US3930154A
Expired / Lapsed
US
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Measurement of subsurface formation lithology, including composition and fluids, using gamma spectroscopy and thermal neutron decay
Assignee: Texaco Inc
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Filing: 1974-12-12
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Granted: 1975-12-30
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Expires: 1994-12-12
Abstract
Abstract Gamma ray spectra of earth formations surrounding an open or cased well borehole are obtained by exciting subsurface formation elements around the borehole with pulsed neutrons and detecting the gamma rays resulting from capture in the subsurface formation of thermalized neutrons from a capture gamma spectroscopy (C.G.S.) well log source. the spectra of gamma rays so obtained are analyzed to form logs of the elements which contribute significantly to the spectra. Simultaneously, the time rate of decay of the number of gamma rays resulting from capture of the thermal neutrons in the formation is obtained to derive a measure of the macroscopic thermal neutron capture cross-section of the formation. The gamma rays obtained from the formation are then compensated for variations the thermal neutron capture crosssection obtained for the formation. From the logs of elements and the macroscopic thermal neutron capture cross-section of the formation, quantitative measurements of the primary formation parameters of formation water salinity, water saturation, porosity, major matrix components and ratios of formation constituents of the earth formations are obtained.
Inventors
- 👤 Hubert D Scott
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 07:56
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
164 words
A METHOD FOR ANALYSIS OF EARTH FORMATIONS SURROUNDING A WELL BOREHOLE COMPRISING THE STEPS OF: A. OBTAINING STANDARD GAMMA RAY ENERGY SPECTRA OF MATERIALS POSTULATED TO BE IN FORMATIONS SURROUNDING A WELL BOREHOLE; B. BOMBARDING THE EARTH FORMATION WITH REPETITIVE PULSE OF FAST NEUTRONS WHICH ARE SLOWED DOWN AND THEREAFTER ENGAGE IN NEUTRON WHICH ARE SLOWED DOWN AND THEREAFTER ENVICINIITY OF THE BOREHOLE; C. OBTAINING GAMMA RAY ENERGY SPECTRA OF THE UNKNOWN MATERIALS SURROUNDING A WELL BOREHOLE; D. COMPARING AN UNKNOWN GAMMA RAY ENERGY SPECTRUM WITH A COMPOSITE WEIGHTED MIXTURE OF THE STANDARD GAMMA RAY SPECTRA TO OBTAIN THEREFROM A QUANTITATIVE MEASURE OF THE PERCENTAGE COMPOSITION OF ELEMENTS IN THE VICINITY OF THE BOREHOLE; E. SIMULTANEOUSLY OBTAINING A MEASURE OF THE MACROSCOPIC THERMAL NEUTRON CAPTURE CROSS SECTION OF THE EARTH FORMATION SURROUNDING THE BOREHOLE; AND F. CONPENSATING THE UNKNOWN GAMMA RAY ENERGY SPECTRA FOR VARIATIONS IN THE TERMAL NEUTRON CAPTURE CROSS SECTION OBTAINED FOR THE MATERIALS PRESENT IN THE FORMATIONS SURROUNDING THE WELL BOREHOLE.
Claim 2
Independent Claim
164 words
A METHOD FOR ANALYSIS OF EARTH FORMATIONS SURROUNDING A WELL BOREHOLE COMPRISING THE STEPS OF: A. OBTAINING STANDARD GAMMA RAY ENERGY SPECTRA OF MATERIALS POSTULATED TO BE IN FORMATIONS SURROUNDING A WELL BOREHOLE; B. BOMBARDING THE EARTH FORMATION WITH REPETITIVE PULSE OF FAST NEUTRONS WHICH ARE SLOWED DOWN AND THEREAFTER ENGAGE IN NEUTRON WHICH ARE SLOWED DOWN AND THEREAFTER ENVICINIITY OF THE BOREHOLE; C. OBTAINING GAMMA RAY ENERGY SPECTRA OF THE UNKNOWN MATERIALS SURROUNDING A WELL BOREHOLE; D. COMPARING AN UNKNOWN GAMMA RAY ENERGY SPECTRUM WITH A COMPOSITE WEIGHTED MIXTURE OF THE STANDARD GAMMA RAY SPECTRA TO OBTAIN THEREFROM A QUANTITATIVE MEASURE OF THE PERCENTAGE COMPOSITION OF ELEMENTS IN THE VICINITY OF THE BOREHOLE; E. SIMULTANEOUSLY OBTAINING A MEASURE OF THE MACROSCOPIC THERMAL NEUTRON CAPTURE CROSS SECTION OF THE EARTH FORMATION SURROUNDING THE BOREHOLE; AND F. CONPENSATING THE UNKNOWN GAMMA RAY ENERGY SPECTRA FOR VARIATIONS IN THE TERMAL NEUTRON CAPTURE CROSS SECTION OBTAINED FOR THE MATERIALS PRESENT IN THE FORMATIONS SURROUNDING THE WELL BOREHOLE.
Claim 3
Dependent Claim
35 words
The method of claim 1, further including the step of: obtaining the primary formation parameters of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 4
Dependent Claim
34 words
The method of claim 1, further including the step of: obtaining the water saturation of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 5
Dependent Claim
33 words
The method of claim 1, further including the step of: obtaining the porosity of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 6
Dependent Claim
35 words
The method of claim 1, further including the step of: obtaining the salinity of water in the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 7
Dependent Claim
37 words
The method of claim 1, further including the step of: obtaining the volume fractions of formation constituents of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 8
Dependent Claim
36 words
The method of claim 1, further including the step of: obtaining the ratios of formation components of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 9
Dependent Claim
121 words
The method of claim 1, wherein said step of simultaneously obtaining a measure of the macroscopic thermal neutron capture cross-section comprises the step of: a. measuring the number of gamma ray counts during a first time interval a predetermined time after a pulse of fast neutrons is emitted into the well borehole and formation during said step of bombarding; b. measuring the number of gamma ray counts during a second time interval a predetermined time after the first time interval; and c. measuring the time rate of decay of gamma ray counts between the first and second time intervals; and d. obtaining the macroscopic thermal neutron capture cross-section from the measured time rate of decay and the velocity of thermal neutrons.
Claim 10
Dependent Claim
77 words
The method of claim 8, further including the steps of: a. measuring the number of background gamma ray counts during a third time interval after the first and second time intervals to obtain the background gamma ray intensity in the borehole and formation; b. subtracting the background gamma ray counts from the gamma ray counts measured during each of the first and second time intervals to thereby compensate for background gamma rays in the borehole and formation.
Claim 11
Dependent Claim
26 words
The method of claim 9, further including the step of: forming a record of the simultaneously derived macroscopic capture cross-section as a function of borehole depth.
Claim 12
Dependent Claim
45 words
The method of claim 1, wherein said step of comparing comprises the step of: performing a least-squares fit by minimizing the squares of the differences between the gamma ray spectra of unknown materials and the standard spectra of elements postulated to be in the borehole.
Claim 13
Dependent Claim
135 words
An automated date processing machine for analysis of earth formations surrounding a well borehole from standard gamma ray energy spectra of materials postulated to be in the formations and gamma ray energy spectra of the unknown materials surrounding the well borehole, comprising: a. means for comparing an unknown gamma ray energy spectrum with a composite weighted mixture of the standard gamma ray spectra to obtain therefrom a quantitative measure of the percentage composition of elements in the vicinity of the borehole; b. means for simultaneously obtaining a measure of the macroscopic thermal neutron capture cross section of the earth formation surrounding the borehole; and c. means for compensating the unknown gamma ray energy spectra for variations in the thermal neutron capture cross section obtained for the materials present in the formations surrounding the well borehole.
Claim 14
Dependent Claim
135 words
An automated date processing machine for analysis of earth formations surrounding a well borehole from standard gamma ray energy spectra of materials postulated to be in the formations and gamma ray energy spectra of the unknown materials surrounding the well borehole, comprising: a. means for comparing an unknown gamma ray energy spectrum with a composite weighted mixture of the standard gamma ray spectra to obtain therefrom a quantitative measure of the percentage composition of elements in the vicinity of the borehole; b. means for simultaneously obtaining a measure of the macroscopic thermal neutron capture cross section of the earth formation surrounding the borehole; and c. means for compensating the unknown gamma ray energy spectra for variations in the thermal neutron capture cross section obtained for the materials present in the formations surrounding the well borehole.
Claim 15
Dependent Claim
34 words
The machine of claim 12, further including: means for obtaining the primary formation parameters of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 16
Dependent Claim
33 words
The machine of claim 12, further including: means for obtaining the water saturation of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 17
Dependent Claim
32 words
The machine of claim 12, further including: means for obtaining the porosity of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 18
Dependent Claim
34 words
The machine of claim 12, further including: means for obtaining the salinity of water in the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 19
Dependent Claim
36 words
The machine of claim 12, further including: means for obtaining the volume fractions of formation constituents of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 20
Dependent Claim
35 words
The machine of claim 12, further including: means for obtaining the ratios of formation components of the earth formation from the compensated gamma ray energy spectra and the simultaneously obtained macroscopic thermal neutron capture cross-section.
Claim 21
Dependent Claim
123 words
The machine of claim 12, wherein said means for simultaneously obtaining a measure of the macroscopic cross-section comprises: a. means for measuring the number of gamma ray counts during a first time interval a predetermined time after a pulse of fast neutrons is emitted into the well borehole and formation during said step of bombarding; b. means for measuring the number of gamma ray counts during a second time interval a predetermined time after the first time interval; and c. means for measuring the time rate of decay of gamma ray counts between the first and second time intervals; and d. means for obtaining the macroscopic thermal neutron capture cross-section from a measured time rate of decay and the velocity of thermal neutrons.
Claim 22
Dependent Claim
79 words
The machine of claim 19, further including: a. means for measuring the number of background gamma ray counts during a third time interval after the first and second time intervals to obtain the background gamma ray intensity in the borehole and formation; and b. means for subtracting the background gamma ray counts from the gamma ray counts measured during each of the first and second time intervals to thereby compensate for background gamma rays in the borehole and formation.
Claim 23
Dependent Claim
44 words
The machine of claim 12, wherein said means for comparing comprises: means for performing a least-squares fit by minimizing the squares of the differences between the gamma ray spectra of unknown materials and the standard spectra of elements postulated to be in the borehole.
References Cited (Backward Citations)
US3739171A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-12-29 | 1979-06-30 | 1979-12-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-12-29 | 1983-06-30 | 1983-12-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-12-29 | 1987-06-30 | 1987-12-30 | $7700.00 | Window Closed / Lapsed |