Design Optimization of Downhole Magnetic Source for Rotary Magnetic Ranging System

In order to improve the magnetic field intensity and extend the range of magnetic field of magnetic source used in RMRS(rotating magnet ranging system),magnetic source optimization design was conducted.Based on static magnetic field theory and the feature of magnetic source,the electric current model of cylindrical permanent magnet used in the magnetic source was established.The relationship among the magnetic intensity and the diameter as well as length of the cylindrical permanent magnet was derived based on magnetic vector potential equation.Spatial magnetic intensity is dependent on diameter and length of the cylindrical permanent magnet.According to the experiments on the different cylindrical permanent magnets,the spatial magnetic intensity of the magnet sub was measured and analyzed.The results show that the spatial magnetic induction density was increased 80% when the diameters of the magnets increase from 10 mm to 20 mm with the same length.Given the same magnet diameter,the spatial magnetic induction density increases 200% when the magnet length increased from 50 mm to 100 mm.For the magnet sub whose permanent magnets are arranged side by side,its spatial magnetic intensity will increase with the increase of diameter and length of cylindrical permanent magnets.Given the same volume,the magnet will have a stronger magnetic intensity with a greater length-to-diameter ratio.The magnet with a length-to-diameter ratio of 8.33 has the twice magnetic intensity as the magnet with a length-to-diameter ratio of 0.53.Consequently,the design optimization of the magnet’s geometrical parameter can effectively improve the performance of the magnetic source.