US3780302A
Expired / Lapsed
US
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Pulsed neutron logging system
Assignee: Texaco Inc
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Filing: 1971-09-20
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Granted: 1973-12-18
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Expires: 1991-09-20
Abstract
Abstract An illustrative embodiment of the invention includes improved nuclear well logging methods and apparatus for investigating subsurface earth formations. A pulsed neutron generator is used to irradiate the earth formations and the gamma rays caused by the inelastically scattered neutrons are observed in four energy windows. The carbon/oxygen ratio and the silicon/calcium ratio and the counting rate in each window are obtained and used to resolve ambiguities in the oil/water content of the formations by appropriately combining the measurements to obtain the lime factor or fraction and the water saturation SW of the formations, which quantities are then recorded as a function of the borehole depth.
Inventors
- 👤 H Smith
- 👤 D Arnold
- 👤 W Schultz
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 16:40
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
90 words
A method of determining the water saturation of earth formations surrounding a well bore comprising the steps of: determining the fractional content of sand and lime in the formation matrix; determining the porosity of the formation; determining the carbon/oxygen counts ratio in the inelastic gamMa ray energy spectrum in regions thereof corresponding to carbon and oxygen inelastic gamma ray and combining the fractional content of sand and lime, the porosity of the formation, and the carbon/oxygen counts ratio in a predetermined manner to compute the water saturation of the matrix.
Claim 2
Independent Claim
90 words
A method of determining the water saturation of earth formations surrounding a well bore comprising the steps of: determining the fractional content of sand and lime in the formation matrix; determining the porosity of the formation; determining the carbon/oxygen counts ratio in the inelastic gamMa ray energy spectrum in regions thereof corresponding to carbon and oxygen inelastic gamma ray and combining the fractional content of sand and lime, the porosity of the formation, and the carbon/oxygen counts ratio in a predetermined manner to compute the water saturation of the matrix.
Claim 3
Dependent Claim
52 words
The method of claim 1 wherein the step of determining the fractional content of sand and lime in the formation matrix is performed by repetitively irradiating the matrix with high energy neutron pulses and measuring gamma radiation due to the inelastic scattering of neutrons by the formation matrix in plural energy ranges.
Claim 4
Dependent Claim
32 words
The method of claim 2 wherein said plural energy ranges are chosen to include gamma radiation resulting from the inelastic scattering of high energy neutrons by carbon, oxygen, silicon and calcium nuclei.
Claim 5
Dependent Claim
42 words
The method of claim 3 wherein the energy ranges are chosen to be 3.17 MEV to 4.65 MEV for carbon, 4.86 MEV to 6.34 MEV for oxygen, 1.65 MEV to 1.86 MEV for silicon and 2.5 MEV to 3.3 MEV for calcium.
Claim 6
Dependent Claim
115 words
The method of claim 1 wherein the step of determining the lime fraction LFX of an unknown formation X, is performed by measuring the counts ratio RX of silicon/calcium counts resulting from gamma radiation due to inelastic fast neutron scattering in energy regions in the gamma ray spectrum corresponding to the production of such gamma radiation by silicon and calcium nuclei in the unknown formation, and combining this measurement according to the relationship LFX (RS - RX)/(RS - RL) where RS is the silicon/calcium counts ratio taken with the same instrumentation in a known water sand formation and RL is the silicon/calcium counts ratio taken with the same instrumentation in a known water lime formation.
Claim 7
Dependent Claim
22 words
The method of claim 5 and further including the step of logging the lime fraction LFX as a function of borehole depth.
Claim 8
Dependent Claim
65 words
The method of claim 1 wherein the step of determining the formation porosity is done by computing the porosity phi in a predetermined manner as a function of the count rates CR in energy regions of the gamma ray energy spectrum corresponding to known gamma ray energies produced by the inelastic scattering of high energy neutrons by the nuclei of carbon, oxygen, silicon and calcium.
Claim 9
Dependent Claim
52 words
The method of claim 7 wherein the porosity phi is computed from said count rate CR according to the relationship phi M e N CR where M and N are predetermined calibration constants for a particular logging tool and borehole size and the constant e 2.718- - -, the Naperian logorithm base.
Claim 10
Dependent Claim
16 words
The method of claim 8 wherein CR is the count rate from the carbon window only.
Claim 11
Dependent Claim
26 words
The method of claim 8 and further including the step of logging the porosity phi as a function of the borehole depth of a well tool.
Claim 12
Dependent Claim
114 words
The method of claim 1 wherein the step of combining the fractional content of sand and lime, the formation porosity, and the carbon/oxygen counts ratio to compute the water saturation SW of the formation is performed by linearly interpolating by an amount (K.LFX), where K is a predetermined constant and LFX is the measured lime fraction in the unknown formation, between two preselected carbon/oxygen counts ratio functions, f1( phi ) and f2( phi ), where f1( phi ) is a function of porosity phi , expressing the carbon/oxygen counts ratio in a water sand and f2( phi ) is a function of porosity phi , expressing the carbon/oxygen counts ratio in an oil sand.
Claim 13
Dependent Claim
25 words
The method of claim 11 wherein the function f1( phi ) and f2( phi ) are preselected to be polynomial functions of porosity phi .
Claim 14
Dependent Claim
27 words
The method of claim 11 and further Including the step of logging the water saturation SW as a function of the borehole depth of a well tool.
Claim 15
Dependent Claim
42 words
The method of claim 1 and further including the step of logging the water saturation SW, the porosity phi , the carbon/oxygen counts ratio and the Si/Ca counts ratio all simultaneously as a function of the borehole depth of a well tool.
Claim 16
Independent Claim
142 words
A method of determining the characteristics of earth formations penetrated by a well borehole comprising the steps of: passing a well tool having a pulsed neutron source and a gamma ray detector through a well bore; repetitively irradiating the earth formations surrounding the well bore with high energy neutrons; measuring the count rates of inelastic gamma rays in the gamma ray energy spectrum in energy regions thereof corresponding to carbon, oxygen, silicon and calcium nuclei excited by the high energy neutron pulses; determining the carbon/oxygen count rate ratio of the formation; determining, from the silicon and calcium count rates, the lime fraction of the formation; determining, from at least one of the above count rates, the formation porosity; and combining the lime fraction, the carbon/oxygen ratio and the porosity data to derive the water saturation of the formations penetrated by the borehole.
Claim 17
Independent Claim
142 words
A method of determining the characteristics of earth formations penetrated by a well borehole comprising the steps of: passing a well tool having a pulsed neutron source and a gamma ray detector through a well bore; repetitively irradiating the earth formations surrounding the well bore with high energy neutrons; measuring the count rates of inelastic gamma rays in the gamma ray energy spectrum in energy regions thereof corresponding to carbon, oxygen, silicon and calcium nuclei excited by the high energy neutron pulses; determining the carbon/oxygen count rate ratio of the formation; determining, from the silicon and calcium count rates, the lime fraction of the formation; determining, from at least one of the above count rates, the formation porosity; and combining the lime fraction, the carbon/oxygen ratio and the porosity data to derive the water saturation of the formations penetrated by the borehole.
Claim 18
Dependent Claim
34 words
The method of claim 15 wherein the neutron pulses have as short a duration as practicable to eliminate interference in the inelastic gamma ray energy spectrum from the buildup of a thermal neutron population.
Claim 19
Dependent Claim
43 words
The method of claim 15 and further including the step of recording the water saturation SW, the porosity phi , the C/O ratio and the Si/Ca ratio as a function of borehole depth of said well tool as it moves through the borehole.
Claim 20
Dependent Claim
59 words
The method of claim 15 wherein said energy regions corresponding to inelastic gamma rays emitted by excited carbon, oxygen, silicon and calcium are located approximately at the energy range of 3.17 MEV to 4.65 MEV for carbon, 4.86 MEV to 6.34 MEV for oxygen, 1.65 MEV to 1.86 MEV for silicon, and 2.5 MEV to 3.3 MEV for calcium.
Claim 21
Dependent Claim
76 words
The method of claim 15 wherein the step of combining the lime fraction, the carbon/oxygen ratio and the porosity to compute the water saturation SW is performed by linearly interpolating between two preselected carbon/oxygen ratio functions, f1( phi ) and f2( phi ) where f1 and f2 are functions of the porosity phi expressing the carbon/oxygen counts ratio in an oil sand and a water sand respectively, by an amount related directly to the lime fraction.
References Cited (Backward Citations)
US3483376A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-12-17 | 1977-06-18 | 1977-12-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-17 | 1981-06-18 | 1981-12-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-17 | 1985-06-18 | 1985-12-18 | $7700.00 | Window Closed / Lapsed |