US3801816A
Expired / Lapsed
US
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Well logging system and method
Assignee: Texaco Inc
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Filing: 1971-05-25
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Granted: 1974-04-02
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Expires: 1991-05-25
Abstract
Abstract A radioactivity well logging system is provided for making both a conventional log and a novel spectral analysis of the activation-produced radiation during the same trip through the borehole. The neutron source is pulsed to provide successive irradiation and quiescent intervals, and the resulting radiation may be detected during the irradiation intervals to provide conventional measurements such as an N-gamma log. During each quiescent interval, and after the neutrons produced during the preceeding irradiation interval have disappeared, a spectral measurement is made of the radiation emitted by the unstable isotopes in the earth. The signals from a multichannel analyzer may further be examined by comparison with a predetermined composite spectrum assumed to relate to a predetermined particular lithology.
Inventors
- 👤 D Mccay
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 11:47
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
159 words
The method of radioactivity well logging, comprising bombarding subsurface earth materials with fast neutrons only during a discrete irradiation time interval whereby said materials emit gamma radiations resulting from the creation of unstable isotopes and the occurrence of inelastic neutron scattering or thermal neutron captures by materials in the vicinity of the well borehole, detecting said resulting gamma radiations during a first detection interval substantially coincident with said irradiation interval, detecting said resulting gamma radiations during a second detection time interval following the termination of said irradiation interval by an increment of time sufficient to allow substantially all of the thermal neutron capture events to die away, measuring said gamma radiations detected during said irradiation interval as a function of the occurrence of thermal neutron capture processes in said bombarded earth materials, and measuring said gamma radiations detected during said second detection interval as a function of substantially only said creation of unstable isotopes in said bombarded earth materials.
Claim 2
Independent Claim
159 words
The method of radioactivity well logging, comprising bombarding subsurface earth materials with fast neutrons only during a discrete irradiation time interval whereby said materials emit gamma radiations resulting from the creation of unstable isotopes and the occurrence of inelastic neutron scattering or thermal neutron captures by materials in the vicinity of the well borehole, detecting said resulting gamma radiations during a first detection interval substantially coincident with said irradiation interval, detecting said resulting gamma radiations during a second detection time interval following the termination of said irradiation interval by an increment of time sufficient to allow substantially all of the thermal neutron capture events to die away, measuring said gamma radiations detected during said irradiation interval as a function of the occurrence of thermal neutron capture processes in said bombarded earth materials, and measuring said gamma radiations detected during said second detection interval as a function of substantially only said creation of unstable isotopes in said bombarded earth materials.
Claim 3
Dependent Claim
50 words
The method described in claim 1, further comprising establishing electrical pulses for said detected radiations, forming selected groups of said pulses into time-dependent electrical signals, and selecting and measuring one of said pulse groups as a function of substantially only said creation of unstable isotopes in said bombarded earth materials.
Claim 4
Independent Claim
218 words
A method of radioactivity well logging, comprising bombarding subsurface earth materials with high energy neutrons during a discrete irradiation interval, interrupting such bombardment during a quiescent interval which commences with the termination of said irradiation interval and which extends at least until said neutrons are substantially all captured, during a first detection interval which begins and terminates during said irradiation interval detecting gamma radiation resulting from inelastic neutron scattering or thermal neutron capture in said bombarded earth materials, establishing an electrical detection signal composed of pulses functionally related in occurrence and amplitude to the occurrence and terminal energy of a selected portion of said gamma radiations detected during said irradiation and quiescent intervals, selecting a first time-dependent portion of said detection signal and forming said first portion into a recordable representation of the occurrence of thermal neutron capture reactions in said bombarded earth materials, selecting a second time-dependent portion of said detection signal and forming said second portion into a recordable representation of the creation of said unstable isotopes in said bombarded earth materials, and making an energy-dependent analysis of said second portion of said signal for dEtermining the part of said second portions which is substantially attributable to those of said detected radiations which are emitted by the nuclei of a preselected one of said unstable isotopes.
Claim 5
Independent Claim
218 words
A method of radioactivity well logging, comprising bombarding subsurface earth materials with high energy neutrons during a discrete irradiation interval, interrupting such bombardment during a quiescent interval which commences with the termination of said irradiation interval and which extends at least until said neutrons are substantially all captured, during a first detection interval which begins and terminates during said irradiation interval detecting gamma radiation resulting from inelastic neutron scattering or thermal neutron capture in said bombarded earth materials, establishing an electrical detection signal composed of pulses functionally related in occurrence and amplitude to the occurrence and terminal energy of a selected portion of said gamma radiations detected during said irradiation and quiescent intervals, selecting a first time-dependent portion of said detection signal and forming said first portion into a recordable representation of the occurrence of thermal neutron capture reactions in said bombarded earth materials, selecting a second time-dependent portion of said detection signal and forming said second portion into a recordable representation of the creation of said unstable isotopes in said bombarded earth materials, and making an energy-dependent analysis of said second portion of said signal for dEtermining the part of said second portions which is substantially attributable to those of said detected radiations which are emitted by the nuclei of a preselected one of said unstable isotopes.
Claim 6
Dependent Claim
53 words
The method described in claim 3, wherein said analysis further includes establishing a plurality of amplitude bands each relating functionally to a different radiation energy range, grouping pulses in said second portion of said second detection signal according to said amplitude bands, and counting the number of pulses in each of said groups.
Claim 7
Dependent Claim
42 words
The method described in claim 4, wherein said analysis further includes establishing said amplitude bands as a function of the original energies of a corresponding number of predetermined different kinds of excited nuclei, and grouping said pulses according to said different energies.
Claim 8
Dependent Claim
41 words
The method described in claim 5, further including deriving from said pulse groups an electrical representation of the composite spectrum of said different kinds of excited nuclei, and comparing said derived electrical representation with a representation of a predetermined standard composite.
Claim 9
Independent Claim
224 words
A method of radioactivity well logging, comprising bombarding a subsurface earth formation with neutrons during a first predetermined discrete irradiation interval, detecting a representative portion of the gamma rays resulting from such bombardment and emanating from said formation during said irradiation interval, thereafter detecting a representative portion of the gamma rays resulting from said bombardment and emanating from said formation after said irradiation interval and during a predetermined quiescent interval, counting said gamma rays detected during said irradiation interval, counting those of said gamma rays detected during said quiescent interval and having an energy within a first predetermined energy range attributable to a first preselected element in said formation, counting those of said gamma rays detected during said quiescent interval and having an energy within a second lower predetermined energy range attributable to a second preselected element in said formation, determining the proportion of said first element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said first range, and determining the proportion of said second element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said second range less a first correction factor proportional to the number of said gamma rays counted in said first energy range.
Claim 10
Independent Claim
224 words
A method of radioactivity well logging, comprising bombarding a subsurface earth formation with neutrons during a first predetermined discrete irradiation interval, detecting a representative portion of the gamma rays resulting from such bombardment and emanating from said formation during said irradiation interval, thereafter detecting a representative portion of the gamma rays resulting from said bombardment and emanating from said formation after said irradiation interval and during a predetermined quiescent interval, counting said gamma rays detected during said irradiation interval, counting those of said gamma rays detected during said quiescent interval and having an energy within a first predetermined energy range attributable to a first preselected element in said formation, counting those of said gamma rays detected during said quiescent interval and having an energy within a second lower predetermined energy range attributable to a second preselected element in said formation, determining the proportion of said first element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said first range, and determining the proportion of said second element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said second range less a first correction factor proportional to the number of said gamma rays counted in said first energy range.
Claim 11
Dependent Claim
124 words
The method described in claim 7, further comprising counting those of said gamma rays detected during said quiescent interval and having an energy within a third energy range lower than said second range and attributable to a third preselected element in said formation, and determining the proportion of said third element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said third range less the sum of a second correction factor proportional to the number of said gamma rays counted in said first energy range and a third correction factor proportional to the difference between said number of gamma rays counted in said second energy range and said first correction factor.
Claim 12
Dependent Claim
103 words
The method described in claim 8, further comprising counting those of said gamma rays detected during said quiescent interval and having an energy within a fouth energy range lower than said third energy range and attributable to a fourth preselected element in said formation, and determining the proportion of said fourth element in said formation as a function of the number of gamma rays detected during said quiescent interval and having an energy within said fourth range less the sum of a fourth, fifth and sixth correCtion factor respectively proportional to a function of the sum of said first, second and third factors.
Claim 13
Dependent Claim
62 words
The method described in claim 9, further comprising establishing a plurality of predetermined values functionally corresponding respectively to the proportions of said first, second, third and fourth elements in an average subsurface earth formation of a predetermined type and character, and comparing each of said determined proportions of said elements in said bombarded formation with a corresponding one of said predetermined values.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-04-01 | 1977-10-01 | 1978-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-04-01 | 1981-10-01 | 1982-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-04-01 | 1985-10-01 | 1986-04-02 | $7700.00 | Window Closed / Lapsed |