Rotating magnetic field range finder and its measurement method for relative separation between drilling wells

A rotating magnetic field rangefinder for measuring relative separation between a drill bit and a well, comprising:

• the drill bit;
• a magnetic drill collar sub assembly is located in the rear of drill bit, the magnetic drill collar sub assembly rotates together with drill bit providing a rotating magnetic field signal source to generate a rotating magnetic field;
• a down hole sensor tool configured to reside in a position in an existing well, the downhole sensor tool including:
• two tri-axial fluxgate magnetometers spaced apart to measure the rotating magnetic field in two locations, the two tri-axial fluxgate magnetometers configured to measure each component of the rotating magneticfield at the position of the downhole sensor tool;
• and three accelerometers, the three accelerometers and two tri-axial fluxgate magnetometers cooperating to establish a coordinate system for the two tri-axial fluxgate magnetometers in the Earth's gravity field and the Earth's magnetic field;
• surface interface gear in electrical communication with the downhole sensor tool, the surface interface gear receiving data from the downhole sensor tool, wherein:
• the magnetic drill collar sub assembly is a permanent magnet drill collar sub assembly including permanent magnets creating the rotating magnetic field;
• the permanent magnet drill collar sub assembly defines a sub assembly axis aligned with the length of the permanent magnet drill collar sub assembly;
• and the permanent magnets comprise both perpendicularly aligned permanent magnets and parallel aligned permanent magnets residing within permanent magnet drill collar sub assembly.