The screw drilling tool is mainly composed of four major assemblies including bypass valve, hydraulic motor, cardan shaft and transmission shaft. The screw motor is the main part of the drilling tool. Many practices and theoretical analysis results show that if the motor is to work normally and effectively, the pressure drop that each stage of the motor can withstand should not exceed 0.8Mpa, otherwise the motor will leak. The speed will decrease rapidly, and in severe cases, it will stop completely and the motor will be damaged. The mud flow used on site should be within the recommended range, otherwise it will affect the efficiency of the motor and even increase the wear. The performance parameter of the screw motor is the main performance parameter of the screw drilling tool. The theoretical output torque of the motor is proportional to the pressure drop of the motor, and the output revolution is proportional to the input mud flow. As the load increases, the revolution of the drilling tool decreases, so as long as the reading of the pressure gauge on the ground and the flow of the pump are controlled, it will be able to control the torque and speed of downhole drilling tools.
The bypass valve is composed of valve body, valve sleeve, valve core and spring. Under the action of pressure, the valve core slides in the valve sleeve, and the movement of the valve core changes the flow direction of the liquid, so that the bypass valve has two functions: bypass and close. First state: During the drilling and running-in operation, the through hole between the valve sleeve and the valve body is not closed, and the bypass valve is in the bypass state, so that the mud in the drill string bypasses the motor and enters the annular space; when the mud flow and pressure reach the standard setting When the value is fixed, the spool moves down and the bypass valve hole is closed. At this time, the mud flows through the motor to convert the pressure energy into mechanical energy. When the mud flow value is too small or the pump is stopped, the spring pushes up the valve core, and the bypass valve hole of the screw drilling tool is in the open position—in the bypass state.
The motor consists of a stator and a rotor. The stator is formed by injecting rubber bushes on the inner wall of the steel pipe, and its inner hole is a spiral with certain geometric parameters; the rotor is a screw with a hard layer. The rotor and the stator are meshed with each other, and the lead difference between the two is used to form a spiral sealed cavity to complete energy conversion. The helix of the motor rotor can be divided into single-end and multi-end. The fewer the number of heads of the rotor, the higher the speed and the smaller the torque; the more the number of heads, the lower the speed and the greater the torque.
The function of the cardan shaft of the screw drilling tool is to convert the planetary motion of the motor into the fixed axis rotation of the drive shaft, and transmit the torque and speed generated by the motor to the drive shaft to the drill bit. The cardan shaft mostly adopts the flex shaft type.
The function of the transmission shaft is to transmit the rotational power of the motor to the drill bit, and at the same time bear the axial and radial loads generated by the drilling pressure. The structure of the drilling tool transmission shaft manufactured by Saigao has applied for a national patent, which has many advantages such as longer life and higher bearing capacity.