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Oilfield Technology
June
2015
Focusing on the second element, one of the most effective ways to
lower drilling costs is to optimise drilling efficiency and increase ROP. By
delivering on this goal, days on well are reduced, and in the drilling world
the main driver of cost for delivering the wellbore is time. This is because so
much of the drilling AFE is driven by day rates for services and equipment.
When drill bit companies develop their research and engineering (R&E)
strategies and start spending their resources, they largely focus on ROP
enhancement centric technologies. It is precisely this R&E focus that has
resulted in the new and innovative MicroCORE™ cutting system that has
been optimised to significantly enhance ROP performance in a variety of
applications around the globe. In the discussion that follows, this cutting
structure technology will be described, the key benefits of the cutting
structure will be reviewed, and then a sample of the field validation results
will be presented.
Technologyoverview
The MicroCORE cutting structure is a significant departure from the
traditional PDC bit cutting structure. Figure 1 shows a top view of a
PDC drill bit with this cutting system. The nose, shoulder, and gauge of the
bit are similar to a traditional PDC cutting structure. However, in the centre
of the cone, one can see that the cutting structure
has been interrupted. Upon casual observation, it
would appear that PDC cutters are missing from
the centre of the drill bit. However, this cutting
structure feature is intentional and has significant
benefits that will be further explained in the next
section of this discussion.
The immediate concern might be that this
cutting structure would have an inherent weakness
in the centre of the bit. But, in actuality, the bit has
been designed such that its integrity in this location
is quite robust. Figure 2 shows an illustration
of how the MicroCORE cutting system cuts and
removes rock in the centre of the bit using a highly
efficient lateral loading mechanism. As is illustrated
in images one and two of the Figure, as the bit is
drilling ahead, a core is being cut in the MicroCORE
chamber. As this core nears the top of the chamber
it encounters a TSP cutter that applies a lateral
load to the core as it is advancing, causing the core
to fracture at its base as shown in image three. After
this, the core is evacuated out of the junk slot and
up the annulus and the process begins again as the
next core is being cut.
Removing the core in this way is highly
efficient. Essentially, this is like applying a lateral
load to a long and brittle cantilever beam, minimal
load is required to shear the core at its base and
more important, the normal component of this
load is essentially insignificant. This is important
because this normal component would be a
counterforce to the weight on bit being applied
to the bit, which would ultimately cause drilling
inefficiency. As the cutting system has been
optimised, crushing mechanisms have been
evaluated as a means to remove the core, but this
means of core removal has been determined to be
less efficient.
Cuttingsystembenefits
As described earlier, the MicroCORE cutting system
was developed with an R&E focus on rate of
Figure 1.
Top viewof a Tercel PDCbit with theMicroCORE cutting
system.
Figure 2.
Cut away of PDCwith theMicroCORE cutting system illustrating the progression of a
core being cut while drillingaheadand then removed out the junk slot.
Figure 3.
Energy consumedby the bit while drilling versus the radial location on the drill bit.
Figure 4.
Comparison of bit radial profiles for PDCbits illustratinga shallowcone PDCprofile
versus adeeper cone profile.
