NMR Logging Tool Pulse Sequence Design for Motion Compensation
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Solution Overview
Problem
NMR echo trains are distorted during NMR logging operations due to tool motion, leading to loss of information about the formation being measured, which prevents the creation of a robust wellbore log.
Innovation Solution
The solution involves characterizing the motion of the NMR logging tool by measuring its amplitude and displacement, and adjusting the bandwidth of refocusing pulses to compensate for motion-induced distortions, using detailed simulations and spin-dynamics modeling to optimize pulse sequences and increase the measurement bandwidth during the echo train.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NMR logging tool moves through wellbore during measurement, then productivity of logging operation is improved, but echo train distortion increases causing information loss
Solution Approach 1:
The patent applies dynamics by making the refocusing pulse bandwidth adjustable rather than fixed. The bandwidth is dynamically increased during the echo train to compensate for motion-induced frequency variations, allowing the system to adapt to changing conditions and maintain measurement accuracy despite tool motion through the wellbore
Solution Approach 2:
The patent changes the bandwidth parameter of refocusing pulses during the echo train. By increasing the bandwidth parameter in response to detected motion, the system counteracts the distortion effects of tool motion and recovers lost information, directly addressing the contradiction between productivity and information loss
2Loss of information
If refocusing pulse bandwidth is increased to compensate for motion, then echo train distortion is reduced, but RF power consumption increases
Solution Approach 1:
The system dynamically adjusts RF power based on real-time motion detection. When motion is detected, RF power is increased to compensate for distortion; when motion is minimal, RF power is reduced. This dynamic approach optimizes the balance between distortion compensation and energy consumption
Solution Approach 2:
The patent implements feedback by continuously monitoring echo train characteristics to detect tool motion. This feedback information is used to adjust refocusing pulse bandwidth and RF power in real-time, ensuring that energy is only consumed when and where needed to compensate for motion-induced distortions
3Measurement precision
If measurement bandwidth is increased during echo train, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by implementing variable bandwidth refocusing pulses that adapt during the echo train. Rather than using a complex multi-parameter pulse sequence, the system dynamically adjusts a single key parameter (bandwidth) in response to motion detection, simplifying the overall device complexity while improving signal-to-noise ratio
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 partially recovers lost information by minimizing echo-train distortion, allowing for more accurate NMR data collection and improved signal-to-noise ratio, even in the presence of tool motion, thereby enhancing the quality of wellbore logs.
Implementation Method 1
NMR may occur when the medium is subjected to a static magnetic field, B0, and to an oscillating magnetic field, B1. When subjected to an applied static magnetic field, polarization of nuclear magnetic spins of the medium occurs based on nuclear magnetic dipole and magnetic field strength.
Implementation Method 2
Applying an oscillating magnetic field to the medium in the static magnetic field may perturb the polarization established by the static magnetic field. Collected responses received from the medium related to the total magnetization of nuclear spins in the medium, in response to these applied fields may be used to investigate properties of the medium.
Data Source
AI summary
A method may comprise disposing a nuclear magnetic resonance logging tool into a wellbore, identifying an upper limit of an amplitude for tool motion, identifying a frequency range based at least in part on the upper limit of the amplitude for tool motion, measuring the one or more frequencies from the echo train, and performing a frequency-domain processing of the one or more frequencies to suppress distortions in an echo train. A system may comprise a nuclear magnetic resonance logging tool and an information handling system. The nuclear magnetic resonance logging tool may further comprise an electromagnetic transmitter configured to emit a magnetic field, a radio frequency transmitter configured to transmit a pulse and one or more refocusing pulses, and a receiver configured to detect one or more frequencies from an echo train.