January 2016
Oilfield Technology
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27
Dri ll Bit Q&A
that quickly renders conventional PDC bits damaged
beyond repair, the highest average ROP achieved
with rollercone bits over the course of hundred of
wells of development was only 19 m/hr. Through the
introduction of the company’s hybrid bit technology, it
was possible to increase the average ROP in this interval
by nearly 50%, while simultaneously drilling an average
distance that was over 10% further than that with
rollercone bits. This same performance advantage has
been seen in many surface hole applications that contain
heavy gravel. The hybrid gouging/shearing cutting
structure produces much higher ROP than rollercone bits
without suffering damage to the PDC cutters as would
happen with conventional PDC bits (Figure 5).
Abrasionresistance
One subject that is often overlooked with respect to PDC
bit performance is the effect of the wear resistance of
the carbide substrate on PDC cutter durability. With the
invention of composite-bodied PDC bits in 2012, a new level
of wear resistance was introduced to drill bit bodies in some
of the most extreme applications in the industry. However,
despite the fact that body wear was virtually eliminated in
many applications, the carbide substrate on the PDC cutters
themselves continued to suffer extreme material loss. When
carbide substrate wear is severe enough, it can lead to
either cutter loss (due to compromising the braze joint) or
to cutter breakage (due to reduced support for the diamond
table), and in rental markets, can quickly render otherwise
successful performance uneconomical.
Unfortunately, merely identifying that carbide
substrate wear was the new weak link in PDC bit durability
did not offer immediate solutions as the carbide substrate,
in many situations, has gone virtually unchanged
for decades. In the pursuit of continually improved
toughness, abrasion resistance and thermal stability, PDC
cutter technology development has become an almost
impossibly complex mixture of extreme materials and
processes. Therefore, changing the carbide substrate, which
is a cornerstone of PDC cutter construction, was generally not
considered a viable option by most PDC cutter manufacturers.
Working closely with an industry leading supplier of PDC
cutters, the company developed HARD Cutters™, a technology
that has addressed carbide wear in some of the world’s most
extreme environments. As seen in Figure 6, the primary row of
PDC cutters are HARD Cutters, and the backup row of PDC cutters
are conventional PDC cutters. Despite the fact that the primary
cutters are longer, and therefore more carbide is exposed to wear,
and despite the fact that fluid velocities are much higher around
the primary cutters, it can plainly be seen that the material loss
of the conventional PDC cutters is quite severe, while there is very
little carbide wear at all on the HARD Cutters.
Figure 4.
Comparative gage padwear for three runs of the same bit in the same
applicationwith diferent coating technologies.
Figure 5.
Relative performance of Pexus HybridDrill Bits compared to
RollerconeBits.
Figure 6.
Resulting carbide substrate conditionafter drilling 8 legs of
an oilsandswell witha 7⅞SH513DPDCdrill bit.
