US3817328A
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Neutron absorption and oxygen log for measuring oil content of formation
Assignee: Chevron USA Inc
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Filing: 1972-08-21
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Granted: 1974-06-18
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Expires: 1992-08-21
Abstract
Abstract This invention discloses a method for accurately determining changes in the fractional-volume oil and gas content of a reservoir from a cased well bore. The first step of the invention is to record the response of both a thermal-neutron-decay-time log and a neutron activated oxygen log to a reservoir formation traversed by the well bore. A purposeful change is then made in the oil saturation in a given region of the formation surrounding the well bore by injecting fluid under sufficient pressure to displace the connate fluids. This change can constitute the removal of substantially all the oil or the removal of as much oil as can be displaced by a proposed flooding technique. The combination of the thermal-neutron-decay-time log and the oxygen log is then run again to record the response of the same given region. The difference in the oil content around the well bore is then determined from the differences between the two sets of logs in a manner whose details are described hereinafter. The method can be modified to measure changes in fluid content over long periods by running the combination of the thermal-neutron-decaytime log and the oxygen log when knowledge about current saturations is desired. The oil content between the first and second logging runs can have been changed only by production of fluids from the reservoir.
Inventors
- 👤 C Neuman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 04:22
CPC Classifications
E; E21; E21B; E21B49/00; G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 45
Claim 1
Independent Claim
128 words
A method of measuring differences in fractional-volume oil content and differences in fractional-volume gas content of an earth formation constituting a given depth interval of the region surrounding a well bore, comprising 1. running a neutron-activation oxygen log and a thermalneutron-decay-time log over said given depth interval, 2. changing the oil content of said earth formation in said region surrounding the well bore, 3. then running a second oxygen log and a second thermalneutron-decay-time log over said given depth interval, and 4. calculating the desired differences in fractional-volume oil content and fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 2
Independent Claim
128 words
A method of measuring differences in fractional-volume oil content and differences in fractional-volume gas content of an earth formation constituting a given depth interval of the region surrounding a well bore, comprising 1. running a neutron-activation oxygen log and a thermalneutron-decay-time log over said given depth interval, 2. changing the oil content of said earth formation in said region surrounding the well bore, 3. then running a second oxygen log and a second thermalneutron-decay-time log over said given depth interval, and 4. calculating the desired differences in fractional-volume oil content and fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 3
Dependent Claim
15 words
changing the gas content of said earth formation in said region surrounding the well bore.
Claim 4
Dependent Claim
15 words
changing the gas content of said earth formation in said region surrounding the well bore.
Claim 5
Independent Claim
26 words
A method of measuring differences in fractional-volume gas content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 6
Independent Claim
26 words
A method of measuring differences in fractional-volume gas content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 7
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 8
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 9
Dependent Claim
15 words
changing the gas content of said earth formation in said region surrounding the well bore,
Claim 10
Dependent Claim
15 words
changing the gas content of said earth formation in said region surrounding the well bore,
Claim 11
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 12
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 13
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 14
Dependent Claim
15 words
changing the oil content of said earth formation in said region surrounding the well bore,
Claim 15
Independent Claim
26 words
A method of measuring differences in fractional-volume oil content of an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 16
Independent Claim
26 words
A method of measuring differences in fractional-volume oil content of an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 17
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 18
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 19
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 20
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 21
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 22
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 23
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 24
Dependent Claim
17 words
then running a second oxygen log and a second thermal-neutron-decay-time log over said given depth interval, and
Claim 25
Dependent Claim
18 words
then running a second oxygen log and a second thermal-neutron-decay time log over said given depth interval, and
Claim 26
Dependent Claim
18 words
then running a second oxygen log and a second thermal-neutron-decay time log over said given depth interval, and
Claim 27
Dependent Claim
188 words
calculating the desired difference in fractional-volume gas content of said earth formation by inserting the total capture cross sections determined in Steps (1) and (3), and the amplitudes of the signals from the oxygen log in Steps (1) and (3) into the Equation: phi (SG1 - SG2) (L2 - L1/K FW) (( Sigma O - Sigma W)/( Sigma O - Sigma G)) + ( Sigma 2 - Sigma 1/ Sigma O- Sigma G) where: the subscripts 1 and 2 refer to the conditions during the first and second measurements respectively, phi porosity of the formation expressed as a fraction. SG fraction of the pore volume containing gas L the amplitude of the signal from the oxygen log. K the calibration constant describing the response of the log to the oxygen content of the material in the formation. FW the oxygen content of water. Sigma W capure cross section of formation water. Sigma G capture cross section of formation gas. Sigma O capture cross section of the formation oil. Sigma 1 total capture cross section from the first measurement. Sigma 2 total capture cross section from the second measurement.
Claim 28
Dependent Claim
188 words
calculating the desired difference in fractional-volume gas content of said earth formation by inserting the total capture cross sections determined in Steps (1) and (3), and the amplitudes of the signals from the oxygen log in Steps (1) and (3) into the Equation: phi (SG1 - SG2) (L2 - L1/K FW) (( Sigma O - Sigma W)/( Sigma O - Sigma G)) + ( Sigma 2 - Sigma 1/ Sigma O- Sigma G) where: the subscripts 1 and 2 refer to the conditions during the first and second measurements respectively, phi porosity of the formation expressed as a fraction. SG fraction of the pore volume containing gas L the amplitude of the signal from the oxygen log. K the calibration constant describing the response of the log to the oxygen content of the material in the formation. FW the oxygen content of water. Sigma W capure cross section of formation water. Sigma G capture cross section of formation gas. Sigma O capture cross section of the formation oil. Sigma 1 total capture cross section from the first measurement. Sigma 2 total capture cross section from the second measurement.
Claim 29
Dependent Claim
46 words
calculating the desired differences in fractional-volume oil content and fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 30
Dependent Claim
46 words
calculating the desired differences in fractional-volume oil content and fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 31
Dependent Claim
186 words
calculating the desired fractional volume oil content of said earth formation by inserting the total capture cross-sections determined in steps (1) and (3), and the amplitudes of the signals from the oxygen log in Steps (1) and (3) into the Equation: phi (S01 - S02) (L2 - L1/K FW) (( Sigma W -Sigma G)/( Sigma O - Sigma G)) - ( Sigma 2 - Sigma 1/ Sigma O - Sigma G) where: the subscripts 1 and 2 refer to the conditions during the first and second measurements respectively, phi porosity of the formation expressed as a fraction. SO fraction of the pore volume containing oil. L the amplitude of the signal from the oxygen log. K the calibration constant describing the response of the log to the oxygen content of the material in the formation. FW the oxygen content of water. Sigma W capture cross section of formation water. Sigma G capture cross section of formation gas. Sigma O capture cross section of the formation oil. Sigma 1 total capture cross section from the first measurement. Sigma 2 total capture cross section from the second measurement.
Claim 32
Dependent Claim
186 words
calculating the desired fractional volume oil content of said earth formation by inserting the total capture cross-sections determined in steps (1) and (3), and the amplitudes of the signals from the oxygen log in Steps (1) and (3) into the Equation: phi (S01 - S02) (L2 - L1/K FW) (( Sigma W -Sigma G)/( Sigma O - Sigma G)) - ( Sigma 2 - Sigma 1/ Sigma O - Sigma G) where: the subscripts 1 and 2 refer to the conditions during the first and second measurements respectively, phi porosity of the formation expressed as a fraction. SO fraction of the pore volume containing oil. L the amplitude of the signal from the oxygen log. K the calibration constant describing the response of the log to the oxygen content of the material in the formation. FW the oxygen content of water. Sigma W capture cross section of formation water. Sigma G capture cross section of formation gas. Sigma O capture cross section of the formation oil. Sigma 1 total capture cross section from the first measurement. Sigma 2 total capture cross section from the second measurement.
Claim 33
Dependent Claim
42 words
calculating the desired difference in fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 34
Dependent Claim
42 words
calculating the desired difference in fractional-volume gas content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 35
Dependent Claim
28 words
The method of claim 3 in which the changing of the oil content in the second step includes the removal of substantially all the oil from said formation.
Claim 36
Dependent Claim
42 words
calculating the desired difference in fractional-volume oil content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 37
Dependent Claim
42 words
calculating the desired difference in fractional-volume oil content of said earth formation within said depth interval from the measured difference in oxygen response between Steps (1) and (3), and the determined difference in neutron capture cross section between Steps (1) and (3).
Claim 38
Dependent Claim
42 words
The method of claim 3 in which the changing of the oil content in the second step corresponds to a proposed flooding technique for said earth formation wherein a fluid is injected as a pilot test for a field-scale assisted recovery project.
Claim 39
Dependent Claim
37 words
The method of claim 3 in which the changing of the oil content in the second step includes production of the field to reduce the original fluid content of said earth formation over said given depth interval.
Claim 40
Dependent Claim
66 words
The method of claim 3 wherein Steps (1) to (4) are performed at least twice, the first time with Step (2) including flooding said region of said earth formation surrounding said well bore with a fluid proposed to be used for assisted recovery of oil from said formation, and the second time with Step (2) including the removal of substantially all the oil from said formation.
Claim 41
Dependent Claim
56 words
The method of claim 3 wherein Steps (1) and (4) are performed at least twice, the first time with Step (2) including production of oil from said earth formation over said given depth interval to reduce said oil content, and the second time with Step (2) including removal of substantially all the oil from said formation.
Claim 42
Independent Claim
26 words
A method of measuring differences in fractional-volume oil content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 43
Independent Claim
26 words
A method of measuring differences in fractional-volume oil content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 44
Independent Claim
26 words
A method of measuring differences in fractional-volume gas content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
Claim 45
Independent Claim
26 words
A method of measuring differences in fractional-volume gas content within an earth formation constituting a given depth interval of the region surrounding a well bore, comprising
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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) | 1977-06-17 | 1977-12-17 | 1978-06-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-06-17 | 1981-12-17 | 1982-06-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-06-17 | 1985-12-17 | 1986-06-18 | $7700.00 | Window Closed / Lapsed |