High Temperature Telemetry Gamma Ray Cartridge (HTGC*)


The HTGC had a gamma-ray detector that was made of a NaI crystal, a photo multiplier tube, a high-voltage generation circuit, and a preamplifier of the gamma-ray pulse, all built in one package. The number of output pulses from the detector was counted at a rate of 8 Hz, and the count sent uphole. Housed in a heatsink and dewar flask that allowed operations in high-temperature environments (260°C), this tool also had a 31-pin upper and lower head asset and was combinable with any standard 3.375-in tool without additional adaptors. The data acquisition software could not distinguish between the tools, but the HTGC had the correct length and measure point and gamma-ray response for the flasked tool.

The HTGC was deployed at the top of the triple combo tool string on two sites during ODP Leg 193.

Tool Specifications

Temperature rating 500° F (260° C)
Pressure rating: 25 kpsi (172 MPa)
Length: 10.7 ft (3.26 m)
Weight: 265 lbs (120 kg)
Diameter: 4.75 in (12.1 cm)

Measurement Specifications 

Range: 0-2,000 GAPI
Accuracy: 5%
Vertical resolution: 12 in (30.48 cm)
Depth of investigation: 2 4in (60.96 cm)
Logging speed: 1,800 ft/hr (549 m/hr)

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