Abstract
In this paper, we present three methods to achieve reliable drillbit angular velocity control for deep drilling operations. We consider a multi-sectional drilling system with the bit off-bottom, which represents the system at the start-up of a drilling operation, e.g., after a connection. The three control procedures are all based on a distributed model for the drilling system. The proposed model has been field validated and considers Coulomb friction between the drillstring and the borehole. The first algorithm we propose combines the industry standard ZTorque controller with a feedforward component. The second procedure is based on a multiplicity-induced-dominancy (MID) design that corresponds to a pole-placement for the downhole state. Finally, the last class of controllers relies on a recursive interconnected dynamics framework. All the controllers are combined with a disturbance rejection procedure whose design is based on a switching-mode approach. These three algorithms are illustrated in simulations with field scenarios on several test-cases. Their complexities, effectiveness and limitations regarding industrial implementation criteria are discussed.
Highlights
Extraction of resources in the earth’s subsurface - oil, gas, minerals, and thermal energy - necessitates drilling long slender boreholes from the surface to the subsurface target
An adaptive soft sensor has been proposed in [40] for the case of a singlesectional drillstring, we present here a new type of estimator, which is based on our recursive dynamics framework
DISTRIBUTED TORSIONAL DYNAMICS We model the dynamics of a directional drilling system of length L (Figure 1)
Summary
Extraction of resources in the earth’s subsurface - oil, gas, minerals, and thermal energy - necessitates drilling long slender boreholes from the surface to the subsurface target. These oscillations, torsional vibrations can appear due to downhole conditions (such as significant drag, tight annular clearances or formation characteristics [6] for instance) or due to side forces induced by Coulomb friction terms [7] These oscillations are known as stick-slip and are considered to be the most destructive as they may cause fatigue of the equipment, a deterioration of the performance of the process, or a premature failing of the bit [8]. The control law combines three terms: a feed-forward term to compensate the effect of the Coulomb friction terms, a trajectory term, and a stabilization term (that corresponds to a ZTorque PI controller), conforming to the canonical 3-DOF controller design for tracking and disturbance rejection Such an add-on requires a minimal implementation effort for practitioners.
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