Working conditions of directional drill pipe
The drill pipe string composed of directional 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 directional drill pipe bears complex alternating loads such as tension, compression, torsion, bending and vibration in three-dimensional space. Coupled with the effect of wear and corrosion, it is likely to fracture at the stress concentration position after a period of aging. At the same time, with the change of geological conditions and the occurrence of sticking and burying accidents, the stress of directional drill pipe will become more complex. The working conditions of the directional drill pipe determine that the directional drill pipe will be a component with complex force and bad working conditions in the drilling process.
The basic loads of directional drill pipe are as follows:
1) Tension and pressure. In the process of drilling, when the directional drill pipe exerts axial pressure on the directional drill bit, the drill pipe is pressed, and when lifting the drill pipe, it is pulled. When dealing with the accident in the hole, the pulling force to the drill pipe will be larger.
2) Twist. Because one of the main functions of the drill pipe is to bear or transmit torque, the drill pipe is in a state of torsion, resulting in torsional stress. Especially when dealing with the accident in the hole (the through cable drill pipe can rotate when dealing with the accident in the hole), the rotation to the drill pipe stops suddenly. At this time, the rotary part of the drilling machine and other equipment and the rotary kinetic energy of the drill pipe string make the drill pipe suffer torsional impact and produce great torsional stress.
3) Bend. In conventional drilling construction, due to the instability of the drill pipe under centrifugal force and axial pressure, bending is produced, and bending stress is generated inside the drill string. In the process of directional hole construction, it is necessary to constantly adjust the drilling trajectory, which will cause the bending deformation of the directional drill pipe in the hole. When the bent drill pipe string rotates, the alternating stress in the drill pipe is easy to cause the fatigue failure of the drill pipe.
4) Elastic vibration. The directional drill string is an elastic system. Under the combined action of bending, torsion and other factors, longitudinal and transverse vibration will occur. When it is serious, the vibration of drill string makes the drilling rig and other supporting equipment vibrate, which affects the service life of drilling tools and supporting equipment.