US3784822A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Radioactivity well logging methods and apparatus
Assignee: Schlumberger Technology Corp
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Filing: 1971-07-13
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Granted: 1974-01-08
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Expires: 1991-07-13
Abstract
Abstract An illustrative embodiment of the invention compensates neutron measurements of the porosity of an earth formation for sudden changes in borehole diameter. Typically, a sidewall porosity logging tool for transport through a borehole is equipped with two neutron detectors spaced at different distances from the neutron source. In order to improve the vertical resolution of the tool, a circuit stores the signal from the longspaced detector until the shorter spaced detector has traversed a distance along the borehole wall that is equal to the separation between the two detectors. This memory feature adjusts the porosity signals to a common zone of observation. These apparent porosity signals then are combined with borehole caliper signals to compensate for the effect of changes in borehole diameter.
Inventors
- 👤 N Schuster
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 12:04
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/107
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
165 words
A borehole logging tool for deriving a signal related to the porosity of an earth formation comprising, a neutron source for irradiating the formation, a short-spaced neutron detector spaced from said source and adapted to produce a signal in response to the neutron distribution in the formation produced by said source, a long-spaced neutron detector spaced from said source a distance greater than the distance separating said first neutron detector and said source and adapted to produce a signal in response to the neutron distribution in the formation produced by said source, memorizer means coupled to at least one of said detectors for storing signals received therefrom until the logging tool is drawn through the borehole a predetermined distance to produce depth referenced signals corresponding to said short-spaced and long-spaced detector signals referenced to a substantially common depth reference level, and circuit means for combining said depth referenced detector signals to establish an output signal that is related to the porosity of the earth formation.
Claim 2
Dependent Claim
165 words
A borehole logging tool for deriving a signal related to the porosity of an earth formation comprising, a neutron source for irradiating the formation, a short-spaced neutron detector spaced from said source and adapted to produce a signal in response to the neutron distribution in the formation produced by said source, a long-spaced neutron detector spaced from said source a distance greater than the distance separating said first neutron detector and said source and adapted to produce a signal in response to the neutron distribution in the formation produced by said source, memorizer means coupled to at least one of said detectors for storing signals received therefrom until the logging tool is drawn through the borehole a predetermined distance to produce depth referenced signals corresponding to said short-spaced and long-spaced detector signals referenced to a substantially common depth reference level, and circuit means for combining said depth referenced detector signals to establish an output signal that is related to the porosity of the earth formation.
Claim 3
Dependent Claim
67 words
A borehole logginG tool according to claim 1 further comprising, measuring means associated with the logging tool for establishing a signal that corresponds to the size of the borehole, means for urging said neutron source and said detectors toward the formation, and function former means responsive to said porosity-related signal and said measuring means signal to produce an output signal that more accurately identifies the formation porosity.
Claim 4
Dependent Claim
49 words
A borehole logging tool according to claim 2 wherein said function former means comprises, a plurality of function former circuits each individual to a respective formation mineral composition and a switch for selectively applying said function former circuits to said porosity-related signal in response to the formation mineral composition.
Claim 5
Independent Claim
145 words
A method for measuring the porosity of an earth formation traversed by a borehole comprising the steps of irradiating a formation with neutrons from a neutron source, measuring the distribution of neutrons originated by said source and scattered back from the formation at a first distance relative to the neutron source, measuring the distribution of neutrons originated by said source and scattered back from the earth formation at a different distance relative to the neutron source than said first relative distance, storing at least one of said neutron distribution measurements, combining said measurements after said storing step to produce a signal that corresponds to the apparent porosity of the formation, measuring the borehole size, and combining said apparent porosity signal with said borehole size measurement in accordance with the formation mineral composition to produce a signal that corresponds to a more accurate formation porosity indication.
Claim 6
Independent Claim
145 words
A method for measuring the porosity of an earth formation traversed by a borehole comprising the steps of irradiating a formation with neutrons from a neutron source, measuring the distribution of neutrons originated by said source and scattered back from the formation at a first distance relative to the neutron source, measuring the distribution of neutrons originated by said source and scattered back from the earth formation at a different distance relative to the neutron source than said first relative distance, storing at least one of said neutron distribution measurements, combining said measurements after said storing step to produce a signal that corresponds to the apparent porosity of the formation, measuring the borehole size, and combining said apparent porosity signal with said borehole size measurement in accordance with the formation mineral composition to produce a signal that corresponds to a more accurate formation porosity indication.
Claim 7
Dependent Claim
165 words
A borehole logging tool for deriving a signal related to a characteristic of an earth formation comprising, a radioactivity source for irradiating the formation, a short-spaced radioactivity detector spaced from said source and adapted to produce a signal in response to the radioactivity distribution in the formation produced by said source, a long-spaced radioactivity detector spaced from said source a distance greater than the distance separating said first radioactivity detector and said source and adapted to produce a signal in response to the radioactivity distribution in the formation produced by said source, memorizer means coupled to at least one of said detectors for storing signals received therefrom until the logging tool is drawn through the borehole a predetermined distance to produce depth referenced signals corresponding to said short-spaced and long-spaced detector signals referenced to a substantially common depth reference level, and circuit means for combining said depth referenced detector signals to establish an output signal that is related to the characteristic of the earth formation.
Claim 8
Dependent Claim
165 words
A borehole logging tool for deriving a signal related to a characteristic of an earth formation comprising, a radioactivity source for irradiating the formation, a short-spaced radioactivity detector spaced from said source and adapted to produce a signal in response to the radioactivity distribution in the formation produced by said source, a long-spaced radioactivity detector spaced from said source a distance greater than the distance separating said first radioactivity detector and said source and adapted to produce a signal in response to the radioactivity distribution in the formation produced by said source, memorizer means coupled to at least one of said detectors for storing signals received therefrom until the logging tool is drawn through the borehole a predetermined distance to produce depth referenced signals corresponding to said short-spaced and long-spaced detector signals referenced to a substantially common depth reference level, and circuit means for combining said depth referenced detector signals to establish an output signal that is related to the characteristic of the earth formation.
Claim 9
Dependent Claim
68 words
A borehole logging tool according to claim 5 further comprising, measuring means associated with the logging tool for establishing a signal that corresponds to the size of the borehole, means for urging said radioactivity source and said detectors toward the formation, and function former means responsive to said characteristic related signal and said borehole size signal to produce an output signal that more accurately identifies the formation characteristic.
Claim 10
Independent Claim
150 words
A method for measuring a characteristic of an earth formation traversed by a borehole comprising the steps of irradiating a formation with neclear radiation from a radioactivity source, measuring the distribution of nuclear radiation originated by said source and scattered back from the formation at a first distance relative to the radioactivity source to produce a first signal, measuring the distribution of nuclear radiation originated by said source and scattered back from the earth formation at a different distance relative to the radioactivity source than said first relative distance to produce a second signal, storing at least one of said first or second signals to produce depth reFerenced first and second signals corresponding to said first and second signals being derived from measurements at substantially the same depth level, combining said depth referenced signals after said storing step to produce a signal that corresponds to said characteristic of the formation.
Claim 11
Independent Claim
150 words
A method for measuring a characteristic of an earth formation traversed by a borehole comprising the steps of irradiating a formation with neclear radiation from a radioactivity source, measuring the distribution of nuclear radiation originated by said source and scattered back from the formation at a first distance relative to the radioactivity source to produce a first signal, measuring the distribution of nuclear radiation originated by said source and scattered back from the earth formation at a different distance relative to the radioactivity source than said first relative distance to produce a second signal, storing at least one of said first or second signals to produce depth reFerenced first and second signals corresponding to said first and second signals being derived from measurements at substantially the same depth level, combining said depth referenced signals after said storing step to produce a signal that corresponds to said characteristic of the formation.
Claim 12
Dependent Claim
47 words
The method of claim 7 and further including measuring the borehole size, and combining said formation characteristic signal with said borehole size measurement in accordance with a predetermined value of the formation mineral composition to produce a signal that corresponds to a more accurate formation characteristic indication.
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) | 1977-01-07 | 1977-07-09 | 1978-01-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-07 | 1981-07-09 | 1982-01-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-07 | 1985-07-09 | 1986-01-08 | $7700.00 | Window Closed / Lapsed |