Gamma Ray Detection in Well Logging

All sedimentary rock contains natural radioactivity. A gamma ray (GR) measurement detects the radioactive isotope combinations of potassium, thorium and/or uranium present in both rock and fluid within geological formations. The ability to distinguish between certain geological formations and the change from one formation to another is critical to the petroleum industry. For over 30 years, Bicron has been the leading supplier of scintillation crystal detectors to the Logging Service Industry. Our detector, as an integral component of a gamma ray logging tool, provides superior performance and survivability under extreme environmental conditions. The early generation wireline GR tools place relatively low demands on the scintillation detector. Since the detector was used in a gross counting mode, it was insensitive to the various modes of signal degradation. Recalibration insured that the gross counts were unaffected, as long as deterioration occurred slowly as compared to the logging operation. Catastrophic failure, rather than performance, was the principal detector packaging design consideration. The extreme operational and survival conditions of Measurement-While-Drilling (MWD) placed increased demands on detector engineering and materials technology. Bicron set the industry standard by providing the required performance and survivability to withstand the environmental and transportation/handling conditions of MWD, as well as the performance and reliability required by Wireline tools.

Geoline Ruggedized Detector Technology

Bicron is the industry leader in ruggedized radiation detector solutions. Built into each Bicron detector is the expertise and experience required to meet both present and future industry demands for reliable performance under extreme environments. Detectors designed for operation in a laboratory environment incorporate static principles. On the other hand, a complex set of dynamic engineering principles is used in the design of Bicron Geoline detectors to assure that they meet both mechanical survivability and performance specifications demanded by the Logging Service Industry.

Detector Design Considerations

Bicron is the largest supplier of NaI(Tl) crystals in the world. Our current capacity approaches six tons per month, and our NaI(Tl) detectors are the industry standard for pulse height resolution over all energies. These range from soft X-ray energies through 1-10 MeV to 300 MeV and above. NaI(Tl) is the most commonly used scintillator for well logging because it offers the best combination of light output, density, handling characteristics and cost. However, Bicron also offers other scintillation materials such as CsI(Na), BGO and YAP:Ce is also used in downhole logging applications and in high temperature industrial processes. These alternative materials have greater densities and, therefore, improved counting efficiency. Tradeoffs to be considered include cost and scintillation performance differences at operating temperatures. Standard designs are available in a variety of geometries for both slimline and standard tool diameters. Custom geometries, performance specifications and prototype detectors can be provided.

Bicron as a Supplier to the Logging Service Industry