Neutron Shielding for Downhole Tool Azimuthal Focusing
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Solution Overview
Problem
Neutron tools used in downhole applications suffer from reduced azimuthal sensitivity due to scattering in the borehole and thick collar, making them unsuitable for accurate formation imaging and porosity measurements.
Innovation Solution
The implementation of a downhole tool with a neutron source and detector configuration that includes an outer shield for azimuthal focusing, either around the source, detector, or both, to reduce scattering and enhance sensitivity by directing neutron flow towards the formation, thereby improving measurement accuracy and imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick collar is used to protect the neutron source and detector, then the tool's mechanical strength and protection are improved, but the azimuthal sensitivity is reduced due to neutron scattering in the collar
Solution Approach 1:
The collar is segmented into different sections with different properties: a first section with higher neutron scattering/absorption and a second section with lower scattering/absorption. This segmentation allows the collar to provide mechanical strength through the first section while minimizing neutron scattering in the second section, thereby resolving the contradiction between strength and measurement precision.
Solution Approach 2:
Different sections of the collar are given different local qualities regarding neutron interaction. The first collar section has properties optimized for mechanical strength and neutron shielding, while the second collar section has properties optimized for minimal neutron scattering. This local differentiation allows each section to fulfill its specific function without compromising the other.
2Device complexity
If conventional neutron tool configuration is used, then the tool structure is simple, but the borehole effects and scattering reduce measurement accuracy
Solution Approach 1:
The detector array is segmented into multiple detectors arranged in different orientations (azimuthal and vertical). This segmentation allows each detector to measure neutrons from specific directions, enabling the tool to distinguish between formation signals and borehole effects, thereby improving measurement accuracy without excessive complexity.
Solution Approach 2:
A borehole compensator or intermediary element is introduced between the neutron source/detector and the borehole environment. This intermediary helps to compensate for borehole effects and scattering, improving measurement accuracy while adding only moderate complexity to the tool structure.
3Volume of moving object
If the detector is positioned close to the neutron source, then the tool size is reduced, but the direct neutron flow from source to detector interferes with formation measurements
Solution Approach 1:
The direct path between neutron source and detector is extracted or removed by positioning the detector behind a shielding element or collar section. This extraction prevents direct neutron flow from the source to the detector, eliminating the interference with formation measurements while maintaining a compact tool size.
Solution Approach 2:
The detector is positioned in a different spatial dimension or orientation relative to the neutron source, such as behind the collar or at an angle. This dimensional repositioning allows the detector to be close to the source in terms of axial distance while preventing direct neutron interference through the collar structure.
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 configuration increases the tool's sensitivity to the formation, mitigates borehole effects, and enhances both azimuthal and vertical resolution, allowing for more accurate porosity measurements and formation imaging.
Implementation Method 1
Neutron tools used in downhole applications suffer from reduced azimuthal sensitivity due to scattering in the borehole and thick collar
Implementation Method 2
a housing having a source for generating neutrons and a detector for detecting the neutrons
Data Source
AI summary
A downhole tool for performing measurement of a formation. The tool comprising a housing surrounding a source for generating neutrons and a detector for detecting the neutrons. A shield is located outside of, or embedded in, the housing and focuses the neutrons.