The downhole mud motor is a part of the screw drilling tool (PDM drill). The screw drilling tool is a volumetric downhole power drilling tool that uses drilling fluid as power and converts fluid pressure energy into mechanical energy. When the mud pumped by the mud pump flows through the bypass valve and enters the mud motor, a certain pressure difference is formed at the inlet and outlet of the motor, which pushes the rotor to rotate around the axis of the stator, and transmits the speed and torque to the motor through the cardan shaft and the transmission shaft. Drill bits to achieve drilling operations.
The downhole mud 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 downhole mud motor is a volumetric downhole power drilling tool powered by mud. The high-pressure mud liquid discharged from the mud pump flows into the joint, and the mud forms a certain pressure difference at the inlet and outlet of the motor to drive the rotor of the motor to rotate, and the torque and speed are transmitted to the drill bit through the cardan shaft and the transmission shaft to achieve the purpose of drilling. The performance of the mud motor mainly depends on the performance parameters of the motor and the displacement you mentioned.
Starting and Drilling of Downhole Mud Motor
Before starting the downhole mud motor, you must ensure that the drill bit is more than 0.3-0.6m away from the bottom of the well. Start the drilling pump and record the reading of the vertical rod pressure gauge. Compare it with the calculated pressure value. If the pressure value exceeds the hydraulic calculation value, it is normal. It is caused by sidetracking of the drill bit. If the factors causing the pressure increase caused by sidetracking have been eliminated, and the circulating pressure is still higher than the calculated value, it may be that the water hole of the drill bit is blocked or the rotating shaft is stuck. If so, the circulating pressure is much higher than the calculated pressure at this time .
○ First start the pump to clean the bottom of the well: especially when drilling a deviated well, the bottom of the well must be “clean” enough, because the debris accumulated or deposited at the bottom of the well will affect the deflection. It is best to use normal drilling fluid circulation to clean up. When cleaning, you can also slowly rotate the drilling tool or rotate the drilling tool in stages (30°-40° each time), and clean up the objects piled at the bottom of the well one by one.
○ After cleaning, lift the drilling tool up 0.3-0.6m, check and record the pump pressure value, go down to the bottom of the well again and slowly apply the drilling pressure, the pressure drop of the motor increases, and the torque of the motor and the pressure value of the vertical rod pressure gauge follow. The increased pressure value should conform to the motor pressure drop value specified by each type of drilling tool. The increased value of this pressure gauge reflects whether the load of the motor is normal, and also reflects whether the drilling pressure is appropriate. Because drilling pump pressure = circulating pump pressure + motor load pressure drop, the driller only needs to apply reasonable drilling pressure and limit the reading of the vertical rod pressure gauge within the recommended range of the selected drilling tool. In the selection of the WOB, it should be noted that the rated WOB of the screw drill with the same specification is different when used with the roller cone bit and the PDC bit. Generally, the WOB of the PDC bit is smaller. But no matter what kind of drill bit is used, it must be based on the footage rate, so that the drill can be fed evenly. When the footage is slow, increasing the drilling pressure in vain will only cause premature damage to the screw drilling tool.