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Oilfield Technology
June
2015
profile, SpeedDrill bits have been designed to increase ROP, lower
MSE, and improve stability for overall greater drilling performance.
These bits initially drill a smaller pilot hole, which effectively
relieves the stress in the surrounding formation. The larger
diameter reamer section of the bit then enlarges the wellbore to
the desired width in this stress-relieved rock, requiring less energy
and resulting in more efficient drilling.
The bit improves stability by increasing gauge pad contact
with the wellbore. Typical PDC bits with a single diameter usually
provide 50% gauge pad contact, but the dual-diameter technology
of SpeedDrill bits offers 100% contact with the wellbore by utilising
the gauge pads on both pilot and reamer sections. With a patented
gauge pad orientation that provides continuous, 360˚ contact,
these bits improve lateral stability, resist string vibration, and
prevent bit whirl. Full borehole coverage also reduces cutter
damage, maintaining sharp cutting structures longer and allowing
the bit to more efficiently remove the rock.
The stress relief effects and improved stability were validated
numerous times in the NOV Pressurized Drilling Laboratory in
Houston. And with these advantages proven in the lab, operators
would see results in the field.
Global casestudies
Mexico
Equipped with Helios™ Impact™ cutters, a 17 ½ in. SpeedDrill
bit set field records for ROP and the interval drilled in Mexico’s
Pareto field. The Paraje Solo and Filisolo formations in the field
feature challenging lithologies of sandstone, quarzitic sandstone
and interbedded shale. The SpeedDrill bit drilled for 77.8 hrs,
penetrating 1797 m of these formations with an average ROP of
23.1 m/hr. This was the first effective run of a PDC bit in an interval
that typically uses roller cone bits, and ROP was 55% higher
compared to the best offset well in the field.
Kuwait
In South Kuwait, an operator hoped to deliver a minimum ROP
of 100 ft/hr on a stiff rotary BHA in a vertical section through
Ahmadi and Burgan formations. With a 12 ¼ in. SpeedDrill bit,
the team was able to drill from 4370 ft to 5132 ft with an ROP of
152.4 ft/hr – a field record. The same bit was then transferred
to another vertical well, drilling from 4340 ft to 4950 ft with an
even better ROP of 152.5 ft/hr. These runs increased ROP by 17%
compared to the field average, and 7% compared to the best
performing offset.
TheNorthSea
A 12 ¼ in. SpeedDrill bit delivered the best performance in a
campaign through the Zechstein sequence in the North Sea,
reducing vibration through tough anhydrite and dolomite beds.
The driller completed the 1335 ft section in only 29 hours – and
with just over 23 hrs on bottom drilling – with an average ROP of
69.4 ft/hr. This was the highest ROP through the Zechstein sequence
in the campaign. And though anhydrite and dolomite are notorious
for causing shocks to be recorded, the operator reported smooth
drilling and noted no vibration throughout the interval. The bit came
out in excellent condition, graded 0-0-CT-G-X-I-NO-TD by the rig.
Brazil
Last year in Brazil, a 12 ¼ bit drilled a total of 378 m in 126.5 hrs
through siltstone, shale, and sandstone lithologies. The bit was
able to drill an interval 107% longer than average offset wells in
the area, and 40% longer than was initially estimated. The bit
exceeded customer expectations even further by doing this at an
ROP 27% faster than estimated. The bit showed excellent stability
and steerability, and was pulled out of the hole with a good dull
condition (1-0-WT-S-X-1-NO-CP).
China
Hoping to save drilling time and costs, an operator in the
Sichuan Basin in China combined a 9 ½ in. SpeedDrill bit featuring
Helios cutters with a 6 ¾ in. HEMIDRIL™ motor with a goal to
complete the section in one run at a high ROP. The assembly
drilled 1146 m of Penglaizhen and Shaximiao formations, which
consist mostly of clay stone, at an average ROP of nearly 88 m/hr.
Achieving an ROP significantly higher than offset wells in the
area, and with a good dull condition for both the pilot section
(2-2-WT-N-X-IN-CT-TD) and the reamer section (1-2-WT-G-X-IN-
LT-TD) of the bit, the SpeedDrill bit exceeded expectations once
again.
Also in China, the bit improved the ROP of a vertical well by
128.6% compared to offset wells in the Northeast Basin. The bit
averaged an ROP of 29.61 m/hr through Sifangtai and Quantou
formations, which mainly consist of mudstone and siltstone
but turned hard and abrasive at 1800 m. Still, the bit performed
extremely well and maintained high efficiency throughout the
section, especially compared to the offset well.
Russia
For its first run in Russia, a 12 ¼ in. SpeedDrill bit running
on a fixed-bend motor housing set a new ROP pad record
Figure 1.
SpeedDrill™high performance drill bits.
