Carbon/oxygen well logging method and apparatus

Claim 3

The method of claim 1 for further determining the percentage of hydrocarbons C b of materials in and of said borehole, comprising the further step of from said step of comparing said near and far inelastic gamma ray spectrum signals respectively with predetermined model representations of said borehole and said formation, producing a representation of said percentage of hydrocarbons of materials in and of said borehole corrected for gamma rays produced by said nuclear rections between said fast neutrons and said formation.

Claim 4

The method of claim 2 wherein its steps are repeated at different depths in the well bore and a signal S 0 proportional to said representation of said percentage of hydrocarbons in said formation is recorded as a function of well bore depth.

Claim 5

The method of claim 2 wherein its steps are repeated at different depths in the well bore and a signal C b proportional to said representation of said percentage of hydrocarbons or materials in and of said borehole is recorded as a function of well bore depth.

Claim 6

The method of claim 2 wherein a signal proportional to 1-S 0 is produced and recorded as a function of well bore depth to indicate water saturation S w of said formation.

Claim 9

The method of claim 6 wherein said formation characteristic is the percentage of hydrocarbons in the formation.

Claim 10

The method of claim 7 further comprising the step of determining a characteristic of the contents of the borehole.

Claim 11

The method of claim 6 wherein its steps are repeated at different depths in the well bore and said characteristic is recorded as a function of well bore length.

Claim 12

The method of claim 6 further comprising the steps of shielding said near detector so that it is primarily sensitive to gamma rays enamating from said borehole, and shielding said far detector so that it is primarily sensitive to gamma rays emanating from said formation.

Claim 15

The method of claim 11 further comprising the step of determining a formation corrected carbon-oxygen ratio of said borehole by combining said estimates in a predetermined reltionship.

Claim 16

The method of claim 11 wherein its steps are repeated at different depths in the well bore and said borehole corrected carbon-oxygen ratio is recorded as a function of well bore length.

Claim 17

The method of claim 11 further comprising the steps of shielding said near detector so that it is primarily sensitive to gamma rays emanating from said borehole, and shielding said far detector so that it is primarily sensitive to gamma rays emanating from said formation.

Claim 18

A well logging apparatus for determining a characteristic of a formation traversed by a borehole, comprising: an elongated housing sleeve, a source of fast neutrons mounted in said housing sleeve, a near detector disposed in said housing sleeve longitudinally at a first distance from said source for producing signals representative of gamma rays produced during inelastic nuclear reactions between said neutrons and materials around said source, a far detector disposed in said housing sleeve longitudinally at a second distance from said source greater than said first distance for producing signals representative of gamma rays produced during inelastic nuclear reactions between said neutrons and materials around said source, means responsive to said near and far detector signals for generating a signal representative of said formation characteristic, and means for enhancing the sensitivity of said near gamma ray detector to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.

Claim 19

A well logging apparatus for determining a characteristic of a formation traversed by a borehole, comprising: an elongated housing sleeve, a source of fast neutrons mounted in said housing sleeve, a near detector disposed in said housing sleeve longitudinally at a first distance from said source for producing signals representative of gamma rays produced during inelastic nuclear reactions between said neutrons and materials around said source, a far detector disposed in said housing sleeve longitudinally at a second distance from said source greater than said first distance for producing signals representative of gamma rays produced during inelastic nuclear reactions between said neutrons and materials around said source, means responsive to said near and far detector signals for generating a signal representative of said formation characteristic, and means for enhancing the sensitivity of said near gamma ray detector to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.

Claim 20

The apparatus of claim 15 wherein said near detector includes a scintillation crystal disposed in said housing, said enhancing means including a generally cylindrical gamma ray shield placed between said source and said scintillation crystal, said shield having a frusto-conical shape facing said crystal.

Claim 21

The apparatus of claim 16 wherein said near detector is covered with a boron shield.

Claim 22

The apparatus of claim 16 wherein said far detector is covered with a boron shield.

Claim 23

The apparatus of claim 15 wherein said housing sleeve defines an internal housing diameter and a housing axis, and wherein said near detector includes a cylindrical scintillation crystal and a cylindrical photomultiplier tube, said crystal and said tube abutting each other and having their axes aligned, said aligned axes defining a detector axis, said crystal and tube being disposed within said housing sleeve with said crystal disposed between said source and said tube, and said borehole enhancing means includes means for mounting said crystal and tube within said housing with said detector axis parallel to but offset from said housing axis, said tube having a diameter less than that of said housing internal diameter such that an external longitudinal edge of said tube substantially coincides with an internal longitudinal edge of said housing sleeve, the space between the outside of said tube and the inside of said sleeve defining a back space, and a gamma ray shield including a lower cylindrical portion disposed within said housing between said crystal and said source, and an upper back shield portion disposed in said back space.

Claim 24

The apparatus of claim 19 wherein said back shield portion and said lower cylindrical portion are integrally connected by a connecting portion having a downwardly sloping surface from said back shield portion to said cylindrical portion and facing said external longitudinal edge, said surface disposed beneath said crystal.

Claim 25

The apparatus of claim 15 wherein said housing sleeve defines an internal housing diameter and a housing axis, wherein said near detector includes a near cylindrical scintillation crystal and a near cylindrical photomultiplier tube, said crystal and said tube abutting each other and having their axes aligned, said aligned axes defining a detector axis, with said near crystal and near tube being disposed within said housing sleeve with said near crystal disposed between said source and said tube, and said near crystal and near tube being mounted coaxially with said housing axis within said housing, said near tube having a diameter less than that of said housing diameter, a space between the outside of said tube and the inside of said sleeve defining a back space, and wherein said borehole sensitivity enhancing means includes a gamma ray shield including a lower cylindrical portion disposed within said housing sleeve between said near crystal and said source, an upper back shield portion disposed in said back space, a sleeve portion connected to said back shield portion and extending longitudinally to a position below said crystal, said sleeve having longtiduinally extending angular opening in its wall, and a connecting portion between said lower cylindrical portion and said sleeve portion having a downwardly sloping surface from the bottom of said sleeve portion to the top of said cylindrical portion, said surface facing in the same direction as said angular opening in the wall of said sleeve portion and said surface disposed substantially beneath said angular opening in said sleeve portion wall and beneath said crystal.

Claim 26

The apparatus of claim 21 wherein said gamma ray shield further includes a top cap portion disposed above said backshield portion and above said tube.

Claim 27

The apparatus of claim 15 wherein said housing sleeve defines an internal housing diameter and a housing axis, wherein, said near detector includes a near cylindrical scintillation crystal and a near cylindrical photomultiplier tube, said crystal and said tube abutting each other and having their axes aligned, said aligned axes defining a detector axis, with said near crystal and near tube being disposed within said housing sleeve with said near crystal disposed between said source and said tube, and said near cyrstal and near tube being mounted coaxially with said housing axis within said housing, said near tube having a diameter less than that of said housing diameter, a space between the outside of said tube and the inside of said sleeve defining a back space, and said borehole enhancing means including a gamma ray shield including a lower cylindrical portion disposed within said housing sleeve between said crystal and said source, and an upper backshield portion disposed in said back space, said backshield portion and said lower cylindrical portion being separated by a longitudinal space substantially corresponding to the longitudinal placement of said crystal.

Claim 28

The apparatus of claim 23 further including a cylindrical top cap portion disposed above said backshield portion and above said tube.

Claim 29

The apparatus of claim 15 further comprising borehole sensitivity abating means for decreasing the sensitivity of said far gamma ray detector means to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.

Claim 30

The apparatus of claim 25 wherein said housing sleeve defines a housing axis, and wherein said near detector includes a near scintillation crystal and a near photomultiplier tube disposed at a near distance from said source, said far detector includes a far scintillation crystal and a far photomultiplier tube disposed a greater distance from said source than said near crystal and tube, and said borehole sensitivity abating means includes a first gamma ray shield disposed adjacent said far scintillation crystal about the outside of said housing sleeve, said first shield extending longitudinally from a position beneath said far crystal to a position above said far crystal, said shield being transparent to gamma rays through an angular segment of the periphery of said housing and being opaque of gamma rays around the remainer of the periphery of said housing.

Claim 31

The apparatus of claim 26 wherein said borehole sensitivity abating means further includes a second gamma ray opaque shield having a generally cylindrical shape with a diameter substantially the same as an internal diameter of said housing sleeve, said second shield being disposed between said near photomultiplier and saif far crystal.

Claim 32

The apparatus of claim 27 wherein said first shield extends longitudinally from a position beneath said second shield to a position above said far crystal.

Claim 33

Well logging apparatus for determining a characteristic of a formation traversed by a well bore comprising, a housing sleeve adapted for translation in said well bore, a source of fast neutrons mounted in said housing sleeve, means, including a scintillation crystal and phototube assembly means disposed in said housing sleeve longitudinally from said source, for producing signals representative of gamma rays produced during nuclear reactions between said fast neutrons and materials in and of said well bore and said formation, means for reducing the effects of magnetic fields in said well bore on said signals producing means, and means responsive to said produced signals for generating a signal representation of said characteristic of said formation.

Claim 34

Well logging apparatus for determining a characteristic of a formation traversed by a well bore comprising, a housing sleeve adapted for translation in said well bore, a source of fast neutrons mounted in said housing sleeve, means, including a scintillation crystal and phototube assembly means disposed in said housing sleeve longitudinally from said source, for producing signals representative of gamma rays produced during nuclear reactions between said fast neutrons and materials in and of said well bore and said formation, means for reducing the effects of magnetic fields in said well bore on said signals producing means, and means responsive to said produced signals for generating a signal representation of said characteristic of said formation.

Claim 35

The apparatus of claim 29 wherein said reducing means includes a first cylinder of a high magnetic permeability material enveloping said scintillation crystal and phototube assembly.

Claim 36

The apparatus of claim 30 wherein said reducing means further includes a second cylinder of high magnetic saturation enveloping said first cylinder.

Claim 37

The apparatus of claim 29 wherein said signals producing means includes means, including a near scintillation crystal and phototube assembly disposed in said housing sleeve longitudinally from said source, for producing near detector signals representative of gamma rays produced during nuclear reactions between said fast neutrons and materials in and of said well bore and said formations, and means, including a far scintillation crystal and phototube assembly means disposed in said housing sleeve longitudinally further from said source than said near crystal and phototube assembly, for producing far detector signals representative of gamma rays produced during nuclear reactions between said fast neutrons and materials in and of said well bore and said formation.

Claim 38

The apparatus of claim 32 wherein said reducing means further includes a respective first and second cylinders of high magnetic permeability enveloping respective ones of said near and far crystal and phototube assemblies.

Claim 39

Well logging apparatus for determining a characteristic of a formation traversed by a well bore comprising, a housing sleeve adapted for translation in said well bore, a source of pulsed fast neutrons mounted in said housing sleve, means, including near gamma ray detector disposed in said housing sleeve, longitudinally from said source, for producing near detector signals representative of gamma rays produced during inelastic nuclear reactions between said fast neutrons and materials in and out said well bore and said formation. means, including far gamma ray detector disposed in said housing sleeve longitudinally further from said source than said near gamma ray detector means, for producing far detector signals representative of gamma rays produced during inelastic nuclear reactions between said fast neutrons and materials in and of said borehole and said formation, means responsive to said near detector signals and said far detector signals for generating a signal representative of a characteristic of said formation substantially corrected for the gamma rays produced by nuclear reactions between said fast neutrons and materials in and of said borehole, and enhancing means for increasing the sensitivity of said near gamma ray detector means to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.

Claim 40

Well logging apparatus for determining a characteristic of a formation traversed by a well bore comprising, a housing sleeve adapted for translation in said well bore, a source of pulsed fast neutrons mounted in said housing sleve, means, including near gamma ray detector disposed in said housing sleeve, longitudinally from said source, for producing near detector signals representative of gamma rays produced during inelastic nuclear reactions between said fast neutrons and materials in and out said well bore and said formation. means, including far gamma ray detector disposed in said housing sleeve longitudinally further from said source than said near gamma ray detector means, for producing far detector signals representative of gamma rays produced during inelastic nuclear reactions between said fast neutrons and materials in and of said borehole and said formation, means responsive to said near detector signals and said far detector signals for generating a signal representative of a characteristic of said formation substantially corrected for the gamma rays produced by nuclear reactions between said fast neutrons and materials in and of said borehole, and enhancing means for increasing the sensitivity of said near gamma ray detector means to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.

Claim 41

The apparatus of claim 34 further comprising borehole sensitivity abating means for decreasing the sensitivity of said far gamma ray detector means to gamma rays produced during said inelastic nuclear reactions between said fast neutrons and materials in and of said borehole.