Method for eliminating ringing during a nuclear magnetic resonance measurement
AssigneeSchlumberger Technology Corporation
InventorsBoqin Sun, Reza Taherian
Life of this patent
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Abstract
The present invention relates generally to a method for eliminating ringing while measuring nuclear magnetic resonance properties of an earth formation traversed by a borehole. The measurement can be made while drilling or using a wireline tool. During a first time period of a single pulse sequence, the measurement includes the desired spin-echoes and the undesired effects, that is, ringing, measurement noise, and baseline shift. During a second time period of the single pulse sequence, the spin-echoes are eliminated but not the undesired effects. Using the signal collected during the second time period, the signals measured during the first time period are corrected to eliminate the ringing component, measurement noise, and baseline shift.
Claims16
A method for eliminating ringing while measuring a nuclear magnetic resonance property of earth formations surrounding a borehole, comprising the steps of:
- a) applying a static magnetic field in a volume of the formation which polarizes the spin nuclei within the volume of formation;
- b) applying oscillating magnetic fields in the volume of formation according to a selected pulse sequence for a plurality of cycles so that a nuclear magnetic resonance signal is generated in the volume of formation;
- c) during a single pulse sequence cycle, step (b) further comprises the steps of:
- i) during a first time period, applying a first plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise a ringing component and a plurality of spin-echoes;
- ii) canceling the spin-echoes;
- iii) during a second time period, applying a second plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise the ringing component and substantially exclude the spin-echoes;
- and,
- iv) correcting the signals measured during the first time period to eliminate the ringing component.
A method for eliminating a baseline signal while measuring a nuclear magnetic resonance property of earth formations surrounding a borehole, comprising the steps of:
- a) applying a static magnetic field in a volume of the formation which polarizes the spin nuclei within the volume of formation;
- b) applying oscillating magnetic fields in the volume of formation according to a selected pulse sequence for a plurality of cycles so that a nuclear magnetic resonance signal is generated in the volume of formation;
- c) during a single pulse sequence cycle, step (b) further comprises the steps of:
- i) during a first time period, applying a first plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise a baseline component and a plurality of spin-echoes;
- ii) canceling the spin-echoes;
- iii) during a second time period, applying a second plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise the baseline component and substantially exclude the spin-echoes;
- and,
- iv) correcting the signals measured during the first time period to eliminate the baseline component.
A method for eliminating ringing while measuring a nuclear magnetic resonance property of earth formations surrounding a borehole, comprising the steps of:
- a) applying a static magnetic field in a volume of the formation which polarizes the spin nuclei within the volume of formation;
- b) applying oscillating magnetic fields in the volume of formation according to a selected pulse sequence for a plurality of cycles so that a nuclear magnetic resonance signal is generated in the volume of formation;
- c) during a single pulse sequence cycle, step (b) further comprises the steps of:
- i) during a first time period, applying a first plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise a ringing component, a plurality of spin-echoes, and a plurality of stimulated echoes;
- ii) canceling the spin-echoes and the stimulated echoes;
- iii) during a second time period, applying a second plurality of oscillating pulses in the volume of formation and measuring the generated signals in the formation, the measured signals comprise the ringing component and substantially exclude the spin-echoes and the stimulated echoes;
- and,
- iv) correcting the signals measured during the first time period to eliminate the ringing component.
Dependencies are inferred from the claim text.