# US 10,310,134 B2 · API unit calibration of gamma ray logging tools using simulated data

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- Number: US 10,310,134 B2
- Document ID: US10310134B2
- Status: Granted
- Kind: B2
- Application number: 15/517,791
- Filed: 2016-09-12
- Published: 2018-08-02
- Granted: 2019-06-04
- Earliest claimed: 2015-10-22
- Assignees: Halliburton Energy Services, Inc.
- Applicants: Halliburton Energy Services, Inc.
- Inventors: James E. Galford
- Web page: https://patentgrep.com/patent/US10310134B2

## CPC

- G01V 13/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
- E21B 41/00: Equipment or details not covered by groups E21B15/00 - E21B40/00
- E21B 47/09: Locating or determining the position of objects in boreholes or wells {, e.g. the position of an extending arm}; Identifying the free or blocked portions of pipes
- E21B 49/00: Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- G01V 5/04: specially adapted for well-logging
- E21B 47/18: through the well fluid {, e.g. mud pressure pulse telemetry}
- E21B 47/26: Storing data down-hole, e.g. in a memory or on a record carrier
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

Gamma ray logging tools are calibrated using gamma emissions data simulated using Monte Carlo modeling techniques. During the simulation, one or more nuclear activity zones of a formation are modeled and photon counting rates are determined. Using the simulated counting rates, an American Petroleum Institute (“API”) unit sensitivity factor is calculated. The API unit sensitivity factor is then applied to convert real logging tool counting responses into API units.

## Claims

### Claim 1

A method for calibrating a gamma ray logging tool, the method comprising:
simulating gamma ray emissions of a formation by:
simulating a low activity zone of the formation and calculating a first counting rate for the low activity zone; and
simulating a high activity zone of the formation and calculating a second counting rate for the high activity zone;
calculating an American Petroleum Institute (“API”) unit sensitivity factor for a logging tool based upon the simulated gamma ray emissions, wherein the API unit sensitivity factor is calculated based upon the first and second counting rates;
deploying the logging tool along a wellbore;
obtaining a counting rate response of the logging tool; and
converting the counting rate response to API units using the API unit sensitivity factor.

### Claim 2 (depends on 1)

A calibration method as defined in claim 1, wherein the gamma ray emissions are simulated using Monte Carlo modeling.

### Claim 3 (depends on 1)

A calibration method as defined in claim 1, wherein simulating the gamma ray emissions comprises:
simulating a single activity zone of the formation; and
calculating a counting rate for the single activity zone,
wherein the API unit sensitivity factor is calculated based upon the counting rate.

### Claim 4 (depends on 1)

A calibration method as defined in claim 1, wherein simulating the gamma ray emissions comprises:
calculating photon activities of the gamma ray emissions for one or more elemental sources;
defining an elemental probability distribution for sampling the gamma ray emissions based upon the photon activities;
defining a mixed source probability distribution for sampling the gamma ray emissions based upon the elemental probability distributions; and
using the mixed source probability distribution, calculating a tally multiplier to express a tally of scoring photons as a counting rate,
wherein the counting rate will be utilized to calculate the API unit sensitivity factor.

### Claim 5 (depends on 1)

A calibration method as defined in claim 1, wherein simulating the gamma ray emissions comprises:
simulating one or more activity zones of the formation and calculating a first counting rate for each zone;
calculating a first API unit sensitivity factor using the first counting rate;
developing a first proxy formation model whose borehole size matches a reference logging condition of a first logging tool simulated to calculate the first counting rate;
using the first proxy formation model, calculating a second counting rate of the first logging tool;
converting the second counting rate to API units using the first API unit sensitivity factor;
developing a second proxy formation model whose borehole size matches a reference logging condition of a second logging tool; and
using the second proxy formation model, calculating a third counting rate of the second logging tool,
wherein the API unit sensitivity factor is a second API unit sensitivity factor calculated using the third counting rate.

### Claim 6

A gamma ray logging tool, comprising:
one or more gamma ray emission sensors communicably coupled to processing circuitry that is operable to perform a method comprising:
obtaining a counting rate response of the logging tool; and
converting the counting rate response to API units using an API unit sensitivity factor obtained using any of methods 1-6.

### Claim 7 (depends on 1)

A calibration method as defined in claim 1, wherein the logging tool is deployed via a wireline, slickline or tubular assembly.

### Claim 8

A method for generating a gamma ray calibration model, the method comprising:
simulating gamma ray emissions of a formation by:
simulating a low activity zone of the formation and calculating a first counting rate for the low activity zone; and
simulating a high activity zone of the formation and calculating a second counting rate for the high activity zone; and
calculating an American Petroleum Institute (“API”) unit sensitivity factor for a logging tool based upon the simulated gamma ray emissions, wherein the API unit sensitivity factor is calculated based upon the first and second counting rates.

### Claim 9 (depends on 8)

A method as defined in claim 8, wherein the gamma ray emissions are simulated using Monte Carlo modeling.

### Claim 10 (depends on 9)

A method as defined in claim 9, wherein simulating the gamma ray emissions comprises:
simulating a single activity zone of the formation; and
calculating a counting rate for the single activity zone,
wherein the API unit sensitivity factor is calculated based upon the counting rate.

### Claim 11 (depends on 9)

A method as defined in claim 9, wherein simulating the gamma ray emissions comprises:
calculating photon activities of the gamma ray emissions for one or more elemental sources;
defining an elemental probability distribution for sampling the gamma ray emissions based upon the photon activities;
defining a mixed source probability distribution for sampling the gamma ray emissions based upon the elemental probability distributions; and
using the mixed source probability distribution, calculating a tally multiplier to express a tally of scoring photons as a counting rate,
wherein the counting rate will be utilized to calculate the API unit sensitivity factor.

### Claim 12 (depends on 9)

A method as defined in claim 9, wherein simulating the gamma ray emissions comprises:
simulating one or more activity zones of the formation and calculating a first counting rate for each zone;
calculating a first API unit sensitivity factor using the first counting rate;
developing a first proxy formation model whose borehole size matches a reference logging condition of a first logging tool simulated to calculate the first counting rate;
using the first proxy formation model, calculating a second counting rate of the first logging tool;
converting the second counting rate to API units using the first API unit sensitivity factor;
developing a second proxy formation model whose borehole size matches a reference logging condition of a second logging tool; and
using the second proxy formation model, calculating a third counting rate of the second logging tool,
wherein the API unit sensitivity factor is a second API unit sensitivity factor calculated using the third counting rate.

### Claim 13 (depends on 1, 9)

A non-transitory computer program product comprising instructions which, when executed by at least one processor, causes the processor to perform any of the methods in claims 1 or 9.

### Claim 14

A system for calibrating a gamma ray logging tool, the system comprising:
a logging tool having one or more gamma ray sensors therein; and
processing circuitry communicably coupled to the logging tool and operable to perform operations comprising applying simulated gamma ray emission data to convert logging tool counting rate responses to American Petroleum Institute (“API”) units, wherein the conversion is achieved by:
simulating a low activity zone of a formation and calculating a first counting rate for the low activity zone;
simulating a high activity zone of the formation and calculating a second counting rate for the high activity zone;
calculating an API unit sensitivity factor for a logging tool based upon the first and second counting rates;
deploying the logging tool along a wellbore;
obtaining a counting rate response of the logging tool; and
converting the counting rate response to API units using the API unit sensitivity factor.

### Claim 15

A system for generating a gamma ray calibration model, the system comprising processing circuitry operable to perform operations comprising:
simulating gamma ray emissions of a formation by:
simulating a low activity zone of the formation and calculating a first counting rate for the low activity zone; and
simulating a high activity zone of the formation and calculating a second counting rate for the high activity zone; and
calculating an American Petroleum Institute (“API”) unit sensitivity factor for a logging tool based upon the simulated gamma ray emissions, wherein the API unit sensitivity factor is calculated based upon the first and second counting rates.

### Claim 16 (depends on 15)

A system as defined in claim 15, wherein the gamma ray emissions are simulated using Monte Carlo modeling.

### Claim 17 (depends on 15)

A system as defined in claim 15, wherein simulating the gamma ray emissions comprises:
simulating a single activity zone of the formation; and
calculating a counting rate for the single activity zone,
wherein the API unit sensitivity factor is calculated based upon the counting rate.

### Claim 18 (depends on 15)

A system as defined in claim 15, wherein simulating the gamma ray emissions comprises:
calculating photon activities of the gamma ray emissions for one or more elemental sources;
defining an elemental probability distribution for sampling the gamma ray emissions based upon the photon activities;
defining a mixed source probability distribution for sampling the gamma ray emissions based upon the elemental probability distributions; and
using the mixed source probability distribution, calculating a tally multiplier to express a tally of scoring photons as a counting rate,
wherein the counting rate will be utilized to calculate the API unit sensitivity factor.

### Claim 19 (depends on 15)

A system as defined in claim 15, wherein simulating the gamma ray emissions comprises:
simulating one or more activity zones of the formation and calculating a first counting rate for each zone;
calculating a first API unit sensitivity factor using the first counting rate;
developing a first proxy formation model whose borehole size matches a reference logging condition of a first logging tool simulated to calculate the first counting rate;
using the first proxy formation model, calculating a second counting rate of the first logging tool;
converting the second counting rate to API units using the first API unit sensitivity factor;
developing a second proxy formation model whose borehole size matches a reference logging condition of a second logging tool; and
using the second proxy formation model, calculating a third counting rate of the second logging tool,
wherein the API unit sensitivity factor is a second API unit sensitivity factor calculated using the third counting rate.