NMR T2 Inversion Motion Artifact Correction
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) measurements in downhole tools are affected by motion artifacts due to lateral movement and non-axially symmetric magnetic fields, leading to inaccurate characterization of earth formations, particularly in logging-while-drilling applications.
Innovation Solution
The method involves joint inversion with motion correction (JIMC) using modified equations that account for motion artifacts, incorporating additional multiplicative terms to fit and correct motion effects in NMR data, allowing for more accurate determination of T2 distributions and formation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NMR measurements are performed in logging-while-drilling applications, then real-time formation characterization is achieved, but motion artifacts are introduced due to lateral movement and drill string rotation
Solution Approach 1:
The patent applies motion correction algorithms that convert the harmful motion artifacts into useful information by analyzing the artifact patterns to determine tool motion characteristics, then using this information to correct the NMR data and recover accurate formation properties despite the drilling-induced motion
Solution Approach 2:
The patent modifies the NMR inversion process by introducing motion correction parameters that account for lateral displacement and rotational effects, transforming the standard inversion algorithm into a motion-compensated version that can handle dynamic drilling conditions while maintaining measurement accuracy
2Productivity
If the drill string rotates causing the drill bit to drill the borehole, then logging-while-drilling operations are enabled, but lateral motion of the drill string varies the distance from the NMR tool to the formation
Solution Approach 1:
The patent transitions from assuming a static tool-formation distance to modeling the distance as a dynamic variable that changes with drill string lateral motion, incorporating time-varying distance parameters into the NMR signal modeling and inversion process to accurately interpret measurements under dynamic drilling conditions
3Measurement precision
If motion correction is applied to NMR data, then measurement accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent divides the motion correction process into distinct segments: motion detection from artifact analysis, motion parameter estimation, and corrected inversion, allowing each segment to be optimized independently and enabling efficient implementation of the complex correction algorithm
Data Source
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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 having an echo train affected by a motion artifact, 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. The method further includes reducing, with the processor, an effect on the NMR measurement data of the motion artifact by using a correcting inversion method that models the motion artifact to provide a corrected transverse relaxation time constant (T2) distribution, the correcting inversion method having a multiplicative term having a term that includes at least one local maximum and an optional decay term.