METHOD OF AND A DEVICE AND AN ELECTRONIC CONTROLLER FOR MITIGATING STICK-SLIP OSCILLATIONS IN BOREHOLE EQUIPMENT

摘要

A method for mitigating stick-slip oscillations in borehole equipment while drilling a borehole in an earth formation is described. The borehole equipment is modelled by a computational model for computer simulation. The model has elements representing a particular mechanical and physical behavior of the borehole equipment. In a simulated stick mode of the borehole equipment, physical quantities are loaded to the elements, which quantities represent an initial state of the borehole equipment prior to a transition from stick mode to slip mode. From a simulation of such transition, a time response of rotational speeds of a drive system and bottom hole assembly of the borehole equipment is recorded and a lower limit of the rotational speed of the drive system is determined for which the rotational driven speed of the bottom hole assembly is zero.

主权项

1. A method of mitigating stick-slip oscillations in borehole equipment for drilling a borehole in an earth formation, said borehole equipment comprising a drill string having a bottom hole assembly and a top end coupled to a rotational drive system, and a speed controller for controlling rotational drive speed of said drive system, the method comprising the steps of:
operating said speed controller such that said drive speed is above a lower drive speed limit while drilling a borehole by said borehole equipment, wherein said lower drive speed limit is determined from: modelling said borehole equipment by an equivalent computational model for computer simulation, loading elements of said model with physical quantities representing an initial state of said borehole equipment causing a transition of said bottom hole assembly from stick mode to slip mode, simulating in said loaded model a transition representative of said transition of said bottom hole assembly from stick mode to slip mode, registering relaxation dynamics in said model from said simulating step and representing rotational driven speed of said bottom hole assembly, and determining from said relaxation dynamics said lower drive speed limit as a drive speed for which said rotational driven speed of said bottom hole assembly is zero.