Methods and system for detecting subsurface minerals

Claim 1

A system for detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising an elongated steel housing adapted to be passed longitudinally through said borehole, a source disposed in said housing and emitting a flux of neutrons for bombarding nuclei in said formation, gamma ray detector means disposed in said housing and spaced from said source for generating electrical pulses functionally representative in occurrence and amplitude of the occurrence and energies of gamma rays in said borehole, a gamma ray shield disposed between said source and said detector, means for sorting pulses from said detector into a first pulse group composed of pulses with amplitudes corresponding to gamma rays within a first preselected energy range and into a second pulse group composed of pulses corresponding to gamma rays within a second lower preselected energy range, said first higher energy range being correlative with the energies of a substantial portion of the gamma rays resulting from thermal neutron capture reactions wIth sulfur nuclei in said formation and said second lower energy range being correlative with the energies of a substantial portion of the gamma rays resulting from thermal neutron capture reactions with nuclei of materials in the vicinity of the borehole but substantially above the 2.23 Mev hydrogen thermal capture gamma ray characteristic energy, and means for deriving an indication of the ratio of the rate of occurrence of said pulses in said first group to the rate of occurrence of said pulses in said second group.

Claim 2

A system for detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising an elongated steel housing adapted to be passed longitudinally through said borehole, a source disposed in said housing and emitting a flux of neutrons for bombarding nuclei in said formation, gamma ray detector means disposed in said housing and spaced from said source for generating electrical pulses functionally representative in occurrence and amplitude of the occurrence and energies of gamma rays in said borehole, a gamma ray shield disposed between said source and said detector, means for sorting pulses from said detector into a first pulse group composed of pulses with amplitudes corresponding to gamma rays within a first preselected energy range and into a second pulse group composed of pulses corresponding to gamma rays within a second lower preselected energy range, said first higher energy range being correlative with the energies of a substantial portion of the gamma rays resulting from thermal neutron capture reactions wIth sulfur nuclei in said formation and said second lower energy range being correlative with the energies of a substantial portion of the gamma rays resulting from thermal neutron capture reactions with nuclei of materials in the vicinity of the borehole but substantially above the 2.23 Mev hydrogen thermal capture gamma ray characteristic energy, and means for deriving an indication of the ratio of the rate of occurrence of said pulses in said first group to the rate of occurrence of said pulses in said second group.

Claim 8

A system for detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising an encapsulated source of radioactive material adapted to be longitudinally passed through said borehole and for bombarding said formation with neutrons, a radiation detector spaced a preselected distance from said source for detecting gamma rays in said borehole as a result of thermal neutron capture reactions with nuclei in said bombarded formation, pulse generating means responsive to said detector for generating electrical pulses functionally representative in occurrence and amplitude to the incidence and energies of said detected gamma rays, pulse sorting means responsive to said generating means and establishing a high energy window for passing only pulses with amplitudes within a first energy range and establishing a low energy window for passing only pulses with amplitudes within a second lower energy range, said energy ranges together encompassing those pulses having amplitudes corresponding to the expected energies of gamma rays resulting from thermal neutron capture reactions with nuclei of calcium, silicon, chlorine and iron, but not hydrogen in the vicinity of the borehole, said higher energy range further encompassing those pulses having amplitudes corresponding to the expected energies of gamma rays resulting from thermal neutron capture reactions with any nuclei of sulfur in said bombarded formation, first count rate means responsive to said high energy window in said pulse sorting means for determining the rate of occurrence of those pulses passed with amplitudes within said higher energy range, second count rate means responsive to said low energy window in said pulse sorting means for determining the rate of occurrence of those pulses passed with amplitudes within said lower energy range, and ratio means for deriving a recordable indication of the ratio of said rates of occurrence.

Claim 9

A system for detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising an encapsulated source of radioactive material adapted to be longitudinally passed through said borehole and for bombarding said formation with neutrons, a radiation detector spaced a preselected distance from said source for detecting gamma rays in said borehole as a result of thermal neutron capture reactions with nuclei in said bombarded formation, pulse generating means responsive to said detector for generating electrical pulses functionally representative in occurrence and amplitude to the incidence and energies of said detected gamma rays, pulse sorting means responsive to said generating means and establishing a high energy window for passing only pulses with amplitudes within a first energy range and establishing a low energy window for passing only pulses with amplitudes within a second lower energy range, said energy ranges together encompassing those pulses having amplitudes corresponding to the expected energies of gamma rays resulting from thermal neutron capture reactions with nuclei of calcium, silicon, chlorine and iron, but not hydrogen in the vicinity of the borehole, said higher energy range further encompassing those pulses having amplitudes corresponding to the expected energies of gamma rays resulting from thermal neutron capture reactions with any nuclei of sulfur in said bombarded formation, first count rate means responsive to said high energy window in said pulse sorting means for determining the rate of occurrence of those pulses passed with amplitudes within said higher energy range, second count rate means responsive to said low energy window in said pulse sorting means for determining the rate of occurrence of those pulses passed with amplitudes within said lower energy range, and ratio means for deriving a recordable indication of the ratio of said rates of occurrence.

Claim 14

A method of detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising bombarding said formation with a flux of neutrons, detecting gamma rays emanating from said bombarded formation and resulting from thermal neutron capture reactions with nuclei therein, generating electrical pulses functionally related in occurrence and amplitude to the incidence and energies of said detected gamma rays, sorting into a first group those pulses having amplitudes within a first preselected higher energy range, sorting into a second group those pulses having amplitudes within a second preselected lower energy range, said ranges together encompassing a substantial proportion of the detected gamma rays resulting from thermal neutron capture reactions with nuclei in the vicinity of the borehole but substantially exclusive of hydrogen capture gamma rays, said high energy range further encompassing the substantial portions of detected gamma rays resulting from thermal neutron capture reactions with nuclei of sulfur in said bombarded formation, and deriving a recordable indication of the ratio of the rate of occurrence of pulses in said first group to the rate of occurrence of pulses in said second group.

Claim 15

A method of detecting and measuring sulfur in a subsurface earth formation traversed by a borehole, comprising bombarding said formation with a flux of neutrons, detecting gamma rays emanating from said bombarded formation and resulting from thermal neutron capture reactions with nuclei therein, generating electrical pulses functionally related in occurrence and amplitude to the incidence and energies of said detected gamma rays, sorting into a first group those pulses having amplitudes within a first preselected higher energy range, sorting into a second group those pulses having amplitudes within a second preselected lower energy range, said ranges together encompassing a substantial proportion of the detected gamma rays resulting from thermal neutron capture reactions with nuclei in the vicinity of the borehole but substantially exclusive of hydrogen capture gamma rays, said high energy range further encompassing the substantial portions of detected gamma rays resulting from thermal neutron capture reactions with nuclei of sulfur in said bombarded formation, and deriving a recordable indication of the ratio of the rate of occurrence of pulses in said first group to the rate of occurrence of pulses in said second group.

Claim 20

A system for investigating the constituency of a subsurface earth formation traversed by a steel casing inserted in a borehole, comprising an elongated steel housing adapted to be passed longitudinally through said casing, a capsule disposed in the lower portion of said housing and containing a mixture of americium and beryllium, a scintillation counter disposed in said housing above said capsule and having a sodium iodide crystal about 4 inches long spaced from said capsule a distance of 15.5 inches measurable between the center of said crystal and the near side of the capsule, a gamma ray shield formed of a high density metal and disposed in said housing between said capsule and said crystal, a sheath of boron disposed about the portion of said housing surrounding said scintillation counter for blocking thermal neutrons in said borehole from engaging in capture reactions with iron nuclei in said housing, a logging cable for suspending said housing longitudinally in said casing and for conducting to the surface electrical pulses generated by said scintilLation counter in functional correlation with the incidence and energies of gamma rays entering said borehole and casing as a result of neutron capture reactions with nuclei of said earth formation, discriminating and sorting means located at the surface and interconnected with said cable for selecting and grouping into a first count rate signal those pulses having energies between 4.23 Mev. and 4.88 Mev. and for selecting and grouping into a second count rate signal those pulses having energies between 3.52 Mev. and 4.23 Mev., ratio means for deriving an analog ratio signal functionally related to the ratio of said first count rate signal to said second count rate signal, digital signalling means for forming said first and second count rate signals respectively into functionally related first and second digital signals and said analog ratio signals into a functionally related digital ratio signal, and recording means for correlatively recording said digital signals together with a functional indication of borehole depth.

Claim 21

A system for investigating the constituency of a subsurface earth formation traversed by a steel casing inserted in a borehole, comprising an elongated steel housing adapted to be passed longitudinally through said casing, a capsule disposed in the lower portion of said housing and containing a mixture of americium and beryllium, a scintillation counter disposed in said housing above said capsule and having a sodium iodide crystal about 4 inches long spaced from said capsule a distance of 15.5 inches measurable between the center of said crystal and the near side of the capsule, a gamma ray shield formed of a high density metal and disposed in said housing between said capsule and said crystal, a sheath of boron disposed about the portion of said housing surrounding said scintillation counter for blocking thermal neutrons in said borehole from engaging in capture reactions with iron nuclei in said housing, a logging cable for suspending said housing longitudinally in said casing and for conducting to the surface electrical pulses generated by said scintilLation counter in functional correlation with the incidence and energies of gamma rays entering said borehole and casing as a result of neutron capture reactions with nuclei of said earth formation, discriminating and sorting means located at the surface and interconnected with said cable for selecting and grouping into a first count rate signal those pulses having energies between 4.23 Mev. and 4.88 Mev. and for selecting and grouping into a second count rate signal those pulses having energies between 3.52 Mev. and 4.23 Mev., ratio means for deriving an analog ratio signal functionally related to the ratio of said first count rate signal to said second count rate signal, digital signalling means for forming said first and second count rate signals respectively into functionally related first and second digital signals and said analog ratio signals into a functionally related digital ratio signal, and recording means for correlatively recording said digital signals together with a functional indication of borehole depth.

Claim 22

A method of detecting and measuring sulfur in a subsurface earth formation traversed by a steel casing inserted in a borehole, comprising generating a flux of neutrons and gamma rays at a first location in said casing adjacent said formation, selectively interrupting and absorbing said gamma rays in said flux to permit substantially only said neturons to permeate through said casing and to slow to thermal energy in said formation. detecting at a second location in said casing spaced a preselected distance above said first location gamma rays produced by capture reactions engaged in between said neutrons and nuclei of said formation, selectively interrupting and absorbing at said second location neutrons arriving at said second location at thermal energy, generating electrical pulses having occurrences coincident with the detection of and having amplitudes corresponding to the energies of said gamma rays produced by capture reactions in said formation, selecting and forming into a first pulse train those pulses having energies greater than 4.23 Mev. but not greater than 4.88 Mev., selecting and forming into a second pulse train those pulses having energies greater than 3.52 Mev. but not greater than 4.23 Mev., deriving the ratio of the pulse rate of said first pulse train to the pulse rate of said second pulse train, and recording said derived ratio together with a correlative indication of the borehole depth of said first and second locations in said casing.

Claim 23

A method of detecting and measuring sulfur in a subsurface earth formation traversed by a steel casing inserted in a borehole, comprising generating a flux of neutrons and gamma rays at a first location in said casing adjacent said formation, selectively interrupting and absorbing said gamma rays in said flux to permit substantially only said neturons to permeate through said casing and to slow to thermal energy in said formation. detecting at a second location in said casing spaced a preselected distance above said first location gamma rays produced by capture reactions engaged in between said neutrons and nuclei of said formation, selectively interrupting and absorbing at said second location neutrons arriving at said second location at thermal energy, generating electrical pulses having occurrences coincident with the detection of and having amplitudes corresponding to the energies of said gamma rays produced by capture reactions in said formation, selecting and forming into a first pulse train those pulses having energies greater than 4.23 Mev. but not greater than 4.88 Mev., selecting and forming into a second pulse train those pulses having energies greater than 3.52 Mev. but not greater than 4.23 Mev., deriving the ratio of the pulse rate of said first pulse train to the pulse rate of said second pulse train, and recording said derived ratio together with a correlative indication of the borehole depth of said first and second locations in said casing.