Downhole NMR Tool Active Magnetic Field Compensation
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Solution Overview
Problem
Downhole NMR sensors face challenges in maintaining accurate data acquisition due to lateral motion and vibration during logging operations, which cause distortion and inability to acquire spin echo signals, especially in LWD and MWD applications.
Innovation Solution
The NMR tool incorporates a compensating assembly with upper and lower electromagnets that adjust the static magnetic field to compensate for lateral motion, using motion sensors to determine the necessary magnetic field adjustments and maintain field stability during measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If downhole NMR sensors are used with small radial extent of sensitivity area, then the tool can be compact and easier to operate, but lateral motion and vibration cause severe distortion of NMR data and inability to acquire spin echo signals
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the magnetic field gradient parameters through compensating electromagnets. When lateral motion is detected, the system changes the gradient field parameters to compensate for the displacement, thereby maintaining measurement precision despite tool motion. This resolves the contradiction by allowing compact tool design while preserving NMR data accuracy through active parameter adjustment.
Solution Approach 2:
The patent implements feedback control by using motion sensors to detect lateral displacement and vibration, then feeding this information back to the compensating electromagnets which adjust the magnetic field gradient accordingly. This closed-loop feedback system maintains measurement precision despite tool motion, resolving the contradiction between compact tool design and data accuracy.
2Productivity
If the NMR tool is moved along the wellbore axis during measurement, then productivity is improved, but lateral motion introduces measurement errors due to static magnetic field variation
Solution Approach 1:
The patent applies preliminary action by pre-positioning compensating electromagnets and motion sensors to detect and compensate for lateral motion before it significantly degrades measurement quality. The system proactively adjusts magnetic field gradients in response to detected motion, allowing continuous tool movement while maintaining measurement accuracy. This resolves the contradiction between logging speed and measurement precision.
Solution Approach 2:
The patent implements dynamics by making the magnetic field gradient adjustable and responsive to tool motion. The compensating electromagnets dynamically change the gradient field parameters in real-time during tool movement, allowing the system to adapt to changing conditions while maintaining measurement precision. This enables high-speed logging without sacrificing data quality.
3Stability of the object's composition
If rotational symmetry is used to reduce rotational sensitivity, then the design becomes more stable, but longitudinal and lateral displacement due to tool motion remains unsolved
Solution Approach 1:
The patent applies segmentation by separating the magnetic field generation into multiple independent components: main magnets for the static field and compensating electromagnets for gradient control. This segmentation allows independent optimization of each component, maintaining design stability while enabling active compensation for lateral displacement through the electromagnet segments.
Solution Approach 2:
The patent introduces compensating electromagnets as intermediary elements between the main magnetic field system and the formation being measured. These intermediaries actively adjust the magnetic field gradient to compensate for lateral motion, resolving the displacement problem while preserving the stable axially symmetrical design of the main sensor 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 solution effectively reduces measurement errors caused by lateral motion, ensuring consistent magnetic field strength and enabling accurate NMR data acquisition even during tool movement.
Implementation Method 1
The compensating assembly includes an upper electromagnet disposed between an upper end magnet of the magnet assembly and the antenna assembly and a lower electromagnet disposed between a lower end magnet of the magnet assembly and the antenna assembly
Implementation Method 2
A static magnetic field is generated by the magnet assembly
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
Nuclear magnetic resonance (NMR) tools, logging systems, and methods for measuring NMR properties of earth formations in a region of interest are provided. The NMR tool includes an antenna assembly, a magnet assembly, a compensating assembly, and a motion sensor. The antenna assembly is operable to generate a radio-frequency magnetic field and the magnet assembly is operable to generate a static magnetic field. The motion sensor is operable to generate readings for lateral motion of the antenna and magnet assemblies. The compensating assembly contains at least one electromagnet and is operable to reduce variation of the static magnetic field in the region of interest due to the lateral motion during NMR measurements based on the readings for the lateral motion.