Patent US2974871A successfully refreshed from Google Patents.
US4972082A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Methods and apparatus for epithermal neutron logging
Assignee: Schlumberger Technology Corp
•
Filing: 1989-03-16
•
Granted: 1990-11-20
•
Expires: 2009-03-16
Abstract
Abstract The porosity of an earth formation is derived in a plused neutron logging tool by use of a directionalized and borehole-shielded eptithermal neutron detector array and by processing detector count rate measurements of the epithermal neutron die-away curve in accordance with a multi-parameter fit to obtain as one parameter the epithermal neutron decay time of the formation and as a second parameter an indication of detector standoff (environmental) effects. The multi-parameter fitting procedure separates the formation and standoff effects on the measured count vs time curve, and yields a decay time measurement that is primarily representative of formation porosity and substantially free of environmental effects. To enhance count rate statistics, the neutron source and one or more of the epithermal neutron detector may be located at the same depth in the borehole. The neutron burst centroid is monitored an used to define a fiducial window for processing the die-way curve data.
Inventors
- 👤 William A. Loomis
- 👤 David J. Le Poire
- 👤 William B. Nelligan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:33
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/104; G01V5/107
Claims Analysis
Total Claims: 63
Claim 1
Independent Claim
262 words
Apparatus for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: a sonde, having an elongate housing, adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time of the formation and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to derive a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 2
Dependent Claim
262 words
Apparatus for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: a sonde, having an elongate housing, adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time of the formation and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to derive a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 3
Dependent Claim
43 words
The apparatus of claim 1 wherein said signal processing means further comprises means for deriving from said plurality of count signals at least one additional signal representative of the effect of detector standoff from the borehole wall on the detected epithermal neutron populations.
Claim 4
Independent Claim
38 words
The apparatus of claims 1 or 2 further comprising means coupled to said signal processing means for recording said decay time signal or said at least one additional signal, respectively, as a function of depth within the borehole.
Claim 5
Dependent Claim
108 words
The apparatus of claim 2 wherein said signal processing means comprises means for processing said plurality of count signals generally in accordance with the relationship N(t)=N.sub.o e.sup.(-t/A+B/t . . . ) +K to derive said first signal and said at least one additional signal, where: N(t) is the epithermal neutron count at time t, N o is the epithermal neutron count at an initial time t o , e is the Napierian log base, A is the epithermal neutron decay time constant of the earth formation, B is a parameter indicative of the effect of detector standoff from the borehole wall, and K is a function of background.
Claim 6
Dependent Claim
40 words
The apparatus of claim 1, wherein the locus of emission of neutrons by said neutron source means and the active volume of said at least one epithermal neutron detector are located at substantially the same elevation along the logging sonde.
Claim 7
Dependent Claim
29 words
The apparatus of claim 1 wherein said at least one epithermal neutron detector comprises an active volume filled with helium-3 gas and clad with a thermal neutron absorbing material.
Claim 8
Dependent Claim
21 words
The apparatus of claim 1 or 6 wherein said shielding means comprises a 1/v-type neutron-absorbing material and an hydrogenous neutron-moderating material.
Claim 9
Dependent Claim
29 words
The apparatus of claim 6 wherein said thermal neutron absorbing material comprises a cadmium layer of from substantially 40 mils (1 mm) to substantially 60 mils (1.5 mm) thick.
Claim 10
Dependent Claim
34 words
The apparatus of claim 6 wherein the sensitive volume of said at least one detector is on the order of 6.5 centimeters (2.5 inches) or less long in the lengthwise direction of the sonde.
Claim 11
Dependent Claim
33 words
The apparatus of claim 1 or claim 9 further comprising a plurality of epithermal neutron detectors carried by the sonde, all of said detectors being shielded against borehole neutrons by said shielding means.
Claim 12
Dependent Claim
33 words
The apparatus of claim 10 wherein at least two of said detectors are spaced apart lengthwise of said sonde to provide an extended vertical area of formation over which epithermal neutrons are detected.
Claim 13
Dependent Claim
33 words
The apparatus of claim 10 wherein at least two of said detectors are spaced apart circumferentially of said sonde to provide an extended horizontal area of formation over which epithermal neutrons are detected.
Claim 14
Dependent Claim
52 words
The apparatus of claim 1 wherein said detector positioning means comprises: a pad carried by said sonde externally of said housing, said at least one detector being mounted on said pad adjacent the outer surface thereof; and means for urging said outer surface of said pad into engagement with the borehole wall.
Claim 15
Dependent Claim
42 words
The apparatus of claim 13 wherein said means for urging said pad into engagement with the borehole wall comprises decentralizing means mounted on the side of said sonde opposite to said pad for engagement with the opposite side wall of the borehole.
Claim 16
Dependent Claim
32 words
The apparatus of claim 13 wherein: said pad is comprised of said shielding means; and said at least one detector is mounted within a recess in the outer surface of said pad.
Claim 17
Dependent Claim
77 words
The apparatus of claim 1 further comprising: means for monitoring the output of the neutron source during one or more bursts and for generating signals representative thereof; and means for processing said neutron source output signals to define a fiducial time window relative to the neutron burst for said processing of said plurality of epithermal neutron count rate signals, so as to compensate for the effect of any variation in the time location of the neutron burst.
Claim 18
Dependent Claim
53 words
The apparatus of claim 16 wherein said neutron source monitoring means comprises an organic scintillator for detecting high-energy neutrons, said scintillator being located closely adjacent to said neutron source so as to reduce the incidence thereon of scattered-back neutrons relative to the incidence thereon of high-energy neutrons emanating directly from the neutron source.
Claim 19
Dependent Claim
21 words
The apparatus of claim 16 further comprising means for processing said neutron source output signals to determine the neutron burst width.
Claim 20
Dependent Claim
60 words
The apparatus of claim 16 wherein said fiducial-window signal processing means comprises means for determining the time position of the neutron burst relative to a reference time and for adjusting the time of occurrence of said fiducial time window to compensate for any departure of the time position of the neutron burst from a predetermined relationship to said reference time.
Claim 21
Dependent Claim
61 words
The apparatus of claim 19 wherein: the time position of the neutron burst is determined by processing said neutron source output signals to derive the centroid of the neutron burst; and the time of occurrence of said fiducial time window is adjusted to compensate for the departure of the derived burst centroid from a predetermined reference time for the burst centroid.
Claim 22
Independent Claim
206 words
A method for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time of the formation and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to derive a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 23
Independent Claim
206 words
A method for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time of the formation and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to derive a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 24
Dependent Claim
36 words
The method of claim 21 further comprising deriving from said plurality of count signals at least one additional signal representative of the effect of detector standoff from the borehole wall on the detected epithermal neutron populations.
Claim 25
Independent Claim
30 words
The method of claims 21 or 22 further comprising recording said decay time signal or said at least one additional signal, respectively, as a function of depth within the borehole.
Claim 26
Dependent Claim
103 words
The method of claim 22 wherein said decay time signal and said at least one additional signal are derived by processing said plurality of count signals generally in accordance with the relationship N(t)=N.sub.o e.sup.(-t/A+B/t . . . ) +K where: N(t) is the epithermal neutron count at time t, N o is the epithermal neutron count at an initial time t o , e is the Napierian log base, A is the epithermal neutron decay time constant of the earth formation, B is a parameter indicative of the effect of detector standoff from the borehole wall, and K is a function of background.
Claim 27
Dependent Claim
29 words
The method of claim 21, wherein the locus of emission of neutrons and the locus of detection of epithermal neutrons are at substantially the same depth in the borehole.
Claim 28
Dependent Claim
29 words
The method of claim 21 wherein said at least one epithermal neutron detector comprises an active volume filled with helium-3 gas and clad with a thermal neutron absorbing material.
Claim 29
Dependent Claim
36 words
The method of claim 21 or 26 wherein said shielding step comprises shielding said at least one detector on all sides except that facing the formation with a 1/v-type neutron-absorbing material and an hydrogenous neutron-moderating material.
Claim 30
Dependent Claim
25 words
The method of claim 26 wherein said thermal neutron absorbing material comprises a cadmium layer of from substantially 40 mils to substantially 60 mils thick.
Claim 31
Dependent Claim
28 words
The method of claim 21 further comprising positioning a plurality of epithermal neutron detectors closely adjacent the borehole wall, and shielding all of said detectors against borehole neutrons.
Claim 32
Dependent Claim
36 words
The method of claim 29 further comprising positioning at least two of said detectors in spaced apart relation lengthwise of said sonde to provide an extended vertical area of formation over which epithermal neutrons are detected.
Claim 33
Dependent Claim
36 words
The method of claim 29 further comprising positioning at least two of said detectors in spaced apart relation circumferentially of said sonde to provide an extended horizontal area of formation over which epithermal neutrons are detected.
Claim 34
Dependent Claim
70 words
The method of claim 21 further comprising: monitoring the output of the neutron source during one or more bursts and generating signals representative thereof; processing said neutron source output signals to define a fiducial time window relative to the neutron burst for said processing of said plurality of epithermal neutron count signals, so as to compensate for the effect of any variation in the time location of the neutron burst.
Claim 35
Dependent Claim
50 words
The method of claim 32 wherein said neutron source monitoring step comprises detecting high-energy neutrons with an organic scintillator located closely adjacent to said neutron source so as to reduce the incidence thereon of scattered-back neutrons relative to the incidence thereon of high-energy neutrons emanating directly from the neutron source.
Claim 36
Dependent Claim
21 words
The method of claim 33 further comprising processing said neutron source output signals to determine the width of the neutron burst.
Claim 37
Dependent Claim
57 words
The method of claim 32 wherein said fiducial-window signal processing means comprises determining the time position of the neutron burst relative to a reference time and adjusting the time of occurrence of said fiducial time window to compensate for any departure of the time position of the neutron burst from a predetermined relationship to said reference time.
Claim 38
Dependent Claim
61 words
The method of claim 35 wherein: the time position of the neutron burst is determined by processing said neutron source output signals to derive the centroid of the neutron burst; and the time of occurrence of said fiducial time window is adjusted to compensate for the departure of the derived burst centroid from a predetermined reference time for the burst centroid.
Claim 39
Dependent Claim
250 words
Apparatus for determining the porosity of an earth formation traversed by a well borehole, comprising: a sonde adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to obtain a signal correlatable with the porosity of the surrounding earth formation.
Claim 40
Dependent Claim
250 words
Apparatus for determining the porosity of an earth formation traversed by a well borehole, comprising: a sonde adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal neutron decay time and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to obtain a signal correlatable with the porosity of the surrounding earth formation.
Claim 41
Dependent Claim
27 words
The apparatus of claim 37 further comprising means coupled to said signal processing means for recording said porosity-correlatable signal as a function of depth within the borehole.
Claim 42
Dependent Claim
84 words
The apparatus of claim 37 wherein said predetermined relationship is generally of the form N(t)=N.sub.o e.sup.(-t/A+B/t . . .)+K where: N(t) is the epithermal neutron count at time t, N o is the epithermal neutron count at an initial time t o , e is the Napierian log base (2.7183), A is the epithermal neutron decay time constant of the earth formation, B is a parameter indicative of the effect of detector standoff from the borehole wall, and K is a function of background.
Claim 43
Dependent Claim
40 words
The apparatus of claim 37, wherein the locus of emission of neutrons by said neutron source means and the active volume of said at least one epithermal neutron detector are located at substantially the same elevation along the logging sonde.
Claim 44
Dependent Claim
29 words
The apparatus of claim 37 wherein said at least one epithermal neutron detector comprises an active volume filled with helium-3 gas and clad with a thermal neutron absorbing material.
Claim 45
Independent Claim
21 words
The apparatus of claims 37 or 41 wherein said shielding means comprises a 1/v-type neutron-absorbing material and an hydrogenous neutron-moderating material.
Claim 46
Dependent Claim
46 words
The apparatus of claim 37 further comprising a plurality of epithermal neutron detectors carried by the sonde in spaced-apart relation to provide an extended area of formation over which epithermal neutrons are detected, all of said detectors being shielded against borehole neutrons by said shielding means.
Claim 47
Dependent Claim
52 words
The apparatus of claim 37 wherein said detector positioning means comprises: a pad carried by said sonde externally of said housing, said at least one detector being mounted on said pad adjacent the outer surface thereof; and means for urging said outer surface of said pad into engagement with the borehole wall.
Claim 48
Dependent Claim
76 words
The apparatus of claim 37 further comprising: means for monitoring the output of the neutron source during one or more bursts and for generating signals representative thereof; means for processing said neutron source output signals to define a fiducial time window relative to the neutron burst for said processing of said plurality of epithermal neutron count rate signals, so as to compensate for the effect of any variation in the time location of the neutron burst.
Claim 49
Dependent Claim
21 words
The apparatus of claim 45 further comprising means for processing said neutron source output signals to determine the neutron burst width.
Claim 50
Independent Claim
199 words
A method for determining the porosity of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning said at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to the neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal decay time and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to obtain a signal correlatable with the porosity of the surrounding earth formation.
Claim 51
Independent Claim
199 words
A method for determining the porosity of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning said at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to the neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and processing said plurality of count signals in accordance with a predetermined relationship, including one time-constant parameter representative of the epithermal decay time and at least one additional parameter representative of the effect of detector standoff from the borehole wall, to obtain a signal correlatable with the porosity of the surrounding earth formation.
Claim 52
Dependent Claim
19 words
The method of claim 47 further comprising recording said porosity-correlatable signal as a function of depth within the borehole.
Claim 53
Dependent Claim
86 words
The method of claim 47 wherein said predetermined relationship is generally of the form N(t)=N.sub.o e.sup.(-t/A+B/t . . . ) +K where: N(t) is the epithermal neutron count at time t, N o is the epithermal neutron count at an initial time t o , e is the Napierian log base (2.7183), A is the epithermal neutron decay time constant of the earth formation, B is a parameter indicative of the effect of detector standoff from the borehole wall, and K is a function of background.
Claim 54
Dependent Claim
40 words
The method of claim 47, wherein the locus of emission of neutrons by said neutron source means and the active volume of said at least one epithermal neutron detector are located at substantially the same elevation along the logging sonde.
Claim 55
Dependent Claim
29 words
The method of claim 47 wherein said at least one epithermal neutron detector comprises an active volume filled with helium-3 gas and clad with a thermal neutron absorbing material.
Claim 56
Independent Claim
37 words
The method of claims 47 or 51 wherein said shielding step comprises a shielding said at least one detector on all sides except that facing the formation with a 1/v-type neutron-absorbing material and an hydrogenous neutron-moderating material.
Claim 57
Dependent Claim
41 words
The method of claim 47 further comprising positioning a plurality of epithermal neutron detectors closely adjacent the borehole wall to provide an extended area of formation over which epithermal neutrons are detected, and shielding all of said detectors against borehole neutrons.
Claim 58
Dependent Claim
71 words
The method of claim 47 further comprising: monitoring the output of the neutron source during one or more bursts and generating signals representative thereof; processing said neutron source output signals to define a fiducial time window relative to the neutron burst for said processing of said plurality of epithermal neutron count rate signals, so as to compensate for the effect of any variation in the time location of the neutron burst.
Claim 59
Dependent Claim
19 words
The method of claim 54 further comprising processing said neutron source output signals to determine the neutron burst width.
Claim 60
Dependent Claim
256 words
Apparatus for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: a sonde, having an elongate housing, adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof, the locus of emission of neutrons by said neutron source means and the active volume of said at least one detector being located at substantially the same elevation along the logging sonde; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for deriving from said plurality of count signals a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 61
Dependent Claim
256 words
Apparatus for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: a sonde, having an elongate housing, adapted to be lowered into and moved through the borehole; neutron source means carried by the sonde for repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; at least one detector carried by the sonde for detecting epithermal neutrons and generating signals representative thereof, the locus of emission of neutrons by said neutron source means and the active volume of said at least one detector being located at substantially the same elevation along the logging sonde; means for positioning said at least one detector closely adjacent the wall of the borehole to minimize the standoff of the detector from the borehole wall; means for shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; means coupled to said at least one detector for measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and signal processing means for deriving from said plurality of count signals a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 62
Independent Claim
195 words
A method for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector form the borehole wall, and such that the locus of emission of neutrons and the locus of detection of epithermal neutrons are simultaneously at substantially the same depth in the borehole; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and deriving from said plurality of count signals a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
Claim 63
Independent Claim
195 words
A method for epithermal decay time logging of an earth formation traversed by a well borehole, comprising: repetitively irradiating the borehole and surrounding earth formation with discrete bursts of high energy neutrons, which neutrons interact with nuclei of the borehole and formation materials to produce corresponding repetitive populations of epithermal neutrons in the borehole and surrounding earth formation; positioning at least one epithermal neutron detector closely adjacent the wall of the borehole to minimize the standoff of the detector form the borehole wall, and such that the locus of emission of neutrons and the locus of detection of epithermal neutrons are simultaneously at substantially the same depth in the borehole; shielding said at least one detector against neutrons incident thereon from all directions except the formation to enhance the sensitivity of the detector to neutrons incident thereon from the formation; measuring the population of detected epithermal neutrons during each of a plurality of time periods subsequent to said neutron bursts and generating a plurality of count signals representative of said respective populations; and deriving from said plurality of count signals a signal representative of a standoff-compensated value of the epithermal decay time of the formation.
References Cited (Backward Citations)
US2991364A
Cited
US3497692A
Cited
US3546512A
Cited
US4047027A
Cited
US4097737A
Cited
US4268749A
Cited
US4241253A
Cited
US4283624A
Cited
US4266126A
Cited
US4302669A
Cited
US4409481A
Cited
US4423323A
Cited
US4524274A
Cited
US4760252A
Cited
US4625110A
Cited
US4581532A
Cited
EP0203690A1
Cited
US4692617A
Cited
US4814611A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-11-19 | 1994-05-21 | 1994-11-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-11-19 | 1998-05-21 | 1998-11-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-11-19 | 2002-05-21 | 2002-11-20 | $7700.00 | Window Closed / Lapsed |