Pipe Cutoff Methods
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Explosive or Jet cutters
Linear explosive charge cutter
Chemical cutter
Radial Cutting Torch
Erosive/Abrasive cutter
Mechanical cutter
Collider (rarely used in interventions)
Electrical arc tools
3/14/2009
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1
Pipe Cutoff Targets
• Pipe, usually tubing, when pulling a packer
• Tailpipe (below a packer)
• Special Targets
– Multiple strings
– Casing recovery
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2
Explosive Cutters
• Continuous or segmented cutters
• A variation of linear shaped charge
• Needs to approach pipe ID: use a cutter with
80% of pipe ID for best performance.
• The charge behavior is similar to how a
perforating shaped charge works.
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Shaped Charge or Explosive Cutter – note the flare remaining. The flare is a result of
yielding the pipe when cut. The flared end may have to be milled away to allow the pipe
to be pulled.
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Minimum flare from a well designed explosive cutter – still requires dressing to fish with an
overshot.
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Cutter Problems
• Large diameter cutter deployment is difficult
die to restrictions in the string.
• Obtaining complete pipe separation
• Excessive flare at cut
• Outer pipe damage
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Chemical Cutters
• A focused spray of bromine trifluoride that corrodes the tubular
wall. BrF3 reacts violently on contact with water to evolve
oxygen.
• Application expertise is critical to success of a chemical cutter.
• Field data - 75% reliable (first cut) above packer, 25% reliable
below packer
• Less reliability at depths beyond 10,000 ft and high alloy pipe
may be more difficult to cut
• Usually cuts about 95% of pipe wall – have to pull apart. Typical
overpulls to part the pipe are > 30,000 lb.
• Steel wool in mixing cavity believed to increase cutting efficiency.
• The performance of chemical cutters is adversely affected by
liquid crossflows from uneven liquid heads or pressures in the
tubing and annulus.
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NotePerfect
the nozzle
spray pattern
this 3-1/2”
S135 drill
pipe. The nozzles
befired.
of One
A Near
Chemical
Cut. 50kinoverpull,
dropped
off immediately
whenmust
cutter
optimum
and cut
at optimum
distance
from the
inside
wall oftubing.
the target pipe for best
joint
in stringsize
above
found backed
off 4-1/2
turns
on pulling
performance. Small amounts of the wall may not be cut under even the best conditions
and overpulls of over 50,000 lbs have been applied in some cases before the pipe finally
separates.
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Chemical Cutter Guidelines
• Avoid cuts in jewelry (profiles, collars, subs,
mandrels and other heavy body or irregular
shaped components), also avoid heavier wall and
higher alloy pipe when possible
• The minimum restriction in a tubing string
above the cut is the number 1 consideration
when determining if a chemical cutter can be
used. Efficiency is dramatically reduced if
the cutter is used in tubing with a larger I.D.
than recommended.
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Nozzle Power Falls Rapidly With Increasing Standoff – The Jet is diffused with
distance from the nozzle.
Note: this is for a fluid jet without particles.
Impact energy remaining at distances away from the nozzle.
The spreading of the jet reduces the amount of chemical
reacting with the cutting zone where pipe separation is
needed.
d
93% to 99%
6 to 8d max
3/14/2009
75% to 92%
9 to 15d max
25% to 75%
16 to 24 d max
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Source unknown
Chemical cutter deployment – critical pieces are max tool diameter, centralization, anchoring
and tool and casing preparation. Pulling pipe tension is often necessary.
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Differential pressure effects
• Chemical tool performance can be severely
reduced if a pressure differential exists
between inside the tubing and the annulus.
• Typically, a small hole is created near the zone
to be cut with a puncher charge and the
pressures are allow to equalize before the
pipe cut is attempted.
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Tubing showing incomplete chemical cut
The remaining steel in this example could not be yielded by overpull. Failures are
due to many problems including small tool diameter, moving well fluids, deposits
inside the tubing, pressure, temperature, depth and pipe grade.
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Courtesy BP
Debris in pipe cut and pulled from a well. Debris, including pipe dope, mill scale,
paraffin, scale, wireline grease, plastic coatings, etc., can be barriers to chemical
cutters.
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Chemical cutter head (Beryllium Bronze) with nozzles. Nozzles wear with use – critical wells
and cuts at the limit of the tool may warrant use of a new nozzle body.
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Chemical Cutter, tool cut 3.5”, 13.3 lb/ft, S-135 DP – no residual (uncut) steel was left – this
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was an
unusually good cut.
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16
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An experiment to measure the outside casing damage when cutting DP - <1”
clearance from 7” casing to 3.5” drill pipe
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Outer casing damage by chemical cutter when DP was touching casing Wall. Depression was
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about3/14/2009
0.15” deep.
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Test of Chemical Cutter on 13.5 ppf DP - 5% metal retaining.
The small uncut area, about 5% of pipe body, would require overpull to complete the pipe
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separation
in the well.
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Chemical cut end of drill pipe, showing small uncut area broken by hand after the test.
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Chemical cut on a recovered pipe –
note the nozzle impact areas and the
areas that had to be pulled apart by
overpull.
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21
Split Shot or Linear Explosive Shaped Charge
• Breaks the strength of the coupling. Usually
requires only minor overpull to separate
unless the connection uses hook-wall threads.
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A SplitShot charge in a coupling – the
effects vary but a high success is typical.
Problems:
Depth control
Hookwall threads
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Courtesy Owen Tool
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Radial Torch Cutter
• Thermite plasma – extreme high temperatures
(~5000oF).
• Nozzle cutter tool.
• Outer string damage potential controllable in
most cases.
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Troika Data
• TBG - 4-1/2" 13.5# 13Cr85
– 1st attempt w/chem cutter failed. Tool OD 31/8" - Over Pull 25K
– 2nd attempt w/same tool failed- Over Pull 55K
– 3rd attempt w/radial cutting torch Tool OD 215/16" - Over Pull 25 – pipe parted
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Courtesy BP
Radial Torch Cut, 13Cr 85 ksi pipe. Note the nozzle patterns and the melted steel.
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String Shot Techniques
• Aid in backoff and jump-out of coupling.
• Stringshot
– 1 to 4 strings of 90 grain (nominal wt) detonation
cord, 3 to 4 ft long, suspended with E-line, across
a coupling.
– Initiated high order
– Tension already pulled into pipe (25k+ overpull) or
torque when doing a back-off
– May not damage coupling or pin.
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Abrasive Cutting
• Abrasives such as sand or pellets of carbonate
carried at high velocity by water or oil can
easily cut steel.
• Multiple layer cuts are possible.
• Control of the cut may be difficult.
• Back pressure in deeper wells slows the
cutting performance.
• Nozzle performance less affected by standoff
when using abrasives.
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Cut End of 3.5” DP, after Abrasive Cutoff
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Washout in drill pipe caused by stall during abrasive jetting with a rotating tool
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Groove and washout in outer casing caused by abrasive tool
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31
Surface Cutoff Test of Abrasive Cutter in 2-3/8” tubing cemented in 4-1/2” . Cut required less
than 20 minutes using frac sand and a rotating head nozzle tool.
Courtesy Charlie Hailey
Company
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32
Mechanical Cutters
• Best choice for pipe where no tension can be
pulled.
• Minimize the number of cutter arms to insure
good load application of cutter
• Must be anchored
• Slowest form of cutting – typically 1 to 10
hours to get a cut.
• Very experience dependent.
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33
Two bladed mechanical cutter – blades pump out with pressure – must be held out and rotated
by a motor powered by the same flow.
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Pipe Cutoff Conclusions
• The optimum cutoff device depends on well
conditions, pipe type, clearances above the
cut, ability to apply overpull and operator
experience.
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