US4433240A
Expired / Lapsed
US
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Method and apparatus for measuring gamma rays in a borehole
Assignee: Schlumberger Technology Corp
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Filing: 1981-06-04
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Granted: 1984-02-21
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Expires: 2001-06-04
Abstract
Abstract A gain stabilization loop for a gamma ray spectroscopy technique uses count rates from a pair of contiguous windows positioned on either side of at least one or more peaks of the detected spectrum. These count rates are combined to generate an error signal which minimizes the statistical errors. The stabilization loop modifies the response of the measurement apparatus so as to cancel the error signal.
Inventors
- 👤 Bronislaw Seeman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 23:15
CPC Classifications
G; G01; G01T; G01T1/00; G01T1/36; G01T1/40; G01V; G01V5/00; G01V5/04; G01V5/06
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
172 words
An apparatus for measuring gamma rays coming from formations traversed by a borehole, comprising: detection means for converting the gamma rays into electric pulses whose amplitudes are related to the energies of the gamma rays; discrimination means for sorting these electric pulses according to their amplitudes in order to furnish information on the energy spectrum of the received gamma rays, said discrimination means comprising means for separating the electric pulses at least into two first contiguous windows located on each side of a first predetermined value and into two second contiguous windows located on each side of a second predetermined value, said predetermined values corresponding to two reference peaks wherein at least one of said reference peaks is a peak provided by thorium, uranium, or potassium gamma ray spectra coming from the formations; means responsive to the pulses of said first and second windows in order to generate an error signal; and means responsive to said error signal for modifying the response of the measurement apparatus in order to stabilize said response.
Claim 2
Independent Claim
172 words
An apparatus for measuring gamma rays coming from formations traversed by a borehole, comprising: detection means for converting the gamma rays into electric pulses whose amplitudes are related to the energies of the gamma rays; discrimination means for sorting these electric pulses according to their amplitudes in order to furnish information on the energy spectrum of the received gamma rays, said discrimination means comprising means for separating the electric pulses at least into two first contiguous windows located on each side of a first predetermined value and into two second contiguous windows located on each side of a second predetermined value, said predetermined values corresponding to two reference peaks wherein at least one of said reference peaks is a peak provided by thorium, uranium, or potassium gamma ray spectra coming from the formations; means responsive to the pulses of said first and second windows in order to generate an error signal; and means responsive to said error signal for modifying the response of the measurement apparatus in order to stabilize said response.
Claim 3
Dependent Claim
30 words
The apparatus according to claim 1, characterized in that the other reference peak is another peak provided by the thorium, uranium or potassium gamma ray spectra coming from the formations.
Claim 4
Dependent Claim
49 words
The apparatus according to claim 2, characterized in that the means for generating the error signal include means for furnishing the count rates of pulses falling within each of said windows, and first and second linear function calculation means for combining the count rates to furnish said error signal.
Claim 5
Dependent Claim
29 words
The apparatus according to claim 3, characterized in that the means for generating the error signal comprises means for correcting the count rates to take into account the background.
Claim 6
Dependent Claim
49 words
The apparatus according to claim 1, characterized in that the means for generating the error signal includes means for furnishing the count rates of pulses falling within each of said windows, and first and second linear function calculation means for combining the count rates to furnish said error signal.
Claim 7
Dependent Claim
55 words
The apparatus according to claim 5, characterized in that said first and second linear function calculation means for combining the count rates includes means for calculating the differences between the count rates of said contiguous windows, and for combining said differences so as to minimize the effects of the statistical variations of said count rates.
Claim 8
Dependent Claim
78 words
The apparatus according to claim 6, characterized in that said first and second linear function calculation means for combining the count rates further include means for calculating the sums of the count rates in said contiguous windows, means for calculating a first linear function of said differences, means for calculating a second linear function of said sums, and means for calculating the ratio of the first function to the second function in order to obtain the error signal.
Claim 9
Dependent Claim
50 words
The apparatus according to claim 7, characterized in that said means for calculating said first function includes means for carrying out a weighted sum of the differences of the count rates and for calculating said second function by carrying out a weighted sum of the sums of the count rates.
Claim 10
Dependent Claim
60 words
The apparatus according to claim 8, characterized in that said means for combining the count rates includes means for weighting each of the differences of the count rates by a factor predetermined according to the central energy of the corresponding reference peak, the width of the windows corresponding to this reference peak and the resolution of the detection means used.
Claim 11
Dependent Claim
48 words
The apparatus according to claim 9, wherein said means for combining the count rates includes means for weighting each of the sums of the count rates by a second predetermined factor equal to the square of the weighting factor applied to the corresponding difference of the count rates.
Claim 12
Independent Claim
38 words
The apparatus according to any one of claims 5, 6, 7, 8, 9, or 10, characterized in that the means for generating the error signal comprises means for correcting the count rates to take into account the background.
Claim 13
Independent Claim
59 words
The apparatus according to any of claims 1 or 2, characterized by further comprising an auxiliary source for emitting monoenergetic gamma rays outside of the investigated range of gamma rays coming from the formations, and means sensitive to the gamma rays emitted by said auxiliary source for carrying out a second stabilization of the response of the measurement apparatus.
Claim 14
Dependent Claim
94 words
The apparatus according to claim 12, characterized in that the discrimination means comprises means for separating the electric pulses whose amplitudes fall within two third contiguous windows located on each side of a third value corresponding to the peak of gamma rays emitted by the auxiliary source, and in that said means for carrying out the second stabilization comprises means for combining the pulses of said two third contiguous windows in order to generate a second error signal, and means controlled by the second error signal for modifying the response of said analysis device.
Claim 15
Dependent Claim
27 words
The apparatus according to claim 13, characterized in that the means controlled by the second error signal includes means for modifying the gain of said detection means.
Claim 16
Dependent Claim
37 words
The apparatus according to claim 14, characterized in that the means controlled by the first error signal includes means for modifying certain comparison thresholds of said discrimination means without having an influence on said second error signal.
Claim 17
Independent Claim
178 words
A method for determining characteristics of geological formations traversed by a borehole by detecting gamma rays coming from said formations, comprising the following steps: converting the received gamma rays into electric pulses whose amplitudes are related to the energies of the gamma rays, classifying these electric pulses according to their amplitudes in order to furnish information on the energy spectrum of the received gamma rays, said step of classifying including the step of separating the electric pulses at least into two first contiguous windows located on each side of a first predetermined value and into two second contiguous windows located on each side of a second predetermined value, these predetermined values corresponding to two reference peaks wherein at least one of said reference peaks is a peak provided by the thorium, uranium or potassium spectra coming from the formations and, consequently, capable of disappearing; generating an error signal in response to the pulses of said first and second windows; and in response to said error signal, stabilizing the electric pulses which correspond to said gamma ray energy spectrum.
Claim 18
Independent Claim
178 words
A method for determining characteristics of geological formations traversed by a borehole by detecting gamma rays coming from said formations, comprising the following steps: converting the received gamma rays into electric pulses whose amplitudes are related to the energies of the gamma rays, classifying these electric pulses according to their amplitudes in order to furnish information on the energy spectrum of the received gamma rays, said step of classifying including the step of separating the electric pulses at least into two first contiguous windows located on each side of a first predetermined value and into two second contiguous windows located on each side of a second predetermined value, these predetermined values corresponding to two reference peaks wherein at least one of said reference peaks is a peak provided by the thorium, uranium or potassium spectra coming from the formations and, consequently, capable of disappearing; generating an error signal in response to the pulses of said first and second windows; and in response to said error signal, stabilizing the electric pulses which correspond to said gamma ray energy spectrum.
Claim 19
Dependent Claim
30 words
The method according to claim 16, characterized in that the other reference peak is another peak provided by the thorium, uranium or potassium gamma ray spectra coming from the formations.
Claim 20
Dependent Claim
70 words
The method according to claim 17, characterized in that the error signal generation step comprises the following steps: producing the count rates of the pulses falling within each of said windows; calculating the sums and differences of the count rates of contiguous windows; and calculating the ratio between a first linear function of said differences and a second linear function of said sums in order to obtain the error signal.
Claim 21
Dependent Claim
26 words
The method according to claim 18, characterized in that it further comprises a step consisting in correcting the count rates to take into account the background.
Claim 22
Dependent Claim
55 words
The method according to claim 18 characterized in that it further comprises the following steps: emitting monoenergetic gamma rays outside of the investigated range of gamma rays coming from the formations; and modifying said classifying step in response to the detected monoenergetic gamma rays in order to carry out a second stabilization of said measurement.
Claim 23
Dependent Claim
70 words
The method according to claim 16, characterized in that the error signal generation step comprises the following steps: producing the count rates of the pulses falling within each of said windows; calculating the sums and differences of the count rates of contiguous windows; and calculating the ratio between a first linear function of said differences and a second linear function of said sums in order to obtain the error signal.
Claim 24
Dependent Claim
48 words
The method according to claim 21, characterized in that said first linear function is calculated by carrying out a weighted sum of said differences of the count rates and said second linear function is calculated by carrying out a weighted sum of said sums of the count rates.
Claim 25
Dependent Claim
54 words
The method according to claim 22, characterized in that the weighting factors used for calculating the first linear function are predetermined factors depending on the central energy of the corresponding reference peak, the width of the windows corresponding to this reference peak and the resolution appropriate for converting the received gamma rays into pulses.
Claim 26
Dependent Claim
36 words
The method according to claim 23, characterized in that the weighting factors used for calculating the second linear function are taken equal to the squares of the weighting factors used for calculating the first linear function.
Claim 27
Independent Claim
33 words
The method according to any one of claims 21, 22, 23 or 24, characterized in that it further comprises a step consisting in correcting the count rates to take into account the background.
Claim 28
Dependent Claim
55 words
The method according to claim 25 characterized in that it further comprises the following steps: emitting monoenergetic gamma rays outside of the investigated range of gamma rays coming from the formations; and modifying said classifying step in response to the detected monoenergetic gamma rays in order to carry out a second stabilization of said measurement.
Claim 29
Dependent Claim
67 words
The method according to claim 26, characterized in that it comprises the following steps: separating the electric pulses into two third contiguous windows located on each side of a third determined value corresponding to the peak of the gamma rays emitted by the auxiliary source; and combining the pulses of said third windows in order to generate a second error signal to carry out said second stabilization.
Claim 30
Dependent Claim
31 words
The method according to claim 27, characterized in that it comprises the step consisting in modifying, by the second error signal, said step for converting the gamma rays into electric pulses.
Claim 31
Dependent Claim
30 words
The method according to claim 28, characterized in that it comprises the step consisting in modifying, by the first error signal, certain comparison thresholds of said electric pulse sorting step.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-02-20 | 1987-08-22 | 1988-02-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-02-20 | 1991-08-22 | 1992-02-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-02-20 | 1995-08-22 | 1996-02-21 | $7700.00 | Window Closed / Lapsed |