Changes

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 [http://wiki.seg.org/wiki/Dictionary:Receiver receivers] are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to [http://wiki.seg.org/wiki/Dictionary:Arrival_time arrival time] (a number), unlike the full [http://wiki.seg.org/wiki/Dictionary:Seismic_trace trace] a [[Checkshots_and_vertical_seismic_profiles#Vertical_seismic_profiles|VSP]] gives. The checkshots help correct for any drift in a [[Basic_open_hole_tools#Sonic|sonic log]] due to missing log intervals or [[Drilling problems|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 [http://wiki.seg.org/wiki/Dictionary:Receiver receivers] are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to [http://wiki.seg.org/wiki/Dictionary:Arrival_time arrival time] (a number), unlike the full [http://wiki.seg.org/wiki/Dictionary:Seismic_trace trace] a [[Checkshots_and_vertical_seismic_profiles#Vertical_seismic_profiles|VSP]] gives. The checkshots help correct for any drift in a [[Basic_open_hole_tools#Sonic|sonic log]] due to missing log intervals or [[Drilling problems|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==

==Density data ==

Density information also contributes to creation of a synthetic seismogram. Density can be estimated from sonic data, but independent density information from a neutron density log is preferred.

Density information can improve the accuracy of a stratigraphic model for seismic analysis.

 

Velocity can be estimated from a density log if a sonic log is not available, but data from a sonic log is much better.

==See also==

==See also==