System Identification of Coupled Vertical and Rotational Stick-Slip Drilling Dynamics on a Modeled Rig for Adaptive Control
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This thesis investigates a system identification method to parametrically identify single input single output (SISO) coupled vertical and rotational drilling dynamics with stick-slip using an excited Rate of Penetration (ROP) command input into a physically modelled drilling rig at fixed rotational top drive speeds. A non-parametric Frequency Response Function (FRF) for the axial dynamics and rotational dynamics is created and compared to the FRF generated by the parametric system ID method at each rotational speed level. If non-parametric and parametric FRFs are in agreement, then the discrete parametric transfer function for both, the axial or rotational dynamics can be used for plant modeling. Likewise, a multiple input multiple output (MIMO) system is identified with persistently excited commanded ROP and RPM as inputs while WOB and Torque are the outputs. These identification methods can be potentially applied in real-time during drilling to identify typical drilling dynamics for adaptive control.