NMR Logging Circular Polarization Correction
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Solution Overview
Problem
NMR logging tools face challenges in accurately measuring hydrogen porosity due to noise and errors caused by high temperatures, antenna coil misalignment, and environmental factors, which affect the quality of circularly polarized pulses used in downhole operations.
Innovation Solution
The implementation of reverse circularly polarized (RCP) pulses from quadrature antennas to correct for deviations in circularly polarized (CP) pulses, allowing for accurate calibration and measurement of transverse magnetization without the need for alternate calibration schemes, even under challenging downhole conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If circularly polarized pulses are used for NMR logging, then measurement capability is improved, but measurement precision deteriorates due to pulse imperfections caused by high temperature, antenna misalignment, and environmental factors
Solution Approach 1:
The patent applies feedback by measuring both CP and RCP pulse responses and using the RCP measurement to correct the CP measurement. The system continuously monitors pulse quality and applies real-time corrections to compensate for deviations caused by environmental factors, thereby maintaining measurement precision despite using CP pulses in challenging downhole conditions.
Solution Approach 2:
The patent combines measurements from two different pulse types (CP and RCP) to create a corrected measurement that compensates for the weaknesses of individual pulse types. By integrating information from both measurement modes, the system achieves higher precision than would be possible with CP pulses alone.
2Measurement precision
If reverse circularly polarized pulses are used to correct CP pulse deviations, then measurement precision is improved, but device complexity increases due to the need for additional pulse sequences and signal processing
Solution Approach 1:
The patent makes the NMR logging tool multi-functional by enabling it to transmit and measure both CP and RCP pulses. This universal capability allows the single device to perform both standard NMR measurements and correction measurements, eliminating the need for separate calibration equipment while improving measurement precision.
Solution Approach 2:
The system performs self-correction by using its own RCP measurement capability to identify and correct errors in its CP measurements. The tool serves itself by generating correction factors from RCP data and applying these to improve CP measurement accuracy, reducing the need for external calibration services.
3Measurement precision
If calibration schemes are implemented to correct pulse deviations, then measurement precision is improved, but loss of time increases due to additional calibration measurements and processing steps
Solution Approach 1:
The patent merges the calibration process with the actual measurement process by acquiring both CP and RCP data during normal logging operations. Rather than performing separate calibration runs, the system combines both measurement types in a unified data acquisition sequence, thereby improving precision without adding significant time overhead.
Solution Approach 2:
The system performs preliminary correction calculations by measuring RCP responses before finalizing CP measurements. This preliminary action allows correction factors to be determined in advance, enabling faster processing of the main measurement data and reducing overall measurement time while maintaining high precision.
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 enhances the accuracy and reliability of NMR measurements by correcting for imperfections in CP pulses, improving the quality of generated pulses and reducing errors, thereby providing more precise hydrogen porosity readings.
Implementation Method 1
tuning a radio frequency (RF) pulse to the correct or selected frequency, a resonant response can be elicited from hydrogen in formation materials
Implementation Method 2
The NMR logging tool includes a magnet assembly that generates a static magnetic field
Implementation Method 3
NMR logging tools face challenges in accurately measuring hydrogen porosity due to noise and errors caused by high temperatures, antenna coil misalignment, and environmental factors, which affect the quality of circularly polarized pulses used in downhole operations
Data Source
AI summary
A method for nuclear magnetic resonance (NMR) logging is disclosed that pulses, using a quadrature antenna of an NMR logging tool in a borehole, a circularly polarized (CP) signal into a formation surrounding the borehole. The method also pulses, using the quadrature antenna, a reverse circularly polarized (RCP) signal into the formation. A sensor of the NMR logging tool detects a first NMR signal from the formation in response to the RCP pulses and a second NMR signal from the formation in response to the CP pulses. A correct transverse magnetization value is then recovered based, at least in part, on the first NMR signal and the second NMR signal.