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Downhole motor (PDM drill) is a volumetric downhole power drilling tool that uses drilling fluid as power and converts liquid pressure energy into mechanical energy. When the mud pumped by the mud pump flows into the motor through the Dump Assembly, a certain pressure difference is formed between the inlet and the outlet of the motor, pushing the rotor to rotate about the axis of the stator, and transmitting the speed and torque to the drill through the universal shaft and the transmission shaft To achieve drilling operations.
Downhole motors are mainly composed of four assemblies: Dump Assembly, hydraulic motor, cardan shaft and transmission shaft. The screw motor is the main component of the drilling tool. Many practical and theoretical analysis results show that if the motor is to work normally and efficiently, the pressure drop that each stage of the motor can withstand is preferably not more than 0.8Mpa, otherwise the motor will lose. The speed decreases quickly, and in severe cases it stops completely and the motor is damaged.
One lead of the motor is one level, and the mud flow used on site should be within the recommended range, otherwise it will affect the efficiency of the motor and even increase wear. The performance parameters of screw motors are the main performance parameters of Downhole motors. The theoretical output torque of the motor is directly proportional to the pressure drop of the motor, and the output revolutions are proportional to the input mud flow. As the load increases, the drill revolutions decrease. Control the torque and speed of downhole drilling tools.
The Dump Assembly is composed of valve body, valve sleeve, valve core and spring. Under the pressure, the valve core slides in the valve sleeve. The movement of the valve core changes the flow direction of the liquid, so that the Dump Assembly has two states of bypass and closing: in the process of tripping, the through-hole between the valve sleeve and the valve body is not closed and the Dump Assembly is in the bypass state, so that the mud in the drill string bypasses the motor and enters the annulus; when the mud When the flow and pressure reach the standard setting value, the valve core moves down, and the Dump Assembly hole is closed. At this time, the mud flows through the motor, transforming the pressure energy into mechanical energy. When the mud flow value is too small or the pump stops, the spring will jack up the valve core, and the Dump Assembly hole is in the open position -- in the bypass state.
The motor is composed of stator and rotor. The stator is made by injecting rubber bushing on the inner wall of the steel tube. The inner hole of the stator is a screw with certain geometric parameters, and the rotor is a screw with a hard layer. The rotor and the stator are meshed with each other, and a spiral sealing cavity is formed by the difference of their lead to complete the energy conversion. The helix of the motor rotor can be divided into single head and multi-head. The less the number of rotor heads, the higher the speed, the smaller the torque; the more the number of heads, the lower the speed, the greater the torque.
The function of cardan shaft is to change the planetary motion of motor into the fixed shaft rotation of transmission shaft, and transfer the torque and rotation speed generated by motor to transmission shaft to drill bit. The cardan shaft is mostly flexible shaft type.
The function of the transmission shaft is to transmit the rotating power of the motor to the drill bit, and bear the axial and radial loads generated by the WOB at the same time. Therefore, the transmission shaft needs high hardness, wear-resistance and service life. At this time, the quenching heat treatment can greatly improve the service life of the transmission shaft.
