| 摘要 |
A method and system of reducing or avoiding at least axial or torsional oscillations in a drillstring (24) with a bit (26) attached to its lower end and controlled by a hoisting (8) and rotation (6) mechanism attached to its top end, where the controllable variables are vertical and rotational speeds and the response variables are axial tension force and torque, referred to the top of the drillstring (24), wherein the method includes the steps of: i) choosing at least one string oscillation mode to be controlled; ii) monitoring the controllable variable and response variable relevant for said oscillation mode; iii) determining the oscillation period of said mode; iv) estimating from the relevant response variable the dynamic bit speed of said mode; v) determining a speed pulse capable of generating an oscillation with an amplitude substantially equal to the amplitude of said estimated bit speed; and vi) starting an open-loop controlled speed variation by adding said speed pulse to the operator set speed command when the amplitude of said bit speed estimate exceeds a certain threshold level and the anti-phase of said bit speed estimate matches the phase of the pulse generated oscillation. |
