Neutron borehole logging correction technique

Claim 2

Apparatus for logging earth formations traversed by a borehole comprising a housing, a source of neutrons in said housing, at least one gamma radiation detector in said housing that is spaced apart from said source, means surrounding said detector that includes a material rarely present in a borehole and in earth formations in anything more than trace amounts for capturing neutrons from a borehole and for producing gamma radiation characteristic of that neutron capture for detection by said gamma radiation detector, means coupled to said detector for producing a representation of the neutron flux in the borehole in selective response to the amount of detected characteristic gamma radiation from said material and a representation of the concentration of a formation constituent element in response to detected gamma radiation, means for producing a representation of a constant of proportionality reflecting the relationship between predetermined representations of the concentration of said element and the neutron flux in a formation which does not contain said element, means for multiplying the produced neutron flux representation by said constant of proportionality to obtain an indication of the effect of borehole neutron capture produced gamma radiation on the produced element concentration representation, and means for subtracting said borehole effect indication from said produced element concentration representation.

Claim 3

Apparatus according to claim 1 wherein said detector surrounding means comprises a sleeve attached to and surrounding said housing opposite said gamma radiation detector.

Claim 4

Apparatus according to claim 2 wherein said sleeve has the element boron distributed therethrough.

Claim 5

Apparatus according to claim 1 wherein said detector surrounding means comprises a shield positioned between said detector and said housing.

Claim 6

Apparatus according to claim 4 wherein said sleeve has the element boron distributed therethrough.

Claim 11

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a first signal representative of the amount of characteristic radiation produced by the boron sleeve and at least a second signal representative of the concentration of a given element in the formation, means for producing a signal representing a constant of proportionality reflecting the relationship between predetermined values of said first and second signals in a formation which does not contain said element, means for multiplying said first produced signal by said proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said second produced signal, and means for subtracting said borehole effect signal from said second produced signal.

Claim 12

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a first signal representative of the amount of characteristic radiation produced by the boron sleeve and at least a second signal representative of the concentration of a given element in the formation, means for producing a signal representing a constant of proportionality reflecting the relationship between predetermined values of said first and second signals in a formation which does not contain said element, means for multiplying said first produced signal by said proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said second produced signal, and means for subtracting said borehole effect signal from said second produced signal.

Claim 13

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a signal representative of the amount of characteristic radiation produced by the boron sleeve and signals representative of the concentrations of hydrogen, silicon and calcium respectively in the formation, means for producing a signal representing a constant of proportionality reflecting the relationship between predetermined values of the hydrogen and boron sleeve signals in a formation which does not contain hydrogen, means for multiplying said produced boron sleeve signal by said proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced hydrogen signal, means for subtracting said borehole effect signal from said produced hydrogen signal to obtain a corrected hydrogen concentration signal, and means for combining the corrected hydrogen signal with the silicon and calcium signals to produce a representation of the formation salinity.

Claim 14

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a signal representative of the amount of characteristic radiation produced by the boron sleeve and signals representative of the concentrations of hydrogen, silicon and calcium respectively in the formation, means for producing a signal representing a constant of proportionality reflecting the relationship between predetermined values of the hydrogen and boron sleeve signals in a formation which does not contain hydrogen, means for multiplying said produced boron sleeve signal by said proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced hydrogen signal, means for subtracting said borehole effect signal from said produced hydrogen signal to obtain a corrected hydrogen concentration signal, and means for combining the corrected hydrogen signal with the silicon and calcium signals to produce a representation of the formation salinity.

Claim 15

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a signal representative of the amount of characteristic gamma radiation produced by the boron sleeve and signals representative of the concentrations of hydrogen and chlorine in the formation, means for producing a signal representing a first constant of proportionality representing the relationship between predetermined values of the hydrogen and boron sleeve signals in a formation which does not contain hydrogen, means for multiplying said produced boron sleeve signal by said first proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced hydrogen signal, means for subtracting said hydrogen borehole effect signal from said produced hydrogen signal to obtain a corrected hydrogen concentration signal, means for producing a signal representing a second constant of proportionality representing the relationship between predetermined values of the chlorine and boron sleeve signals in a formation which does not contain chlorine, means for multiplying said produced boron sleeve signal by said second proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced chlorine signal, means for subtracting said chlorine borehole effect signal from said produced chlorine signal to obtain a corrected chlorine concentration signal, and means for combining the corrected hydrogen and chlorine signals to produce a representation of the formation salinity.

Claim 16

Apparatus for logging earth formations traversed by a borehole, comprising a housing, a source of neutrons in said housing, a gamma radiation detector in said housing that is spaced apart from said source, a boron sleeve surrounding said detector for capturing neutrons from the borehole and producing gamma radiation characteristic of that neutron capture for detection by the detector, a spectrum analysis computer coupled to said detector for producing a signal representative of the amount of characteristic gamma radiation produced by the boron sleeve and signals representative of the concentrations of hydrogen and chlorine in the formation, means for producing a signal representing a first constant of proportionality representing the relationship between predetermined values of the hydrogen and boron sleeve signals in a formation which does not contain hydrogen, means for multiplying said produced boron sleeve signal by said first proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced hydrogen signal, means for subtracting said hydrogen borehole effect signal from said produced hydrogen signal to obtain a corrected hydrogen concentration signal, means for producing a signal representing a second constant of proportionality representing the relationship between predetermined values of the chlorine and boron sleeve signals in a formation which does not contain chlorine, means for multiplying said produced boron sleeve signal by said second proportionality constant signal to obtain a signal representative of the effect of borehole neutron capture produced gamma radiation on said produced chlorine signal, means for subtracting said chlorine borehole effect signal from said produced chlorine signal to obtain a corrected chlorine concentration signal, and means for combining the corrected hydrogen and chlorine signals to produce a representation of the formation salinity.