Nuclear Density Tool Layer Resolution via Multi-Detector Compton Scattering
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Solution Overview
Problem
Current nuclear density tools are unable to measure the density of individual annular layers within a wellbore, as they only provide bulk density measurements averaged over a depth, lacking the ability to resolve intrinsic differences in layers due to their design and calculation algorithms.
Innovation Solution
A nuclear density tool utilizing a combination of radioactive gamma sources and multiple gamma detectors with an optimized source-to-detector configuration, employing a multiple Compton scattering scheme and analytical methods based on high-energy photons to directly compute densities of individual layers, utilizing the Lambert W-function to resolve layer densities from detector count rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single gamma detector is used to measure bulk density, then the measurement is simple and robust, but the ability to resolve individual layer densities is lost
Solution Approach 1:
The patent divides the measurement function into multiple detectors positioned at different locations and angles around the gamma source. Each detector measures gamma rays from different path lengths and angles through the annular layers, enabling the system to resolve and independently determine the density of each layer (casing, cement, formation) rather than measuring only bulk density.
Solution Approach 2:
The patent introduces angular and radial dimensions to the measurement geometry by positioning detectors at multiple angles (e.g., 0°, 90°, 180°, 270°) and distances from the source. This multi-dimensional detector arrangement creates a system of equations that can be solved to extract individual layer densities, transforming a single bulk measurement into multiple directional measurements that reveal layer-specific properties.
2Measurement precision
If existing density tools use near and far detectors for borehole correction, then borehole environment effects are compensated, but knowledge of borehole parameters is required and layer-specific densities cannot be resolved
Solution Approach 1:
The patent designs the detector array to simultaneously perform multiple functions: (1) measure bulk density for traditional borehole correction, (2) resolve individual layer densities through multi-layer analysis algorithms, and (3) provide borehole environment characterization. This multi-functional approach eliminates the need for separate correction procedures and additional borehole parameter inputs required by conventional tools.
Solution Approach 2:
The system uses iterative algorithms that incorporate measured gamma ray counts from multiple detectors to refine estimates of individual layer densities. The measurement process itself provides feedback about the borehole environment (through the measured bulk density and layer configurations), allowing the system to automatically adapt and correct for borehole effects without requiring external borehole parameter inputs.
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, improving upon existing tools by providing detailed layer-specific data, enhancing the accuracy of cement evaluation and formation density determination in both cased and open-hole environments.
Implementation Method 1
employing a multiple Compton scattering scheme and analytical methods based on high-energy photons to directly compute densities of individual layers
Data Source
AI summary
A nuclear density tool may comprise a gamma source, a gamma detector, wherein the gamma detector and the gamma source are disposed on a longitudinal axis of the nuclear density tool, and a housing, wherein the gamma source and the gamma detector are disposed in the housing. The nuclear density tool may further comprise a first cutout in the housing positioned to allow the gamma source to emit an energy through the housing and a second cutout in the housing posited to allow the gamma detector to detect the energy through the housing. A method for determining a density may comprise disposing a nuclear density tool into a wellbore, transmitting an energy from the gamma source, detecting the energy reflected with the gamma detector, recording a count rate of the energy at the gamma detector, determining an average density based at least in part on the count rate, creating one or more layers from the average density, forming a layer construction using at least in part the one or more layers from the average density, comparing the layer construction to count rates form individual energy channels, and determining a final layer density for each of the one or more layers.