CBG gamma tools are supplied with an API (American Petroleum Institute) calibration factor. Tools are placed within the KUTh verifier (model# 188074) supplied by AEA Technology that simulates the gamma test formation located at the University of Houston. Unlike other devices that are commonly used to calibrate gamma tools, the KUTh verifier contains the same relative amounts of Potassium (K), Uranium (U) and Thorium (Th) as is found in the API test pits.
Counts are collected and used to calculate the API correction in units of CPS per API. This value is then used when applying corrections for collar wall thickness, mud thickness and Potassium. Each gamma ray logging tool is supplied with a Certificate of Calibration. It is recommended that tools be recalibrated annually.