Side-Looking NMR Logging Tool Borehole Signal Reduction
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Solution Overview
Problem
Conventional side-looking Nuclear Magnetic Resonance (NMR) logging tools are sensitive to borehole signals, which interfere with measurements, leading to inaccurate data due to the proximity of the tool to the borehole, and existing solutions like active RF spoilers introduce complexity and reliability issues.
Innovation Solution
A side-looking NMR logging tool design featuring a magnetic assembly with magnets having different magnetization directions to shift the static magnetic field away from the borehole, combined with a short RF transceiver antenna and reduced flipping angles for RF pulses to minimize borehole signals, effectively reducing the borehole signal contribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a side-looking NMR tool is positioned close to the borehole wall to minimize separation between the RF field generating assembly and the formation, then measurement sensitivity to formation is improved, but borehole signal interference increases
Solution Approach 1:
The tool is divided into two independent NMR assemblies positioned at opposite sides of the tool body. Each assembly has its own RF transmitter and receiver, allowing independent positioning and signal acquisition. This segmentation enables one assembly to be positioned close to the borehole wall for high sensitivity while the other can be positioned to minimize borehole signal interference.
Solution Approach 2:
The two NMR assemblies are positioned asymmetrically relative to the tool body and borehole wall. One assembly is positioned closer to the borehole wall to maximize formation signal, while the other is positioned farther away to minimize borehole signal contamination. This asymmetric positioning creates different signal characteristics that can be combined to eliminate borehole effects.
2Object-affected harmful factors
If an active RF spoiler is added to reduce borehole signal, then borehole signal reduction is achieved, but tool complexity and reliability issues increase
Solution Approach 1:
Instead of adding a spoiler component to actively cancel borehole signals, the invention extracts and utilizes the natural signal differences between two independently positioned NMR assemblies. The borehole signal reduction is achieved by combining signals from assemblies with different borehole signal levels, eliminating the need for active cancellation hardware.
Solution Approach 2:
The invention uses two copies of the NMR assembly with slightly different positioning. One assembly serves as the primary measurement device positioned close to the borehole wall, while the other serves as a reference or compensation device positioned to minimize borehole signal. The combination of these two copies achieves borehole signal reduction without requiring complex active cancellation circuitry.
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 design significantly reduces borehole signal interference, enhancing measurement accuracy and tool reliability by minimizing sensitivity to borehole signals while maintaining tool simplicity and effectiveness across various borehole sizes.
Implementation Method 1
a magnet assembly to generate a static magnetic field in a volume of interest
Implementation Method 2
a radio frequency ("RF") antenna to induce an RF field into the volume of interest and to receive corresponding total signals from the volume of interest
Implementation Method 3
NMR logging tools for determining, among other things porosity, hydrocarbon saturation and permeability of the rock formations. The NMR logging tools are utilized to excite the nuclei of the fluids in the geological formations
Data Source
AI summary
A side-looking Nuclear Magnetic Resonance (“NMR”) logging tool is designed to reduce and/or eliminate a borehole signal. The logging tool includes a magnetic assembly and a radio frequency (“RF”) transceiver antenna. The axial extent of the RF transceiver antenna has a length selected to reduce a borehole signal.