EP0045686A1
Expired / Lapsed
EP
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Spectroscopic analysis with background compensation
Assignee: SLB NV
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Filing: 1981-07-28
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Granted: —
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Expires: 2001-07-28
Abstract
Abstract The composition of an earth formation is investigated by repetitively irradiating the formation with bursts of incident radiation and generating an unknown energy spectrum from radiation resulting from the interaction of the incident radiation with nuclei of the formation. A background energy spectrum is generated from radiation detected during a time interval adjacent to the interval in which the unknown energy spectrum is measured. A percentage of the background spectrum, shifted to have the best energy-versus-channel number match with that of the unknown spectrum, is then subtracted from the unknown spectrum to produce an improved, unknown spectrum substantially free of background contributions from which an improved, compensated, inelastic neutron interaction log may be generated.
Inventors
- 👤 James A. Grau
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-04 01:30
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
186 words
A method for spectroscopically analyzing the elemental constituents of a geological formation, the method comprising the steps of: a) repetitively irradiating the formation with bursts of primary radiation; b ) for each burst, detecting secondary radiation emanating from the formation during a first time interval; c) generating a gross energy spectrum from a series of said first time intervals, said gross energy spectrum including a portion due to b ackg round; d) for each burst, detecting secondary radiation emanating from the formation during a different, second time interval; e ) generating a background spectrum from a series of said second time intervals; and characterized by f ) adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum by repetitively changing the offset of said background spectrum by different amounts and selecting the changed background spectrum which most closely resembles the background portion of said gross energy spectrum; and g) reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum relatively free of background.
Claim 2
Independent Claim
186 words
A method for spectroscopically analyzing the elemental constituents of a geological formation, the method comprising the steps of: a) repetitively irradiating the formation with bursts of primary radiation; b ) for each burst, detecting secondary radiation emanating from the formation during a first time interval; c) generating a gross energy spectrum from a series of said first time intervals, said gross energy spectrum including a portion due to b ackg round; d) for each burst, detecting secondary radiation emanating from the formation during a different, second time interval; e ) generating a background spectrum from a series of said second time intervals; and characterized by f ) adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum by repetitively changing the offset of said background spectrum by different amounts and selecting the changed background spectrum which most closely resembles the background portion of said gross energy spectrum; and g) reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum relatively free of background.
Claim 3
Dependent Claim
115 words
2) The method as recited in claim 1 characterized in that steps (f) and (g) include the steps of: (i) off-setting the baseline of said background spectrum; (ii) reducing said gross energy spectrum by said offset background spectrum to generate a net energy spectrum; (iii) producing a composite energy spectrum from one or more elemental standard spectra; (iv) comparing at least a portion of said net energy spectrum with at least a portion of said composite energy spectrum and determining its goodness of fit; and (v) repeating steps (i) through (iv) with a plurality of different offsets to determine the offset and the corresponding net energy spectrum for which the goodness of fit is optimized.
Claim 4
Dependent Claim
59 words
3) The method as recited in claim 1 or 2 characterized in that said step of adjusting said background spectrum includes the step of: a) adjusting the magnitude of said background spectrum by a factor proportional to the ratio of the number of background counts in said gross energy spectrum to the number of counts in said background spectrum.
Claim 5
Dependent Claim
91 words
4) The method as recited in claim 3 characterized in that said step of adjusting the magnitude of said background spectrum includes- the steps of: a) combining one or more elemental estimators of those elements thought to be background contributors, to produce a combination estimator; b) combining each of said gross energy spectrum and said background spectrum with said combination estimator and taking the ratios of the resultants to generate a subtraction factor; and c) multiplying said background spectrum by said subtraction factor to generate said background spectrum of adjusted magnitude.
Claim 6
Dependent Claim
100 words
5 ) The method as recited in claim 3 characterized in that said step of reducing the magnitude of said background spectrum includes the steps of: a) identifying some of those elements which contribute to the background; b ) from said identified elements, selecting one or more elements and determining their elemental estimators; c ) combining each of said gross energy spectrum and said background spectrum with said selected elemental estimators and taking the ratios thereof to generate a subtraction factor; and d ) combining said background spectrum and said subtraction factor to generate said background spectrum of adjusted magnitude.
Claim 7
Dependent Claim
80 words
6) The method as recited in any one of the previous claims, wherein said bursts of primary radiation comprise bursts of neutrons, said detected secondary radiation is gamma radiation, said gross energy spectrum is a gross gamma ray energy spectrum which comprises an inelastic gamma ray contribution and a capture gamma ray portion, said improved net energy spectrum is a net inelastic energy spectrum, and characterized in that said second time interval is timewise adjacent to said first time interval.
Claim 8
Dependent Claim
42 words
7) The method as recited in claim 6 characterized by the step of deriving elemental constituents of the geological formation from a plurality of said net inelastic energy spectra and generating a log indicative of inelastic elemental formation constituents versus depth therefrom.
Claim 9
Dependent Claim
171 words
8) An apparatus for spectroscopically analyzing the elemental constituents of a geological formation, the apparatus comprising: a) means for repetitively irradiating the formation with bursts of primary radiation; b) means for detecting secondary radiation emanating from the formation during a first time interval, and for generating a gross energy spectrum, said gross energy spectrum including a portion due to background; c) means for detecting secondary radiation emanating from the formation during a different, second time interval,and generating a background spectrum therefrom; and characterized by d) means for adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum including means for repetitively changing the offset of said background spectrum by different amounts and for selecting the changed background spectrum which most closely resembles the background portion of said gross energy spectrum; and e) means for reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum substantially free of background.
Claim 10
Dependent Claim
171 words
8) An apparatus for spectroscopically analyzing the elemental constituents of a geological formation, the apparatus comprising: a) means for repetitively irradiating the formation with bursts of primary radiation; b) means for detecting secondary radiation emanating from the formation during a first time interval, and for generating a gross energy spectrum, said gross energy spectrum including a portion due to background; c) means for detecting secondary radiation emanating from the formation during a different, second time interval,and generating a background spectrum therefrom; and characterized by d) means for adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum including means for repetitively changing the offset of said background spectrum by different amounts and for selecting the changed background spectrum which most closely resembles the background portion of said gross energy spectrum; and e) means for reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum substantially free of background.
Claim 11
Dependent Claim
120 words
9) The apparatus as recited in claim 8 characterized in that means (d) and (e) include: (i) means for off-setting the baseline of said background spectrum; (ii) means for reducing said gross energy spectrum by said offset background spectrum to generate .a net energy spectrum; (iii) means for producing a composite energy spectrum from one or more elemental standard spectra; (iv) means for comparing at least a portion of said net energy spectrum with at least a portion of said composite energy spectrum and determining its goodness of fit; and (v) means for optimizing the goodness of fit between said at least a portion of said net energy spectrum and said at least a portion of said composite energy spectrum.
Claim 12
Dependent Claim
58 words
10) The apparatus as recited in claim 8 or 9 characterized in that said means for adjusting said background spectrum includes: a) means for adjusting the magnitude of said background spectrum by a factor proportional to the ratio of the number of background counts in said gross energy spectrum to the number of counts in said background spectrum.
Claim 13
Dependent Claim
94 words
11) The apparatus as recited in claim 10 characterized in that said means for adjusting the magnitude of said background spectrum includes: a) means for combining one or more elemental estimators of those elements thought to be background contributors, to produce a combination estimator; b) means for combining each of said gross energy spectrum and said background spectrum with said combination estimator and taking the ratios of the resultants to generate a subtraction factor; and c) means for multiplying said background spectrum by said subtraction factor to generate said background spectrum of adjusted magnitude.
Claim 14
Dependent Claim
43 words
12) The apparatus as recited in claim 11 further characterized by means for deriving elemental constituents of the geological formation from a plurality of said net inelastic energy spectra and for generating a log indicative of inelastic elemental formation constituents versus depth therefrom.
Claim 15
Dependent Claim
174 words
13) A method for spectroscopically analyzing the elemental constituents of a geological formation, the method comprising the steps of: a) repetitively irradiating the formation with bursts of primary radiation; b) for each burst, detecting secondary radiation emanating from the formation during a first time interval; c) generating a gross energy spectrum from a series of said first time intervals, said gross energy spectrum including a portion due to background; d) for each burst, detecting secondary radiation emanating from the formation during a different, second time interval; e) generating a background spectrum from a series of said second time intervals; and characterized by f) adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum by adjusting the magnitude of said background spectrum by a factor proportional to the ratio of the number of background counts in said gross background spectrum; and g) reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum.
Claim 16
Dependent Claim
174 words
13) A method for spectroscopically analyzing the elemental constituents of a geological formation, the method comprising the steps of: a) repetitively irradiating the formation with bursts of primary radiation; b) for each burst, detecting secondary radiation emanating from the formation during a first time interval; c) generating a gross energy spectrum from a series of said first time intervals, said gross energy spectrum including a portion due to background; d) for each burst, detecting secondary radiation emanating from the formation during a different, second time interval; e) generating a background spectrum from a series of said second time intervals; and characterized by f) adjusting said background spectrum to more closely resemble the background portion of said gross energy spectrum by adjusting the magnitude of said background spectrum by a factor proportional to the ratio of the number of background counts in said gross background spectrum; and g) reducing said background portion of said gross energy spectrum by combining said gross energy spectrum and said adjusted background spectrum to generate an improved net energy spectrum.
Claim 17
Dependent Claim
91 words
14) The method as recited in claim 13 characterized in that said step of adjusting the magnitude of said background spectrum includes the steps of: a) combining one or more elemental estimators of those elements thought to be background contributors, to produce a combination estimator; b) combining each of said gross energy spectrum and said background spectrum with said combination estimator and taking the ratios of the resultants to generate a subtraction factor; and c) multiplying said background spectrum by said subtraction factor to generate said background spectrum of adjusted magnitude.
Claim 18
Dependent Claim
96 words
15) The method as recited in claim 13 characterized in that said step of reducing the magnitude of said background spectrum includes the steps of: a) identifying some of those elements which contribute to the background; b) from said identified elements, selecting one or more elements and determining their elemental estimators; c) combining each of said gross energy spectrum and said background spectrum with said selected elemental estimators and taking the ratios thereof to generate a subtraction factor; and d) combining said background spectrum and said subtraction factor to generate said background spectrum of adjusted magnitude.
References Cited (Backward Citations)
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