The use and maintenance of the cable drill pipe-beneficial mining technology.

The cable drill pipe is the signal transmission device between the hole bottom inclinometer unit and the hole inclinometer equipment, and is an important supporting drilling tool to ensure the smooth implementation of directional drilling, mainly used in coal mine underground directional drilling, coal mine underground rotary drilling and other geological controlled directional drilling conditions.

The signal transmission mode of the MWD system is divided into wired (cable) and wireless. As a wired (cable) transmission mode, the central through-cable drill pipe can directly supply power to the hole bottom sensor to realize two-way communication between the hole bottom and the orifice equipment, with good real-time performance and high data transmission rate. At the same time, the central cable drill pipe solves the installation problem of the connection between the cable and the drill pipe and the connection between the cables in the past, and can effectively ensure the signal transmission of the wired (cable) measurement while drilling system.

Structural Principle of 1. Cable Drill Pipe

The cable drill pipe is composed of four parts: the drill pipe body, the conduction device, the insulation device and the support device. The conduction device, the insulation device and the support device constitute the central cable device of the drill pipe, which affects the transmission of the measurement signal while drilling.

1. Drill pipe body

The drill pipe body and the male and female joints are welded as a whole by friction welding. The drill pipe body is not only the carrier of other parts of the cable drill pipe, but also the primary condition to ensure the directional drilling construction, and its performance directly determines the safety of the construction.

2. Conduction device

The cable passage device is composed of a cone connector, a wire, a column connector and a reducing spring, and its function is to transmit a two-way communication signal between the hole bottom and the orifice device.

3. Insulation device

The insulation device is composed of a plastic male connector, a conduit and a plastic female connector. Its main function is to isolate the central conduction device from the flushing fluid, ensure the communication safety of the central conduction device, and prevent the loss of communication signals during the conduction process.

4. Support device

The supporting device is composed of a positioning retaining ring and a stabilizer. The function of the positioning retaining ring is to axially position the plastic male and female joints in the drill pipe body to prevent the central conduction device and the insulation device from moving when the drill pipe is connected, so as to ensure the reliability of signal transmission. The stabilizer can reduce the disturbance of mud or other media to the pipeline, and avoid the conduction of the conduction device and the drilling medium due to the fracture of the pipeline.

Working conditions of 2. cable drill pipe

1. Main functions of cable drill pipe

The cable drill pipe is an important part of directional drilling equipment, which is the component with the most complex force and the worst working condition in the process of directional drilling. Its main functions are:

1) Translate the axial pressure applied by the drill to the drill bit during drilling, and bear the reaction torque of the motor at the bottom of the hole;

2) Transfer the pushing and pulling force applied by the drilling rig when tripping the drilling tools;

3) As a medium channel, the flushing liquid is delivered to the bottom of the hole.

In order to facilitate the treatment of accidents in the hole, the cable drill pipe can be used for both directional drilling and regular rotary drilling. Therefore, the central cable drill pipe should also meet the requirements of applying torque to the drill bit during regular rotary drilling.

2. Working conditions of cable drill pipe

The drill pipe string composed of cable drill pipe is an elastic system, in the process of directional drilling, the size and direction of the load on the drill pipe are changing, the cable drill pipe in the three-dimensional space bear complex alternating tension, pressure, torsion, bending, vibration and other loads, coupled with wear and corrosion and other effects, after a period of aging is likely to fracture in the stress concentration position. At the same time, with the change of geological conditions and the occurrence of accidents such as sticking and burying, the force of the drill pipe will become more complex. The working conditions of the cable drill pipe determine that the cable drill pipe will be the most complex and the worst part in the drilling process.

The basic loads of the drill pipe are:

1) tension and pressure. During the drilling process, the drill pipe is compressed when the drill pipe applies axial pressure to the drill bit, and the drill pipe is pulled when lifting the drill. When dealing with accidents in the hole and pulling out with force, the drill pipe will be subject to a large pulling force.

2) Reverse. Since one of the main functions of the drill pipe is to bear or transmit torque, the drill pipe is in a twisted state and produces torsional stress. Especially when dealing with accidents in the hole (the central cable type drill pipe can rotate when dealing with accidents in the hole), the drill pipe suddenly stops rotating. At this time, the rotating part of the drilling rig and the rotating kinetic energy of the drill pipe string make the drill pipe subject to torsional impact, resulting in great torsional stress.

3) Bend. In the regular drilling construction, due to the instability of the drill pipe under the action of centrifugal force and axial pressure, bending, bending stress is generated inside the drill string. In the process of constructing directional holes, it is necessary to constantly adjust the drilling trajectory, which will cause the bending deformation of the drill pipe in the hole. When the bent drill string is rotated, the alternating stress generated in the drill pipe is easy to cause the fatigue failure of the drill pipe.

4) Elastic vibration. Drill string is an elastic system, which can vibrate longitudinally and transversely under the combined action of bending and torsion. In severe cases, the vibration of the drill string makes the drilling rig and other supporting equipment forced to vibrate, affecting the life of the drilling tool and supporting equipment.

Main technical parameters of 3. cable drill pipe

Main technical parameters of cable drill pipe are as follows:

1) Drill pipe size: drill pipe body 73 × 5.6mm, joint outer diameter 75mm;

2) Length of drill pipe: 3m;

3) Tensile capacity of drill pipe: 800kN;

4) Torsion resistance of drill pipe: 6500N · m;

5) Insulation resistance:>2MΩ;

6) Resistance of central cable device:<0.5 Ω;

7) Service life: 20000m or 1 year.

Assembly process of 4. cable drill pipe

1. Assembly steps of cable drill pipe

In the process of directional hole construction, the cable drill pipe transmits the hole bottom signal to the hole monitor, so its resistivity is low, and the signal output is stable and reliable. The assembly of drill pipe shall be careful to ensure the assembly quality. Therefore, the assembly of drill pipe shall be carried out in strict accordance with the following steps:

1) Install the stabilizer 6 into the drill pipe body first, then install the hole circlip into the drill pipe body with the inner circlip pliers, and install the positioning circlip 4 into the circlip;

2) After installing the sealing ring into the sealing groove of the pipe line 5, assemble it with the plastic female connector 7, and install the assembly body into the drill pipe body from the male connector end of the drill pipe body;

3) Use special tools to connect the plastic male connector 2 with the assembly of the plastic female connector 7 and the conduit 5;

4) Adjust the distance from the left end face of the plastic male connector 2 to the left end face of the drill pipe body to 14±0.5mm, and the distance from the right end face of the plastic female connector 7 to the right end face of the drill pipe body to 23±0.5mm;

5) Install the wire 10 into the conduit 5, then install the column connector 8 at the plastic female connector 7 end, and install the cone connector 3 at the plastic male connector 2 end;

6) Measure the resistance of the center through cable with a multimeter. Insert the multimeter probe into the column connector and the cone connector at both ends of the center through cable device to measure the resistance of the center through cable device. If the resistance is less than 0.5 Ω, the center cable assembly is qualified, otherwise it is unqualified;

7) Put the variable diameter spring 9 into the column joint 8, apply a small amount of butter evenly on the sealing ring of the plastic male and female joint and the thread of the drill pipe, and finally put on the thread protection cap to complete the assembly.

2. Inspection of cable drill pipe

During the assembly of the through cable drill pipe, the following items should be carefully checked:

1) Check whether the central conduction device and insulation device can move in the drill pipe body. If the central conduction device and the insulation device move axially in the drill pipe body, it will inevitably affect the sealing of the insulation device and its service life, and then affect the reliability and stability of the central cable-type drill pipe signal transmission.

2) Check the assembly of plastic joints to ensure firm connection. Measure the distance from the left end face of the plastic male connector 2 to the left end face of the drill pipe body and the distance from the right end face of the plastic female connector 7 to the right end face of the drill pipe body. Ensure that the distance between the left end face of the plastic male connector 2 and the left end face of the drill pipe body is 14±0.5mm, and the distance between the right end face of the plastic female connector 7 and the right end face of the drill pipe body is 23±0.5mm.

3) Use a multimeter to measure the resistance of the central cable device. If the measurement result is unqualified, it must be replaced in time.

4) Check whether the reducer spring 9 is loose and ensure that the reducer spring 9 does not come out of the male connector 3.

5) Check whether the drill pipe thread is coated with butter.

Precautions for the use of 5. cable drill pipe

The cable drill pipe has been assembled and passed the inspection before leaving the factory. Users should not disassemble the internal devices of the drill pipe body at will during use. In the process of handling the cable drill pipe in the loading and unloading center, it is not allowed to bump or throw to avoid damaging its parts.

1. Reasonable storage of cable drill pipe

Drill pipe storage should pay attention to several points:

1) The drill pipe must be stored on the drill pipe rack;

2) When the drill pipe is stored, the screw thread shall be coated with anti-rust oil and a protective cap shall be put on;

3) Drill pipe storage shall be clean and free of corrosive articles (especially when stored underground, water shall be avoided, and anti-corrosion work shall be done in high hydrogen sulfide mine);

4) New and old drill pipes shall be stored in different areas.

2. Reasonable use of cable drill pipe

The cable drill pipe is the necessary drilling tool for the implementation of directional drilling technology, and the rational use of drill pipe is the first measure to improve its working conditions and enhance the stability of signal transmission, which plays an important role in the smooth implementation of directional drilling technology. Attention should be paid to several points when using central cable type drill pipe:

1) Strictly follow the drilling procedures, formulate reasonable drilling process, and select appropriate curvature radius for drilling inclined holes or branch holes.

2) After transporting the drill pipe to the drilling field, check whether the plastic male and female joints of the drill pipe are loose or other defects, and check the connection and disconnection of the cable device in the center of the drill pipe to ensure the normal communication of the drill pipe.

3) When connecting the drill pipe, lubricant must be applied to the drill pipe thread and male plastic joint, and check whether the spring is installed in place.

4) When connecting the drill pipe, use the free clamp to tighten the drill pipe, and do not use the drill to screw it (avoid the thread part of the drill pipe when using the free clamp).

5) When unloading the drill pipe, loosen the screw thread by 1~2 turns with a drilling rig, and then manually unload the drill pipe.

6) When the drill pipe is not in use, the protective cap must be put on in time to prevent pulverized coal from entering.

7) When construction is carried out in high hydrogen sulfide mine, the drill pipe shall be lifted up in time after use.

8) Record the use of drill pipes to avoid mixing old and new drill pipes.

During the use of the drill pipe, if it is found that the male and female thread end faces cannot be tightened to contact or cannot be easily unbuckled, it means that the drill pipe thread is seriously worn and a new drill pipe needs to be replaced. If the drill pipe thread is intact and the signal transmission fails, it is necessary to maintain the central cable device and replace the corresponding parts.

Maintenance of 6. cable drill pipe

In order to improve the service life of the drill pipe, it is necessary to carry out daily maintenance on the cable drill pipe.

1) After using the drill pipe, it shall be checked in time. If any problem is found, it shall be recorded and handled in time.

2) After the cumulative footage of drill pipe reaches 20000m or the service life reaches 1 year, the overall performance of drill pipe shall be inspected. The inspection items shall include: ① wear of drill pipe screw thread; ② wear of drill pipe body; ③ whether the plastic male and female joints are loose or have other defects; ④ whether the sealing ring on the plastic male and female joints is in good condition; ⑤ whether the positioning retaining ring is deformed or cracked; ⑥ resistance of central cable device; ⑦ check whether the stainless steel column joints and cone joints are corroded, etc.

The drill pipe body is the part of the central through-cable drill pipe to transmit pressure and bear torque. If the drill pipe screw thread is seriously worn or the drill pipe body is worn more than 2mm in the diameter direction, it shall be scrapped. The central through-cable device of the central through-cable drill pipe is easily damaged under the long-term disturbance of flushing fluid and the corrosion of other media, so the corresponding parts shall be replaced and maintained, and the drill pipe maintenance records shall be kept.

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