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OilfieldTechnology
February
2014
Casestudy1:Alargediameterverticalintervaldrilled
innortheastBritishColumbia,Canada
The first application thatwill be reviewed is a largediameter
vertical interval drilled innortheast BritishColumbia, Canada. This
is a16 in. diameter hole size throughquite competent formations,
includingabrasive sands and severe transitions. Historically, the
application requiredone rollerconebit todrill the first ~150m
(~500 ft) and then1 ‑ 2PDCbits to complete the interval toadepth
of around600m (1970 ft). Inaneffort to complete this surface
application inmuch less time, anewbitwas custom‑designed for
this application. The first SHEARBITS16 in. SV613, with sixblades
and13mm cutters, usingHDCutters, successfully completed the
interval inone runat anROPof 24.5m/hr (80.4 ft/hr).
Thiswas the first time that this intervalwas completed in
one run in this area in this hole size. This result is a testament
to the superior toughness of HDCutters –not onlywas thisbit
able todrill the lower sectionof the interval, which ismore
commonlydrilledwithPDCbits, it successfullydrilled theentire
surface interval, including the top section that is alwaysdrilled
with rollerconebitsdue to the fact that PDCbits typically take
toomuchdamage in this section. Further, inorder tomanage
the inherent torque fluctuations encounteredwhenoperating
largediameter PDCbits, thebitwas runwithquitehighRPM –
between190 ‑ 220.Withabit this large indiameter, highRPM
results in veryhigh tangential velocityon the cutters in theouter
portionof theprofileof thebit, and typicallyputs them intoa
wear condition that ismostly related to the thermal stabilityof the
cutters (as the frictional heating is veryhighwhenhigh tangential
velocities are combinedwithabrasive sand formations). The fact
that thebitwas able todrill through formations typicallyonly
drilledby rollerconebits, and then finish the interval at a veryhigh
RPM, isproof positiveof the combinationof toughness andwear
resistanceachievedwithHDCutters.
However, despite thepositive results of the first run, it
wasdesired to further improveperformance for thenextwell.
Therefore, a thorough reviewof the first dullwasperformed in
order toeffectively categorise thewear condition to identify
opportunities for further improvement. As seen inFigure2, the
cutters on theouter sectionof theprofilewereworn flatwith
the topof theblade. Thiswear conditionbeganaspurewear to
the cutters, thenwhena sharpwear flat edgewas exposed to
the formation, chippingat that edgeaccelerateddiamond loss,
which led to furtherwear to the cutters andultimately to thedull
condition shown inFigure2. Itwas thereforedecided to change
the cutter type toadifferentHDCutterwithevenmoreabrasion
resistance.
The second runalso completed theentire interval inone run,
andat a very similar ROP to the first run, but resulted inamuch
improveddull condition.While the cutters still experienceda
substantial amount ofwear, withassociatedminor chippingat
the cutter edge, the improvement inwear resistancewasdramatic
compared to the first run (Figure3). This is an important result as
it demonstrates the rangeof performance that canbeachieved
withHDCutters – this new technology canbeapplied to various
different cutter configurations tomaximiseperformance ina very
wide rangeof applications.
Casestudy2:Ahorizontalintervalthroughthe
CardiumsandstoneinAlberta,Canada
The second case study is a 16
⅛
in. horizontal interval through a
competent sandstone formation called theCardium sandstone
inAlberta, Canada. Aswith the first case study, the runs tobe
compared are on the same rig, are close offsets to another,
used the sameBHA, samemud system, etc. These runswere
completedon conventional directional assemblieswith a
total RPMbetween 160 and 200. It is critically importantwhen
comparingbit runs to ensure that asmany variables as possible
are left unchanged so the actual results of the variables that
have changed canbe confidently verified. In this case, there are
many runs to analyse using standarddensity cutters (SD cutters)
andHDCutters, whichbetter confirm the improvements realised
with this new technology.
Historically, this application typically required two513‑type
PDCbits (5blades, 13mm cutters) to complete the interval.
However, usinga customisedSHEARBITSHorizontal Series
PDCdesign (SH613DE), thebest of theSD cutter runswereable to
drill theentire interval inone run. Thebest run in thedata setwith
SD cuttersdrilled1367m (4485 ft) of horizontal interval through
theCardium sandstoneat anROPof 21.7m/hr (71.2 ft/hr).
Figure7.
SHEARBITS6
⅛
in.SH513DEHorizontalSeriesPDCbit.
Figure6.
6¼ in.HorizontalSeries-SH613DEdullbitwithHDCutters.
