The CBG NGT-CN Gamma tool is our third-generation version of the NGT-T, with NextGen electronics and a larger scintillator crystal to almost double the usual count-rates.
The tool is electrically and mechanically interchangable with the NGT-T, so it is fully backwards compatible. The NextGen electronics offer advanced performance and functionality, including a wider range of input voltage and significantly lower current drain. This reduces the load on expensive Lithium batteries.
The output circuits employ advanced protection and noise-suppression components for more reliable system performance.
The standard model is equipped with an MDM 15-pin male connector on the top electronics end of the tool and an MDM 15-pin female connector on the bottom.
Electrical connections are: Pin #1 for Ground, Pin #4 for Power and Pin #8 for Signal Output. All 15 bus wires are passed along a protected wire guide from top connector to bottom.
Electronics are encapsulated for additional shock protection. The crystal and photomultiplier are packaged in-house, utilizing our proprietary and unique design for ease of replacement or repair. All tools include the power-down option defined in the qBus standard, by pulling the output line to ground potential. In this condition, all internal functions are disabled and current demand is less than 1 mA. Also, all CBG gamma tools incorporate floating Battery-ground connection so that they can be used with EM telemetry systems without any problems.
The NGT-CN Gamma Tool can also be ordered to include the complete Tensor/GE-compatible mechanical assembly, for a plug-and-play solution.
The NGT-CN can be mounted to the Bottom Bulkhead Retainer through a standard Shock Snubber Assembly, but we recommend our new SNB-55 snubber that provides 6x better Z-axis shock protection.
At the bottom end, a connector pigtail converts the MDM 15-pin connector on the tool to a 200 deg.C, GE, 4Pin/6Socket connector mounted within the bottom Intermodule End.
At the top, a pigtail converts the MDM 15-pin connector on the NGT-T to a 200 deg.C, GE, 6Pin/4Socket connector mounted within the top Intermodule End.
A custom 24-inch long BeCu Pressure Barrel is available, resulting in a significantly shorter and lower-cost tool than was previously available to the market.
A version in the original 52-inch long BeCu Pressure Barrel is also available, at a higher price, for those customers who want to retain the standard tool length.
The graph below shows a typical temperature calibration chart for the NGT-CN. Notice that we carefully control the maximum heating and cooling rate of the tool, similar to the rates experienced when tripping the well. Failure to observe this procedure when testing the tool will void the warranty.
The graph below shows a typical vibration calibration chart for the NGT-CN. Notice that we ramp the vibration level (measured in “G” force – or units of gravitational acceleration) up to 20G and down again, similar to the rates experienced while drilling the well. Every tool is checked on our shake-table to ensure no extra counts are observed at any level of vibration.
The first graph below shows the gamma attenuation effect of various thicknesses of drill collar and barrel. The second graph shows the effect of various weights of mud. The correction factor is the number that the Gamma probe readings should be multiplied by to find the true API log value.
Both graphs can be used separately or in combination to correct log data when correlation with existing logs is required. When combining the corrections, it is important to multiply the individual correction factors to get the total correction factor.
For the collar correction, subtract the collar I.D. from the O.D. and divide by two to get the thickness. The Tensor/GE barrel is 3/16 inch BeCu. For the mud correction, subtract the collar O.D. from the bit size and divide by two, then subtract the barrel O.D. from the collar I.D. and divide by two, add both parts to get the total mud thickness.
Potassium is naturally slightly radioactive. The following chart can be used to compute the additional API recorded by the Gamma probe in Potassium Chloride muds. Use the bit size for borehole diameter and the KCl mud concentration to find the API, then divide by the correction factor from the Collar/Mud weight graphs above to get the final amount of API shift on the Gamma log.