A magnetic torque optimization method for a hydraulic – magnetic coupling-drive cuttings cleaning tool

Abstract During the drilling process, cuttings carrying in the horizontal well section is relatively difficult, and cuttings beds form easily. A new type of hydraulic – magnetic coupling transmission cuttings cleaning tool is proposed, but the magnetic torque transmission influence mechanism, the optimal magnetic circuit structure and the magnet configuration are still yet to be studied. To this end, the finite element numerical simulation method is applied to analyze the influence of magnetic circuit structure and permanent magnet geometry on magnetic torque. The results of numerical simulation and laboratory experiments show that (1) the magnetic torque transmission efficiency can be improved by increasing the air gap flux density, reducing the magnetic reluctance and increasing the magnetostatic energy accumulation; (2) the magnetic torque increases first and then decreases as the number of pole-pair increases. The magnetic torque of 12 pairs of pole pairs reaches the maximum value; (3) by the coupling of the amount of magnets under the constraints of the effective section magnet coverage area percentage and the thickness of the magnet, it is obtained that when the thickness of the permanent magnet is 8.4 mm and the magnet coverage area percentage on the effective section of the tool is 71%, the maximum magnetic torque is generated per unit volume of magnet; (4) the absolute error of the indoor experimental result and the numerical simulation result is less than 17%, which can meet the engineering calculation accuracy requirements. It is concluded that the established numerical simulation model is reasonable and can be used as a technical means for the optimization analysis of the tool structure.