Downhole NMR Sensor Motion Correction via Variable Acquisition Windows
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Solution Overview
Problem
Downhole nuclear magnetic resonance (NMR) sensors face challenges with lateral motion, such as vibration, which causes distortion and prevents the acquisition of accurate spin echo signals during logging while drilling (LWD) or measurement while drilling (MWD).
Innovation Solution
The method involves acquiring first and second NMR signals using different acquisition windows, determining motion indicator data to indicate lateral motion of the NMR sensor, and estimating a motion multiplier vector to correct NMR relaxation data and reduce motion effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If NMR sensors are used in downhole environments with small radial sensitivity area, then the device complexity is reduced, but the measurement precision deteriorates due to sensitivity to lateral motion and vibration
Solution Approach 1:
The patent applies dynamics by making the acquisition window duration variable rather than fixed. The system dynamically adjusts the acquisition window duration based on detected motion conditions, allowing the measurement parameters to adapt to changing lateral motion and vibration environments, thereby maintaining measurement precision without increasing device complexity
Solution Approach 2:
The patent changes the parameter of acquisition window duration to resolve the contradiction. By varying this temporal parameter based on motion detection, the system compensates for lateral motion effects and maintains measurement accuracy while keeping the sensor design simple with small radial sensitivity area
2Productivity
If the NMR sensor operates in vibrating drilling environments, then the productivity is improved by enabling logging while drilling, but the measurement precision deteriorates due to lateral motion distortion
Solution Approach 1:
The patent applies preliminary action by detecting lateral motion and adjusting the acquisition window duration before the actual NMR measurement is completed. This proactive adjustment compensates for motion effects during the measurement process, maintaining signal accuracy while enabling continuous logging operations during drilling
Solution Approach 2:
The system dynamically modifies the acquisition parameters in response to real-time motion conditions, allowing the NMR logging to proceed accurately despite the vibrating drilling environment, thus maintaining both productivity and measurement precision
3Reliability
If shorter acquisition windows are used to reduce motion effects, then the reliability of NMR data is improved, but the loss of information increases due to truncated spin echo signals
Solution Approach 1:
The patent changes the acquisition window duration parameter dynamically rather than using a fixed short window. By adjusting this parameter based on detected motion conditions, the system achieves motion-resistant data while capturing complete spin echo signals, preventing information loss that would occur with permanently truncated acquisition windows
Solution Approach 2:
The system uses feedback from motion detection to adjust the acquisition window duration. This feedback mechanism allows the system to extend the acquisition window when motion is minimal to capture complete signals, and reduce it when motion is severe to maintain reliability, thus balancing both reliability and information completeness
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 approach effectively reduces the impact of lateral motion on NMR data, allowing for more accurate acquisition and analysis of NMR relaxation data, even in challenging drilling environments.
Implementation Method 1
Downhole nuclear magnetic resonance (NMR) sensors sometimes have a relatively small radial extent of the sensitivity area
Data Source
AI summary
A method to perform nuclear magnetic resonance measurements, and nuclear magnetic resonance tools in a wellbore includes acquiring using an NMR sensor a first NMR signal from a volume in the subterranean region, where the first NMR signal is acquired using a first acquisition window, and acquiring using the NMR sensor a second NMR signal from a volume in the subterranean region, where the second NMR signal is acquired using a second acquisition window different from the first acquisition window. The method also includes determining using the first NMR signal and the second NMR signal, a motion indicator data indicative of a lateral motion of the NMR sensor and substantially independent of the intrinsic NMR relaxation parameters of the earth formation in the volume in the subterranean region, estimating a motion multiplier vector directly from the motion indicator data.