NMR Pulse Sequence Wait Time Variation for Echo Amplitude Accuracy
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Solution Overview
Problem
Traditional NMR logging techniques, such as CPMG echo trains, suffer from measurement inaccuracies due to steady state buildup and remaining spin order from repeated applications, leading to deviations from theoretically predicted echo amplitudes.
Innovation Solution
Interspersing different wait times between successive sequences of radio frequency pulses in NMR pulse sequences, allowing for more accurate interpretation of trainlets and T1/T2 measurements by reducing spin saturation and phase alternation errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional CPMG echo trains are used with repeated applications, then measurement efficiency is improved, but measurement precision deteriorates due to steady state buildup and remaining spin order
Solution Approach 1:
The patent implements periodic variation of wait times between successive CPMG echo train applications. Instead of using a constant wait time, the system alternates between different wait times (e.g., short wait time followed by long wait time) to periodically disrupt steady state buildup and remaining spin order effects, thereby maintaining measurement precision while preserving measurement efficiency
Solution Approach 2:
The patent changes the wait time parameter dynamically between different echo train applications. By varying the wait time parameter (switching between short and long wait times), the system prevents the formation of steady state conditions that cause measurement errors, while still allowing sufficient time for spin relaxation to maintain measurement productivity
2Measurement precision
If wait time is extended to reduce spin saturation, then measurement precision improves, but productivity deteriorates due to longer measurement time
Solution Approach 1:
The system uses periodic alternation between short and long wait times. During periods with shorter wait times, multiple echo trains can be applied rapidly to maintain productivity. During periods with longer wait times, spin saturation is reduced to improve measurement precision. This periodic switching allows the system to achieve both high productivity and high precision without requiring consistently long wait times
Solution Approach 2:
The measurement process is segmented into multiple echo train applications with varying wait times between them. Rather than using a single extended wait time, the system divides the measurement into segments (individual echo trains) separated by varying wait periods, allowing rapid sequential measurements while periodically allowing sufficient relaxation time to minimize saturation effects
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 significantly improves the correlation of measured echo train amplitudes with theoretically predicted values, enhancing the accuracy of NMR logging by minimizing steady state distortions and spin order effects.
Implementation Method 1
NMR logging is considered to be one of the most effective techniques for determining geologic parameters. NMR technology has many advantages over other logging techniques... one of the most significant being the independence of NMR measurements from formation lithology
Data Source
AI summary
A method and system for interspersing different wait times in trainlet and partial recovery sequences is provided. The method includes introducing a nuclear magnetic resonance (NMR) tool into a wellbore penetrating a subterranean formation. The method also includes applying an NMR pulse sequence to the subterranean formation using the NMR tool, in which the NMR pulse sequence includes at least two different wait times interspersed between successive sequences of radio frequency (RF) pulses. The method also includes measuring one or more echo signals corresponding to a substance in the subterranean formation based on the applied NMR pulse sequence. The method also includes determining a distribution of a characteristic of the substance based on the measured one or more echo signals.