Downhole Nuclear Tool Clean Inelastic Spectra
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing downhole gamma ray measurement systems face distortion due to detector-born gamma rays, which interfere with the acquisition of accurate inelastic and capture spectra, complicating formation evaluation and mineralogy measurements.
Innovation Solution
A downhole nuclear measurement tool with a neutron source and dual detectors (gamma ray and neutron detectors) is used to measure backscatter radiation, allowing for the determination of a neutron count rate and application of correction factors to remove detector-born gamma ray noise, thereby obtaining clean inelastic and capture spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a gamma ray detector is used to detect backscatter radiation, then gamma radiation detection capability is improved, but detector-born gamma rays interfere with the spectrum and reduce measurement precision
Solution Approach 1:
The patent extracts and removes the harmful detector-born gamma rays from the measured spectrum through mathematical correction. A neutron detector measures the neutron count rate, which is used to calculate a correction factor that quantifies the detector-born gamma ray interference. This correction factor is then applied to subtract the interference from the gamma ray detector spectrum, extracting only the useful formation backscatter signal.
Solution Approach 2:
The patent implements a feedback mechanism where the neutron detector continuously monitors the neutron count rate, and this information feeds back to dynamically adjust the correction applied to the gamma ray detector spectrum. The correction factor is calculated based on real-time neutron measurements, creating a closed-loop system that adapts to changing conditions and maintains spectrum accuracy throughout the measurement process.
2Measurement precision
If correction factors are applied to remove detector-born gamma rays, then measurement precision is improved, but device complexity increases due to dual detectors and additional processing
Solution Approach 1:
The neutron detector serves multiple functions: it measures the neutron count rate for correction purposes, characterizes the neutron field, and provides normalization data. This multi-functionality reduces the need for additional specialized components, as the same neutron detector is used for multiple measurement and correction tasks throughout the process.
Solution Approach 2:
The patent changes the operational parameters of the existing detectors to enable the correction process. The gamma ray detector operates in a mode where it measures both useful backscatter gamma rays and harmful detector-born gamma rays, while the neutron detector measures neutron count rate. By changing how these parameters are utilized and combined through mathematical relationships, the system achieves spectrum correction without adding fundamentally new detector types.
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 enables the acquisition of accurate, undistorted inelastic and capture spectra, improving the quality of downhole formation evaluation and mineralogy measurements by isolating detector-born gamma ray interference.
Implementation Method 1
pulsed neutron generators may be used to emit neutron radiation into the formation
Implementation Method 2
detect backscatter radiation or gamma emission
Implementation Method 3
a gamma ray detector may interact with a neutron, which may generate (e.g., via absorption or scattering) a gamma ray
Implementation Method 4
a detector may be particularly suited to detect a certain kind of radiation (e.g., gamma radiation in response to gamma emission)
Implementation Method 5
a second detector, positioned radially outward from the first detector, the second detector receiving the backscatter radiation, the second detector being a neutron detector, wherein the backscatter radiation at the second detector corresponds to a neutron count rate incident on the first detector
Implementation Method 6
a source monitor positioned proximate the neutron source, the source monitor recording emission information for the neutron source
Data Source
AI summary
A method for obtaining nuclear measurement data includes measuring a burst gate source intensity. The method also includes measuring at least one of burst gate neutron count rate or a capture gate neutron count rate at a neutron detector arranged proximate a gamma ray detector. The method further includes determining, based at least in part on the burst gate source intensity and at least one of the burst gate neutron count rate or the capture gate neutron count rate, a normalized neutron count rate. The method also includes determining at least one of an inelastic spectrum or a capture spectrum. The method includes determining based at least in part on the normalized neutron count rate, at least one of a corrected inelastic spectrum or a corrected capture spectrum.