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Oilfield Technology
January
2016
Dri ll Bit Q&A
Steve Drews, Kevin
Schader, Devin Mintz,
and Thomas Gallifet,
Varel International,
USA
Rollerconebitdesign
C
arbonate formations in the Middle East and North Sea
regions present significant challenges to roller cone
bit durability. The low abrasion, high toughness
formations require the use of specially formulated tungsten
carbide grades with enhanced toughness.
Varel’s Everest high performance, large diameter roller
cone product line incorporates re-engineered life enhancing
features including carbonate specific tungsten carbide
grades, shirttail wear protection and a pressure attenuator
to protect seals. With both tungsten carbide insert (TCI)
and steel tooth configurations, and in large sizes from
14 ¾ - 45 in., the bit line provides performance options to
improve any large diameter carbonate drilling.
The bit line provides sealed-bearing options with
premium Summit and economy base models. The
Everest Open delivers an open-bearing option for drilling
surface sections. The Summit model reduces cutting
structure wear in carbonate formation with TCI insert
grades that maximise toughness and reduce heat checking.
Diamond enhanced cutting structures are also available for
highly abrasive formation drilling.
A significant advance in durability is achieved with
EdgeGuard shirttail protection, a feature that strategically
places tungsten carbide shields on vulnerable areas of the
bit shirttail.
Bit life is further enhanced with seal technology that
employs a pressure attenuator. The technology dampens
pressure spikes that can lead to damaging grease
displacement, particularly in horizontal wells. A canister
style compensator also extends bit life by increasing
grease capacity and providing a more reliable pressure
compensation system.
Hybriddesigns
With 15 to 40 frack plugs typically used in multizone
completions, greater drillout efficiency is an important
factor in completion time and cost. But bridge and frack plug
drillout can be an inefficient task because of the variety of
materials used in their construction.
A hybrid roller cone bit design featuring a dual cutting
structure is addressing these different materials to improve
drillout performance. In a 57 well study conducted in the
Eagle Ford shale play in south Texas, the company’s 4 ½ in.
SlipStream RC Pro roller cone bits drilled an average
8.1 min/plug – 13.6% faster than standard tooth bits. The
bits averaged 3.3 more plugs per use than the competitive
tooth bit for less trip time, and produced much smaller
cuttings to significantly decrease wash down time between
plugs.
Frack plugs are typically comprised of very hard outer
slips surrounding ductile composites and elastomer cores.
The design challenges bit performance. Hard outer slips
can quickly wear bit teeth, making the bit increasingly less
effective with each plug drilled. It is also difficult to achieve
Figure 1.
SlipStreamRCPro’s dual cutting structure is designed to
drill both hardand soft frack plug components.
