Suppression of Drill-String Stick-Slip Vibration
MATEC Web of Conferences
Suppression of Drill-String Stick-Slip Vibration
Vahid Vaziri 0
Marcin Kapitaniak 0
Marian
Wiercigroch 0
0 Centre for Applied Dynamic Research, University of Aberdeen , UK
We investigate experimentally and numerically suppression of drill-string torsional vibration while drilling by using a sliding mode control. The experiments are conducted on the novel experimental drilling rig developed at the University of Aberdeen [1] and using PDC commercial drill-bits and real rock-samples. A mathematical model of the experimental setup which takes into account the dynamics of the drill-string and the driving motor, is proposed. Then a sliding mode control method is employed to suppress stick-slip oscillations. The experimental and numerical results considering a time delay of the actuator are in a close agreement. Stick-slip vibration is eliminated and significant reduction in vibration amplitude has been observed when using the controller.
1 Introduction
During a downhole drilling process excessive
vibrations can occur, which in most cases have a
negative impact on the effectiveness of the
process and the drilling equipment [
2
]. Such
vibration may lead to an accelerated wear and
premature damage of the expensive drilling
equipment. Often different dynamic effects such as
bit-bounce, stick–slip, forward and backward
whirls may appear in the drilling process.
Recently several attempts have been made to
replicate these vibrations in academic laboratories.
However, in most studies the cutting process is
simulated by a friction between two disks [
3
].
In this work we focus on suppression of
stick-slip phenomenon while drilling, which
nature is still not well understood and can lead to
a catastrophic failure of the drill-stings.
Therefore, firstly, a 2-DOF lumped mass model is
developed using the torque-on-bit curves, which
capture both the frictional and cutting
components of the drill-bit rock interactions [
4
]. Then,
a sliding surface is defined and consequently a
sliding mode controller is developed which
accommodates the parameters uncertainties. The
experimental and numerical results demonstrate
the predictive capabilities of the mathematical
models and the power of the controller to
eliminate the stick-slip vibrations in the given
conditions.
2 Drill-String Experimental Stand
A novel experimental drilling facility has been
designed and built at the University of
Aberdeen, capable of reproducing all major types
of drill-string vibration [
4–7
]. It allows to
investigate nonlinear behaviour between the
drillbit and the formation and to introduce
different control methods of vibration suppression.
Unlike typical other research experimental
academic facilities, our rig is configured in such a
way that the cutting process is undertaken
using real commercial drill-bits and rock samples.
The rig shown in Fig.1 is equipped with a
variety of different sensors and transducers.
Angular positions are measured by two
quadrature encoders having 500 pulse per revolution,
where axial motion of the drill-bit is captured
by a P1010 position transducer attached to the
Bottom Hole Assembly. Horizontal and vertical
forces as well as torque coming from the bit to
the rock are measured by a 4-component Kistler
dynamometer placed under the rock sample. All
the voltage signals are sent to a NI PCIe-6321
data acquisition card which has multiple
analogue input (16-Bit, 250 kS/s) and output (900
kS/s) channels and four 32bit counters/timers.
Accessing to 4 counters, allows us to precisely
synchronise two encoders. This is important as
then the drill-pipe twist can be calculated
accurately. Furthermore, the card high performance
allows high frequency data sampling up to 30
kHz. This card is controlled by a LabVIEW
programme with custom built graphical interface
allowing to monitor responses of the system and
to present time histories of variables and phase
portraits in real-time. This program also sends
the command to the top AC motor through the
NI card and the ABB frequency convertor. This
convertor can work in speed or torque control
modes which control the velocity or torque
provided by the motor. Different speed or torque
nonlinear control methods can be implemented
in the LabVIEW program such as a sliding mode
control in Fig.1.
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Labview program
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axial dispalacement
bit speed
torque and weight on bit
0
17.5
0
17.5
t[s]
27.5
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Tt
ct
θt
c, k
θb
motor
& gearing
drill-pipe
BHA
drill-bit
t[s]
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Tb
3 Mathematical Model and
Sliding Model Control
The most used class of models for capturing
uncoupled torsional vibration consists of
several parallel disks, rotating around their common
axis and connected to each other by torsional
spring and damper. Top disk in all these
models represents the rotary table and the bottom
disk represents the drill-bit. The bit-rock
interaction is modeled by th (...truncated)