Sliding Mode Control of Rotary Drilling System with Stick Slip Oscillation

In this paper, a conventional model describing the torsional behaviour of a generic vertical oilwell drillstring has been presented, and a dynamical sliding mode control has been used to eliminate bit sticking phenomena. In the control system, the bit angular velocities are driven to a desired reference value in spite of the presence of a dry friction modelling the bit-rock contact. The key idea of the controller is to introduce a sliding surface in the system which the desired dynamics is accomplished. Three reaching law in the sliding mode are applied in the drilling rotary system. The simulation results showed that the control law is capable of accurately controlling the bit speed, has faster dynamics responses and suppress stick-slip in oil well drill string.