Induction logging methods and apparatus using more than one phase component of the received signal

Claim 1

Apparatus for investigating earth formations traversed by a borehole, comprising: a. a coil array adapted for movement through a borehole and having at least one transmitter coil and at least one receiver coil; b. means for energizing said at least one transmitter coil with current to thereby cause a voltage to be induced into said at least one receiver coil, which induced voltage is at least in part representative of certain electrical characteristics of an adjoining formation; c. means for detecting selected parameters of the receiver coil voltage; and d. means for combining representations of said selected parameters of the receiver coil voltage in a non-linear manner to produce a parameter which is non-linearly related to said selected parameters and representative of the average conductivity or the heterogeneity of a media surrounding the coil array.

Claim 19

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals in a non-linear manner to compute a parameter which is non-linearly related to both of said phase components and representative of the average conductivity or the heterogeneity of an earth formation.

Claim 20

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals in a non-linear manner to compute a parameter which is non-linearly related to both of said phase components and representative of the average conductivity or the heterogeneity of an earth formation.

Claim 25

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including generating representations of an approximation of the conductivity and heterogeneity of an earth formation, computing representations of equivalent phase component signals which would result from a formation of the type which would possess said conductivity and heterogeneity, comparing said representations of the equivalent phase component signals with said representations of the measured phase component signals and producing a representation of the difference therebetween, repeatedly adjusting the values of said approximate representations of the conductivity and heterogeneity and re-computing representations of said equivalent phase component signals from said adjusted values for re-comparison with said measured phase component values until said difference representation is reduced below a predetermined value, whereupon the last adjusted values of conductivity and heterogeneity are selected as representative of the true formation conductivity and heterogeneity.

Claim 26

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including generating representations of an approximation of the conductivity and heterogeneity of an earth formation, computing representations of equivalent phase component signals which would result from a formation of the type which would possess said conductivity and heterogeneity, comparing said representations of the equivalent phase component signals with said representations of the measured phase component signals and producing a representation of the difference therebetween, repeatedly adjusting the values of said approximate representations of the conductivity and heterogeneity and re-computing representations of said equivalent phase component signals from said adjusted values for re-comparison with said measured phase component values until said difference representation is reduced below a predetermined value, whereupon the last adjusted values of conductivity and heterogeneity are selected as representative of the true formation conductivity and heterogeneity.

Claim 27

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including computing a first parameter representative of a non-linear transformation of said in-phase component to a corresponding phase-quadrature representation thereof, and using said first parameter and said phase-quadrature component of the receiver coil voltage for computing a second parameter representative of the heterogeneity of an earth formation.

Claim 28

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including computing a first parameter representative of a non-linear transformation of said in-phase component to a corresponding phase-quadrature representation thereof, and using said first parameter and said phase-quadrature component of the receiver coil voltage for computing a second parameter representative of the heterogeneity of an earth formation.

Claim 29

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of sAid phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including combining representations of said phase component signals to produce a first signal, forming a non-linear function of said first signal to produce a second signal, and combining said first and second signals to produce an output signal representative of the average conductivity of an earth formation.

Claim 30

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of sAid phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including combining representations of said phase component signals to produce a first signal, forming a non-linear function of said first signal to produce a second signal, and combining said first and second signals to produce an output signal representative of the average conductivity of an earth formation.

Claim 31

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including combining representations of said phase component signals to produce a first signal, forming a non-linear function of said first signal to produce a second signal, combining said first and second signals to produce a third signal, and combining said third signal with said phase-quadrature component signal to produce an output signal representative of the heterogeneity of an earth formation.

Claim 32

A method of investigating earth formations traversed by a borehole, comprising: a. generating current having a reference phase; b. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; c. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; d. detecting the in-phase and phase-quadrature components, relative to said reference phase, of said electrical signal and generating phase component signals representative thereof; and e. combining representations of said phase component signals to compute a parameter which is representative of the average conductivity or the heterogeneity of an earth formation, including combining representations of said phase component signals to produce a first signal, forming a non-linear function of said first signal to produce a second signal, combining said first and second signals to produce a third signal, and combining said third signal with said phase-quadrature component signal to produce an output signal representative of the heterogeneity of an earth formation.

Claim 33

A method of investigating earth formations traversed by a borehole, comprising: a. moving a coil array having at least one transmitter coil and at least one receiver coil through a borehole; b. energizing said at least one transmitter coil with current to thereby cause a voltage to be induced into said at least one receiver coil, said induced voltage being expressed by the relationship: where At is the product of the cross-sectional area and the number of turns for the mth transmitter coil, Ar is the product of the cross-sectional area and the number of turns of the nth receiver coil, Lmn is the spacing between coil centers of the mth transmitter coil and the nth receiver coil, omega is the radian frequency of the transmitter coil current, Mu is the magnetic permeability of the response region of the coils, gamma j omega Mu ( sigma u + j sigma v), and Vr and Vx'' are the in-phase and phase-quadrature components respectively of the received voltage; c. detecting those portions Vr and Vx'' of the receiver coil voltage which are in-phase with the transmitter coil current and in phase-quadrature with the transmitter coil current; and d. combining representations of said in-phase and phase-quadrature components of the receiver coil voltage to compute the parameters sigma u and sigma v, which parameter sigma u is representative of the average conductivity of a media surrounding the coil array and which parameter sigma v is representative of the heterogeneity of a media surrounding the coil array.

Claim 34

A method of investigating earth formations traversed by a borehole, comprising: a. moving a coil array having at least one transmitter coil and at least one receiver coil through a borehole; b. energizing said at least one transmitter coil with current to thereby cause a voltage to be induced into said at least one receiver coil, said induced voltage being expressed by the relationship: where At is the product of the cross-sectional area and the number of turns for the mth transmitter coil, Ar is the product of the cross-sectional area and the number of turns of the nth receiver coil, Lmn is the spacing between coil centers of the mth transmitter coil and the nth receiver coil, omega is the radian frequency of the transmitter coil current, Mu is the magnetic permeability of the response region of the coils, gamma j omega Mu ( sigma u + j sigma v), and Vr and Vx'' are the in-phase and phase-quadrature components respectively of the received voltage; c. detecting those portions Vr and Vx'' of the receiver coil voltage which are in-phase with the transmitter coil current and in phase-quadrature with the transmitter coil current; and d. combining representations of said in-phase and phase-quadrature components of the receiver coil voltage to compute the parameters sigma u and sigma v, which parameter sigma u is representative of the average conductivity of a media surrounding the coil array and which parameter sigma v is representative of the heterogeneity of a media surrounding the coil array.

Claim 40

A method of investigating earth formations traversed by a borehole, comprising: a. moving a coil array through a borehole, said coil array having at least one transmitter coil and at least one receiver coil; b. energizing said at least one transmitter coil with current to thereby cause a voltage to be induced into said at least one receiver coil, which induced voltage is at least in part representative of certain electrical characteristics of an adjoining formation to the field initiated by the transmitter coil current; c. detecting those portions of the receiver coil voltage which are in-phase with the transmitter coil current and in phase-quadrature with the transmitter coil current; and d. converting representations of said phase components to orthogonally related parameters which are non-linearly related to said phase components and representative of the average conductivity and heterogeneity of an earth formation.

Claim 41

A method of investigating earth formations traversed by a borehole, comprising: a. moving a coil array through a borehole, said coil array having at least one transmitter coil and at least one receiver coil; b. energizing said at least one transmitter coil with current to thereby cause a voltage to be induced into said at least one receiver coil, which induced voltage is at least in part representative of certain electrical characteristics of an adjoining formation to the field initiated by the transmitter coil current; c. detecting those portions of the receiver coil voltage which are in-phase with the transmitter coil current and in phase-quadrature with the transmitter coil current; and d. converting representations of said phase components to orthogonally related parameters which are non-linearly related to said phase components and representative of the average conductivity and heterogeneity of an earth formation.

Claim 48

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce a first output signal; forming a non-linear function of said first output signal to produce a second output signal; and combining said first and second output signals to produce a third output signal representative of the average conductivity of an earth formation.

Claim 49

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce a first output signal; forming a non-linear function of said first output signal to produce a second output signal; and combining said first and second output signals to produce a third output signal representative of the average conductivity of an earth formation.

Claim 50

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representAtive of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce a first output signal; forming a non-linear function of said first output signal to produce a second output signal; combining said first and second output signals to produce a third output signal; and combining said third output signal with one of said phase component signals to produce a signal representative of the heterogeneity of an earth formation.

Claim 51

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representAtive of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce a first output signal; forming a non-linear function of said first output signal to produce a second output signal; combining said first and second output signals to produce a third output signal; and combining said third output signal with one of said phase component signals to produce a signal representative of the heterogeneity of an earth formation.

Claim 52

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals in a non-linear manner to produce representations of the average conductivity and heterogeneity of a formation at least one of said representations being non-linearly related to both of said phase components; and recording said representations of conductivity and heterogeneity as a function of the depth level at which the phase component signals were obtained.

Claim 53

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals in a non-linear manner to produce representations of the average conductivity and heterogeneity of a formation at least one of said representations being non-linearly related to both of said phase components; and recording said representations of conductivity and heterogeneity as a function of the depth level at which the phase component signals were obtained.

Claim 54

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of mutually quadrature phase components of the electromagnetic field produced by said current flow, one of said phase components being in-phase with the current which induces current flow in a formation and the other phase component being in phase-quadrature therewith, comprising: computing a first parameter representative of a non-linear transformation of a representation of said in-phase component to a corresponding phase-quadrature representation thereof; and using said first parameter and a representation of said phase-quadrature component of the receiver coil voltage for computing a second parameter representative of the heterogeneity of an earth formation.

Claim 55

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of mutually quadrature phase components of the electromagnetic field produced by said current flow, one of said phase components being in-phase with the current which induces current flow in a formation and the other phase component being in phase-quadrature therewith, comprising: computing a first parameter representative of a non-linear transformation of a representation of said in-phase component to a corresponding phase-quadrature representation thereof; and using said first parameter and a representation of said phase-quadrature component of the receiver coil voltage for computing a second parameter representative of the heterogeneity of an earth formation.

Claim 56

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce first and second representations of the average conductivity and heterogeneity of a formation; and combining said values of average conductivity and heterogeneity to produce individual measurements of the conductivity of different radial portions of a formation.

Claim 57

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce first and second representations of the average conductivity and heterogeneity of a formation; and combining said values of average conductivity and heterogeneity to produce individual measurements of the conductivity of different radial portions of a formation.

Claim 58

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: generating representations of an approximation of the conductivity and heterogeneity of an earth formation, computing representations of equivalent phase component signals which would result from a formation of the type which would possess said conductivity and heterogeneity comparing said representations of the equivalent phase component signals with said representations of the measured phase component signals and producing a representation of the difference therebetween, repeatedly adjusting the values of said approximation representations of the conductivity and heterogeneity and re-computing representations of said equivalent phase component signals from said adjusted values for re-comparison with said measured phase component values until said difference reprEsentation is reduced below a predetermined value whereupon the last adjusted values of conductivity and heterogeneity are selected as representative of the true formation conductivity and heterogeneity.

Claim 59

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: generating representations of an approximation of the conductivity and heterogeneity of an earth formation, computing representations of equivalent phase component signals which would result from a formation of the type which would possess said conductivity and heterogeneity comparing said representations of the equivalent phase component signals with said representations of the measured phase component signals and producing a representation of the difference therebetween, repeatedly adjusting the values of said approximation representations of the conductivity and heterogeneity and re-computing representations of said equivalent phase component signals from said adjusted values for re-comparison with said measured phase component values until said difference reprEsentation is reduced below a predetermined value whereupon the last adjusted values of conductivity and heterogeneity are selected as representative of the true formation conductivity and heterogeneity.

Claim 60

A method of investigating earth formations traversed by a borehole, comprising: a. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; b. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; c. detecting selected parameters of said electrical signal and generating parameter signals representative thereof; and d. combining representations of said parameter signals in a non-linear manner to produce representations of the average conductivity and the heterogeneity of an earth formation, each of said produced representations being non-linearly related to at least one of said selected parameters.

Claim 61

A method of investigating earth formations traversed by a borehole, comprising: a. producing an electromagnetic field in an earth formation surrounding a borehole in response to said generated current; b. detecting said electromagnetic field and producing an electrical signal representative of the effect of an earth formation on said electromagnetic field; c. detecting selected parameters of said electrical signal and generating parameter signals representative thereof; and d. combining representations of said parameter signals in a non-linear manner to produce representations of the average conductivity and the heterogeneity of an earth formation, each of said produced representations being non-linearly related to at least one of said selected parameters.

Claim 62

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce representations of the average conductivity and heterogeneity of a formation; and dividing a representation of the heterogeneity by a representation of at least the average conductivity to produce a normalized indication of the formation heterogeneity.

Claim 63

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals to produce representations of the average conductivity and heterogeneity of a formation; and dividing a representation of the heterogeneity by a representation of at least the average conductivity to produce a normalized indication of the formation heterogeneity.

Claim 64

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals in a non-linear manner to produce representations of the average conductivity and heterogeneity of a formation, each of said representations being non-linearly related to at least one of said phase component signals; and recording said representations of conductivity and heterogeneity as a function of the depth level at which the phase component signals were obtained.

Claim 65

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow, comprising: combining representations of said two phase component signals in a non-linear manner to produce representations of the average conductivity and heterogeneity of a formation, each of said representations being non-linearly related to at least one of said phase component signals; and recording said representations of conductivity and heterogeneity as a function of the depth level at which the phase component signals were obtained.

Claim 66

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of two parameters of the electromagnetic field produced by said current flow, comprising: combining representations of said two signals to produce representations of the average conductivity and heterogeneity of a formation; and combining said representations of average conductivity and heterogeneity to produce individual output representations of different radial portions of a formation.

Claim 67

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of two parameters of the electromagnetic field produced by said current flow, comprising: combining representations of said two signals to produce representations of the average conductivity and heterogeneity of a formation; and combining said representations of average conductivity and heterogeneity to produce individual output representations of different radial portions of a formation.

Claim 72

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow comprising: combining representations of said two phase component signals to produce first and second representations of different formation parameters; and combining said formation parameter representations to produce individual measurements of the conductivity of different, non-exclusive radial portions of a formation.

Claim 73

A method of processing signals derived from an induction logging tool of the type which induces a flow of alternating current in an earth formation and produces signals representative of the magnitude of first and second mutually quadrature phase components of the electromagnetic field produced by said current flow comprising: combining representations of said two phase component signals to produce first and second representations of different formation parameters; and combining said formation parameter representations to produce individual measurements of the conductivity of different, non-exclusive radial portions of a formation.