DGA-C Focused Gamma Tool

DGA-C

Directional Gamma Tool

DGAThe DGA-C, Directional Gamma Tool, is a Tungsten-collimated version of the NGT-T gamma tool.  These tools are sometimes referred to as “focused” or “shielded” gamma tools.  In this design a 67° “window” is machined along the length of the Tungsten shield that surrounds the crystal/phototube detector.  Only gamma ray entering from the formation through this window can be detected and counted.  When aligned with the tool face or other physical reference, the DGA-C indicates the direction from which gamma ray energies originate.

The DGA-C is interchangeable with the standard NGT-T gamma tool.  It is same overall length and diameter.  Because of the required thickness of the Tungsten shield, the Nal(TI) scintillator crystal is of a smaller diameter.  The length is increased to 6.0” however, to deliver an equivalent volume of crystal material as in the NGT-T to provide maximum sensitivity.

DGA-C

Directional Gamma Tool

DGA

The new DGA-C is a more sensitive version of the popular DGA focused gamma tool.  It contains a larger scintillator crystal and improved eccentric tungsten-collimated shield.  These two improvements combine to offer higher count-rates and a 50% higher counts per API Sensitivity over the DGA.  In this design a 72° “window” is machined along the length of the Tungsten shield that surrounds the crystal/phototube detector.  Only gamma rays entering from the formation through this window can be detected and counted.  When aligned with the tool face or other physical reference, the DGA-C indicates the direction from which gamma ray energies originate.

The DGA-C is interchangeable with the standard DGA gamma tool.  It is same overall length and diameter. 

DGA-C Specifications

Detector  Nal(TI) Scintillator Crystal 0.725” Diameter  X 6.65” Length  
Photomultiplier R3991A (Hamamatsu)  
Mechanical Diameter (OD) 1.36”  
Length (make-up) 13.7”  
Weight 4.0 lb  
End Connectors Micro-D Subminiature, 15-Pin  
Material Aluminum Alloy (chassis), Tungsten (shield)  
Performance Sensitivity 0.52* CPS/API (decreased due to Tungsten shield)  
Accuracy +/- 5% to 300°F
+/- 10% to 350°F
 
Thin-Bed Resolution (8” hole Diameter) 8.8”  
Operating Temperature 0°F to 350°F  
Survival Temperature -40°F to 400°F  
Vibration (3 axis) 50-1000Hz, Random 20G RMS  
Environmental Heat/Cool Rate, Max.  5°F per minute  
Shock (3 axis) 1000G, 0.5ms, half-sine  
Power Requirements DC Input Voltage 17-48 VDC, 50VDC Max.  
Tool Current 8-11 mA  
Output Signal Negative Pulse +5V to GND, 5 uSec width  

* Counts are collected with gamma tool mounted within standard BeCu pressure barrel, (OD 1.875″, ID 1.500″).  API Calibration performed with AEA Technology, QSA Inc., KUTh Field Verifier #188074, S/N 255 Radionuclides: K-40(11.7%), U-238(90 ppm), Th-232(40 ppm).

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