System and method for determining fault location

Abstract

Apparatus and method for locating faults in wired drill pipe while drilling. In one embodiment, a fault location system includes a plurality of conductively coupled media sections, impedance measurement electronics, and a fault locator. Each media section includes conductive couplers on opposing ends of the media section, and conductive media connected to and communicatively coupling the conductive couplers. The impedance measurement electronics is configured to measure an input impedance of the media sections. The fault locator is configured to determine a propagation constant for the media sections, and to determine, as a function of the input impedance and the propagation constant, a location of a fault in the media sections.

What is claimed is: 
     
         1 . A method for locating a fault in wired drill pipe, comprising:
 disposing a drill string comprising a plurality of wired drill pipes in a borehole;   measuring the input impedance of the wire drill pipes while drilling:   determining a propagation constant for the wire drill pipes;   determining, based on the input impedance, whether a fault in the wired drill pipe is an open circuit or a short circuit.   
     
     
         2 . The method of  claim 1 , wherein the analyzing comprising analyzing an imaginary portion of the input impedance and determining, based on the imaginary part of the input impedance, whether the fault is an open circuit or a short circuit. 
     
     
         3 . The method of  claim 2 , wherein the analyzing further comprises:
 determining that the fault is an open circuit based on the imaginary part being negative below a predetermined frequency; and   determining that the fault is a short circuit based on the imaginary part being positive below the predetermined frequency.   
     
     
         4 . The method of  claim 1 , further comprising determining a distance from a point of input impedance measurement to the fault as a function of the propagation constant, the measured input impedance, and whether the fault is an open circuit or a short circuit. 
     
     
         5 . The method of  claim 4 , wherein determining the distance further comprising averaging a plurality of distances to the fault determined for a number of different frequencies. 
     
     
         6 . The method of  claim 1 , further comprising:
 identifying a zero crossing in an imaginary portion of the input impedance; and   determining a distance from a point of impedance measurement to the fault as a function of a frequency at the zero crossing and phase velocity at the frequency.   
     
     
         7 . The method of  claim 6 , wherein the identifying comprises identifying a plurality of zero crossings in the imaginary portion of the input impedance; determining the distance comprises determining a different distance for each of the zero crossings and averaging the different distances. 
     
     
         8 . The method of  claim 1 , further comprising:
 least squares fitting the measured input impedance to a function for a real portion of the input impedance and a function for an imaginary portion of the input impedance; and   determining a distance from a point of impedance measurement to the fault based on the fitting.   
     
     
         9 . The method of  claim 1 , further comprising determining a location of the fault based on a first input impedance measured from downhole of the fault in the wired drill pipe. 
     
     
         10 . The method of  claim 9 , further comprising determining a location of the fault based on a second input impedance measured from uphole of the fault in the wired drill pipe. 
     
     
         11 . Apparatus for drilling a borehole in formations, comprising:
 a drill string comprising a plurality of wired drill pipes; and   a wired drill pipe fault monitor coupled to the wired drill pipes, the fault monitor comprising:
 an impedance measuring system configured to measure an input impedance of the wired drill pipes while drilling the borehole; and 
 a fault locator configured to:
 determine a propagation constant for the wired drill pipes; and 
 determine, as a function of the input impedance and the propagation constant, a location of a fault in the wired drill pipes. 
 
   
     
     
         12 . The apparatus of  claim 11 , wherein the fault locator is configured to determine, based on the input impedance whether the fault in the wired drill pipes is an open circuit or a short circuit, 
     
     
         13 . The apparatus of  claim 12 , wherein the fault locator is further configured to determine the location of the fault in the wired drill pipes based on whether the fault is an open or a short. 
     
     
         14 . The apparatus of  claim 12 , wherein the fault locator is configured to analyze an imaginary part of the input impedance and determine, based on the imaginary portion of the input impedance whether the fault is an open circuit or a short circuit. 
     
     
         15 . The apparatus of  claim 14 , wherein the fault locator is configured to:
 determine that the fault is an open circuit based on the imaginary part being negative at predetermined low frequencies; and   determine that the fault is a short circuit based on the imaginary part being positive at predetermined low frequencies.   
     
     
         16 . The apparatus of  claim 11 , wherein the fault locator is configured to determine a plurality of distances from the impedance measuring system to the fault, each distance corresponding to a different frequency; and average the plurality of distances to obtain a final distance to the fault. 
     
     
         17 . The apparatus of  claim 11 , wherein the fault locator is configured to:
 identify a zero crossing in an imaginary portion of the input impedance; and   determine a distance from the impedance measuring system to the fault as a function of a frequency at the zero crossing and phase velocity at the frequency.   
     
     
         18 . The apparatus of  claim 17 , wherein the fault locator is configured to:
 identify a plurality of zero crossings in the imaginary part of the input impedance;   determine a different distance to the fault for each of the zero crossings; and   average the different distances to obtain a final distance to the fault.   
     
     
         19 . The apparatus of  claim 11 , wherein the fault locator is configured to:
 least squares fit the measured input impedance to a function for a real portion of the input impedance and a function for an imaginary portion of the input impedance; and   determine a distance from the impedance measuring system to the fault based on the fit functions.   
     
     
         20 . The apparatus of  claim 11 , further comprising:
 a plurality of subs, each sub separated from the next by a plurality of wired drill pipes;   wherein each sub comprises an instance of the wired drill pipe fault monitor; and
 each sub is configured to:
 measure at least one of an uphole input impedance of wired drill pipes uphole of the repeater and a downhole input impedance of wired drill pipes downhole of the repeater; 
 
   wherein a computer disposed at the surface is configured to determine the location of the fault in the wired drill pipes between two subs based on the downhole input impedance.   
     
     
         21 . The apparatus of  claim 20 , wherein the computer is configured to determine the location of the fault in the wired drill pipes between two subs based on both the uphole input impedance and the downhole input impedance. 
     
     
         22 . A fault location system, comprising:
 a plurality of conductively coupled media sections, each media section comprising:
 a length of conductive media; and 
 conductive couplers communicatively connected to opposing ends of the conductive media; 
   impedance measurement electronics configured to measure an input impedance of the media sections; and   a fault locator configured to:
 determine a propagation constant for the media sections; 
 analyze the input impedance and determine, as a function of the input impedance and the propagation constant, a location of a fault in the media sections. 
   
     
     
         23 . The fault location system of  claim 22 , wherein the media sections are joints of wired drill pipe. 
     
     
         24 . The fault location system of  claim 22 , wherein the fault locator is configured to:
 determine, based on the input impedance whether the fault is an open circuit or a short circuit; and   determine the location of the fault based on whether the fault is an open or a short.   
     
     
         25 . The fault location system of  claim 24 , wherein the fault locator is configured to:
 determine that the fault is an open circuit based on an imaginary part of the input impedance being negative at predetermined low frequencies; and   determine that the fault is a short circuit based on the imaginary part being positive at predetermined low frequencies.   
     
     
         26 . The fault location system of  claim 22 , wherein the fault locator is configured to determine a plurality of distances from the impedance measurement electronics to the fault, each distance corresponding to a different frequency; and average the plurality of distances to obtain a final distance to the fault. 
     
     
         27 . The fault location system of  claim 22 , wherein the fault locator is configured to:
 identify a zero crossing in an imaginary portion of the input impedance; and   determine a distance from the impedance measurement electronics to the fault as a function of a frequency at the zero crossing and phase velocity at the frequency.   
     
     
         28 . The fault location system of  claim 27 , wherein the fault locator is configured to:
 identify a plurality of zero crossings in the imaginary part of the input impedance;   determine a different distance to the fault for each of the zero crossings; and   average the different distances to obtain a final distance to the fault.   
     
     
         29 . The fault location system of  claim 22 , wherein the fault locator is configured to:
 least squares fit the measured input impedance to a function for a real portion of the input impedance and a function for an imaginary portion of the input impedance; and   determine a distance from the impedance measurement electronics to the fault based on the fit functions.   
     
     
         30 . The fault location system of  claim 22 , wherein the fault locator is configured to determine the location of fault based on impedance measurements taken from two sides of the fault. 
     
     
         31 . A channel characterization system, comprising:
 a first calibration unit, and a second calibration unit coupled to the first calibration unit via a conductive medium; and   a processor coupled to the first calibration unit and the second calibration unit;   wherein the first and second calibration units are configured to:
 exchange characterization signals via the conductive medium; 
 measure amplitude and phase of the characterization signal received via the conductive medium from the other calibration unit; and 
 provide the amplitude and phase measurements to the processor; and 
   wherein the processor is configured to determine a propagation constant of the conductive medium based on the measurements.   
     
     
         32 . The system of  claim 31 , wherein each calibration unit comprises an oscillator configured to:
 generate a characterization signal having a predetermined frequency for transmission via the conductive medium based on the calibration unit being set to transmit the characterization signal; and   based on the calibration unit being set to receive the characterization signal via the conductive medium, to:
 generate a first comparison signal at the predetermined frequency; and 
 generate a second comparison signal at the predetermined frequency having quadrature phase offset from the first comparison signal. 
   
     
     
         33 . The system of  claim 31 , wherein each calibration unit comprises:
 a first mixer configured to mix the characterization signal received via the conductive medium with a sine signal generated by an oscillator of the calibration unit; and   a second mixer configured to mix the characterization signal received via the conductive medium with a cosine signal generated by the oscillator of the calibration unit.   
     
     
         35 . The system of  claim 33 , further comprising an integrator configured to:
 integrate output of the first mixer over time; and   integrate output of the second mixer over time.   
     
     
         34 . The system of  claim 31 , wherein each calibration unit comprises:
 a low pass filter configured to:
 block a sum of the frequency of the characterization signal received via the conductive medium and a signal generated by an oscillator of the calibration unit; and 
 pass a difference of the frequency of the characterization signal received via the conductive medium and the signal generated by the oscillator of the calibration unit 
   
     
     
         35 . The system of  claim 31 , wherein the processor is configured to:
 determine an imaginary portion of the propagation constant based on the characterization signal transmitted from the first calibration unit to the second calibration unit; and   determine a real portion of the propagation constant based on the characterization signal transmitted from the first calibration unit to the second calibration unit and the characterization signal transmitted from the second calibration unit to the first calibration unit.   
     
     
         36 . The system of  claim 35 , wherein the processor is configured to determine the imaginary portion as a logarithm of a sum of a time integrated sum of the received characterization signal and a locally generated sine signal and a time integrated sum of the received characterization signal and a locally generated cosine signal. 
     
     
         37 . The system of  claim 35 , wherein the processor is configured to determine the real portion as a difference of an inverse tangent of values derived from the characterization signal transmitted from the first calibration unit to the second calibration unit and an inverse tangent of values derived from the characterization signal transmitted from the second calibration unit to the first calibration unit. 
     
     
         38 . The system of  claim 31 , wherein conductive medium is wired drill pipe. 
     
     
         39 . A method for characterizing a communication channel, comprising:
 splitting, by a first calibration unit, a calibration signal transmitted by a second calibration unit via a conductive medium connecting the first and second calibration units into a first two signals;   mixing, by the first calibration unit, a first of the first two signals with a first oscillator signal generated by the first calibration unit to produce a first mixed signal; and   mixing, by the first calibration unit, a second of the first two signals with a second oscillator signal generated by the first calibration unit to produce a second mixed signal; wherein the first and second oscillator signals generated by the first calibration unit have a same frequency and quadrature phase offset;   filtering a sum of the first of the first two signals and the first oscillator signal generated by the first calibration unit from the first mixed signal to produce a first filtered signal;   filtering a sum of the second of the first two signals and the second oscillator signal generated by the first calibration unit from the second mixed signal to produce a second filtered signal;   integrating the first filtered signal over time to generate a first integrated signal;   integrating the second filtered signal over time to generate a second integrated signal; and   computing a propagation constant for the conductive medium based on the first and second integrated signals.   
     
     
         40 . The method of  claim 39 , wherein computing the propagation constant comprises computing an imaginary portion of the propagation constant based on the first and second integrated signals. 
     
     
         41 . The method of  claim 39 , further comprising:
 splitting, by the second calibration unit, a calibration signal transmitted by the first calibration unit via the conductive medium into a second two signals;   mixing, by the second calibration unit, a first of the second two signals with a first oscillator signal generated by the second calibration unit to produce a third mixed signal; and   mixing, by the second calibration unit, a second of the second two signals with a second oscillator signal generated by the second calibration unit to produce a fourth mixed signal; wherein the first and second oscillator signals generated by the second calibration unit have a same frequency and quadrature phase offset;   filtering a sum of the first of the second two signals and the first oscillator signal generated by the second calibration unit from the third mixed signal to produce a third filtered signal;   filtering a sum of the second of the second two signals and the second oscillator signal generated by the second calibration unit from the fourth mixed signal to produce a fourth filtered signal;   integrating the third filtered signal over time to generate a third integrated signal;   integrating the fourth filtered signal over time to generate a fourth integrated signal; and   computing the propagation constant for the conductive medium based on the third and fourth integrated signals.   
     
     
         42 . The method of  claim 41 , wherein computing the propagation constant comprises computing an imaginary portion of the propagation constant based on the third and fourth integrated signals. 
     
     
         43 . The system of  claim 42 , wherein computing the imaginary portion of the propagation constant comprises computing a logarithm of a sum of the third and fourth integrated signals squared. 
     
     
         44 . The method of  claim 41 , wherein computing the propagation constant comprises computing a real portion of the propagation constant based on the first, second, third and fourth integrated signals. 
     
     
         45 . The method of  claim 44 , wherein computing the real portion of the propagation constant comprises computing a difference of:
 an inverse tangent of a ratio of the third and fourth integrated signals, and   an inverse tangent of a ratio of the first and second integrated signals.   
     
     
         46 . A phase calibration system, comprising:
 a first unit and a second unit configured to communicate via a communication medium that can propagate sinusoidal waves and data; and   a processor coupled to the first unit and the second unit;   wherein each of the first unit and the second unit comprises an oscillator, and is configured to:
 exchange sinusoidal signals via the communication medium; 
 measure phase of the sinusoidal signals received via the communication medium from the other of the first unit and the second unit; and 
 provide phase measurements to the processor; 
   wherein the processor is configured to determine the phase difference between the two calibration units.