Rotating Azimuthal Neutron Porosity Tool for Cased-Hole Imaging
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Solution Overview
Problem
Existing neutron logging tools lack azimuthal logging capabilities for porosity measurement of formation and cement volumes surrounding a borehole, particularly in cased-hole environments, and do not provide sufficient azimuthal resolution without increasing the number of circumferentially located detectors, which are shielded from one another such that each detector assemblies are spaced apart longitudinally along the body of the neutron logging tool.
Innovation Solution
The solution is to provide a rotating system that includes at least an internal length comprising a sonde section, a slip-ring and motor section; a plurality of tool logic electronics and PSUs; a means for rotation that rotates the tool inside a tool housing being driven by a motor, and a far space detector; a near space detector; and a source located within a moderator shield to cause a strong directional bias of the neutron flux output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple circumferentially located detectors are used to increase azimuthal resolution, then azimuthal logging capability is improved, but device complexity and cost increase due to more detectors and shielding requirements
Solution Approach 1:
The patent applies the dynamics principle by rotating the entire tool assembly (or a subset containing detectors and source) around the borehole axis. This dynamic rotation allows a single detector assembly to sample multiple azimuthal positions sequentially, achieving azimuthal imaging capability without requiring multiple simultaneously positioned detectors. The rotation transforms a static multi-detector configuration into a dynamic single-detector (or fewer detectors) system that achieves the same measurement coverage through temporal sampling.
2Ease of manufacture
If detectors are spaced apart longitudinally to reduce shielding requirements, then ease of manufacture is improved, but measurement precision deteriorates due to reduced azimuthal resolution
Solution Approach 1:
The rotation mechanism allows detectors to achieve azimuthal discrimination through temporal separation of signals from different azimuthal positions, rather than requiring spatial separation and physical shielding. This dynamic approach eliminates the need for complex inter-detector shielding while maintaining or improving azimuthal resolution, as the same detector can measure different azimuthal sectors at different rotation angles.
Solution Approach 2:
The patent introduces the time dimension (through rotation) to solve the spatial shielding problem. Instead of relying solely on spatial arrangement and physical shielding to achieve azimuthal separation, the system uses temporal sampling during rotation to distinguish signals from different azimuthal directions. This adds a temporal dimension to the measurement process, allowing azimuthal resolution without the need for complex spatial shielding arrangements.
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 arrangement enables azimuthal neutron porosity imaging of formation and cement volumes surrounding a borehole, allowing for evaluation of cement integrity and zonal isolation, particularly useful in plug and abandonment operations, and determining fracture efficiencies and fracture biases in the formation after fracking operations.
Implementation Method 1
a source located within a moderator shield to cause a strong directional bias of the neutron flux output
Implementation Method 2
the neutron 'slowing down time,' as measured by one or more of the detectors, is a shallow measurement of hydrogen index and very sensitive to standoff
Implementation Method 3
Modem tools typically use pulsed neutron sources and thermal and/or epithermal neutron detectors for the measurement of the neutron flux of the neutrons at several distances from the neutron source
Data Source
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AI summary
A first example azimuthal neutron porosity tool for imaging formation and cement volumes surrounding a borehole is provided, the tool including at least an internal length comprising a sonde section, wherein said sonde section further comprises one sonde-dependent electronics; a slip-ring and motor section; and a plurality of tool logic electronics and PSUs. An alternative azimuthal neutron porosity tool for imaging formation and cement volumes surrounding a borehole is also provided, the tool including at least a far space detector; a near space detector; and a source located within a moderator shield that rotates around an internal tool axis.