Velocity, in this context, is the speed (distance / time) of sound (a compression wave) through rock (which may contain fluid and gas). Velocity may be used to determine rock densities and convert seismic information from time to depth. The rock velocity which correlates to its density is measured as interval velocity. That is the velocity between two depths; i.e., a thickness interval. It is implicit that the density of interest lies between these two depths. Velocity data sources from G&G operations include wellbore surveys such as sonic logs, checkshots, and seismic profiles and various 2D and 3D seismic data analysis methods. Data types will be discussed first then conversion of velocity to density methods and typical value reference tables and then conversion from time to depth methods.
After completing this unit, you’ll be able to:
- Describe what data and methods will best convert velocity to density and time to depth.
- Explain how an understanding of velocity methods will benefit your exploration
objective through improved delineation of geologic structure and lithology.