CBG Corp, state-of-the-art logging tools and sensors

MWD Gamma Ray Tools

Overview | Specifications | PDF Brochure

The Gamma ray tool produces a measurement of the naturally occurring radiation found in rock formations.

CBG Corp. NGT-T Gamma Ray Tool: Click for larger image.

The Gamma Log produced by these tools is commonly used for geosteering, correlation with open hole logs and identifying low radiation and high radiation lithologies. A major application is in geosteering of horizontal boreholes in shale-gas wells where the highest gas-producing zones are often associated with high Uranium concentration.

CBG Gamma ray tools use a super sensitive hermetically sealed Sodium Iodide Scintillator crystal and a ruggedized high temperature Photomultiplier for maximum log quality. Mechanical design techniques have been developed specifically for the MWD/Steering tool environment to ensure a rugged and reliable tool. The short single piece aluminum chassis not only provides maximum strength and rigidity but minimizes vibration loads due to the low mass.

The electronics are fully temperature compensated to maintain consistent count rates through the 350F temperature rating. The tool uses a gross counting discriminator with an energy threshold set at approximately 15KeV, significantly lower than other tools, resulting in higher count rates and greater accuracy.

High-Temperature Operation

CBG provides customized models of Gamma ray tools for Geosteering and MWD. We can also provide tools tested and calibrated for operation at temperatures up to 400 degrees F. (204 degrees C.), with survival temperature of 437 degrees F. (225 degrees C.). The tools may require recalibration by CBG at regularly scheduled intervals. These are unique among Scintillator type tools, and only available from CBG Corporation!


CBG Gamma tools are calibrated in the laboratory using an AEA Technology KUTh Field Verifier, Product Code No. 188074, to determine the API calibration factor for each tool. The nuclides described are carefully chosen and combined to closely approximate the proper ratios as found in the KUTh API Calibration Test Pits located at the University of Houston, Houston, Texas, USA.

Temperature Stability

CBG Gamma Tools are fully rated to 350F, with a survival rating up to 400F. Electronic circuits are temperature compensated to maintain consistent count rates. Each tool, new and repaired, is logged in the oven from room temperature to 350F and back to room temperature, to ensure a count rate stability of no less than 95%.

Shock and Vibration Testing

Shock and Vibration testing is routinely employed to insure that environmental specifications are being met as well as for troubleshooting some repairs. We test 100% of our tools for any excess counts under the full range of frequencies and acceleration levels. CBG has in-house shaker-tables made by Vibration Test Systems and Ling Dynamic Systems to perform these tests. They are capable of broad spectrum random vibration at levels matching closely the drilling environment. Logging of data is performed to verify meeting tool specifications of 50-1000 Hz and 20G RMS.

Service and Repair

All tools are 100% assembled and tested by CBG. Each component of the tool can be readily repaired or replaced. CBG has developed a reputation for fast turn around times when service is required. The proprietary detector assembly allows access to the scintillator crystal and photomultiplier tube for troubleshooting and replacement, without having to send the entire assembly away to a third party for repair. Components, assembly and test procedures are continually updated by CBG to insure the most accurate and reliable tool on the market today!

Custom Designs

CBG will work with your Engineers to develop a customized gamma tool design for your specific application. We have developed numerous designs for companies that require electrical and/or mechanical changes from our standard products.