DDG Duel Detector Gamma Tool

DDG

Directional Gamma Tool

DDGThe new CBG Dual Detector MWD Gamma tool for Azimuthal Geosteering consists of two opposed, tungsten-collimated shielded Nal(TI) scintillation detectors housed within a single ruggedized assembly.  Each detector contains its own set of electronics for powering its photomultiplier tube and processing the detected gamma signals.

Two 72° “windows” are machined along the length of the Tungsten shield positioned 180° apart from one another.  The eccentric tungsten shielding has a 0.23” maximum thickness that provides the highest front to back gamma count ratio.  It is designed to maximize gamma rays entering the crystal through the window while effectively blocking them from penetrating the non-window area of the crystal.  This unique shielding design and dual detectors effectively doubles the too sensitivity while maintain the directionality.

The DDG supplies an output signal from each detector for processing in a customer supplied controller.  Power and GND are input to either MDM connector.  Output counts from each detector can be individually processed or summed together.  In addition, either tool can be turned off if a problem is detected by the controller.

DDG

Directional Gamma Tool

DDGThe new CBG Dual Detector MWD Gamma tool for Azimuthal Geosteering consists of two opposed, tungsten-collimated shielded Nal(TI) scintillation detectors housed within a single ruggedized assembly.  Each detector contains its own set of electronics for powering its photomultiplier tube and processing the detected gamma signals.

Two 72° “windows” are machined along the length of the Tungsten shield positioned 180° apart from one another.  The eccentric tungsten shielding has a 0.23” maximum thickness that provides the highest front to back gamma count ratio.  It is designed to maximize gamma rays entering the crystal through the window while effectively blocking them from penetrating the non-window area of the crystal.  This unique shielding design and dual detectors effectively doubles the too sensitivity while maintain the directionality.

The DDG supplies an output signal from each detector for processing in a customer supplied controller.  Power and GND are input to either MDM connector.  Output counts from each detector can be individually processed or summed together.  In addition, either tool can be turned off if a problem is detected by the controller.

DDG Specifications

DetectorNal(TI) Scintillator Crystal (X2)0.725” Diameter  X 4.0” Length
Photomultiplier (X2)R3991A (Hamamatsu)
MechanicalDiameter (OD)1.40”
Length (make-up)22.17”
Weight5.5 lb
End ConnectorsMicro-D Subminiature, 15-Pin
MaterialAluminum Alloy (chassis), Tungsten (shield)
PerformanceSensitivity0.29* CPS/API (each detector)
Accuracy+/- 5% to 300°F
+/- 10% to 350°F
Thin-Bed Resolution (8” hole Diameter)8.8”
EnvironmentalOperating Temperature0°F to 350°F
Survival Temperature (reduced accuracy)-40°F to 400°F
Heat/Cool Rate, Max. 5°F per minute
Vibration (3 axis) 50-1000Hz, Random20G RMS
Shock (3 axis)1000G, 0.5ms, half-sine
Power RequirementsDC Input Voltage17-48 VDC, 50VDC Max.
Tool Current18 mA – 22mA
Output SignalNegative 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)