This is the name of a log measured along a well bore (a well-log). You might have encountered this acronym
RACESL in your log evaluation software or any (ASCII) log files provided by the logging company. The abreviatin stands for
'Resistivity Attenuation Compensated Borehole and Dielectric Corrected Short 400kHz'. This log is not used too often in the industry. The values of this log represent the formation resistivity as measured by the attenuation of a high frequency (hundreds of KHz to several MHz) electromagnetic wave; these measurements are typically deeper than measurements based on phase shift, but their vertical resolution is less sharp and they often cannot be used reliably in high-resistivity formations.
Furthermore, this can be explained by looking at the electromagnetic propagation resistivity. Better said, the formation resistivity as measured by the attenuation or phase shift of a high frequency electromagnetic wave; the frequency range for these measurements is higher than that of induction measurements, typically hundreds of KHz to several MHz, and over 1 GHz in the case of the Schlumberger EPT tool.This log usually has the unit
'Resistivity'. This is the property of a material which resists the flow of electrical current. The ratio of electric-field intensity to current density. The reciprocal of conductivity.
Data for this log is produced by a tool that uses a electromagnetic logging technique and can be used to investigate the resistivity of the formation. Similar logs are listed below:
