Automation of winch optimal braking modes at rotary method of drilling vertical wells
A single-mass dynamic model of the drill string is introduced, which describes the process of its immersion as the hole bottom deepens. The arising torsional self-oscillations of the relaxation type are taken into account, which can be accompanied by short-term jamming of the bit, both in the rotational and translational components of the motion. The process of sinking the drill string is modeled when drilling vertical wells, taking into account the strength properties of the occurrence rocks and the cyclical nature of the drilling process, caused by the need to periodically increase the length of the string with another stand. To maintain a constant tension of the drill string suspension rope, a purely theoretical method is proposed for finding the optimal braking mode for the winch of the traveling system. The method involves, first, the determination of the law of change in the rate of immersion of the drill string and the law of braking. There is a law of change in the pressure force on the brake pad, following which it is possible to achieve the desired braking mode. This law can be established before the start of field operations, if the strength properties of the rocks in the soils of the forthcoming drilling are known. A detailed algorithm for numerical simulation of the drilling process is presented, based on the assumption that torsional self-oscillations of the drill string will prevail. The results of numerical simulation can serve as the basis for the complete automation of this technological process, setting the brake pad pressing force in time according to a previously known law. The implementation of the optimal winch braking mode can be carried out without any participation of the drilling foreman. And although the initial model of the drill string still does not take into account all the main factors affecting drilling, it can be considered as the initial stage in the automation of oil and gas production. The mathematical description of the winch braking by dry friction forces is made taking into account the amendments to the Amonton - Coulomb law determined by the kinematic zone method - here this friction law does not work directly.