Working principle of Downhole Motor
Downhole Motor is a kind of downhole power tool powered by drilling mud. The mud liquid pumped by the mud pump flows through the bypass valve and enters the motor. A certain pressure difference is formed 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 drive shaft. The performance of the Downhole Motor mainly depends on the performance parameters of the Downhole Motor.
The composition of screw drilling tools
The Downhole Motor is composed of four major assemblies, a Bypass Valve, a Motor, a Universal Coupling Assembly and a Drive Shaft.
Bypass Valve
It has two positions: bypass and closed. It is in the bypass position during the tripping operation, so that the mud in the drill string passes through the non-working motor and enters the annulus, so that the mud does not overflow on the well platform when tripping. When the mud flow and pressure reach the standard setting value, the valve core moves down and closes the bypass valve hole. At this time, the mud flows through the motor and converts the pressure energy into mechanical energy. When the mud flow value is too small or the pump is stopped, the generated pressure is not enough to overcome the spring force and static friction force, the spring pushes up the valve core, and the bypass valve hole is in the open position again. Under normal circumstances, substitute joints are often used in well depths, highly deviated wells, horizontal wells, and hollow rotors.
Motor
It consists of a stator and a rotor. The stator is made by injecting rubber bushing on the inner wall of the steel tube. The inner rubber hole is a spiral with a certain set of parameters. The rotor is a chrome-plated screw.
The rotor and the stator mesh with each other, which is a spiral sealing line formed by the lead difference between the two, and a sealed cavity is formed at the same time. As the rotor rotates in the stator, the sealed cavity moves along the axial direction, continuously generating and disappearing, completing its energy conversion, which is the basic working principle of the screw motor.
The helix of the motor rotor is divided into single-end and multi-end (the number of helix ends of the stator is 1 more than that of the rotor). The fewer the number of rotor heads, the higher the speed, and the smaller the torque; the more heads, the lower the speed, and the greater the torque. It is the cross-sectional profile of several typical motors
A lead of the motor stator forms a sealed cavity, also called a first stage. The rated working pressure drop of each stage is 0.8MPa, and the maximum pressure drop is 1.3 times of the rated working pressure. For example, for a four-stage motor, the rated pressure drop should be 3.2MPa, and the maximum pressure drop should be 5.2MPa. If the pressure drop exceeds this value, the motor will leak, the speed will drop quickly, and it will stop rotating in severe cases, and even cause damage to the motor. The user should pay special attention to it.
In order to ensure the sealing effect of the motor, the matching size between the rotor and the stator is related to the temperature of different well depths. Therefore, when selecting the drilling tool, the well temperature of the drilling tool application site should be provided to the manufacturer as accurately as possible. It is recommended to use a tight fit. Motor in suitable condition. The flow rate used on site should be within the recommended range, otherwise it will affect the efficiency of the motor, and even accelerate the damage of the motor.
The output torque of the motor is proportional to the pressure drop of the motor, and the output speed is proportional to the amount of mud input. As the load increases, the speed of the drilling tool decreases. Therefore, you only need to control the pressure according to the pressure gauge on the ground and control the pump according to the flowmeter. The flow rate can control the torque and speed of the downhole drilling tool.
According to the temperature motor can be divided into
Rated operating temperature 95℃, and Maximum working temperature of 125℃ Conventional Stator.
Rated operating temperature 135℃, and Maximum working temperature of 150℃ High Temperature Stator.
Rated operating temperature 150℃, and Maximum working temperature of 180℃ Ultra-High Temperature Stator.
According to the media motor can be divided into:
Motor for Oil Based Mud
Motor for Saltwater Mud
Air Motor for Air or Foam Unbalanced System
Motor with equal wall thickness
Motor with equal wall thickness is a new type of development in recent years as a long-life and high-power motor. The motor is mainly used in horizontal well drilling, large displacement well drilling and geological steering drilling environment. This kind of motor has the following advantages: Rubber is heated evenly and stressed swelled uniformly. The motor can withstand higher pressure drops. The motor can output a larger torque. The motor can adapt to the higher operating temperature. The motor has longer working life.
Universal Coupling Assembly
The function of the Universal Coupling Assembly is to transform the planetary motion of the motor into the fixed-axis motion of the drive shaft, and transmit the torque and speed generated by the motor to the drive shaft to the drill bit. Motech drilling tools use advanced ball drive universal joint shafts. The ball drive universal joint shafts are connected by ball transmission. The moving part of the steel ball is sealed with a rubber sleeve to isolate the drilling fluid. Special surface treatment is performed on the working surface to make the surface The hardness and high temperature resistance are relatively improved; the working life is correspondingly prolonged.
After the drilling tool is used, it should be disassembled immediately and the Universal Coupling Assembly should be checked. If the wear exceeds the maintenance standard, the relevant wearing parts should be replaced in time, otherwise the drilling tool will not work normally due to the excessive use of the Universal Coupling Assembly.
Drive Shaft
The function of the drive 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 weight on bit. The drill drive shaft assembly manufactured by our company has two structures:
(1) The water eye pressure drop of the drill bit is 7.0MPa, and the drive shaft assembly of the hard alloy radial bearing and the middle set of thrust bearing is adopted (see Figure 6).
(2) The water eye pressure drop of the drill bit is 14.0MPa, and the plane thrust bearing adopts cemented carbide radial bearing and diamond composite disc (PDC), which has a longer life and higher load capacity.
Advantages of ZH Downhole Motor-Drilling Motor
- The motor performance parameters are closer to the theoretical design
- Uniform temperature affects decreased due to the rubber deformation, reduced motor correction difficulty.
- During work the rubber becomes more resistant to deformation, rigidity increases, single stage pressure heightens, stiffness increases, wear slows down, becomes more efficient, and prolongs motor service life.
- Sensitive to temperature decreases, slow rubber thermal aging.
- Ensures reliability and stability of downhole motor. After the single stage confined height, output efficiency increases.
Radial Bearing of ZH Downhole Motor-Drilling Motor
Radial Bearing are produced using high temperature and mosaics technology. In order to avoid hard alloy from high temperature damage. Base hardness of bearing can be 300HB above. Not only ensure the strength but also improve wear resistance of cemented carbide.
Axial Bearing of ZH Downhole Motor-Drilling Motor
Bearing is designed with different pressure angle, and special treatment on the surface to make it more abrasion in the working state.
