedure where the medium parameters are directly inverted for. In this thesis a new method on inverse scattering for the estimation of the medium properties of a onedimensional acoustic layered medium from single scattering data is presented. The method provides an explicit, non-iterative and fully data-driven solution of the inverse one-dimensional scattering problem.