Iterative Inversion of Focusing Operators

Abstract

The estimation of a velocity model is an important step in seismic imaging. To a large extend, seismic data interpretation is implicitly based on this model. Thus, the velocity model influences important conclusions such as size and shape of the reservoir and the expected volume of producible hydrocarbons. In the Common Focus Point (CFP) technology, the estimation of the velocity-depth model is split into two separate processes. First, one-way focusing operators are estimated from the seismic data. These focusing operators can be seen as the response of a secondary source (called a focal point) in the subsurface towards receivers at the surface, therefore they can be considered one-way Green's function of the subsurface. Second, these one-way operators are translated into a velocity-depth model via tomographic inversion. In this way, one complicated problem is split into two simpler problems. This thesis deals with the second step of this procedure, the inversion of the focusing operators with the goal of recovering the depth-velocity model of the subsurface. Therefore, the input of the inversion consists of the focusing operators, while the output are both the velocity model and the location of the focal points. We consider two options for the way these one-way focusing operators are defined: simple one-way traveltimes operators and one-way full waveform operators. The presented approach of one-way full waveform operator inversion can be seen as a way of accounting for the non-linearity between the measured data and the velocities in the subsurface. The low frequencies brought in the data will help in our challenge of obtaining accurate initial or background models.ISTApplied Science