Apparatus for improving signal-to-noise ratio in logging-while-drilling system

Claim 3

The method of claim 1 wherein the step of combining said electrical pressure measurement signals to reduce said accoustical noise substantially includes: generating an output signal representative of the difference between said time-shifted, electrical pressure measurement signal and said other electrical pressure measurement signal.

Claim 4

The method of claim 1 wherein the step of combining said electrical pressure measurement signals to reduce said acoustical noise substantially includes: reversing the polarity of said time-shifted, electrical pressure measurement signal; and adding said polarity-reversed and time-shifted, electrical pressure measurement signal and said other electrical pressure measurement signal.

Claim 5

The method set forth in claim 1 wherein: said first and second points are spaced from each other at a distance approximately equal to a quarter wavelength of the sound wave in the drilling fluid.

Claim 6

The method recited in claim 1 wherein said time shifting step is carried out by: filtering said one electrical pressure measurement signal with a filter - e i where: omega is the frequency of the desired acoustic signal, and Tau is the travel time of sound between said two spaced points.

Claim 7

The method recited in claim 5 further comprising: filtering the combined pressure measurement signals with a filter

Claim 8

In a logging-while-drilling system wherein a downhole signal representative of a downhole parameter is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing the uphole noise from said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said first point and for converting said pressure into a corresponding electrical pressure measurement signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; means for filtering one of said electrical measurement signals with a filter A( omega ) having characteristics related to the distortion of said conduit means between said two spaced points; means for time shifting said filtered electrical pressure measurement signal by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means; and means for generating an output signal representative of the difference between said time-shifted, electrical pressure measurement signal and the other said electrical pressure measurement signal.

Claim 9

In a logging-while-drilling system wherein a downhole signal representative of a downhole parameter is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing the uphole noise from said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said first point and for converting said pressure into a corresponding electrical pressure measurement signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; means for filtering one of said electrical measurement signals with a filter A( omega ) having characteristics related to the distortion of said conduit means between said two spaced points; means for time shifting said filtered electrical pressure measurement signal by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means; and means for generating an output signal representative of the difference between said time-shifted, electrical pressure measurement signal and the other said electrical pressure measurement signal.

Claim 10

The apparatus of claim 7 wherein said means for generating an output signal representative of the difference between said electrical pressure measurement signals comprises: means for reversing the polarity of said time-shifted, pressure measurement signal; and adding means for summing said polarity-reversed and time-shifted electrical pressure measurement signal and said other electrical pressure measurement signal.

Claim 11

The apparatus set forth in claim 7 wherein: said first and second transducer means are spaced from each other at a distance equal to a quarter wavelength of the sound wave in the drilling fluid.

Claim 12

In a logging-while-drilling system wherein a downhole signal is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing uphole Noise from said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said first point and for converting said pressure into a corresponding electrical pressure measurement signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; amplifier means having a gain control for matching the outputs of said first and second transducers when uphole noise but no downhole signal is present in said conduit means; means for processing said electrical pressure measurement signals to time shift one of said electrical pressure measurement signals relative to the other of said electrical pressure measurement signals by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means so that the uphole noise component in each of said electrical pressure measurement signals are in phase with each other; means for further processing said electrical pressure measurement signals to shift the uphole noise components of said signals relative to each other so that said noise components are 180* out of phase with each other; and means for combining said further processed electrical pressure measurement signals to generate an output signal from which said uphole noise components have been effectively cancelled.

Claim 13

In a logging-while-drilling system wherein a downhole signal is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing uphole Noise from said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said first point and for converting said pressure into a corresponding electrical pressure measurement signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; amplifier means having a gain control for matching the outputs of said first and second transducers when uphole noise but no downhole signal is present in said conduit means; means for processing said electrical pressure measurement signals to time shift one of said electrical pressure measurement signals relative to the other of said electrical pressure measurement signals by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means so that the uphole noise component in each of said electrical pressure measurement signals are in phase with each other; means for further processing said electrical pressure measurement signals to shift the uphole noise components of said signals relative to each other so that said noise components are 180* out of phase with each other; and means for combining said further processed electrical pressure measurement signals to generate an output signal from which said uphole noise components have been effectively cancelled.

Claim 14

The apparatus set forth in claim 10 wherein: said first and second transducer means are spaced from each other at a distance equal to a quarter wavelength of the sound wave in the drilling fluid.

Claim 15

In a logging-while-drilling system wherein a downhole signal is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing the uphole noise in said drilling fluid which would normally interfere with said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said point and for converting said pressure into a corresponding electrical signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; an amplifier having an input and an output, said input of said amplifier connected to said first transducer, said amplifier further having a gain control for matching the outputs of said first and second transducers when uphole noise but no downhole signal is present in said conduit means; means for summing electrical signals having at least two inputs and an output; means connecting said output of said amplifier to one of said inputs of said summing means; means for time shifting said electrical pressure measurement signal from said second transducer by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means so that the noise components of each signal are in phase with each other; means for reversing the polarity of said time-shifted electrical pressure measurement signal so that the noise component of said time-shifted signal is 180* out of phase with the noise component of said other signal; and means for connecting the output of said polarity reversing means to another of said inputs of said summing means to cancel said noise components.

Claim 16

In a logging-while-drilling system wherein a downhole signal is transmitted to the surface in the form of an acoustical wave in the drilling fluid of the system, apparatus for substantially reducing the uphole noise in said drilling fluid which would normally interfere with said downhole signal comprising: conduit means for conducting drilling fluid from a source to the well in which the downhole signal is originating; a first transducer means at a first point on said conduit means for measuring the acoustical pressure at said point and for converting said pressure into a corresponding electrical signal; a second transducer means at a second point on said conduit means, spaced from said first point, for measuring said acoustical pressure at said second point and for converting said pressure into a corresponding electrical pressure measurement signal; an amplifier having an input and an output, said input of said amplifier connected to said first transducer, said amplifier further having a gain control for matching the outputs of said first and second transducers when uphole noise but no downhole signal is present in said conduit means; means for summing electrical signals having at least two inputs and an output; means connecting said output of said amplifier to one of said inputs of said summing means; means for time shifting said electrical pressure measurement signal from said second transducer by an amount corresponding with the travel time of sound in said drilling fluid from one of said transducer means to said other transducer means so that the noise components of each signal are in phase with each other; means for reversing the polarity of said time-shifted electrical pressure measurement signal so that the noise component of said time-shifted signal is 180* out of phase with the noise component of said other signal; and means for connecting the output of said polarity reversing means to another of said inputs of said summing means to cancel said noise components.