Target well ranging method, apparatus, and system

Abstract

A ranging signal and a reference signal are generated. The reference signal has a lower frequency than the ranging signal. The reference signal is transmitted through a geological formation to be received by a ranging tool in a ranging well while the ranging signal is launched down a target well. The reference signal is reconstructed in the ranging well and a signal that is a combination of the ranging signal launched from the target well and noise are received in the ranging well. The received signal may be in the form of magnetic or electric field values or changes in these fields. The reconstructed reference signal, in combination with the received signal, is used to produce a filtered ranging signal. A relative location of the target well can then be determined in relation to the ranging well based on the filtered ranging signal. The location information can be used to direct drilling operations.

1 . A method for ranging between a target well and a ranging well, the method comprising:
 generating a clock signal;   generating a ranging signal from the clock signal;   generating a reference signal from the clock signal;   launching the ranging signal from the target well;   transmitting the reference signal;   receiving the reference signal with a first receiver in the ranging well;   reconstructing the clock signal as a reconstructed clock signal;   using one of the first receiver or a second receiver in the ranging well, receiving a signal that is a combination of noise and of the ranging signal launched from the target well;   producing a filtered ranging signal using the reconstructed clock signal in combination with the received signal; and   determining a relative location of the target well in relation to the ranging well based on the filtered ranging signal.   
     
     
         2 . The method of  claim 1  wherein reconstructing the clock signal comprises:
 receiving a propagated reference signal; 
 generating a pair of quadrature signals from the received propagated reference signal; and 
 generating a rectangular signal from the received propagated reference signal. 
 
     
     
         3 . The method of  claim 2  further comprising integrating the magnetic field over a time period determined by the rectangular signal. 
     
     
         4 . The method of  claim 3  wherein the time period comprises an integer multiple of an inverse of a fundamental frequency of the clock signal. 
     
     
         5 . The method of  claim 1  further comprising steering a drill bit while drilling the ranging well in response to the relative location. 
     
     
         6 . The method of  claim 1  wherein generating the reference signal comprises:
 multiplying a frequency of the clock signal by an integer “m” to produce a result; and 
 dividing the result by an integer “n” to produce the reference signal wherein m/n<1. 
 
     
     
         7 . The method of  claim 1  further comprising monitoring a magnetic field generated by the target well in response to the ranging signal using one of a magnetometer or a gradiometer in the ranging well. 
     
     
         8 . The method of  claim 1  wherein transmitting the reference signal comprises launching the reference signal into a surface of a geological formation that includes the target well and the ranging well. 
     
     
         9 . The method of  claim 8  wherein launching the reference signal into the surface comprises launching the reference signal with at least one of: a loop antenna coupled to the surface or a plurality of ground contacts coupled to the surface. 
     
     
         10 . (canceled) 
     
     
         11 . The method of  claim 1  further comprising:
 launching the reference signal to a well head of a well casing of the ranging well; 
 creating a signal that contains the reference signal and the ranging signal by summing the reference signal and the clock signal; and 
 launching the signal that contains the reference signal and the ranging signal down a well head of a casing of the target well. 
 
     
     
         12 . A system, comprising:
 a signal generator circuit to generate both a ranging signal and a reference signal based on a clock signal, wherein the ranging signal has a first frequency, and the reference signal has a second frequency, wherein the ranging signal is coupled to a target well, and wherein the second frequency is less than the first frequency;   a downhole tool;   at least one of a magnetometer or a gradiometer attached to the downhole tool, the at least one of the magnetometer or the gradiometer to provide detected signals in the form of magnetic or electric field values or changes in the magnetic or electric fields that, in combination with a reconstructed reference signal, produce a filtered ranging signal in response to the ranging signal being launched down the target; and   a signal processor to monitor the detected signals in a ranging well to determine a relative location of the ranging well in relation to the target well based on the filtered ranging signal.   
     
     
         13 . The system of  claim 12  further comprising:
 an oscillator to generate the clock signal; and 
 a frequency scaling circuit coupled to the oscillator to generate the reference signal by multiplying the clock signal by an integer “m” and dividing by an integer “n” to produce the reference signal wherein m/n<1. 
 
     
     
         14 . (canceled) 
     
     
         15 . The system of  claim 14  further comprising a transmitter of the reference signal coupled to the frequency scaling circuit. 
     
     
         16 . The system of  claim 15  wherein the transmitter of the reference signal comprises at least one of: a loop antenna, a plurality of dipole antennas, a power amplifier that can be used to couple the frequency scaling circuit to a casing of the ranging well, or a summing amplifier coupled to the clock circuit and the frequency altering circuit to generate a signal that contains the reference signal and the ranging signal by summing the reference signal and the clock signal. 
     
     
         17 . An apparatus comprising:
 a reconstruction circuit to receive a signal and generate a reconstructed reference signal from the received signal, the reconstructed reference signal based on a clock signal;   at least one of a magnetometer or a gradiometer to couple to the reconstruction circuit, the at least one of the magnetometer or the gradiometer to provide detected signals in the form of magnetic or electric field values or changes in the magnetic or electric fields that, in combination with a reconstructed reference signal to produce a filtered ranging signal in response to the ranging signal being launched down a target well; and   a signal processor, coupled to the at least one magnetometer or the gradiometer, to monitor the detected signals in a ranging well to determine a location of the ranging well in relation to the target well based on the filtered ranging signal.   
     
     
         18 . The apparatus of  claim 17  wherein the circuit to receive the signal and generate the reconstructed reference signal comprises one of a resonant circuit or a bandpass filter to filter out noise from the reference signal wherein the resonant circuit comprises a capacitor coupled in parallel. 
     
     
         19 . (canceled) 
     
     
         20 . The apparatus of  claim 18  wherein the circuit to receive the signal and generate the reconstructed reference signal comprises:
 a frequency multiplier circuit, coupled to one of the resonant circuit or the bandpass filter, to multiply the frequency of the received signal by an integer “n” to produce a result; and 
 a frequency divider circuit to divide the resulting frequency by an integer “m” wherein m/n<1. 
 
     
     
         21 . The apparatus of  claim 20  further comprising an integrator period generator, coupled to the frequency divider circuit, to generate an integrated signal wherein the integrated signal is derived from the reconstructed reference signal over a time period of 1/f 0  wherein f 0  is a fundamental frequency of the reference signal. 
     
     
         22 . The apparatus of  claim 21  further comprising a lock-in amplifier, coupled to the at least one magnetometer or the gradiometer and the reconstruction circuit, to generate the filtered ranging signal based on the detected signals, representing the magnetic or electric field values or changes in the magnetic or electric fields or the gradiometer, generated in response to the ranging signal being launched down the target well. 
     
     
         23 . The apparatus of  claim 21  further comprising:
 at least one analog-to-digital converter coupled to the at least one magnetometer or the gradiometer and the reconstruction circuit; and 
 a digital signal processor coupled to the at least one A/D converter to generate the filtered ranging signal based on the detected signals representing the magnetic or electric field values or changes in the magnetic or electric fields. 
 
     
     
         24 . The apparatus of  claim 17  further comprising a bandpass filter coupled to an output of the at least one magnetometer or the gradiometer to remove effects of the reference signal from detected signals. 
     
     
         25 . (canceled) 
     
     
         26 . A transmitter apparatus comprising:
 an oscillator circuit that generates a clock signal having a clock frequency;   a frequency scaler circuit, coupled to the oscillator circuit, that generates a reference signal having a lower frequency than the clock frequency;   a ranging signal generation circuit, coupled to the oscillator circuit, to generate a ranging signal having the clock frequency, the ranging signal coupled to a target well; and   a transmitter circuit, coupled to the frequency scaler circuit, configured to transmit the reference signal into a surface of a geological formation.   
     
     
         27 . The transmitter apparatus of  claim 26  wherein the transmitter circuit is at least one of: a loop antenna coupled to the surface or a plurality of dipole antenna coupled to the surface. 
     
     
         28 . (canceled)