US3780301A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Pulsed neutron logging systems for detecting gas zones
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 methods and apparatus for producing inelastic neutron scattering logs of earth formations surrounding a well borehole. The gamma rays emitted by nuclei of at least carbon, oxygen, silicon and calcium which are excited by inelastically scattered fast neutrons are observed by energy separation and are individually logged as a function of borehole depth. The silicon/calcium and carbon/oxygen inelastic gamma ray counts ratios are also logged as a function of borehole depth. Low hydrogen content of the formations may be estimated by detecting a high count rate in each of the four energy windows and then by comparing the Si/Ca and C/O ratios in these regions to the Si/Ca and C/O ratios for a known water sand, the relative abundance of limestone in the low hydrogen content formations may be estimated thus distinguishing gas zones from water saturated low porosity limestone.
Inventors
- 👤 H Smith
- 👤 D Arnold
- 👤 W Schultz
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 15:35
CPC Classifications
G; G01; G01V; G01V5/00; G01V5/04; G01V5/08; G01V5/10; G01V5/101; G01V5/102
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
93 words
The method of claim 1 wherein the step of computing the approximate proportion of limestone in said formations is performed by comparing the carbon/oxygen and silicon/calcium ratios for a formation being investigated with corresponding carbon/oxygen and silicon/calcium ratios for a known water saturated sand in the well and, if the carbon/oxygen ratio for the investigated formation is greater than in the known water sand and the silicon/calcium ratio for the investigated formation lower that in the known water sand, deriving a high value for the approximate proportion of limestone in said investigated formation.
Claim 2
Dependent Claim
70 words
The method of claim 1 wherein the step of determining the location of relatively low hydrogen content formation iS performed by passing a well tool having a pulsed source of fast neutrons and a gamma ray detector through the borehole and measuring in preselected regions of the gamma ray energy spectrum, the number of gamma ray counts produced by inelastically scattered fast neutrons from the materials surrounding the well borehole.
Claim 3
Dependent Claim
43 words
The method of claim 3 wherein said preselected energy regions in the gamma ray energy spectrum are chosen to include energy regions for gamma rays produced by the nuclei of carbon, oxygen, silicon and calcium excited by the inelastic scattering of fast neutrons.
Claim 4
Dependent Claim
52 words
The method of claim 4 and further including the step of recording as a function of the borehole depth of said well tool, the counts occurring in each of said preselected energy regions of the gamma ray spectrum due to the inelastic neutron scattering excited nuclei of carbon, oxygen, silicon and calcium.
Claim 5
Dependent Claim
46 words
The method of claim 5 and further including the step of recording as a function of the borehole depth of said well tool the ratio of counts due to inelastic gamma rays occurring in the carbon/oxygen and silicon/calcium energy regions of the gamma ray energy spectrum.
Claim 6
Dependent Claim
84 words
The method of claim 1 wherein the step of computing the approximate proportion of limestone in said formation includes the step of determining beforehand the carbon/oxygen and silicon/calcium inelastic neutron scattering gamma ray counts ratios for a known water sand in the well to establish a calibration base and the step of comparing the carbon/oxygen and silicon/calcium inelastic neutron scattering gamma ray counts ratio of the earth formation being investigated to said calibration base to determine the approximate limestone content of said investigated formation.
Claim 7
Independent Claim
162 words
A method for performing radiological well surveys to distinguish natural hydrocarbon gas bearing zones from lower porosity water saturated limestone zomes in a well, comprising the steps of: passing a well tool having a pulsed neutron source and a gamma ray detector through a well bore; repetitively iradiating the earth formation surrounding the well bore with relatively short duration pulses of fast neutrons; detecting, primarily during said neutron pulses, gamma radiation resulting from a plurality of preselected nuclei in formations surrounding said well bore being excited by inelastically scattered neutron; determining, based on said detected radiation, the location in the well of relatively low hydrogen content formations; determining from said detected radiation the relative ratios of inelastic gamma ray counts of at least two preselected sets of elements in said relatively low hydrogen content formations surrounding the borehole; and computing, based on said ratios, the approximate proportion of limestone in said formation, thereby distinguishing gas zones from low porosity water saturated limestones.
Claim 8
Dependent Claim
24 words
The method of claim 8 wherein said preselected nuclei whose excitation by inelastically scattered neutron is measured include carbon, oxygen, silicon and calcium nuclei.
Claim 9
Dependent Claim
73 words
The method of claim 9 wherein the step of determining the location of relatively low hydrogen content formations is performed by logging, as a function of depth of said well tool, the count rates of inelastic gamma rays from each of said carbon, oxygen, silicon and calcium energy regions of the gamma ray energy spectrum and determining the zones in which the count rates in each of these energy regions is relatively high.
Claim 10
Dependent Claim
70 words
The method of claim 9 wherein the step of computing, based on said ratios, the approximate proportion of limestone in said formation is performed by comparing the relative carbon/oxygen inelastic gamma ray counts ratio and the relative silicon/calcium counts ratio from a known water sand in the well to the same ratios from the formation under investigation, to thereby estimate the abundance of limestone relative to said known water sand.
Claim 11
Dependent Claim
27 words
The method of claim 11 wherein said carbon/oxygen and said silicoN/calcium counts ratios are also logged as a function of the borehole depth of said logging tool.
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 |