Multicoil NMR Tool Azimuthal Imaging via Inversion
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Solution Overview
Problem
Current NMR tools for subterranean formation imaging lack the ability to perform effective azimuthal imaging due to uniform applied magnetic fields and varying sensitivity of multicoil signal detectors, which limits the accuracy of formation parameter measurements such as porosity and permeability.
Innovation Solution
A multicoil NMR tool with multiple receiver coils is deployed in a borehole, utilizing a forward model and inversion algorithm to analyze azimuthal and lateral formation data, allowing for the estimation of T2 distribution profiles and other formation parameters by deconvolving measured data with a time-dependent kernel, even when the applied magnetic field is uniform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform applied magnetic field is used in NMR tools, then the tool structure is simplified and easier to manufacture, but the ability to perform azimuthal imaging is lost and measurement precision deteriorates
Solution Approach 1:
The patent divides the single uniform magnetic field into multiple discrete magnetic field sources arranged in specific geometries (e.g., Helmholtz pairs, quadrupole arrangements). Each magnetic field source generates a localized field component, and their combined effect creates the desired non-uniform field pattern. This segmentation allows the system to achieve complex field distributions while maintaining manageable individual component designs.
Solution Approach 2:
The patent implements spatially varying magnetic field properties by positioning magnetic field sources at specific locations and orientations. Different regions of the measurement volume experience different field strengths and directions, enabling azimuthal discrimination. For example, magnetic field sources are arranged to create field gradients that vary with azimuthal angle, allowing the system to distinguish signals from different directional sectors of the formation.
2Measurement precision
If multiple receiver coils are used to enable azimuthal imaging, then measurement capability is improved, but the complexity of signal detection and data processing increases
Solution Approach 1:
The patent combines signals from multiple receiver coils through coherent summation and phase manipulation. By controlling the phase and amplitude of signals from individual coils, the system merges them to enhance azimuthal resolution. The combined signal processing approach integrates information from all coils to reconstruct azimuthal images, reducing the effective complexity compared to processing each coil independently.
Solution Approach 2:
The patent employs dynamic signal processing techniques where the system adapts its response based on the rotating tool configuration. As the tool rotates, the relative positions of magnetic field sources and receiver coils change, requiring real-time adjustment of signal processing parameters. This dynamic approach enables the system to maintain optimal azimuthal imaging performance throughout the rotation cycle.
3Loss of information
If multicoil NMR measurements are performed with rotating tool, then azimuthal information is captured, but the sensitivity of signal detectors varies during rotation causing measurement inconsistency
Solution Approach 1:
The patent incorporates feedback mechanisms where the system continuously monitors the actual signal strengths and sensitivity variations during rotation. This information is fed back to adjust processing parameters in real-time, compensating for the varying sensitivity of receiver coils as the tool rotates. The feedback loop ensures that azimuthal information is accurately captured despite the changing detection conditions.
Solution Approach 2:
The patent adjusts processing parameters dynamically based on the rotational position and detected signal characteristics. By changing parameters such as gain settings, filtering characteristics, and reconstruction algorithms according to the current operational state, the system maintains measurement reliability throughout the rotation cycle. This parameter adaptation compensates for sensitivity variations and ensures consistent data quality.
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 enables accurate azimuthal imaging and geo-steering by providing detailed formation parameter measurements, including porosity, bound fluid volume, and permeability, enhancing the resolution and precision of subterranean imaging.
Implementation Method 1
a permanent magnet that produces a static magnetic field at a desired test location
Implementation Method 2
The static magnetic field produces a magnetization in the fluid. The magnetization is aligned along the direction of the static field.
Implementation Method 3
A transmitter antenna produces a time-dependent radio frequency magnetic field that has a component perpendicular to the direction of the static field
Implementation Method 4
The radio frequency magnetic field produces a torque on the magnetization vector that causes it to rotate about the axis of the applied radio frequency field. The rotation results in the magnetization vector developing a component perpendicular to the direction of the static magnetic field. This causes the magnetization vector to precess around the static field at the Larmor frequency.
Implementation Method 5
A series of radio frequency pulses are applied to generate spin echoes that are measured with the antenna
Data Source
AI summary
Systems and methods are provided for investigating a downhole formation using a nuclear magnetic resonance (NMR) tool having two or more radio frequency receiving coils. While the tool is moving through the borehole, the formation is magnetized and resulting signals are obtained. In accordance with the present approach, the acquired signals can be resolved azimuthally and can be reconstructed to obtain an indication of a parameter of the formation at multiple locations along the length of the borehole.