Duff (2013) defined the stick-slip in oil drilling operation as ‘The cyclic reduction and corresponding increase of instantaneous rotation speed.’ This vibration occurs due to the nonlinear interaction between bit/formation and
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drillstring/borehole (Leine and Van Campen 2005), which leads to the BHA
sticking for a finite time interval and then slipping. It should be noted that this
definition differs from the classical definition of stick-slip of tribological systems
where the stick-slip is related to the generation (stick) and breaking (slip) of
adhesive bonds. During the ‘slip’ phase, the angular velocity of the BHA can exceed the imposed velocity by two to three times as shown in Figure 2-8 (Kriesels et al. 1999.). This vibration can continue for several minutes (Sassan
and Halimberdi 2013).
The period of stick-slip oscillation depends on many factors such as the length
of the drillpipe, rotary speed, nature and location of the friction. It is possible for
the stick-slip to appear in up to 50% of the drilling time (Brett 1992; Jardine et
al. 1994; Christoforou and Yigit 2001).
The main parameters of drilling such as weight on bit(WOB), rotary torque and
rotary speed range from 0 to 3000kN, 0.5 to 70kN and 50 to 200 rev/min
respectively (Macdonald and Bjune 2007). However, during the drilling
operation the desired speed of drilling is typically in the range of 120 to
125rev/min in the ordinary mode when there is no stick-slip (slip phase) and 50 rev/min when stick-slip occurs (Kriesels et al. 1999.). It has been observed by
several authors that the stick-slip vibration occurs mostly with low angular
velocity and a significant weight (when compared to the type of rock formation)
on the bit (Brett 1992; Yigit and Christoforou 2000; Abdulgalil and Siguerdidjane
2005). Another cause can be attributed to the high difference between the static
and dynamic friction which leads to a transfer of the stored energy in the
drillpipe to inertial energy in the BHA, subsequently increasing the rotational
speed of the BHA (Brett 1992). Some researchers have attributed the stick-slip
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more common with polycrystalline diamond compact (PDC) bits (Brett 1992).
However, other authors refer to the size of the bit since an increase the size this
leads to an increase in the reactive torque on the bit (Jain et al. 2011).
Besides the associations with the drill bit, other factors such as the condition
and tortuosity of the wellbore, the type of formation and the lubricity of the
drilling fluid have a significant impact on the occurrence of stick-slip (Sassan
and Halimberdi 2013).
Figure 2-8 Example of stick-slip oscillation of a drillstring (Kriesels et al. 1999.)
The stick-slip mechanism can be explained as follows: the bit may become
trapped due to many factors such as formation characteristics, significant drag
torque or tight bit/hole clearance which leads to the BHA becoming stationary
whilst the rotary table continues to rotate. This leads to wind-up of the shaft
(similar to a wound-up torsional spring) and an increase in the torsional energy
trapped in the drillstring causing an increase in the applied torque. When this
torque overcomes the frictional force at the bit/rock interface (static friction),
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generation of a torsional wave which travels up to the rotary table before being
reflected back to the bottom hole assembly (Macdonald and Bjune 2007;
Saldivar et al. 2011). The process may repeat many times until the stick-slip
decays. Hence, this oscillatory motion is similar to classical stick-slip motion in
tribological systems where the build-up and release of energy generates the
stick-slip motion.
Stick-slip vibration is undesirable in the oil drilling process due to many reasons
which can be summarised as follows:
1- Reduction in the rate of penetration (ROP) of the drilling operation due to
the lateral and longitudinal vibrations in the slip phase (Halsey et al.
1988; Sassan and Halimberdi 2013; Liu 2015).
2- Increase in the cost of drilling due to a decrease in the ROP and increase
in the drilling duration (Jardine et al. 1994; Dubinsky and Baecker 1998;
Kriesels et al. 1999.; Guerrero and Kuli 2007; Sassan and Halimberdi
2013; Zhu et al. 2015).
3- Affecting the borehole quality resulting in lateral vibration (backwards and
forward whirling) (Zhu et al. 2015).
4- Fatigue problems in the drillpipe due to the large cyclic stresses which
lead to an increase in tool failures (Kriesels et al. 1999.; Christoforou and
Yigit 2001).
5- Failures of the components of the BHA (measurement while drilling
(MWD) sensors, and motors) due to severe lateral vibration in the slip
phase (Kriesels et al. 1999.).
6- Instability of the wellbore structure which may lead to collapse (Placido et
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7- Severe axial and lateral vibrations in the bottom hole assembly due to
the high speed in the sliding phase. These vibrations lead to excessive
bit wear (Henneuse 1992; Warren and Oster 1998; Macpherson et al.
2001; Besselink et al. 2011).
8- Decrease in the accuracy of measurement while drilling (MWD) as a
result of noise due to the vibrations; this could lead to inaccurate
measurement of sensitive parameters (velocity and torque on bit signals)
(Bailey et al. 2008).
9- Decrease the drilling efficiency (Besselink et al. 2011).
Therefore, due to these problems, the understanding of the stick-slip
mechanism, the causes, and the methods that are used to suppress it is a very
significant field of research in the oil drilling industry to improve overall
performance.