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Oilfield Technology
January
2016
Dri ll Bit Q&A
SebastianDesmette,
BenoitDeschamps,
JamesLangford, and
MikeDoster,
TercelOilfieldProducts
BoostingROP
R
OP is the result of the transformation of mechanical
and hydraulic energy transmitted to the bit. There
are two options available to the driller in order to
increase ROP:
Choose the most efficient drilling system.
Increase power to the drilling system as much as possible.
Most companies concentrate on maximising the
efficiency of drilling systems and there are many different
ways to achieve this. Tercel have taken the approach that
cutting less rock improves drilling speed. Even more so
if the rock that would otherwise have been drilled was
particularly tough to cut. On a fixed cutter bit, the centre
of the hole is the most difficult part to cut. To solve this,
the MicroCORE Cutting system leaves a core in the centre.
Once the core is long enough, the rock becomes unconfined
and in some cases, it seems that the pore pressure
from the core leads to its desegregation automatically.
In any case, a special feature simply breaks out the
core and directs to the outside of the bit. This simple
idea has been proven to increase ROP by 35% in most
applications and by up to 200% in some cases. The
lower the ROP without MicroCORE bit, the higher the
increase once it is used. The MicroCORE cutting system
is fully integrated into the cutting structure, and has
proven itself in directional applications and even
contributed to bit stability.
What most do not realise is that ROP is primarily
affected by the amount of power placed on the drilling
system, especially at bit level. Mechanical specific energy
(MSE) refers to how efficient a drilling process is. A spike
in the MSE shows that the drilling process has suddenly
become inefficient, due to vibrations, cleaning or other
issues. The MSE is a measurement of mechanical power
per unit volume of rock drilled. The ROP is hidden in such
measurements. The MSE can indicate good efficiency
and yet drilling progress can still be slow. When drillers
talk about hydraulic power, they use hydraulic power per
square inch (HSI). Most drillers will say that the higher
the HSI, the higher the increase in ROP. Therefore, the
more power added into the system, the faster drilling
becomes. Mechanical horsepower per inch (MSI) is
a different measurement that is not commonly used
but provides great insight on the drilling process. The
more power that is placed on the bit, the faster drilling
becomes. Tercel’s OptiMASTER system allows an insight
into the downhole mechanics that act
on the bit, including the forces. This
gives an indication of the real power at
the bit. This MSI typically ranges from
0.3 to 3 depending on the driving system
used, which means an average power at
the cutter as low as 600 W or as high as
4000 W. If there is 10 times more power at
the bit, per square inch of hole, ROP will
be definitively boosted.
Measuring the power at the bit
allows the driller to understand what
is going on in the hole. Compared to
surface power, downhole power is
typically around 80% in vertical drilling
and as low as 30% in ERD wells.
Designs must be able to cope with
such additional power. Detailed design
considerations, and numerous FEA and
CFD on every single design need to ensure
Figure 1.
Identical application in Europe, 600 ft through challengingapplications. Left:
previous cutters. Right: 2015 latest Phoenix cutters.
