Gamma Spectral Deconvolution for Annular Layer Density Measurement
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Solution Overview
Problem
Existing nuclear density tools measure bulk density averaged over the depth of investigation, failing to provide detailed information on density variations as a function of radial distance from the sensor, particularly in complex borehole environments.
Innovation Solution
A nuclear density tool with an optimized source-to-detector configuration and gamma spectral deconvolution method to isolate and measure individual annular layer densities, utilizing multiple gamma detectors and a feedback mechanism to refine layer densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer bulk density measurement is used, then the measurement process is simple, but detailed density information of individual layers is lost
Solution Approach 1:
The patent divides the bulk density measurement into separate layer-specific measurements by segmenting the gamma ray detection process. Multiple detectors are positioned at different distances from the source, each detecting gamma rays that have passed through different numbers of layers. This segmentation allows the system to isolate and measure the density of individual annular layers (cement, casing, formation) separately, rather than measuring them as a single averaged bulk density.
Solution Approach 2:
The patent transitions from a single-dimensional bulk density measurement to a multi-dimensional measurement by adding radial distance as a dimension. By placing detectors at different radial distances from the gamma source (near detector closer, far detector farther), the system creates multiple measurement dimensions that correspond to different layer depths. This dimensional expansion enables the extraction of density information for each layer individually.
2Measurement precision
If multiple detectors at different distances are used, then layer-specific density information is obtained, but the measurement system becomes more complex
Solution Approach 1:
The patent makes the gamma ray detection system multi-functional by using the same basic detector components for multiple measurement purposes. The near and far detectors, while positioned at different distances, both detect gamma rays and provide data that serves multiple functions: characterizing borehole conditions (standoff, fluid density) and measuring formation/cement density. This universality allows the system to perform both borehole correction and layer-specific density measurement with the same detector assembly.
Solution Approach 2:
The patent implements a feedback mechanism where the near detector measurements are used to characterize borehole conditions (standoff distance, fluid density), and this characterization feeds back into the interpretation of far detector measurements. The system uses the near detector data to correct and refine the density calculations from the far detector, creating a feedback loop that improves measurement accuracy while managing system complexity through iterative refinement.
3Measurement precision
If borehole correction is applied using near and far detectors, then measurement accuracy improves, but additional information about borehole environment is required
Solution Approach 1:
The patent makes the measurement system self-sufficient by using the near detector to automatically characterize borehole conditions without requiring external input. The near detector measures gamma ray attenuation that is influenced by standoff and borehole fluid density, and this information is extracted and used to correct the far detector measurements. The system serves itself by generating its own borehole characterization data from the near detector, eliminating the need for separate measurements or external input about borehole conditions.
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
Enables precise measurement of individual annular layer densities, even in challenging borehole conditions, providing detailed density information and enhancing the accuracy of cement evaluation and formation analysis.
Implementation Method 1
a gamma source and a gamma detector disposed on a longitudinal axis of the nuclear density tool
Implementation Method 2
performing a spectral deconvolution, determining an energy channel for a first measurement layer, recording a count rate with the gamma detector for the first measurement layer
Data Source
AI summary
A method and system for determining a density. The method may comprise disposing a nuclear density tool into a wellbore, performing a spectral deconvolution, determining an energy channel for a first measurement layer, recording a count rate with the gamma detector for the first measurement layer, applying a slope operator to the count rate, and identifying a first density of the first measurement layer. The system may comprise a nuclear density tool that includes a gamma source and a gamma detector configured to record a count rate, wherein the gamma detector and the gamma source are disposed on a longitudinal axis of the nuclear density tool. The system may also comprise an information handling system.