# US 11,906,690 B2 · Obtaining inelastic spectra free of detector born gamma rays induced by neutrons

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- Number: US 11,906,690 B2
- Document ID: US11906690B2
- Status: Granted
- Kind: B2
- Application number: 16/596,871
- Filed: 2019-10-09
- Published: 2020-04-16
- Granted: 2024-02-20
- Earliest claimed: 2018-10-10
- Assignees: Baker Hughes Oilfield Operations LLC
- Applicants: Baker Hughes Oilfield Operations LLC
- Inventors: Feyzi Inanc; Toyli Anniyev; Peng Yuan; Maxim Vasilyev; David Chace
- Web page: https://patentgrep.com/patent/US11906690B2

## CPC

- E21B 1/00: Percussion drilling
- G01V 5/045: {Transmitting data to recording or processing apparatus; Recording data}
- G01T 3/06: with scintillation detectors
- G01V 5/101: {and detecting the secondary Y-rays produced in the surrounding layers of the bore hole}
- G01V 5/12: using gamma or X-ray sources {(gamma sources using isotopes G21G4/00; X-ray tubes H01J35/00)}
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- G01T: MEASUREMENT OF NUCLEAR OR X-RADIATION (radiation analysis of materials, mass spectrometry G01N23/00; tubes for determining the presence, intensity, density or energy of radiation or particles H01J47/00)

## Abstract

In an embodiment, a method includes receiving a first measurement of gamma rays via a detector during a first period of time, receiving a second measurement of gamma rays via the detector during a second period of time, removing the second measurement from the first measurement to produce an inelastic spectrum, determining a spectral slope from the inelastic spectrum, determining a scaling factor based on the spectral slope, determining a spectral shape associated with the detector, determining a detector-induced spectrum by applying the scaling factor to the spectral shape, and removing the detector-induced spectrum from the inelastic spectrum to produce a clean inelastic spectrum.

## Claims

### Claim 1

A method of measuring properties of a formation or well structure, comprising:
receiving a first measurement of gamma rays from the formation or well structure via a detector during a first period of time;
receiving a second measurement of gamma rays from the formation or well structure via the detector during a second period of time;
removing the second measurement from the first measurement to produce an inelastic spectrum;
determining a spectral slope from the inelastic spectrum;
determining a scaling factor based on the spectral slope;
determining a spectral shape associated with the detector;
determining a detector-induced spectrum by applying the scaling factor to the spectral shape; and
removing the detector-induced spectrum from the inelastic spectrum to produce a clean inelastic spectrum for use in evaluating properties of the formation or well structure.

### Claim 2 (depends on 1)

The method of claim 1, wherein the first period of time corresponds to a burst gate and the first measurement corresponds to a total spectrum.

### Claim 3 (depends on 1)

The method of claim 1, wherein the second period of time corresponds to a capture gate and the second measurement corresponds to capture gamma rays.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
determining a higher gamma count rate from a first segment of a gamma ray spectrum;
determining a lower gamma count rate from a second segment of the gamma ray spectrum;
comparing the higher count rate and the lower count rate to determine the spectral slope.

### Claim 5 (depends on 1)

The method of claim 1, further comprising:
obtaining a correlation between the spectral slope and the scaling factor.

### Claim 6 (depends on 1)

The method of claim 1, wherein the detector comprises a crystal, and the detector-induced spectrum is associated with characteristics of the crystal.

### Claim 7

A computing device for measuring properties of a formation or well structure, comprising:
a microprocessor; and
memory including instructions that, when executed by the microprocessor, cause the computing device to:
receive a first measurement of gamma rays from the formation or well structure via a detector during a first period of time;
receive a second measurement of gamma rays from the formation or well structure via the detector during a second period of time;
remove the second measurement from the first measurement to produce an inelastic spectrum;
determine a spectral slope from the inelastic spectrum;
determine a scaling factor based on the spectral slope;
determine a spectral shape associated with the detector;
determine a detector-induced spectrum by applying the scaling factor to the spectral shape; and
remove the detector-induced spectrum from the inelastic spectrum to produce a clean inelastic spectrum for use in evaluating properties of the formation or well structure.

### Claim 8 (depends on 7)

The computing device of claim 7, wherein the first period of time corresponds to a burst gate and the first measurement corresponds to a total spectrum.

### Claim 9 (depends on 7)

The computing device of claim 7, wherein the second period of time corresponds to a capture gate and the second measurement corresponds to capture gamma rays.

### Claim 10 (depends on 7)

The computing device of claim 7, wherein the instructions, when executed by the microprocessor, further cause the computing device to:
determining a higher gamma count rate from a first segment of a gamma ray spectrum;
determining a lower gamma count rate from a second segment of the gamma ray spectrum; and
compare the higher count rate and the lower count rate to determine the spectral slope.

### Claim 11 (depends on 7)

The computing device of claim 7, wherein the instructions, when executed by the microprocessor, further cause the computing device to:
obtain a correlation between the spectral slope and the scaling factor.

### Claim 12 (depends on 7)

The computing device of claim 7, wherein the detector comprises a crystal, and the detector-induced spectrum is associated with characteristics of the crystal.

### Claim 13

A system for conducting measurement operations for measuring properties of a formation or well structure, the system comprising:
a neutron measurement device forming at least a portion of a downhole tool string, the neutron measurement device operable to generate measurement data for detecting a wellbore characteristic, wherein the neutron measurement device comprises:
a neutron generation unit operable to emit neutrons toward a target;
a detector unit fixed relative to the neutron generator and operable to detect gamma rays from the target;
a microprocessor; and
memory including instructions that, when executed by the microprocessor, cause the system to:
receive a first measurement of gamma rays from the formation or well structure via a detector during a first period of time;
receive a second measurement of gamma rays from the formation or well structure via the detector during a second period of time;
remove the second measurement from the first measurement to produce an inelastic spectrum;
determine a spectral slope from the inelastic spectrum;
determine a scaling factor based on the spectral slope;
determine a spectral shape associated with the detector;
determine a detector-induced spectrum by applying the scaling factor to the spectral shape; and
remove the detector-induced spectrum from the inelastic spectrum to produce a clean inelastic spectrum for use in evaluating properties of the formation or well structure.

### Claim 14 (depends on 13)

The system of claim 13, wherein the first period of time corresponds to a burst gate and the first measurement corresponds to a total spectrum.

### Claim 15 (depends on 13)

The system of claim 13, wherein the second period of time corresponds to a capture gate and the second measurement corresponds to capture gamma rays.

### Claim 16 (depends on 13)

The system of claim 13, wherein the instructions, when executed by the microprocessor, further cause a computing device to:
determining a higher gamma count rate from a first segment of a gamma ray spectrum;
determining a lower gamma count rate from a second segment of the gamma ray spectrum; and
compare the higher count rate and the lower count rate to determine the spectral slope.

### Claim 17 (depends on 13)

The system of claim 13, wherein the instructions, when executed by the microprocessor, further cause a computing device to:
obtain a correlation between the spectral slope and the scaling factor.

### Claim 18 (depends on 13)

The system of claim 13, wherein the detector comprises a crystal, and the detector-induced spectrum is associated with characteristics of the crystal.

### Claim 19 (depends on 13)

The system of claim 13, wherein the neutron generation unit is a pulsed neutron generator.

### Claim 20 (depends on 13)

The system of claim 13, wherein the detector unit includes at least one gamma ray detector.