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Oilfield Technology
June
2015
Casestudies
An operator in western Canada drilling a 12 ¼ in. diameter
intermediate build section in the Fort McMurray area landing
in the oilsands (Wilrich‑Bluesky formation) recently introduced
Pexus technology to their drilling programme. The immediate
area around these wells has been heavily developed, with
hundreds of close offsets. Attempts to introduce PDC bits into
this application met with very limited success – due to their
aggressive torque response, it was necessary to dramatically
reduce the differential pressure across the motor to help control
the toolface response. Consequently, the ROP for the PDC runs
were actually a low lower than the rollercone bits runs, contrary
to what is typically achievable by PDC bits. However, the 12 ¼ in.
Pexus hybrid bits that were used in this application were able
to significantly increase the ROP through the interval while also
improving both bit durability and torque response.
As shown in Figure 6, in addition to the cost and time
savings resulting from drilling three wells with the same bit
and BHA, the ROP achieved with Pexus is over 30% higher than
rollercone bits, and 50% higher than PDC bits. This performance
increase is a direct result of the smooth drilling behaviour of
Pexus hybrid bits, which allows for excellent toolface control
even at higher differential pressure and ROP.
In another 12 ¼ in. directional application with a major
operator in Alberta, Canada, Pexus hybrid bits were selected
to drill S curve intervals where achieving one run from shoe
to shoe was proving very challenging. In this application it
was not uncommon to require two rollercone bits to complete
the interval, and most PDC bits that were tried in these
formation were damaged beyond repair. Each Pexus 12 ¼ in.
SVP616 hybrid bit that was used in these applications drilled
the entire interval in one run at a high ROP, and the resulting
dull condition was excellent. As seen in Figure 7, a photo taken
at the rig site soon after the run, the dull condition of one
particular Pexus hybrid bit was excellent after completing the
interval.
To date, over 400 runs have been completed with these
hybrid bits, but most have been in larger hole sizes. The vast
majority of applications that have experienced this new
technology so far have been intervals of 10 ⅝ in. up to 24 in.
diameter. This is mainly due to the complexities of downsizing
the RNG components. Because each gouging insert is free
to rotate as the bit drills, the mechanical aspects of each
RNG assembly must be considered when changing to a smaller
hole size. The large RNG assemblies used in large diameter
Pexus hybrid bits have undergone extensive development since
the technology was first introduced to the industry in order
to assure excellent consistency, and that same effort is now
underway for small RNG assemblies.
In one of the very first runs ever completed with a small
diameter design, the 6 ¼ in. SHP613D shown in Figure 5, the
resulting performance was impressive. In a lateral application
known for significant deposits of chert and pyrite that
commonly damage or destroy PDC bits, the Pexus hybrid bit
was able to complete the entire interval in one run at the
fastest ROP yet recorded by the operator in this area. The
directional team on location commented that the Pexus
“steered like a rollercone bit” while it drilled further and
faster than any PDC bit in the offsets. As shown in Figure 8,
the toolface response of the bit was extremely smooth, which
allowed consistent directional response to geosteering
requirements.
As seen in Figure 9, again mostly due to the presence of
chert and pyrite randomly located throughout the interval,
the average PDC bit run was barely over ⅓ the length of the
interval. However, the Pexus hybrid bit was able to drill the
entire section in one run, and was pulled with no damage at all
to any PDC cutters.
In addition to drilling nearly three times further than the
average of close offset runs, the SHP613D also drilled over 30%
faster than the average offset ROP (see Figure 10), and recorded
the fastest ROP achieved by any bit that drilled over 1000 m in
this formation in the area.
Conclusions
Especially since PDC bits were introduced to the market, the
oilfield drill bit industry has experienced rapid technological
change that has resulted in continuously improving
performance. However, despite some incredible developments
in the field of PDC cutters over the past five years,
3
it appears
that the market shift between rollercone bits and PDC bits
has slowed. Up until very recently, every year brought with it
another significant increase in the percentage of rock drilled
around the world by PDC bits compared to rollercone bits, but
the industry may be approaching the technical limit of what
conventional PDC bits can achieve.
Hybrid drill bit technology is creating a new environment for
the industry. Similar in many ways to when PDC bits were first
introduced back in the mid 1970s, the proliferation of hybrid
bits is now creating a step change in performance in many
challenging applications. It will be very interesting to see what
the next 40 years has in store for drill bit technology.
References
1.
Beaton, T., ‘A Hybrid Solution’, Oilfield Technology, (November, 2014),
pp. 45 - 49.
2.
Beaton, T., Cyre, J., Isnor, S., and Herman, J.J., New Technologies
Eliminate Drill Bit Wear in Oil Sands Applications, SPE 167133 presented
at the SPE Unconventional Resources Conference, (November, 2013).
3.
Beaton, T., ‘When the going gets tough, the tough get going’,
Oilfield Technology, (February 2014), pp. 20 - 25.
Figure 9.
Comparison of slimhole Pexus durability to close offsets.
Figure 10.
Comparison of slimhole Pexus rate of penetration to close
offsets.
