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 bypass valve, 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.
A progressive cavity volumetric hole bottom power machine, referred to as auger drill. The auger drill, which uses mud and clean water as the power medium and is conveyed to the bottom of the hole through the center hole of the drill rod, is essentially an energy conversion device that converts liquid pressure energy into mechanical energy. During drilling, the auger directly drives the core tube and drill bit connected to the transmission shaft at the bottom of the hole to rotate. The entire drill string is only used as a channel for conveying high-pressure working medium and a rod supporting the counter torque of the drill bit. Compared with conventional drilling, screw drilling has many advantages, such as greatly reduced drill pipe wear and high drilling speed. It is the main tool for directional drilling and has played a role in the field of drilling.
The auger drill was first used to punch vertical holes, mainly used to drill a variety of directional holes and special engineering holes (such as mine frozen holes). The maximum drilling depth is 9023 meters. At present, the minimum diameter of auger drills in the world is 44.5 mm and the maximum diameter is 304.8 mm. When auger drilling is used for core drilling, a core tube should be added between the drive shaft and the drill bit to take the core.
The auger drill consists of a bypass valve, a screw motor (rotor and stator), a universal joint, a bearing and a drive shaft. Its core is a screw motor. In the screw motor rotor and stator transmission pairs, the number of stator teeth Z1 is one more than the number of rotor teeth Z2: Z1 = Z2 + 1. Their gear ratio is usually called the transmission ratio, and they can be chosen arbitrarily when designing (1: 2, 2: 3, ..., 9:10). The high speed screw drill should be designed with a small gear ratio screw motor, while the low speed and high torque screw drill should be designed with a large gear ratio screw motor. With the increase of the rotor-to-stator gear ratio, its efficiency gradually decreases; the output torque of the screw drill depends on the working pressure drop through the motor, and the output speed depends on the flow of working medium through the screw motor.
When drilling, conventional drilling equipment such as rigs, mud pumps, drill rods, and rigs are still needed. When constructing a directional borehole, an orienter is used to orient the tilting tool. The tool used to match the auger drill includes curved joints, curved outer tubes and eccentric blocks. The use of auger drill to construct directional holes can improve the quality of drilling, provide accurate geological data, save footage, reduce costs, and solve many engineering problems that cannot be constructed. Therefore, it is a special tool for drilling engineering.
The service life of auger drills is generally 150 to 200 hours. The weak link is that the stator rubber has a low temperature resistance and the bearings are easily damaged. Intensify the research and development of wear-resistant and high-temperature resistant elastic materials and reliable bearing systems for manufacturing stators, so that the working life of screw drills is significantly improved. And develop low-speed high-torque screw for drilling deep holes and ultra-deep holes.
The screw drilling tool is mainly composed of four assemblies, such as a bypass valve, a liquid motor, a universal shaft and a 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 leak. The speed decreases quickly, and in severe cases it stops completely and the motor is damaged. (One lead of the motor is level one.) 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 the screw motor are the main performance parameters of the screw drill. The theoretical output torque of the motor is directly proportional to the pressure drop of the motor, and the number of output revolutions is proportional to the input mud flow rate. As the load increases, the number of drilling tool revolutions decreases. Control the torque and speed of downhole drilling tools.
By-pass valve section
The bypass valve is composed of valve body, valve sleeve, valve core and spring. The valve core slides in the valve sleeve under the action of pressure. The movement of the valve core changes the flow direction of the liquid, which makes the bypass valve bypass and close. Each state: During the start-up and down-drilling operations, the valve sleeve and the through hole of the valve body are not closed, and the bypass valve is in a bypass state, allowing the mud in the drill string to bypass the motor and enter the annulus; When the value is set, the valve core 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 lifts the valve core and the bypass valve hole is in the open position-in a bypass state.
The motor consists of a stator and a rotor. The stator is made by injecting a rubber bushing on the inner wall of a steel pipe. The inner hole is a spiral with certain geometric parameters; the rotor is a screw with a hard layer. The rotor and the stator mesh with each other, and the lead difference between the two is used to form a spiral sealed cavity to complete the energy conversion. The rotor of the motor is divided into single and multiple ends. The fewer the number of rotors, the higher the speed and the smaller the torque; the larger the number of rotors, the lower the speed and the greater the torque.
Cardan shaft introduction
The function of the universal shaft is to transform the planetary motion of the motor into the fixed-axis rotation of the transmission shaft, and transmit the torque and speed generated by the motor to the transmission shaft to the drill. Cardan shafts are mostly flexible.
Axis of rotation
The function of the transmission shaft is to transmit the rotary power of the motor to the drill bit, and at the same time to bear the axial and radial loads generated by the drilling weight. The drilling tool transmission shaft structure (shown in Figure 7) manufactured by our company has applied for a national patent, and has many advantages such as longer life and higher bearing capacity.
1. Drilling fluid requirements: Screw drilling tools can work effectively for a variety of muds, including oil-based muds, emulsified muds and clay muds, and even clear water. Mud viscosity and specific gravity have little effect on the drilling tool, but have a direct impact on the pressure of the entire system. If the pressure at the recommended displacement is greater than the rated pump pressure, the mud displacement must be reduced, or it is necessary to reduce Pressure drop in the drill. Impurities such as sand particles in the mud will affect drilling tool performance and accelerate the wear of bearings and motor stators. Therefore, the sand content in the mud must be controlled below 1%. Each type of drilling tool has its own input flow range. Only within this range can the drilling tool have higher efficiency. Generally, the middle value of the input flow range should be taken as the best input flow value.
2. Mud pressure requirements: When the drilling tool is suspended, the displacement does not change, so the mud pressure drop through the drilling tool does not change. As the drilling pressure increases when the drill bit contacts the bottom of the well, the mud circulation pressure increases and the pump pressure increases. Drilling can be controlled by the following formula: Drilling pump pressure = circulating pump pressure + drilling tool load pressure. Circulating pump pressure is the pump pressure when the drilling tool does not contact the bottom of the well, also called off-bottom pump pressure. The pressure is about to rise. At this time, the reading of the pressure gauge is called drilling pressure. Off-bottom pump pressure is not a constant. It changes with the depth of the well and the characteristics of the mud. However, in actual operation, it is not necessary to measure the accuracy of the circulating pump pressure at any time. Generally, the off-bottom pump pressure after each single connection is taken as An approximate value, this can fully meet the accuracy requirements of the formula. When the drilling tool is working, when the drilling pump pressure reaches the maximum recommended pressure, the drilling tool produces the optimal torque. Continued increase in drilling pressure will increase the pump pressure. When the maximum design pressure is exceeded, the motor may be braked. Pressure to prevent internal damage to the drill.
Before the screw drilling tool is shipped from the factory, the connecting threads between the various components have been coated with anaerobic adhesive and tightened according to the specified torque. There is no need to re-tighten the screws before use.
1. Ground inspection before going down the well: Lift the drilling tool with the lifting sub-joint into the turntable slip, so that the bypass valve is above the turntable, install the safety slip, remove the lift sub-link, and check the flexibility of the bypass valve The method is to press the valve core with a wooden rod, and then release it. The valve core returns to normal under the action of the spring force, and is repeatedly pressed 3-5 times. The valve core is not blocked, and the movement is flexible. Then the drill is bypassed. The pump is opened below the hole, the bypass hole is closed, the motor is started, the joint is driven to rotate, the valve core is reset after the pump is stopped, the mud is discharged from the bypass hole, and the drilling tool is normal.
2. Drilling tool is lowered into the well (1) When the drilling tool is lowered, strictly control the lowering speed to prevent the motor from reversing when it is too fast, tripping the internal connection screw, and preventing collisions through sand bridges and casing shoes Drilling tools. (2) When entering deep well sections or encountering high-temperature well sections, and when passing through flowing sand layer well sections, the mud should be periodically cooled to cool the drilling tool to protect the stator rubber and prevent sand blockage. (3) When the drilling tool approaches the bottom of the well, the speed should be slowed down, and the drilling should be continued after the circulation in advance. The circulation should first be a small displacement. After the mud is returned from the wellhead, increase the displacement. (4) It is not allowed to drill or drill the bottom of the well.
3. Drilling tool drilling (1) The bottom of the well should be thoroughly cleaned and the circulating pump pressure measured before drilling tool drilling. (2) Drilling pressure should be slowly added at the beginning of drilling. When drilling normally, the driller can use the following formula to control the operation: Drilling pump pressure = circulating pump pressure + drilling tool load pressure drop (3) Start drilling, drilling The speed should not be too fast. At this time, the drilling tools and drill bits are very tight, the bottom of the well has not been cleaned, and the mud pack of the drill bit is likely to occur. (4) The torque generated by the drilling tool is directly proportional to the pressure drop of the motor, so increasing the drilling weight can increase the torque. (5) Uniform drilling can ensure the smooth curve and directional accuracy of the well section.
4. Take out and inspect the drilling tool from the wellbore (1) Flush the bypass valve with clean water, and use a wooden stick to move the valve core up and down so that it can be closed flexibly. (2) Use a pipe wrench to bite the drilling tool, use a chain wrench to turn the drive joint clockwise, and inject clean water from the upper part of the bypass valve to clean the inside of the drilling tool, and finally inject a small amount of mineral oil into the motor. (3) Pay attention to the starting speed to prevent drilling from damaging the drilling tool. (4) Measure the bearing clearance of the drilling tool. If the bearing clearance exceeds the maximum tolerance, the drilling tool should be repaired and replaced with a new bearing (for workover drilling, the axial clearance of the bearing should be adjusted).
Surface inspection before screw drilling
Surface inspection before screw drilling
1. Except for the connection of the lifting sub-junction and the bypass valve, the other parts of the shell connection are coated with locking agent.
2. Install the screw bit with the screw bit unloader, only use the chain pliers to rotate the screw drill drive shaft head, and only rotate counterclockwise (top view, the same below) to prevent the internal thread from loosening.
3. Lift the lifting nipple, put the screw drill into the turntable, and place the bypass valve in a position easy to observe in the turntable. Use the slip to fasten the auger and remove the lifting joint.
4. Check the bypass valve: Use a hammer handle or a wooden rod to press the bypass valve core down, and fill the bypass valve with water from the top. At this time, the bypass valve should not leak, and the water surface does not drop significantly. Then remove the wooden rod. The valve core should be reset by the spring, and the injected water should flow out uniformly from the holes on the side, which is considered normal.
5. After lowering, place the bypass valve under the drill pipe for easy observation. Start the drilling pump and gradually increase the displacement until the bypass valve is closed. Raise the screw drill to see if the screw drill is rotating. At this time, the bypass valve is at "Off" position. No drilling fluid should flow from the bypass hole. After stopping the pump, pay attention to observe whether the bypass valve is opened again, so that the drilling fluid is discharged from the bypass hole. Do not raise the bypass valve above the turntable until the pump is completely stopped to prevent contamination of the well floor.
6. According to the designed screw drill assembly, connect the elbow joint, non-magnetic drill collar, stabilizer, etc. respectively.
Lower the auger to the wellbore
When drilling down-screw drilling tools, the down-speed should be controlled, otherwise it will be easily damaged by sand bridges, well shoulders and casing shoes in the wellbore. When encountering such a well section, it is often necessary to start a drilling pump and slowly expand the wellbore before passing.
If curved joints or curved shells are used, the side of the auger bit will more easily hit the hard rock formations and casing shoes on the well wall. The auger drill tool should be rotated periodically to eliminate the effect of side drilling.
For deep wells and high-temperature wells, it is recommended to periodically circulate halfway when lowering the screw drill, this can prevent the screw drill from being blocked or the screw drill stator from being damaged due to high temperature.
In the well, if the drilling fluid cannot quickly pass through the valve of the bypass valve, it should slow down the speed of the well, or stop to fill the mud from time to time. When drilling, pay attention not to pierce or put the screw drill directly into the bottom of the well.
Start screw drill:
If the screw drilling tool is at the bottom of the well, you must lift 0.3-0.4m and start the drilling pump. At this time, record the reading of the pressure gauge of the stem and compare it with the calculated pressure value. If the pressure calculated by the hydraulic pressure is normal, this is Caused by auger bit side drilling.
Clean the bottom of the well: Especially for inclined wells, the bottom of the well must be sufficiently "clean", because the debris deposited or deposited on the bottom of the well affects the speed or deflection. It is best to clean up with normal drilling fluid circulation. When cleaning, you can also slowly rotate the screw drill or the screw drill to rotate in stages (30o-40o each time) to clean up the objects piled up in the bottom of the well in turn. After cleaning up, raise the screw auger 0.3-0.4m, check the pressure value, and record it.
Re-enter the bottom of the well and gradually increase the drilling pressure. The motor torque increases and the pressure value of the vertical rod pressure gauge increases. This increased pressure value should conform to the motor pressure drop value specified by each model of screw drill. The value of this pressure gauge increases. It reflects whether the load of the motor is normal and whether the drilling pressure is appropriate. Therefore, the motor speed is basically stable and the drilling pressure is basically stable, as long as the reading of the vertical pressure gauge is limited to the recommended range of the selected screw drill. It enables the driller to keep abreast of the working conditions of screw drilling tools.
When the auger bit is not at the bottom of the well, if the circulating pressure is high, the water hole of the auger bit may be blocked or the transmission shaft may be stuck.
During the start-up, the bypass valve is in the bypass state, allowing the drilling fluid in the drill string to drain into the annulus, but the screw drilling tool itself cannot discharge the drilling fluid. Usually, a portion of the weighted drilling fluid is injected into the upper part of the drill string before the start of the drill. .
1. After the screw drill is raised to the position of the bypass valve, remove the parts on the bypass valve port, rinse with clean water from the top of the bypass valve, and then use a wooden stick or hammer handle to press and release the valve core Its movement is unobstructed. After cleaning, screw on the lifting nipple and raise the screw drill.
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