Aspen Epos Applications also support the following sources of Well Velocities:

1. Sonic Log
   • High Resolution (few Inches) measure of slowness (transit time) along borehole. 
   • Principal source of well velocity data and related measurement
   • Provides direct information about the borehole and the rocks penetrated by the drill bit
2. Checkshot survey
   • One-way-time arrival between a source on the surface and a receiver depth along borehole
   • A direct seismic wave is received by the geophone and recorded
   • Need to know geophone depth, distance from the well head to the source and the travel-time of the seismic wave
3. Vertical Seismic Profile (VSP)
   • Travel time measurements of acoustic energy recorded between sources on the surface and receivers along the borehole.
4. Time-Depth Relationship
   • Defines the relationship between Depth and Two-Way-Time (TWT) along borehole
   • Updated by performing calibration of well synthetic with seismic
5. Geologic Markers
   • Used to derive well velocity markers (Average, Interval)
   • If Time Migrated interpretation maps are used instead of Well TD relation, pseudo velocity markers are calculated.