Magnetic Gradient and Curvature Based Ranging Method

Abstract

Methods for determining a distance from a drilling well to a magnetized target well include acquiring magnetic field measurements from the drilling well. The acquired magnetic field measurements are made at a plurality of spaced apart locations in the drilling well. The acquired magnetic field measurements are processed to obtain a ratio including at least one of the following: (i) a ratio of a magnetic field intensity to a first spatial derivative of a magnetic field, (ii) a ratio of a magnetic field intensity to a second spatial derivative of a magnetic field, and (iii) a ratio of a first spatial derivative of a magnetic field to a second spatial derivative of the magnetic field. The ratio (or ratios) is then processed to obtain the distance from the drilling well to the magnetized target well.

What is claimed is: 
     
         1 . A method for determining a distance from a drilling well to a magnetized target well, the method comprising:
 (a) deploying a drill string in the drilling well, the drill string including at least one magnetic field sensor in sensory range of magnetic flux emanating from the magnetized target well;   (b) making a plurality of spaced apart magnetic field measurements in the drilling well;   (c) processing the spaced apart magnetic field measurements to obtain a ratio of a magnetic field intensity to a first spatial derivative of a magnetic field; and   (d) processing the ratio computed in (c) to obtain the distance from the drilling well to the magnetized target well.   
     
     
         2 . The method of  claim 1 , wherein the target well is magnetized such that it includes a substantially periodic pattern of opposing north-north (NN) magnetic poles and opposing south-south (SS) magnetic poles spaced apart along a longitudinal axis thereof. 
     
     
         3 . The method of  claim 2 , wherein the plurality of spaced apart magnetic field measurements are made in (b) at locations adjacent to one of the opposing NN or SS magnetic poles. 
     
     
         4 . The method of  claim 1 , wherein:
 the magnetic field measurements made in (b) are radially spaced apart; and   the magnetic field measurements are processed in (c) to obtain a ratio of the magnetic field intensity of a radial component of the magnetic field to the first spatial derivative of the radial component of the magnetic field in the radial direction.   
     
     
         5 . The method of  claim 1 , wherein:
 the magnetic field measurements made in (b) are axially spaced apart; and   the magnetic field measurements are processed in (c) to obtain a ratio of the magnetic field intensity of a radial component the magnetic field to the first spatial derivative of an axial component of the magnetic field in the axial direction.   
     
     
         6 . The method of  claim 1 , further comprising:
 (e) processing the magnetic field measurements made in (b) to compute a tool face to target direction.   
     
     
         7 . A method for determining a distance from a drilling well to a magnetized target well, the method comprising:
 (a) deploying a drill string in the drilling well, the drill string including a magnetic field sensor in sensory range of magnetic flux emanating from the magnetized target well;   (b) making a plurality of spaced apart magnetic field measurements in the drilling well;   (c) processing the spaced apart magnetic field measurements to obtain a ratio of a magnetic field intensity to a second spatial derivative of a magnetic field; and   (d) processing the ratio computed in (c) to obtain the distance from the drilling well to the magnetized target well.   
     
     
         8 . The method of  claim 7 , wherein the target well is magnetized such that it includes a substantially periodic pattern of opposing north-north (NN) magnetic poles and opposing south-south (SS) magnetic poles spaced apart along a longitudinal axis thereof. 
     
     
         9 . The method of  claim 8 , wherein the plurality of spaced apart magnetic field measurements are made in (b) at locations adjacent to one of the opposing NN or SS magnetic poles. 
     
     
         10 . The method of  claim 17 , wherein:
 the magnetic field measurements made in (b) are radially spaced apart; and   the magnetic field measurements are processed in (c) to obtain a ratio of the magnetic field intensity of a radial component the magnetic field to the second spatial derivative of the radial component of the magnetic field in the radial direction.   
     
     
         11 . The method of  claim 10 , wherein:
 the magnetic field measurements made in (b) are axial spaced apart;   the magnetic field measurements are processed in (c) to obtain a ratio of the magnetic field intensity of a radial component the magnetic field to the second spatial derivative of the radial component of the magnetic field in the axial direction.   
     
     
         12 . The method of  claim 10 , further comprising:
 (e) processing the magnetic field measurements made in (b) to compute a tool face to target direction.   
     
     
         13 . A method for determining a distance from a drilling well to a magnetized target well, the method comprising:
 (a) deploying a drill string in the drilling well, the drill string including a magnetic field sensor in sensory range of magnetic flux emanating from the magnetized target well;   (b) making a plurality of spaced apart magnetic field measurements in the drilling well;   (c) processing the spaced apart magnetic field measurements to obtain a ratio of a first spatial derivative of the magnetic field and a second spatial derivative of the magnetic field; and   (d) processing the ratio computed in (c) to obtain the distance from the drilling well to the magnetized target well.   
     
     
         14 . The method of  claim 13 , wherein the target well is magnetized such that it includes a substantially periodic pattern of opposing north-north (NN) magnetic poles and opposing south-south (SS) magnetic poles spaced apart along a longitudinal axis thereof. 
     
     
         15 . The method of  claim 14 , wherein the plurality of spaced apart magnetic field measurements are made in (b) at locations adjacent to one of the opposing NN or SS magnetic poles. 
     
     
         16 . The method of  claim 13 , wherein:
 the magnetic field measurements made in (b) are radially spaced; and   the magnetic field measurements are processed in (c) to obtain a ratio of the first spatial derivative of a radial component of the magnetic field in the radial direction to the second spatial derivative of the radial component of the magnetic field in the radial direction.   
     
     
         17 . The method of  claim 13 , wherein:
 the magnetic field measurements made in (b) are axially spaced; and   the magnetic field measurements are processed in (c) to obtain a ratio of the first spatial derivative of an axial component of the magnetic field in the axial direction to the second spatial derivative of a radial component of the magnetic field in the axial direction.   
     
     
         18 . The method of  claim 13 , wherein:
 the magnetic field measurements made in (b) are both axially spaced and radially spaced;   the magnetic field measurements are processed in (c) to obtain a ratio of the first spatial derivative of an axial component of the magnetic field in the axial direction to the second spatial derivative of a radial component of the magnetic field in the radial direction.   
     
     
         19 . The method of  claim 13 , wherein:
 the magnetic field measurements made in (b) are both axially spaced and radially spaced;   the magnetic field measurements are processed in (c) to obtain a ratio of the first spatial derivative of a radial component of the magnetic field in the radial direction to the second spatial derivative of the radial component of the magnetic field in the axial direction.   
     
     
         20 . The method of  claim 13 , further comprising:
 (e) processing the magnetic field measurements made in (b) to compute a tool face to target direction.