Magnetic sensor system useful for detecting tool joints in a downhole tubing string

A method of identifying ferrous changes as a plurality of the tool joints connecting a jointed tubing string move in and out of a well bore, the method comprising:

• (A) moving a tubing string in or out of a well bore;
• (B) causing the tubing string to pass through a nonmagnetic cylindrical spool;
• (C) creating an alternating magnetic field across the nonmagnetic cylindrical spool;
• (D) sensing a deviation in the alternating magnetic field;
• and
• (E) identifying the deviation in the alternating magnetic field as the presence of a ferrous change within the nonmagnetic cylindrical spool, the ferrous change indicative of the presence within the nonmagnetic cylindrical spool of a tool joint on the tubing string.

A method of identifying ferrous changes while moving a jointed tubing string in and out of a well bore, a plurality of tool joints connecting the jointed tubing string, the method comprising:

• (A) moving the tubing string through an upper BOP, a lower BOP, and a nonmagnetic cylindrical spool;
• (B) separating the upper BOP and the lower BOP with the nonmagnetic cylindrical spool;
• (C) creating an alternating magnetic field across the nonmagnetic cylindrical spool;
• (D) sensing a deviation in the alternating magnetic field;
• (E) identifying the deviation in the alternating magnetic field as the presence of ferrous change within the nonmagnetic cylindrical spool, the ferrous change indicative of the presence within the nonmagnetic cylindrical spool of a tool joint on the tubing string;
• and
• (F) moving the tubing string in or out of the well bore without the tool joint contacting the upper BOP and the lower BOP.

An apparatus for identifying ferrous changes in a jointed tubing string, a plurality of tool joints connecting the jointed tubing string, the tubing string moving in and out of a well bore, the apparatus comprising:

• a nonmagnetic cylindrical spool, an upper BOP, and a lower BOP, the tubing string moving in or out of the well bore through the nonmagnetic cylindrical spool, the upper BOP, and the lower BOP;
• the nonmagnetic cylindrical spool separating the upper BOP and the lower BOP;
• the upper BOP closable around the tubing string to form a pressure lock;
• the lower BOP closable around the tubing string to form a pressure lock;
• a rotatable permanent magnet attached to the nonmagnetic cylindrical spool, the permanent magnet rotatable about an axis substantially orthogonal to the cylindrical axis of the nonmagnetic cylindrical spool;
• a motor secured to the nonmagnetic cylindrical spool, the motor disposed to rotate the permanent magnet;
• a source field shaper secured to the nonmagnetic cylindrical spool, the source field shaper disposed to shape the magnetic field created by the rotating permanent magnet;
• at least two sensors secured to the nonmagnetic cylindrical spool, the sensors disposed to identify changes in the magnetic field;
• the sensors further disposed to create a processor-readable signal whose signature corresponds to changes in the magnetic field;
• at least one sensor field shaper attached to the nonmagnetic cylindrical spool, the sensor field shaper disposed to shield the sensors from external magnetic interference;
• the upper BOP openable to allow passage of the tool joint;
• and
• the lower BOP openable to allow passage of the tool joint.

A method of identifying ferrous changes as a coiled tubing string moves in and out of a well bore, the method comprising:

• (A) moving a coiled tubing string in and out of a well bore;
• (B) causing the coiled tubing string to pass through a nonmagnetic cylindrical spool;
• (C) creating an alternating magnetic field across the nonmagnetic cylindrical spool;
• (D) sensing a deviation in the alternating magnetic field;
• and
• (E) identifying the deviation in the alternating magnetic field as the presence of a ferrous change within the nonmagnetic cylindrical spool, the ferrous change indicative of the presence within the nonmagnetic cylindrical spool of the coiled tubing string.