1. adj. [Formation Evaluation]

Pertaining to two or more logging curves that have been aligned in depth. Logs recorded on different runs will not be exactly aligned at all depths because of the difficulty of perfect depth control. If the two logs are offset by the same amount throughout the log, then only a simple depth shift is required. If the offset varies, then the logs need to be depth matched. Depth matching is simplest if both runs contain the same type of log, such as a gamma ray. The two gamma rays can then be aligned, either manually or with software, and the other logs shifted by the same amount. Otherwise the alignment is based on two logs that respond in a similar fashion, such as a neutron porosity and a shallow laterolog. Depth matching also may be needed for logs recorded on the same run. Although there is a fixed distance between the measure points and the depth reference, the apparent distance will vary if the tool moves unevenly up the hole, due to stick and slip or yo-yo effects. Depth matching is then necessary.

See: base log,  curve,  depth control,  gamma ray log,  neutron porosity,  stick and slip