Changes

==Velocities from sonic logs==

==Velocities from sonic logs==

Velocities can be acquired from sonic logs with or without a checkshot survey. A checkshot survey is like a baby VSP. The receivers are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to arrival time (a number), unlike the full trace a VSP gives. The checkshots help correct for any drift in a sonic log due to missing log intervals or hole problems. This makes the calculated traveltimes more reliable. One can obtain good velocity data from sonic logs without checkshots. However, if there are any hole integrity problems, significant errors can exist in the sonic data. If a sonic log is not available, very coarse velocity data can be obtained from a checkshot survey with only 5 or 6 traveltimes per well.

Velocities can be acquired from sonic logs with or without a [[Checkshots_and_vertical_seismic_profiles#Checkshot_surveys|checkshot survey]]. A checkshot survey is like a baby VSP. The receivers are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to arrival time (a number), unlike the full trace a VSP gives. The checkshots help correct for any drift in a sonic log due to missing log intervals or hole problems. This makes the calculated traveltimes more reliable. One can obtain good velocity data from sonic logs without checkshots. However, if there are any hole integrity problems, significant errors can exist in the sonic data. If a sonic log is not available, very coarse velocity data can be obtained from a checkshot survey with only 5 or 6 traveltimes per well.

==Velocity from density==

==Velocity from density==