US Patent 7703548 Magnetic ranging while drilling parallel wells

Methods are disclosed for drilling a first well and a second well. The method includes measuring direction and inclination for at least one of the bottom hole assemblies (BHAs) in the wells, generating a magnetic field in at least one of the BHAs and measuring the magnetic field at the other BHA. The method includes determining the geometrical relationship of one BHA with respect to the other BHA. The method further includes determining the position of one BHA with respect to the Earth's geology or geometry. The method further includes automatically positioning one well with respect to the other well to maintain a predetermined geometrical relationship between them.