This is the name of a log measured along a well bore (a well-log). You might have encountered this acronym FXS in your log evaluation software or any (ASCII) log files provided by the logging company. Density Formation Exposure Time is the full name for this log. The usage of this log is well established.

The values of this log represent the time delay between the drill bit and a density sensor reaching a given point in the wellbore during MWD/LWD logging.

Furthermore, this can be explained by looking at the delay time. In other words, the time difference by which one event lags another. In refraction seismic work, the additional time required to traverse a raypath over the time which would be required to traverse the horizontal component at the highest velocity encountered on the raypath.

This log usually has the unit 'Time (hour)'.

Data from this log can be used to investigate the time interval of the formation. Similar logs are listed below:

• Time Since Drilled from Phase Difference (PDT)
• ISONIC Time After Bit (TAB_ISONIC)
• Detector Blade Face Formation Exposure Time (BFX)
• Smoothed Neutron Formation Exposure Time (SFXN)
• Neutron Formation Exposure Time (FXN)
• Smoothed Mud Transit Time (SMTT)
• Time Since Drilled from Gamma Ray, Memory (GRTM)
• Density Time After Bit (TAB_DEN)
• Time Since Drilled from MPR Attenuation 400kHz (ATTL)
• ARC Resistivity Time After Bit (ARTM)