NMR Tool Motion Artifact Correction via Dual Polarization
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) measurements in earth formations are affected by motion artifacts due to the lateral movement of downhole tools, leading to inaccurate characterization of formation properties.
Innovation Solution
The method involves processing NMR measurement data using both long and short echo trains to identify and correct motion artifacts, specifically by modifying the joint inversion equations with additional terms to account for the varying magnetic field magnitude caused by tool motion, thereby improving the accuracy of T2 distribution and formation property quantification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NMR measurements are performed using a downhole tool conveyed through a borehole, then formation properties can be characterized, but motion artifacts are introduced due to lateral movement of the tool
Solution Approach 1:
The patent applies parameter changes by acquiring NMR data under two different polarization time conditions (long TWET and short TWTL) and using the differential response to identify and correct motion artifacts. The correction process modifies the inversion parameters to account for the varying magnetic field magnitude caused by tool motion, thereby restoring measurement accuracy.
Solution Approach 2:
The patent implements feedback by using the comparison between long and short echo train data to detect motion artifacts, then feeding this information back into the inversion process to correct the T2 distribution. The system continuously monitors for inconsistencies indicative of motion and adjusts the interpretation accordingly.
2Productivity
If the NMR tool is rotated without drilling, then the borehole can be advanced, but lateral motion of the tool occurs causing motion artifacts
Solution Approach 1:
The patent maintains productivity by allowing continuous rotation and conveyance of the tool, while compensating for the resulting motion artifacts through parameter-based correction. The dual polarization time approach enables the system to distinguish between legitimate formation responses and motion-induced variations, preserving both operational efficiency and data quality.
3Ease of operation
If the distance from the NMR tool to the formation varies continuously, then the tool can navigate the borehole, but motion artifacts are induced in the NMR data
Solution Approach 1:
The patent maintains ease of operation by allowing free tool movement through the borehole, while using feedback from the dual echo train comparison to detect and correct motion artifacts. The system monitors for distance variations and their effect on the NMR signal, then applies appropriate corrections to maintain measurement accuracy despite tool navigation.
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 motion artifacts in NMR data, resulting in more accurate determination of porosity, pore size, and fluid type within the earth formation, enhancing the reliability of NMR logging-while-drilling operations.
Implementation Method 1
One type of downhole tool is a nuclear magnetic resonance (NMR) tool that performs NMR measurements on the formation to determine various properties such as porosity
Data Source
AI summary
A method for processing nuclear magnetic resonance (NMR) measurement data includes: receiving, with a processor, NMR measurement data obtained from an NMR tool, the NMR measurement data being affected by a motion artifact and having a first echo train obtained with a long polarization time TWET and a second echo train obtained with a short polarization time TWTL that is shorter than TWET; and at least one of (i) reducing, with a processor, an effect on the NMR measurement data of the motion artifact using the first echo train and the second echo train and (ii) identifying, with a processor, the motion artifact using the first echo train and the second echo train; wherein the motion artifact is related to a magnetic field magnitude that varies in a volume of interest due to a motion of the NMR tool.