US4556793A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Epithermal neutron lifetime logging
Assignee: Mobil Oil AS
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Filing: 1983-04-07
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Granted: 1985-12-03
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Expires: 2003-04-07
Abstract
Abstract A radioactive borehole logging tool employs an epithermal neutron detector having a neutron counter surrounded by an inner thermal neutron filter and an outer thermal neutron filter. Located between the inner and outer thermal neutron filters is a neutron moderating material for extending the lifetime of epithermal neutrons to enhance the counting rate of such epithermal neutrons by the neutron counter.
Inventors
- 👤 Linus S. Allen
- 👤 William R. Mills
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 21:21
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/107; G01V5/108
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
78 words
A method for measuring the epithermal neutron lifetime characteristic of a subsurface formation surrounding a borehole, comprising the steps of: (a) irradiating the subsurface formation surrounding the borehole with repetitive bursts of fast neutrons, and (b) moderating the neutron radiation returning to the borehole between said repetitive bursts of fast neutrons to extend the epithermal neutron lifetime of said returning neutron radiation without merging said epithermal neutron lifetime into the thermal neutron lifetime of said returning neutron radiation.
Claim 2
Independent Claim
78 words
A method for measuring the epithermal neutron lifetime characteristic of a subsurface formation surrounding a borehole, comprising the steps of: (a) irradiating the subsurface formation surrounding the borehole with repetitive bursts of fast neutrons, and (b) moderating the neutron radiation returning to the borehole between said repetitive bursts of fast neutrons to extend the epithermal neutron lifetime of said returning neutron radiation without merging said epithermal neutron lifetime into the thermal neutron lifetime of said returning neutron radiation.
Claim 3
Independent Claim
72 words
A method for measuring the epithermal neutron die-away characteristics of a subsurface formation surrounding a borehole, comprising the steps of: (a) irradiating the subsurface formation surrounding the borehole with bursts of fast neutrons, (b) filtering the neutron radiation returning to the borehole in response to the irradiation of said formations to remove thermal neutrons, and (c) moderating the unfiltered portion of said returning radiation to extend the die-away time of epithermal neutrons.
Claim 4
Independent Claim
72 words
A method for measuring the epithermal neutron die-away characteristics of a subsurface formation surrounding a borehole, comprising the steps of: (a) irradiating the subsurface formation surrounding the borehole with bursts of fast neutrons, (b) filtering the neutron radiation returning to the borehole in response to the irradiation of said formations to remove thermal neutrons, and (c) moderating the unfiltered portion of said returning radiation to extend the die-away time of epithermal neutrons.
Claim 5
Dependent Claim
32 words
The method of claim 2 further comprising the step of filtering said moderated portion of said returning radiation to remove any thermal equilibrium neutrons created during the moderating of said returning radiation.
Claim 6
Dependent Claim
84 words
A borehole logging system for measuring epithermal die-away of the formations surrounding the borehole, comprising: (a) a pulsed neutron source, (b) a neutron counter, (c) a filtering material surrounding said neutron counter for absorbing thermal neutrons to prevent them from penetrating said neutron counter, and (d) a moderating material located between said neutron counter and said filtering material for extending the epithermal neutron die-away rate while minimizing any thermal neutron equilibrium effect on said epithermal neutron die-away measurement due to the extended die-away rate.
Claim 7
Dependent Claim
84 words
A borehole logging system for measuring epithermal die-away of the formations surrounding the borehole, comprising: (a) a pulsed neutron source, (b) a neutron counter, (c) a filtering material surrounding said neutron counter for absorbing thermal neutrons to prevent them from penetrating said neutron counter, and (d) a moderating material located between said neutron counter and said filtering material for extending the epithermal neutron die-away rate while minimizing any thermal neutron equilibrium effect on said epithermal neutron die-away measurement due to the extended die-away rate.
Claim 8
Dependent Claim
29 words
The borehole logging system of claim 4 wherein said moderating material has a thickness which does not permit the establishment of a thermal neutron equilibrium within said moderating material.
Claim 9
Dependent Claim
22 words
The borehole logging system of claim 4 wherein said moderating material has a hydrogen atom density no greater than that of water.
Claim 10
Dependent Claim
18 words
The borehole logging system of claim 4 wherein said moderating material does not exceed three millimeters in thickness.
Claim 11
Dependent Claim
13 words
The borehole logging system of claim 4 wherein said moderating material is polyethylene.
Claim 12
Dependent Claim
13 words
The borehole logging system of claim 4 wherein said filtering material is cadmium.
Claim 13
Dependent Claim
13 words
The borehole logging system of claim 4 wherein said filtering material is gadolinium.
Claim 14
Dependent Claim
39 words
The borehole logging system of claim 4 further comprising a second filtering material located between said counter and said moderating material for absorbing any neutrons which have reached thermal equilibrium, thereby permitting only epithermal neutrons to reach said counter.
Claim 15
Dependent Claim
14 words
The borehole logging system of claim 11 wherein said second filtering material is lighium.
Claim 16
Dependent Claim
14 words
The borehole logging system of claim 11 wherein said second filtering material is boron.
Claim 17
Dependent Claim
14 words
The borehole logging system of claim 11 wherein said second filtering material is gadolinium.
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) | 1988-12-02 | 1989-06-03 | 1989-12-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-12-02 | 1993-06-03 | 1993-12-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-12-02 | 1997-06-03 | 1997-12-03 | $7700.00 | Window Closed / Lapsed |