The fundamental idea of inversion to seismic impedance is very simple. A reflectivity seismic section contains reflections that can be studied by the methods discussed in chapters 3–5. These reflections show where there are changes in acoustic impedance in the subsurface. Inversion is the process of constructing from this reflectivity dataset a section that displays the acoustic impedance variation in the subsurface directly. As we shall see, this often makes it easier to interpret the data in geological terms, because it focuses attention on layers and lateral variations within them, rather than on the properties of the interfaces between layers that cause the seismic reflections. This is an idea that has been known for many years (see, for example, Lindseth, 1979) but has not been used very much until recently, probably because good results require input reflectivity data of excellent quality; the availability of modern 3-D datasets has triggered an upsurge of interest in the technique.

This chapter begins with a summary of the principles, then discusses some practical processing workflows with particular attention to the issues that are critical for the quality of the results, continues with some practical examples to demonstrate the benefits of the technique, and concludes with a summary of some specialised advanced applications.

Principles

A simple model for zero-offset seismic response is illustrated in fig 6.1.