Multi-loop feedback control of oil well drillstrings
Abstract
A drillstring mechanism used for oil or gas drilling behaves as a torsionalpendulum. The lowest part of the drillstring exhibitsself-excited vibrations induced by nonlinear friction at the rock-crushingtool. Since these vibrations can lead to premature degradation of highlyexpensive mechanical and electronic components, a control strategy isnecessary to attenuate or even eliminate their adverse effects. A multi-loop control design is proposed, which is composed by an inner and anouter loop. The aim of the inner-loop is to add enough damping to suppressstick-slip vibrations, while the objective of the outer-loop is to achieve thedesired drillstring velocity.
