Spectral Gamma Ray Logging Tool Temperature Sensitivity Correction
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Solution Overview
Problem
Spectral gamma ray sensors used in downhole logging tools experience sensitivity drift due to temperature changes, leading to inaccurate measurements, and the inclusion of radioactive calibration sources poses safety, regulatory, and spectral distortion issues.
Innovation Solution
The implementation of temperature-binned correction factors derived from gamma ray spectra data to stabilize sensitivity, addressing both reversible and irreversible temperature-dependent sensitivity changes, without the need for radioactive sources, by using a gamma ray detector thermally coupled with a temperature sensor and processor-driven adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a radioactive calibration source is included inside the logging tool, then sensitivity drift correction is enabled, but safety risks, regulatory burdens, and spectral distortion increase
Solution Approach 1:
The patent removes the radioactive calibration source from the logging tool entirely. Instead of including a radioactive source inside the tool, the invention uses naturally occurring radioactive isotopes in the formation itself as the calibration reference, thereby eliminating safety and regulatory issues while maintaining sensitivity stabilization capability
Solution Approach 2:
The patent introduces an intermediary approach by using the formation's natural radioactivity as a mediator for calibration. Rather than using an artificial radioactive source, the system utilizes naturally occurring isotopes (uranium, thorium, potassium) in the formation as the reference, which serves as both the calibration standard and the measurement target
2Reliability
If a radioactive calibration source is included inside the logging tool, then sensitivity drift correction is enabled, but the measured spectrum is distorted due to superposition of reference source radiation and formation radiation
Solution Approach 1:
The patent extracts the calibration reference from the tool itself and places it in the formation. By removing the radioactive source from the tool, the measured spectrum no longer contains superposition of tool-source radiation and formation radiation, eliminating spectral distortion while maintaining the ability to correct sensitivity drift
Solution Approach 2:
The patent creates a copy of the calibration reference function using natural formation radioactivity. Instead of carrying an artificial radioactive source, the system copies the calibration function by utilizing the naturally occurring radioactive isotopes already present in the formation, which provide the same reference signal without adding distortion
3Temperature
If photomultiplier tubes are exposed to high temperatures, then downhole logging capability is maintained, but sensitivity is permanently lost due to cumulative thermal exposure
Solution Approach 1:
The patent implements feedback by continuously monitoring the formation's natural radioactivity signal and using it to track and correct PMT sensitivity changes. The system measures the known natural radioactivity signature, compares it against expected values, and applies correction factors to compensate for thermal degradation, enabling long-term operation without permanent sensitivity loss
Solution Approach 2:
The patent enables self-service by allowing the formation itself to provide the calibration reference needed for sensitivity correction. The naturally occurring radioactive isotopes in the formation serve as an automatic, continuous calibration source that compensates for PMT thermal degradation without requiring external intervention or radioactive sources in the tool
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides stable sensitivity over time and temperature, enhancing the accuracy of gamma ray spectrum measurements and reducing operational costs and regulatory burdens by eliminating the need for radioactive sources, while maintaining the quality of acquired data.
Implementation Method 1
scintillators converting the incoming gamma ray photons to visible light
Implementation Method 2
photomultiplier tubes (PMTs) converting visible light photons to a pulse of electrical energy
Implementation Method 3
temperature sensor thermally coupled to the gamma ray detector
Data Source
AI summary
A variety of applications can include a gamma ray logging system having a gamma ray detector, where temperature sensitivity of the gamma ray detector is accounted for in the operation of the logging system. Correction of sensitivity of the gamma ray detector can include using a measure of sensitivity drift derived from temperature binned gamma ray spectra from measurements by the gamma ray detector over a calibration period for a number of calibration periods. Additional apparatus, systems, and methods are disclosed.