Distance determination from a magnetically patterned target well

A method for estimating the distance between a twin well and a magnetized target well in substantially real time during drilling of the twin well, the target well being 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, the method comprising:

• (a) deploying a drill string in the twin well, the drill string including a magnetic sensor in sensory range of magnetic flux emanating from the target well;
• (b) measuring an axial component of the magnetic flux in substantially real time during drilling, the axial component substantially parallel with a longitudinal axis of the twin well;
• (c) processing the axial component of the magnetic flux measured in (b) to estimate a magnitude of an interference magnetic field vector attributable to the target well;
• and
• (d) processing the magnitude estimated in (c) to estimate the distance between the twin and target wells.

A method for determining a distance between a twin well and a target well, the target well being 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, the method comprising:

• (a) deploying a drill string in the twin well, the drill string including a magnetic sensor in sensory range of magnetic flux emanating from the target well;
• (b) measuring a magnetic field with the magnetic sensor;
• (c) processing the magnetic field measured in (b) to determine first and second components of an interference magnetic field vector attributable to the target well, the first and second components being selected from the group consisting of (i) a magnitude of the interference magnetic field vector and an angle of the interference magnetic field vector with respect to a fixed reference and (ii) magnitudes of first and second orthogonal components of the interference magnetic field vector;
• and
• (d) processing the first and second components determined in (c) in combination with a model relating the first and second components to (i) the distance and (ii) an axial position of the magnetic field sensor relative to the target well to determine the distance between the magnetic field sensor and the target well.

A method for determining a distance between a twin well and a target well, the target well being 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, the method comprising:

• (a) deploying a drill string in the twin well, the drill string including a magnetic sensor in sensory range of magnetic flux emanating from the target well;
• (b) measuring a magnetic field at first and second longitudinally spaced locations in the borehole;
• (c) processing the first and second magnetic field measurements to determine first and second directions of an interference magnetic field vector at the corresponding first and second locations;
• and
• (d) processing the first and second directions determined in (c) and a difference in measured depth between the first and second locations with a model relating a direction of the interference magnetic field vector to the distance between the twin well and the target well to determine the distance.