Method and apparatus for high signal-to-noise ratio NMR well logging
First Claim
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1. A method for measuring nuclear magnetic resonance (NMR) relaxation properties of a formation with a high signal to noise ratio (SNR), the method comprising:
- applying a magnetic field to nuclei of the formation during a polarizing interval, the magnetic field comprising a polarizing intensity having a constant magnitude resulting in a longitudinal magnetization (Mz) of the nuclei wherein the polarizing interval begins and ends before the (Mz) decreases;
decreasing the applied magnetic field to a measurement intensity having a constant magnitude, the measurement intensity magnetic field applied to the nuclei of the formation during a measurement interval wherein a time interval for the decreasing is substantially shorter than a minimum longitudinal relaxation time of the nuclei;
applying to the formation at least one radio frequency (RF) pulse train during the measurement interval;
measuring an NMR signal from the formation in order to measure the NMR relaxation properties with the high SNR; and
using a processor in order to perform at least one of the following tasks;
store the NMR signal, analyze the NMR signal, use the NMR signal for equipment operation, and present the NMR signal to a user.
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Abstract
A method for measuring nuclear magnetic properties (NMR) properties of a formation, the method including applying a magnetic field to nuclei of the formation during a polarizing interval, the magnetic field having a polarizing intensity; changing the magnetic field to a measurement intensity, the measurement intensity applied to the nuclei of the formation during a measurement interval; applying to the formation at least one radio frequency (RF) pulse train during the measurement interval; and measuring an NMR signal from the formation.
65 Citations
19 Claims
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1. A method for measuring nuclear magnetic resonance (NMR) relaxation properties of a formation with a high signal to noise ratio (SNR), the method comprising:
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applying a magnetic field to nuclei of the formation during a polarizing interval, the magnetic field comprising a polarizing intensity having a constant magnitude resulting in a longitudinal magnetization (Mz) of the nuclei wherein the polarizing interval begins and ends before the (Mz) decreases; decreasing the applied magnetic field to a measurement intensity having a constant magnitude, the measurement intensity magnetic field applied to the nuclei of the formation during a measurement interval wherein a time interval for the decreasing is substantially shorter than a minimum longitudinal relaxation time of the nuclei; applying to the formation at least one radio frequency (RF) pulse train during the measurement interval; measuring an NMR signal from the formation in order to measure the NMR relaxation properties with the high SNR; and using a processor in order to perform at least one of the following tasks;
store the NMR signal, analyze the NMR signal, use the NMR signal for equipment operation, and present the NMR signal to a user. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An instrument configured for measuring nuclear magnetic resonance (NMR) relaxation properties of a formation with a high signal to noise ratio (SNR) from a borehole, the instrument comprising:
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a magnetic core; at least one switching winding disposed about the magnetic core, wherein the winding conducts electrical current to magnetize the core and is configured to switch from a polarizing magnetic field comprising a polarizing intensity having a constant magnitude to a measurement magnetic field comprising a measurement intensity having a constant magnitude that is less than the polarizing intensity during a time interval that is substantially shorter than a minimum longitudinal relaxation time of nuclei in the formation wherein the instrument is configured to apply the polarizing magnetic field during a polarizing interval resulting in a longitudinal magnetization (Mz) of the nuclei wherein the polarizing interval begins and ends before the (Mz) decreases and wherein the instrument is further configured to apply the magnetic field with the measurement intensity during a measurement interval; and an antenna for at least one of transmitting a radio frequency (RF) pulse train during the measurement interval and receiving an NMR signal configured for measuring the NMR relaxation properties with the high SNR. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. A computer readable medium, the medium comprising computer readable instructions which when executed by a computer measure nuclear magnetic resonance (NMR) relaxation properties of a formation with a high signal to noise ratio (SNR), by implementing a method comprising:
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applying a magnetic field to nuclei of the formation during a polarizing interval, the magnetic field comprising a polarizing intensity having a constant magnitude resulting in a longitudinal magnetization (Mz) of the nuclei wherein the polarizing interval begins and ends before the (Mz) decreases; decreasing the magnetic field to a measurement intensity having a constant magnitude, the measurement intensity magnetic field applied to the nuclei of the formation during a measurement interval wherein a time interval for the decreasing is substantially shorter than a minimum longitudinal relaxation time of the nuclei; applying to the formation at least one radio frequency (RF) pulse train during the measurement interval; measuring an NMR signal from the formation in order to measure the NMR relaxation properties with the high SNR; and performing at least one of the functions of storing the NMR signal on a storage medium and providing the NMR signal to a user via a user interface.
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19. A method for producing a logging instrument configured for measuring nuclear magnetic resonance (NMR) relaxation properties of a formation from a borehole with a high signal to noise ratio (SNR), the method comprising:
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selecting a magnetic core; placing at least one switching winding about the magnetic core, wherein the winding conducts electrical current in order to magnetize the core and is configured to switch from a polarizing magnetic field comprising a polarizing intensity having a constant magnitude to a measurement magnetic field comprising a measurement intensity having a constant magnitude that is less than the polarizing intensity during a time interval that is substantially shorter than a minimum longitudinal relaxation time of nuclei in the formation wherein the instrument is configured to apply the polarizing magnetic field during a polarizing interval resulting in a longitudinal magnetization (Mz) of the nuclei; wherein the polarizing interval begins and ends before the (Mz) decreases; and wherein the instrument is further configured to apply the magnetic field with the measurement intensity during a measurement interval; selecting an antenna configured to perform the function of at least one of a) transmitting a radio frequency (RF) pulse train during the measurement interval; b) receiving an NMR signal, which measures the NMR relaxation properties with the high SNR; and placing the magnetic core, the at least one switching winding, and the selected antenna into an assembly, wherein the logging instrument comprises the assembly into which the magnetic core, the at least one switching winding, and the selected antenna are placed.
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Specification