# US 2014/0152301 A1 · Determining the Larmor Frequency for NMR Tools

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- Number: US 2014/0152301 A1
- Document ID: US20140152301A1
- Status: Published application
- Kind: A1
- Application number: 14/173,405
- Filed: 2014-02-05
- Published: 2014-06-05
- Earliest claimed: 2010-03-22
- Assignees: Schlumberger Technology Corporation
- Applicants: Schlumberger Technology Corporation
- Inventors: Vivek Anand; Robert Freedman; Anatoly Dementyev; Payam Tabrizi; Daniel Catina
- Web page: https://patentgrep.com/patent/US20140152301A1

## CPC

- G01V 3/32: operating with electron or nuclear magnetic resonance
- G01R 33/4625: {Processing of acquired signals, e.g. elimination of phase errors, baseline fitting, chemometric analysis}
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

The Larmor frequency for an in situ nuclear magnetic resonance (NMR) tool is determined and used to acquire NMR data. An NMR tool is provided and placed in situ, for example, in a wellbore. An initial estimate of the Larmor frequency for the in situ NMR tool is made and NMR data are acquired using the in situ NMR tool. A spectral analysis is performed on the NMR data, or optionally, the NMR data are digitized and a discrete Fourier transform (DFT) is performed on the digitized NMR data. The modal frequency of the spectral analysis or DFT is determined, and the Larmor frequency for the in situ NMR tool is determined using the modal frequency. The NMR tool is modified to transmit at the determined Larmor frequency and then used to acquire further NMR data.

## Claims

### Claim 1

A method, comprising:
positioning a tool in a wellbore;
acquiring NMR data using the tool;
digitally extracting echo data from the acquired NMR data from the NMR tool;
performing a spectral analysis on the NMR data; and
determining a Larmor frequency for the NMR tool.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
modifying a transmission frequency of an antenna on the NMR tool to a determined Larmor frequency; and
acquiring further NMR data using the modified NMR tool.

### Claim 3 (depends on 1)

The method of claim 1, wherein the NMR tool is one of a wireline, sampling and while-drilling tool.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
making an initial estimate of a Larmor frequency for the NMR tool.

### Claim 5 (depends on 1)

The method of claim 1, further comprising:
determining a maximum value of the spectral analysis.

### Claim 6 (depends on 5)

The method of claim 5, wherein the determining a Larmor frequency for the NMR tool is done through using the maximum value of the spectral analysis.

### Claim 7 (depends on 4)

The method of claim 4, wherein the initial estimate of the Larmor frequency is based on one of a temperature and a Hall probe measurement.

### Claim 8 (depends on 1)

The method of claim 1, wherein the NMR data are FID data or spin-echo data.

### Claim 9 (depends on 1)

The method of claim 1, further comprising digitizing the NMR data and stacking the digitized NMR data prior to performing a spectral analysis.

### Claim 10 (depends on 1)

The method of claim 1, further comprising digitizing the NMR data and rotating the digitized NMR data to a zero phase angle prior to performing the spectral analysis.

### Claim 11 (depends on 5)

The method of claim 5, wherein determining the Larmor frequency comprises at least one of:
determining a maximum magnitude of the spectral analysis;
determining a phase-rotated real component of the spectral analysis; and
determining a zero crossing of a phase-rotated imaginary component of the spectral analysis.

### Claim 12 (depends on 1)

The method of claim 1 wherein determining the Larmor frequency comprises equating the Larmor frequency to a frequency for which the spectrum has a maximum.