Systems for neutron decay time well logging

Claim 2

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutron pulses; detector means for generating a plurality of electrical pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; and digital-counting means for adding at least a portion of those electrical pulses which are generated during a selected time interval after irradiation with a given neutron pulse and subtracting at least a portion of those electrical pulses which are generated during another time interval after irradiation with said given neutron pulse whereby the accumulated count in said digital counting means will be representative of a formation characteristic.

Claim 3

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; means for passing at least a portion of those pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for adding said first interval pulses and subtracting said second interval pulses from said first time interval pulses to produce an accumulated count in said counting means after each irradiation; and means responsive to the accumulated count of said counting means after each irradiation for adjusting said first and second time intervals until said accumulated count assumes a substantially constant level for each repetitive irradiation, said time intervals being representative of a formation characteristic.

Claim 4

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; means for passing at least a portion of those pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for adding said first interval pulses and subtracting said second interval pulses from said first time interval pulses to produce an accumulated count in said counting means after each irradiation; and means responsive to the accumulated count of said counting means after each irradiation for adjusting said first and second time intervals until said accumulated count assumes a substantially constant level for each repetitive irradiation, said time intervals being representative of a formation characteristic.

Claim 5

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation after each repetitive irradiation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least a portion of those pulses generated during a first time interval after each irradiation and at least a portion of those pulses generated during a second time interval after each irradiation; digital-counting means for adding said first interval pulses and subtracting said second interval pulses to produce an accumulated count in said counting means; means responsive to said accumulated count for generating a control signal having a frequency representative of said accumulated count; means responsive to said control signal for energizing said gating means, the frequency of said control signal determining said first and second time intervals; and means responsive to the period of said control signal for indicating the rate of decay of the neutron population in a formation.

Claim 6

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation after each repetitive irradiation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least a portion of those pulses generated during a first time interval after each irradiation and at least a portion of those pulses generated during a second time interval after each irradiation; digital-counting means for adding said first interval pulses and subtracting said second interval pulses to produce an accumulated count in said counting means; means responsive to said accumulated count for generating a control signal having a frequency representative of said accumulated count; means responsive to said control signal for energizing said gating means, the frequency of said control signal determining said first and second time intervals; and means responsive to the period of said control signal for indicating the rate of decay of the neutron population in a formation.

Claim 7

Apparatus for investigating earth formations traversed by a borehole, comprising: means repetitively for irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least a portion of those pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for counting the pulses passed by said gating means; means responsive to the accumulated count of said counting means after said first and second time interval pulses have been counted for generating a control signal having a frequency representative of said accumulated count; and means responsive to said control signal for energizing said gating means to pass said first and second series of pulses to said counting means and complementing said counting means before and after said second time interval so that said second series of pulses will be subtracted from said first series of pulses to produce an accumulated count representative of a formation characteristic.

Claim 8

Apparatus for investigating earth formations traversed by a borehole, comprising: means repetitively for irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least a portion of those pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for counting the pulses passed by said gating means; means responsive to the accumulated count of said counting means after said first and second time interval pulses have been counted for generating a control signal having a frequency representative of said accumulated count; and means responsive to said control signal for energizing said gating means to pass said first and second series of pulses to said counting means and complementing said counting means before and after said second time interval so that said second series of pulses will be subtracted from said first series of pulses to produce an accumulated count representative of a formation characteristic.

Claim 9

Apparatus for investigating earth formations traversed by a borehole, comprising: means for irradiating a formation with neutrons and generating a sync pulse representative of the occurrence of said irradiation; detector means for generaTing a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population arising from said irradiation; means for adding at least a portion of those pulses which are generated during a first time interval after irradiation and subtracting at least a portion of those pulses which are generated during a second time interval after irradiation to produce a control signal; means responsive to said control signal for adjusting said first and second time intervals, the frequency of said control signal being representative of a formation characteristic; and converting means responsive to said control signal for generating an output signal representative of the period of said control signal to provide a measure of another formation characteristic, said converting means including: means for dividing the frequency of said control signal by a given factor; sawtooth generator means responsive to the divided control signal for generating a sawtooth wave having a constant voltage slope and a peak amplitude representative of the period of said control signal; means responsive to said peak amplitude for generating said output signal representative of the period; and means for resetting said frequency-dividing means with said sync pulse to thereby synchronize the phase of said sawtooth wave with said sync pulse.

Claim 10

Apparatus for investigating earth formations traversed by a borehole, comprising: means for irradiating a formation with neutrons and generating a sync pulse representative of the occurrence of said irradiation; detector means for generaTing a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population arising from said irradiation; means for adding at least a portion of those pulses which are generated during a first time interval after irradiation and subtracting at least a portion of those pulses which are generated during a second time interval after irradiation to produce a control signal; means responsive to said control signal for adjusting said first and second time intervals, the frequency of said control signal being representative of a formation characteristic; and converting means responsive to said control signal for generating an output signal representative of the period of said control signal to provide a measure of another formation characteristic, said converting means including: means for dividing the frequency of said control signal by a given factor; sawtooth generator means responsive to the divided control signal for generating a sawtooth wave having a constant voltage slope and a peak amplitude representative of the period of said control signal; means responsive to said peak amplitude for generating said output signal representative of the period; and means for resetting said frequency-dividing means with said sync pulse to thereby synchronize the phase of said sawtooth wave with said sync pulse.

Claim 11

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutron pulses; detector means for generating a plurality of electrical pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; and means for adding at least portions of those electrical pulses which are generated during first and second time intervals after irradiation with a given neutron pulse and subtracting at least a portion of those electrical pulses which are generated during a third time interval after irradiation with said given neutron pulse whereby the accumulated count in said digital-counting means will be representative of a formation characteristic.

Claim 12

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutron pulses; detector means for generating a plurality of electrical pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; and means for adding at least portions of those electrical pulses which are generated during first and second time intervals after irradiation with a given neutron pulse and subtracting at least a portion of those electrical pulses which are generated during a third time interval after irradiation with said given neutron pulse whereby the accumulated count in said digital-counting means will be representative of a formation characteristic.

Claim 13

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least portions of those pulses which are generated during first, second and third time intervals after irradiation; digital-counting means for adding said pulses which are passed by said gating means; and means responsive to the accumulated count of said counting means after said first, second and third time interval pulses have been counted for energizing said gating means to pass said pulses and for complementing said digital-counting means before and after said second time interval so that said second interval pulses will be subtracted from said first and third interval pulses, said accumulated count being representative of a formation characteristic.

Claim 14

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing at least portions of those pulses which are generated during first, second and third time intervals after irradiation; digital-counting means for adding said pulses which are passed by said gating means; and means responsive to the accumulated count of said counting means after said first, second and third time interval pulses have been counted for energizing said gating means to pass said pulses and for complementing said digital-counting means before and after said second time interval so that said second interval pulses will be subtracted from said first and third interval pulses, said accumulated count being representative of a formation characteristic.

Claim 15

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing one of every two of said pulses during a first time interval after irradiation, all of said pulses during a second time interval after irradiation, and three of every four of said pulses during a third time interval after irradiation; and digital-counting means for subtracting Said second time interval pulses from said first and third time interval pulses whereby the accumulated count in said counting means will be representative of a formation characteristic.

Claim 16

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing one of every two of said pulses during a first time interval after irradiation, all of said pulses during a second time interval after irradiation, and three of every four of said pulses during a third time interval after irradiation; and digital-counting means for subtracting Said second time interval pulses from said first and third time interval pulses whereby the accumulated count in said counting means will be representative of a formation characteristic.

Claim 17

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing one of every two of said pulses during a first time interval after irradiation, all of said pulses during a second time interval after irradiation, and three of every four of said pulses during a third time interval after irradiation; digital counting means for counting said pulses passed by said gating means; and means responsive to the accumulated count of said counting means for energizing said gating means to pass said pulses during said first, second, and third time interval and for complementing said digital-counting means before and after said second time interval so that said second time interval pulses will be subtracted from said first and third time interval pulses, the accumulated count of said counting means being representative of a formation characteristic.

Claim 18

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of pulses which vary with time as a function of the neutron population in a formation, at least part of said pulses representing the neutron population due to said irradiation; gating means for passing one of every two of said pulses during a first time interval after irradiation, all of said pulses during a second time interval after irradiation, and three of every four of said pulses during a third time interval after irradiation; digital counting means for counting said pulses passed by said gating means; and means responsive to the accumulated count of said counting means for energizing said gating means to pass said pulses during said first, second, and third time interval and for complementing said digital-counting means before and after said second time interval so that said second time interval pulses will be subtracted from said first and third time interval pulses, the accumulated count of said counting means being representative of a formation characteristic.

Claim 19

Apparatus for investigating earth formations traversed by a borehole, comprising: means adapted for repetitively irradiating a formation with neutrons; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due to irradiation of a formation with neutrons; gating means for passing at least a portion of those signal pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for adding said first interval pulses and subtracting said second interval signal pulses from said first time interval signal pulses to produce an accumulated count in said counting means after each repetitive irradiation; and control means responsive to the accumulated count of said counting means for energizing said gating means during said first and second time intervals and generating a control signal for energizing said irradiating means after said first and second time intervals associated with each repetitive irradiation, whereby the time period of said time intervals is representative of the rate of decay of the neutron population in an earth formation.

Claim 20

Apparatus for investigating earth formations traversed by a borehole, comprising: means adapted for repetitively irradiating a formation with neutrons; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due to irradiation of a formation with neutrons; gating means for passing at least a portion of those signal pulses generated during a first time interval and at least a portion of those pulses generated during a second time interval; digital-counting means for adding said first interval pulses and subtracting said second interval signal pulses from said first time interval signal pulses to produce an accumulated count in said counting means after each repetitive irradiation; and control means responsive to the accumulated count of said counting means for energizing said gating means during said first and second time intervals and generating a control signal for energizing said irradiating means after said first and second time intervals associated with each repetitive irradiation, whereby the time period of said time intervals is representative of the rate of decay of the neutron population in an earth formation.

Claim 21

The apparatus of claim 10 wherein the control means includes means responsive to the accumulated count of said counting means for generating timing pulses having a period representative of said neutron decay rate, second counting means for counting said timing pulses; means responsive to the count of said second counting means for generating first and second time interval control signals for energizing said gating means to pass said generated signal pulses and for generating said control signal for energizing said irradiating means.

Claim 22

Apparatus for processing well-logging data derived from an exploring means in a borehole for investigating adjacent earth formations, comprising: input means for receiving well-logging data in the form of a plurality of pulses; digital counting means for adding at least a portion of those pulses which are received during a first time interval and subtracting at least a portion of those pulses which are received during a second time interval; means responsive to the accumulated count of said digital-counting means for generating a control signal whose frequency is representative of said accumulated count; and means responsive to said control signal for adjusting said first and second time intervals to cause said accumulated count to assume a substantiAlly constant level, whereby the frequency of said control signal will be representative of a formation characteristic.

Claim 23

Apparatus for processing well-logging data derived from an exploring means in a borehole for investigating adjacent earth formations, comprising: input means for receiving well-logging data in the form of a plurality of pulses; digital counting means for adding at least a portion of those pulses which are received during a first time interval and subtracting at least a portion of those pulses which are received during a second time interval; means responsive to the accumulated count of said digital-counting means for generating a control signal whose frequency is representative of said accumulated count; and means responsive to said control signal for adjusting said first and second time intervals to cause said accumulated count to assume a substantiAlly constant level, whereby the frequency of said control signal will be representative of a formation characteristic.

Claim 24

Apparatus for processing well-logging data derived from an exploring means in a borehole, comprising: input means for receiving well-logging data which is in the form of a plurality of pulses; gating means for passing a first series of pulses during a first time interval and a second series of pulses during a second time interval; digital-counting means for adding at least a portion of those pulses which are received during said first time interval and subtracting at least a portion of those pulses which are received during said second time interval; means responsive to the accumulated count of said digital-counting means for generating a control signal whose frequency is representative of said accumulated count; means responsive to said control signal for energizing said gating means to pass said first and second series of pulses, the frequency of said control signal being adjusted until said accumulated count assumes a substantially constant level; and means for measuring the frequency of said control signal to provide an indication of a formation characteristic.

Claim 25

Apparatus for processing well-logging data derived from an exploring means in a borehole, comprising: input means for receiving well-logging data which is in the form of a plurality of pulses; gating means for passing a first series of pulses during a first time interval and a second series of pulses during a second time interval; digital-counting means for adding at least a portion of those pulses which are received during said first time interval and subtracting at least a portion of those pulses which are received during said second time interval; means responsive to the accumulated count of said digital-counting means for generating a control signal whose frequency is representative of said accumulated count; means responsive to said control signal for energizing said gating means to pass said first and second series of pulses, the frequency of said control signal being adjusted until said accumulated count assumes a substantially constant level; and means for measuring the frequency of said control signal to provide an indication of a formation characteristic.

Claim 26

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for adding the first interval of pulses and subtracting the second interval pulses; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to the frequency of said control signal for energizing said gating means to pass said pulses during said first and second time intervals whereby the frequency of said control signal will be representative of the rate of change of said well-logging signal.

Claim 27

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for adding the first interval of pulses and subtracting the second interval pulses; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to the frequency of said control signal for energizing said gating means to pass said pulses during said first and second time intervals whereby the frequency of said control signal will be representative of the rate of change of said well-logging signal.

Claim 28

Apparatus for determining the rate of change of a well-logging signal which is in the form of a repetitive train of pulses, the repetition rate of the pulses in each repetitive pulse train decreasing with time, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval of each pulse train and at least a portion of those pulses received during a second time interval of each pulse train; reversible digital-counting means for subtracting said second interval pulses from said first interval pulses of each pulse train; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to the frequency of said control signal for energizing said gating means to pass said first and second interval pulses whereby said first and second time intervals will be functions of said control frequency and the rate of change of the pulse repetition rate will be related to said control frequency.

Claim 29

Apparatus for determining the rate of change of a well-logging signal which is in the form of a repetitive train of pulses, the repetition rate of the pulses in each repetitive pulse train decreasing with time, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval of each pulse train and at least a portion of those pulses received during a second time interval of each pulse train; reversible digital-counting means for subtracting said second interval pulses from said first interval pulses of each pulse train; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to the frequency of said control signal for energizing said gating means to pass said first and second interval pulses whereby said first and second time intervals will be functions of said control frequency and the rate of change of the pulse repetition rate will be related to said control frequency.

Claim 30

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for counting the pulses passed during said first and second time intervals; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to said control signal for complementing said digital-counting means before and after said second time interval so that said second interval pulses will be subtracted from said first interval pulses and energizing said Gating means to pass said first and second interval pulses whereby the frequency of said control signal will be representative of the rate of change of said well-logging signal.

Claim 31

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for counting the pulses passed during said first and second time intervals; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; and means responsive to said control signal for complementing said digital-counting means before and after said second time interval so that said second interval pulses will be subtracted from said first interval pulses and energizing said Gating means to pass said first and second interval pulses whereby the frequency of said control signal will be representative of the rate of change of said well-logging signal.

Claim 32

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for adding the first series of pulses and subtracting the second series of pulses; means responsive to the accumulated count of said counting means for generating control pulses whose period is representative of the time constant of said well-logging signal; and means responsive to said pulses for energizing said gating means to pass said first and second interval pulses, said first and second time intervals being correlated with the period of said control pulses whereby the accumulated count of said counting means will remain constant so long as the period of said control pulses is accurately representative of the time constant of said well-logging signal.

Claim 33

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during a first time interval and at least a portion of those pulses received during a second time interval; digital-counting means for adding the first series of pulses and subtracting the second series of pulses; means responsive to the accumulated count of said counting means for generating control pulses whose period is representative of the time constant of said well-logging signal; and means responsive to said pulses for energizing said gating means to pass said first and second interval pulses, said first and second time intervals being correlated with the period of said control pulses whereby the accumulated count of said counting means will remain constant so long as the period of said control pulses is accurately representative of the time constant of said well-logging signal.

Claim 34

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses whose repetition rate decays with time and eventually levels off to a background or quiescent level, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during first, second and third time intervals; digital-counting means for subtracting those pulses passed during the second time interval from those pulses passed during the first and third time intervals; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; means responsive to the frequency of said control signal for energizing said gating means to pass said pulses, said third time interval being selected to coincide with that portion of the well-logging signal which reflects the background level; and means responsive to the frequency of said control signal for providing an indication of the rate of change of said well-logging signal.

Claim 35

Apparatus for determining the rate of change of a well-logging signal which is in the form of a plurality of pulses whose repetition rate decays with time and eventually levels off to a background or quiescent level, comprising: input means for receiving the pulses; gating means for passing at least a portion of those pulses received during first, second and third time intervals; digital-counting means for subtracting those pulses passed during the second time interval from those pulses passed during the first and third time intervals; means responsive to the accumulated count of said counting means for generating a control signal at a control frequency; means responsive to the frequency of said control signal for energizing said gating means to pass said pulses, said third time interval being selected to coincide with that portion of the well-logging signal which reflects the background level; and means responsive to the frequency of said control signal for providing an indication of the rate of change of said well-logging signal.

Claim 36

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulse representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals; and means responsive to each sync pulse for generating a gain control signal for application to said gain adjustment means to adjust the gain thereof so as to maintain the amplitude of said sync pulses substantially constant.

Claim 37

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulse representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals; and means responsive to each sync pulse for generating a gain control signal for application to said gain adjustment means to adjust the gain thereof so as to maintain the amplitude of said sync pulses substantially constant.

Claim 38

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulses representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals to produce gain adjusted well-logging signals; and means responsive to gain adjusted sync pulses for generating a gain-control signal for application to said gain adjustment means to adjust the gain thereof so as to maintain the amplitude of said sync pulses constant.

Claim 39

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulses representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals to produce gain adjusted well-logging signals; and means responsive to gain adjusted sync pulses for generating a gain-control signal for application to said gain adjustment means to adjust the gain thereof so as to maintain the amplitude of said sync pulses constant.

Claim 40

The apparatus of claim 20 wherein said means for generating a gain-control signal includes: charge storage means; means for comparing the amplituDe of each gain-adjusted sync pulse with a reference amplitude and changing the charge in said charge storage means in proportion to the difference between said compared amplitudes; and means for generating said gain-control signal in accordance with the amount of charge stored by said charge storage means whereby the amplitude of said gain-adjusted sync pulses will be maintained substantially the same as said reference amplitude.

Claim 41

The apparatus of claim 20 wherein said means for generating a gain-control signal includes: means for comparing the amplitude of said gain-adjusted sync pulse with a reference amplitude and producing an output signal representative of the difference between said two amplitude levels each time a sync pulse is received; and means responsive to said output signal for generating said gain-control signal whereby said gain-control signal will operate to maintain said sync pulse amplitude and reference amplitude substantially the same.

Claim 42

The apparatus of claim 20 wherein said means for generating a gain-control signal includes: means for comparing the amplitude of said gain-adjusted sync pulse with a reference amplitude and producing an output signal having a voltage representative of the difference between said two amplitude levels each time a sync pulse is received; storage means for accumulating said voltages; and means responsive to said accumulated voltages for generating said gain-control signal whereby said gain-control signal will act to maintain said sync pulse amplitude substantially the same as said reference amplitude.

Claim 43

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulse representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals; means for detecting said sync pulses; means responsive to said detected sync pulses for gating said gain-adjusted well-logging signals so that only sync pulses will be gated; and gain control means responsive to said gated gain-adjusted well-logging signals for generating a gain-control signal for application to said gain-adjustment means to adjust the gain thereof.

Claim 44

Apparatus for adjusting the signal strength of well-logging signals derived from an exploring means of the type which repetitively emits energy into a media surrounding an exploring means and produces a sync pulse representative of the time of such emission as well as information signals representative of the reaction of the media to said emitted energy, comprising: input means for receiving well-logging signals; gain adjustment means for adjusting the signal strength of said well-logging signals; means for detecting said sync pulses; means responsive to said detected sync pulses for gating said gain-adjusted well-logging signals so that only sync pulses will be gated; and gain control means responsive to said gated gain-adjusted well-logging signals for generating a gain-control signal for application to said gain-adjustment means to adjust the gain thereof.

Claim 45

The apparatus of claim 24 wherein said means for generating a gain-control signal includes: means for comparing the amplitude of said gated sync pulse with a reference amplitude and producing an output signal having a voltage representative of the difference between said two amplitude levels each time a sync pulse is gated to said gain-control means; storage means for accumulating said voltages; and means responsive to said accumulated voltages for generating said gain-control signal whereby said gain-control signal will act to maintain said gated sync pulse amplitude substantially the same as said reference amplitude.

Claim 46

Apparatus for investigating earth formations traversed by a borehole, comprising: means for irradiating a formation with neutrons and generating a sync pulse representative of the time of occurrence of said irradiation; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due said irradiation; transmission means for transmitting said sync and signal pulses to the surface of the earth; gain-adjustment means for adjusting the signal strength of the transmitted well-logging signals received at the surface of the earth; means responsive to each received sync pulse for generating a gain-control signal for application to said gain adjustment means to adjust the gain thereof so as To maintain the amplitude of said sync pulse substantially constant; and means responsive to said received signal pulses from said gain-adjustment means for determining a characteristic of a formation surrounding a borehole.

Claim 47

Apparatus for investigating earth formations traversed by a borehole, comprising: means for irradiating a formation with neutrons and generating a sync pulse representative of the time of occurrence of said irradiation; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due said irradiation; transmission means for transmitting said sync and signal pulses to the surface of the earth; gain-adjustment means for adjusting the signal strength of the transmitted well-logging signals received at the surface of the earth; means responsive to each received sync pulse for generating a gain-control signal for application to said gain adjustment means to adjust the gain thereof so as To maintain the amplitude of said sync pulse substantially constant; and means responsive to said received signal pulses from said gain-adjustment means for determining a characteristic of a formation surrounding a borehole.

Claim 48

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due to said irradiation; transmission means for transmitting said signal pulses to the surface of the earth, said transmission means having transmission characteristics which tend to merge closely spaced signal pulses; pulse-resolving means for resolving the transmitted signal pulses received at the surface of the earth into separate, individual pulses, said pulse-resolving means including means for generating, for each received signal pulse, a trigger pulse having a pulse width proportional to the pulse width of said received signal pulses and a reference pulse having a pulse width slightly greater than the pulse width of a single, unmerged signal pulse, means responsive to related trigger and reference pulses for generating resolved signal pulses, and automatic pulse width adjustment means responsive to said trigger and reference pulses for adjusting the reference pulse width to maintain a fixed relationship between the pulse widths of said trigger and reference pulses; digital-counting means for adding at least a portion of those pulses which are generated during a first time interval after irradiation and subtracting at least a portion of those pulses which are generated during a second time interval after irradiation; means responsive to the accumulated count of said counting means after said first and second time intervals for generating a control signal having a frequency representative of the rate of change of the repetition rate of said pulses; and means responsive to said control signal for controlling said first and second time intervals and disabling said automatic pulse width adjustment means during a time period following irradiation of a formation with neutrons so that said adjustment means will be disabled during time intervals when the repetition rate of said signal pulses is relatively high.

Claim 49

Apparatus for investigating earth formations traversed by a borehole, comprising: means for repetitively irradiating a formation with neutrons; detector means for generating a plurality of signal pulses which vary with time as a function of the neutron population in a formation, at least part of said signal pulses representing the neutron population due to said irradiation; transmission means for transmitting said signal pulses to the surface of the earth, said transmission means having transmission characteristics which tend to merge closely spaced signal pulses; pulse-resolving means for resolving the transmitted signal pulses received at the surface of the earth into separate, individual pulses, said pulse-resolving means including means for generating, for each received signal pulse, a trigger pulse having a pulse width proportional to the pulse width of said received signal pulses and a reference pulse having a pulse width slightly greater than the pulse width of a single, unmerged signal pulse, means responsive to related trigger and reference pulses for generating resolved signal pulses, and automatic pulse width adjustment means responsive to said trigger and reference pulses for adjusting the reference pulse width to maintain a fixed relationship between the pulse widths of said trigger and reference pulses; digital-counting means for adding at least a portion of those pulses which are generated during a first time interval after irradiation and subtracting at least a portion of those pulses which are generated during a second time interval after irradiation; means responsive to the accumulated count of said counting means after said first and second time intervals for generating a control signal having a frequency representative of the rate of change of the repetition rate of said pulses; and means responsive to said control signal for controlling said first and second time intervals and disabling said automatic pulse width adjustment means during a time period following irradiation of a formation with neutrons so that said adjustment means will be disabled during time intervals when the repetition rate of said signal pulses is relatively high.

Claim 54

The method of claim 29 and further including the steps of counting at least a portion of the pulses generated during a third time interval after each irradiation whereby said second time interval pulses will be subtracted from said first and third time interval pulses.

Claim 59

In apparatus for energizing a pulsed neutron source, apparatus for producing a pulse representative of the termination of said energization, comprising: means for generating a pulse for application to a pulsed neutron source to cause the production of neutrons for emission into a surrounding media, said pulse having amplitude oscillations on the trailing edge portion thereof; means responsive to the first amplitude change on the trailing edge portion of said pulse for generating a timing pulse of a fixed time duration, which time duration exceeds said amplitude oscillations; and means responsive to the leading edge of said timing pulse for generating a pulse representative of the termination of neutron emission for transmission to the surface of the earth to enable said termination to be detected at the surface of the earth.

Claim 60

In apparatus for energizing a pulsed neutron source, apparatus for producing a pulse representative of the termination of said energization, comprising: means for generating a pulse for application to a pulsed neutron source to cause the production of neutrons for emission into a surrounding media, said pulse having amplitude oscillations on the trailing edge portion thereof; means responsive to the first amplitude change on the trailing edge portion of said pulse for generating a timing pulse of a fixed time duration, which time duration exceeds said amplitude oscillations; and means responsive to the leading edge of said timing pulse for generating a pulse representative of the termination of neutron emission for transmission to the surface of the earth to enable said termination to be detected at the surface of the earth.

Claim 61

Apparatus for irradiating a formation traversed by a borehole, with neutrons and producing signals representative of the formation reaction to the neutrons and the time of termination of said irradiation for transmission to the surface of the earth, comprising: a pulsed neutron source; means for generating an energization pulse for energizing said neutron source to irradiate a formation with neutrons; detector means responsive to the neutron population produced by said neutron source for generating a plurality of signal pulses represEntative of said neutron population; means responsive to the trailing edge of said energization pulse for generating a delay pulse of a fixed time duration; means responsive to the leading edge of said delay pulse for generating a sync pulse representative of the time of termination of said neutron irradiation; means for transmitting the sync and signal pulses to the surface of the earth; and means responsive to the leading edge of said energization pulse and the trailing edge of said delay pulse for inhibiting the application of said signal pulses to said transmitting means during the time interval between the leading edge of said energization pulse and the trailing edge of said delay pulse.

Claim 62

Apparatus for irradiating a formation traversed by a borehole, with neutrons and producing signals representative of the formation reaction to the neutrons and the time of termination of said irradiation for transmission to the surface of the earth, comprising: a pulsed neutron source; means for generating an energization pulse for energizing said neutron source to irradiate a formation with neutrons; detector means responsive to the neutron population produced by said neutron source for generating a plurality of signal pulses represEntative of said neutron population; means responsive to the trailing edge of said energization pulse for generating a delay pulse of a fixed time duration; means responsive to the leading edge of said delay pulse for generating a sync pulse representative of the time of termination of said neutron irradiation; means for transmitting the sync and signal pulses to the surface of the earth; and means responsive to the leading edge of said energization pulse and the trailing edge of said delay pulse for inhibiting the application of said signal pulses to said transmitting means during the time interval between the leading edge of said energization pulse and the trailing edge of said delay pulse.