Neutron logging of formation porosity and chlorinity

Claim 1

A system for observing earth formation properties comprising: means for irradiating the earth formation with a pulse of high energy neutrons; means for detecting over a broad energy band gamma radiation produced by the inelastic scattering of said neutrons by nuclei of the formation elements during an interval of 10 Mu sec or less in the early part of said neutron pulse and for producing an output signal in response thereto; and circuit means for converting said inelastic gamma ray output signal, according to a predetermined relationship relating such inelastic gamma radiation signals to the hydrogenous matter content of earth formations, to provide an output signal indicative of a characteristic of the formation Under observation.

Claim 2

A system for observing earth formation properties comprising: means for irradiating the earth formation with a pulse of high energy neutrons; means for detecting over a broad energy band gamma radiation produced by the inelastic scattering of said neutrons by nuclei of the formation elements during an interval of 10 Mu sec or less in the early part of said neutron pulse and for producing an output signal in response thereto; and circuit means for converting said inelastic gamma ray output signal, according to a predetermined relationship relating such inelastic gamma radiation signals to the hydrogenous matter content of earth formations, to provide an output signal indicative of a characteristic of the formation Under observation.

Claim 9

A method for observing earth formation properties comprising the steps of: irradiating an earth formation with a pulse of high energy neutrons; observing over a wide energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during an interval of not more than 10 Mu sec early in the neutron pulse and generating an output signal in response thereto; observing the gamma radiation produced by the capture of thermal neutrons during a period that commences about two thermal neutron decay times after the termination of said neutron pulse and generating an output signal in response thereto; normalizing said inelastic gamma radiation output signal in accordance with said observed thermal neutron radiation signal to provide a normalized inelastic gamma radiation signal representative of the hydrogenous matter content of the formation; and indicating a property of an earth formation characterized by said normalized signal.

Claim 10

A method for observing earth formation properties comprising the steps of: irradiating an earth formation with a pulse of high energy neutrons; observing over a wide energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during an interval of not more than 10 Mu sec early in the neutron pulse and generating an output signal in response thereto; observing the gamma radiation produced by the capture of thermal neutrons during a period that commences about two thermal neutron decay times after the termination of said neutron pulse and generating an output signal in response thereto; normalizing said inelastic gamma radiation output signal in accordance with said observed thermal neutron radiation signal to provide a normalized inelastic gamma radiation signal representative of the hydrogenous matter content of the formation; and indicating a property of an earth formation characterized by said normalized signal.

Claim 13

A system for computing hydrogenous and neutron properties in an earth formation which has been irradiated with pulses of high energy neutrons comprising: a source of signals that characterize the neutron induced gamma radiation activity over a broad energy band in the earth formation during at least the neutron pulses; circuit means for measuring that portion of said characterizing signals that generally reflect inelastic neutron scattering gamma rays produced during an early part of said neutron pulses and for generating output signals in response thereto; normalizing means for compensating said output signals for variations in the strength of said neutron pulses to provide signals that are more nearly indicative of the hydrogenous properties of the earth formation; and hydrogenous property computation means for converting said normalized signals into output signals that are directly related to the hydrogenous character of the earth formation.

Claim 14

A system for computing hydrogenous and neutron properties in an earth formation which has been irradiated with pulses of high energy neutrons comprising: a source of signals that characterize the neutron induced gamma radiation activity over a broad energy band in the earth formation during at least the neutron pulses; circuit means for measuring that portion of said characterizing signals that generally reflect inelastic neutron scattering gamma rays produced during an early part of said neutron pulses and for generating output signals in response thereto; normalizing means for compensating said output signals for variations in the strength of said neutron pulses to provide signals that are more nearly indicative of the hydrogenous properties of the earth formation; and hydrogenous property computation means for converting said normalized signals into output signals that are directly related to the hydrogenous character of the earth formation.

Claim 17

A system for logging thermal neutron absorption and porosity characteristics of an earth formation penetrated by a borehole comprising: a housing for passage through the borehole; a neutron generator within said housing for producing pulses of high-energy neutrons to irradiate the earth formation; a gamma radiation detector within said housing and spaced from said generator for producing signals in response to a broad energy band of gamma radiation induced in the formation by said neutron pulses; circuit means responsive to selected detector signals for producing an output signal representative of inelastic neutron scattering gamma rays that occur following the initiation of each neutron pulse but before the influence of thermal neutron absorption gamma radiation becomes predominant; circuit means responsive to selected gamma radiation detector signals for producing signals that vary with the strength of the neutron generator; normalization circuit means responsive to said inelastic scattering gamma signals and said neutron generator strength signals for producing an inelastic scattering signal that has been compensated for neutron generator strength fluctuation; and further circuit means for converting said compensated signal into an output that is related to the earth formation porosity.

Claim 18

A system for logging thermal neutron absorption and porosity characteristics of an earth formation penetrated by a borehole comprising: a housing for passage through the borehole; a neutron generator within said housing for producing pulses of high-energy neutrons to irradiate the earth formation; a gamma radiation detector within said housing and spaced from said generator for producing signals in response to a broad energy band of gamma radiation induced in the formation by said neutron pulses; circuit means responsive to selected detector signals for producing an output signal representative of inelastic neutron scattering gamma rays that occur following the initiation of each neutron pulse but before the influence of thermal neutron absorption gamma radiation becomes predominant; circuit means responsive to selected gamma radiation detector signals for producing signals that vary with the strength of the neutron generator; normalization circuit means responsive to said inelastic scattering gamma signals and said neutron generator strength signals for producing an inelastic scattering signal that has been compensated for neutron generator strength fluctuation; and further circuit means for converting said compensated signal into an output that is related to the earth formation porosity.

Claim 19

A method for observing earth formation properties comprising the steps of: irradiating an earth formation with pulses of high-energy neutrons; detecting over a wide energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation elements during the time interval commencing after the initiation of each neutron pulse and terminating before thermal neutron absorption gamma radiation becomes predominant and generating an output signal in response thereto; and converting said inelastic gamma radiation output signal, in accordance with a previously established relationship relating such inelastic gamma radiation signals to the hydrogenous matter content of earth formations, to an output signal indicative of a characteristic of the formation under observation.

Claim 20

A method for observing earth formation properties comprising the steps of: irradiating an earth formation with pulses of high-energy neutrons; detecting over a wide energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation elements during the time interval commencing after the initiation of each neutron pulse and terminating before thermal neutron absorption gamma radiation becomes predominant and generating an output signal in response thereto; and converting said inelastic gamma radiation output signal, in accordance with a previously established relationship relating such inelastic gamma radiation signals to the hydrogenous matter content of earth formations, to an output signal indicative of a characteristic of the formation under observation.

Claim 24

A method for observing earth formation properties, comprising the steps of: repetitively irradiating an earth formation with pulses of high-energy neutrons; observing over a broad energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during a first time interval commencing with or after the initiation of each neutron pulse and terminating before thermal neutron absorption gamma radiation becomes predominant and generating a signal representative thereof; observing radiation produced by the interaction of said neutrons with the formation nuclei during a second time interval commencing with or after the initiation of each neutron pulse and generating a signal in response thereto that is representative of the strength of the neutron pulses; and combining said inelastic gamma radiation signal and said neutron pulse strength signal to normalize said inelastic gamMa radiation signal for variations in the neutron pulse strength.

Claim 25

A method for observing earth formation properties, comprising the steps of: repetitively irradiating an earth formation with pulses of high-energy neutrons; observing over a broad energy band the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during a first time interval commencing with or after the initiation of each neutron pulse and terminating before thermal neutron absorption gamma radiation becomes predominant and generating a signal representative thereof; observing radiation produced by the interaction of said neutrons with the formation nuclei during a second time interval commencing with or after the initiation of each neutron pulse and generating a signal in response thereto that is representative of the strength of the neutron pulses; and combining said inelastic gamma radiation signal and said neutron pulse strength signal to normalize said inelastic gamMa radiation signal for variations in the neutron pulse strength.

Claim 31

A system for observing earth formation properties, comprising: means for repetitively irradiating an earth formation with pulses of high-energy neutrons; means responsive over a broad energy band for measuring the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during a first time interval commencing with or after the initiation of each neutron pulse and terminating before thermal neutron gamma radiation become predominant and for generating a signal representative thereof; means responsive to radiation produced by the interaction of said neutrons with formation nuclei during a second time interval commencing with or after the initiation of each neutron pulse and for generating a signal in response thereto that is representative of the strength of the neutron pulses; and means for combining said gamma radiation measurement signal and said neutron pulse strength signal to normalize said gamma radiation measurement signal for variations in the neutron pulse strength.

Claim 32

A system for observing earth formation properties, comprising: means for repetitively irradiating an earth formation with pulses of high-energy neutrons; means responsive over a broad energy band for measuring the gamma radiation produced by inelastic scattering of said neutrons by nuclei of the earth formation during a first time interval commencing with or after the initiation of each neutron pulse and terminating before thermal neutron gamma radiation become predominant and for generating a signal representative thereof; means responsive to radiation produced by the interaction of said neutrons with formation nuclei during a second time interval commencing with or after the initiation of each neutron pulse and for generating a signal in response thereto that is representative of the strength of the neutron pulses; and means for combining said gamma radiation measurement signal and said neutron pulse strength signal to normalize said gamma radiation measurement signal for variations in the neutron pulse strength.