Systems and methods for guiding the drilling of a horizontal well

Abstract

System and methods for guiding the drilling of a horizontal well are disclosed. A current is provided in at least one conductor positioned in a target vertical well. A magnetic field generated by the current is measured at a drilling assembly that is drilling the horizontal well. A direction from the drilling assembly to the target vertical well is determined based at least in part on the measured magnetic field. A distance from the drilling assembly to the target vertical well is determined based at least in part on the measured magnetic field. The determination of the distance includes determining at least one gradient.

1 . A method for guiding the drilling of a horizontal well, comprising:
 providing a current in at least one conductor positioned in a target vertical well;   measuring, at a drilling assembly that is drilling the horizontal well, a magnetic field generated by the current;   determining, based at least in part on the measured magnetic field, a direction from the drilling assembly towards the target vertical well; and   determining, based at least in part on the measured magnetic field, a distance from the drilling assembly to the target vertical well, wherein determining the distance comprises determining at least one gradient.   
   
   
       2 . The method of  claim 1 , wherein providing a current comprises providing a low frequency alternating current by a current generation source. 
   
   
       3 . The method of  claim 2 , further comprising:
 terminating the at least one conductor to earth ground at a distal end of the at least one conductor that is opposite to an end that is terminated to the current generation source.   
   
   
       4 . The method  claim 1 , further comprising:
 outputting at least one of the determined direction and the determined distance to a directional driller controlling the path of the drilling assembly.   
   
   
       5 . The method of  claim 4 , wherein outputting at least one of the determined direction and the determined distance comprises displaying the determined direction, and further comprising:
 correcting the determined direction to true north prior to displaying the determined direction.   
   
   
       6 . The method of  claim 1 , further comprising:
 adjusting the path of the drilling assembly based at least in part on one or more of the determined distance and the determined direction.   
   
   
       7 . The method of  claim 1 , wherein determining the at least one gradient comprises:
 determining a rate of change of the magnetic field as the distance from the drilling assembly to the target vertical well changes.   
   
   
       8 . The method of  claim 7 , wherein determining the rate of change of the magnetic field as the distance from the drilling assembly to the target vertical well changes comprises:
 measuring the intensity of the magnetic field at a first position of the drilling assembly in the horizontal well and at a second position of the drilling assembly in the horizontal well;   determining a difference in intensity between the measured intensity at the first position and the measured intensity at the second position;   determining a distance between the first position and the second position; and   determining the rate of change of the intensity of the magnetic field as the distance from the drilling assembly to the target vertical well changes based at least in part on the determined difference in intensity and the determined distance between the first position and the second position.   
   
   
       9 . The method of  claim 1 , wherein determining the at least one gradient comprises:
 determining a plurality of gradient calculations; and   averaging the plurality of determined gradient calculations.   
   
   
       10 . The method of  claim 1 , wherein determining the direction from the drilling assembly to the target vertical well comprises:
 determining a plurality of components of the measured magnetic field along respective axes;   determining a radial value of the direction based at least in part on at least one of the plurality of components;   determining an axial value of the direction based at least in part on at least one of the plurality of components; and   determining the direction based at least in part on the determined radial value and the determined axial value.   
   
   
       11 . A system for guiding the drilling of a horizontal well, comprising:
 at least one conductor positioned in a target vertical well and operable to carry a current signal;   one or more sensors associated with a drilling assembly that is drilling the horizontal well, wherein the one or more sensors are operable to measure the intensity of a magnetic field generated by the current signal; and   a processor operable (i) to receive the intensity measurements from the one or more sensors, (ii) to determine a direction from the drilling assembly towards the target vertical well based at least in part on the received intensity measurements, and (iii) to determine a distance from the drilling assembly to the target vertical well based at least in part on the received intensity measurements, wherein at least one gradient calculation is utilized to determine the distance.   
   
   
       12 . The system of  claim 11 , wherein the current signal comprises a low frequency alternating current signal generated by a current generation source. 
   
   
       13 . The system of  claim 12 , wherein the at least one conductor is terminated to earth ground at a distal end of the at least one conductor that is opposite to an end that is terminated to the current generation source. 
   
   
       14 . The system  claim 11 , further comprising at least one output device operable to display at least one of the determined direction and the determined distance to a directional driller controlling the path of the drilling assembly. 
   
   
       15 . The system of  claim 14 , wherein:
 the at least one output device is operable to display the determined direction; and   the control unit is further operable to correct the determined direction to true north prior to the display of the determined direction.   
   
   
       16 . The method of  claim 11 , wherein the path of the drilling assembly is adjusted based at least in part on one or more of the determined distance and the determined direction. 
   
   
       17 . The system of  claim 11 , wherein the processor determines the at least one gradient calculation by determining a rate of change of the intensity of the magnetic field as the distance from the drilling assembly to the target vertical well changes. 
   
   
       18 . The system of  claim 17 , wherein the one or more sensors are operable to measure the intensity of the magnetic field a first position of the drilling assembly in the horizontal well and at a second position of the drilling assembly in the horizontal well; and
 the processor determines the rate of change of the intensity of the magnetic field as the distance from the drilling assembly to the target vertical well changes by:
 determining a difference in intensity between the measured intensity at the first position and the measured intensity at the second position; 
 determining a distance between the first position and the second position; and 
 determining the rate of change of the intensity of the magnetic field as the distance from the drilling assembly to the target vertical well changes based at least in part on the determined difference in intensity and the determined distance between the first position and the second position. 
   
   
   
       19 . The system of  claim 11 , wherein the at least one gradient calculation comprises a plurality of gradient calculations that are averaged together. 
   
   
       20 . The system of  claim 11 , wherein the processor determines the direction from the drilling assembly towards the target vertical well by:
 identifying a plurality of components of the measured intensity along respective axes;   determining a radial value of the direction based at least in part on at least one of the identified plurality of components;   determining an axial value of the direction based at least in part on at least one of the identified plurality of components; and   determining the direction based at least in part on the determined radial value and the determined axial value.