Hybrid NMR Pulse Sequence for Fast-Relaxing Component Detection
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Solution Overview
Problem
NMR logging techniques face challenges in accurately measuring T1 relaxation times, particularly in environments with fast-relaxing components, as existing methods either require long measurement times or suffer from reduced sensitivity, especially in gas shale and heavy oil formations.
Innovation Solution
A hybrid pulse sequence combining saturation-recovery and inversion-recovery methods is introduced, which improves sensitivity to fast-relaxing components without extending measurement time, using a sequence that includes a saturation pulse, an inversion pulse, and a detection sequence, allowing for variable time intervals to optimize sensitivity and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inversion-recovery method is used for T1 measurements, then measurement accuracy is improved, but measurement time becomes very long
Solution Approach 1:
The patent combines saturation-recovery and inversion-recovery pulse sequences into a hybrid sequence. The saturation pulse is applied first to eliminate steady-state magnetization, followed by an inversion pulse after a wait time Tw. This merging allows the sequence to achieve inversion-recovery's sensitivity to fast-relaxing components while avoiding its long measurement time requirement, as the saturation preparation enables shorter total echo train durations.
2Loss of time
If saturation-recovery method is used for T1 measurements, then measurement time is reduced, but sensitivity to fast-relaxing components is reduced
Solution Approach 1:
The patent applies a saturation pulse as a preliminary action before the inversion pulse. This saturation preparation eliminates steady-state magnetization and creates a known initial state, allowing the subsequent inversion pulse to effectively probe fast-relaxing components. The preliminary saturation action enables the sequence to achieve both short measurement time and high sensitivity to fast-relaxing components by properly initializing the magnetization state before measurement.
3Measurement precision
If longer wait time Tw is used in hybrid pulse sequence, then sensitivity to fast-relaxing components is improved, but measurement time increases
Solution Approach 1:
The patent makes the wait time Tw a dynamic, variable parameter that can be optimized based on the specific formation being measured. By allowing Tw to be adjusted rather than fixed, the sequence can adapt to different T1 distributions and optimize sensitivity to fast-relaxing components without unnecessarily extending measurement time. This dynamic parameter adjustment enables flexibility in balancing sensitivity and measurement duration based on actual downhole conditions.
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
The hybrid pulse sequence enhances the accuracy and dynamic range of T1 measurements, providing better characterization of fast-relaxing components and reducing measurement time, as demonstrated by improved Fréchet distance and misfit calculations compared to traditional methods.
Implementation Method 1
nuclear magnetic resonance (NMR) logging. NMR logging tools operate by using an imposed static magnetic field, B0, to give nuclei with non-zero nuclear spin (non-zero magnetic moment and angular momentum) split energy levels. This state creates a net magnetic moment and produces a bulk magnetization.
Implementation Method 2
the tool applies a perturbing field, usually in the form of a radio frequency electromagnetic pulse whose magnetic component (B1) is perpendicular to the static field (B0). This perturbing field moves the orientation of the magnetization into the transverse (perpendicular) plane.
Implementation Method 3
The precessing nuclei generate a detectable radio frequency signal that can be used to measure statistical distributions of T1, T2, porosities, and/or diffusion constants.
Data Source
AI summary
A nuclear magnetic resonance (NMR) logging method includes providing a hybrid pulse sequence having a saturation pulse, an inversion pulse, and a detection sequence. The method also includes measuring echo signals in response to the hybrid pulse sequence. The method also includes deriving a spin-lattice time constant (T1) distribution from the measured echo signals. A NMR system includes a hybrid pulse sequence module to provide a hybrid pulse sequence with a saturation pulse, an inversion pulse, and a detection sequence. The NMR system also includes a control module to select a time interval between the saturation pulse and the inversion pulse.