Velocities, Imaging, and Waveform Inversion – The evolution of characterizing the Earth’s subsurface is part of Ian Jones’ EAGE Education Tour and will be a fusion of practical industrial elements, concentrating on the origin and nature of the geological complexities that give rise to imaging problems, as well as a physical (rather than mathematical) understanding of subsurface parameter estimation, and will also look at some possible future directions. The course is designed for: practising geoscientists who desire to better understand the principles and limitations of both current and emerging technologies involved in subsurface parameter estimation and imaging and geoscience students. Following this course, participants should ideally understand how contemporary velocity estimation methods work, and what approximations are involved in obtaining computationally tractable solutions.
In using sound waves to characterise the Earth’s subsurface, we can employ ray theory and/or wave theory, and both migration algorithms and parameter estimation schemes employ one or other of these theoretical descriptions. In this course, we will review the evolution of the industry’s approaches to building earth models via velocity estimation and imaging, outlining the evolution from ray tomography to full waveform inversion, and look towards the emerging possibilities for replacing imaging techniques with direct subsurface parameter inversion methods.
The approach will be mostly non-mathematical, concentrating on an intuitive understanding of the principles, demonstrating them via case histories, and will be divided into the following sections:
– Dealing with the near surface
– The effects of strong vertical velocity contrasts
– The effects of strong lateral velocity contrasts
– Waves versus rays
– Model building using ray methods (tomography)
– Model building using wavefield extrapolation methods (FWI)
– Data examples and comparisons
– Future developments
The first three sections outline the nature of the problems we face when building images representing subsurface impedance contrasts, and the next three deal with the technology we deploy to address the problems. In addition, I have included three appendices to outline: the historical development of model building, anisotropy and pre-processing considerations for complex imaging. Several of the individual chapters build on a series of recent tutorial papers which I published in First Break. However, only the key points from these tutorial papers are included, so I refer readers to the original papers for more detail and/or a range of real data examples for each of their topics.
However, due to space and time constraints in the EET format, I have had to omit or limit coverage of various topics, including migration of multiples, Marchenko and inverse scattering series migration, joint migration-inversion, least-squares migration and uncertainty estimation.