Presentation

Schematic view of the cutting process of a drill bit

Recently, detailed analysis of pre-existing experimental data (Black, Walker, Tibbits & Sandstrom, 1986), has revealed that friction forces resulting from a drilling process are independent of the angular velocity of the drillbit. How to explain, in this context, the field observations that the bit was subject to a velocity-dependent torque? Further investigation of the experimental data show (Richard, Germay, & Detournay, 2007):

that both cutting and friction forces must be taken into account to accurately model the bit dynamics,
that the bit is indeed subject to a torque that depends on the rotary velocity imposed at the surface, but as a consequence of the overall drillstring–bit dynamics rather than as a constitutive property of the bit-rock interaction..

This project aims at focusing on the analysis and corresponding control of this very new model accounting for the torsional instabilities occurring for drilling processes. The control objective is to suppress, or at least reduce, the unwanted stick-slip oscillations. It proposes to develop three different Work Packages, following a standard control approach consisting of three steps:

Modeling of the physical problem at stake in a control-oriented spirit (WP1), to better understand the root of instabilities and rule out on the importance of the underlying phenomena into the overall dynamics.
Control design (WP2) to suppress the limit cycle and improve tracking of the desired operating conditions
Experimental validations (WP3) of the two previous steps on a dedicated test-bench available at GIPSA-lab to evaluate their practical merits.

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