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CT Reverse Circulating - Basics
Reverse circulating with aqueous fluid to unload fracsand from large wellbores
If sufficient annular velocities are possible with normalcirculation, usually dont use reverse circulating.
Hydraulics for lift are the critical issueLow shear support fluids 2.5 to 3.5 ppb biopolymer
Ability to quickly shift from reverse to normal circulation
Hydrocarbons are never intentionally reversed up thecoil extreme care is required.
Data from Alaska and North Sea
Sources Charlie Michel, RodneyStephens, Walter Crow.
3/14/2009 1George E. King EngineeringGEKEngineering.com
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Normal Path Circulation Rateand ability to lift depends on CT
capacity.
3/14/2009 2George E. King EngineeringGEKEngineering.com
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Solids Transport in Annuli
(Conventional Jetting)
Difficult to unload sand from 7 casing even with 1-3/4 CT
Very difficult over 20o deviation and Boycott setting
range of 30 to 60
o
is most difficult. Low reservoir pressure and dense particles (bauxite
and BaSO4) are an added problem.
Example Well North Sea 60o deviation, 9-5/8
casing and 3-1/2 tailpipe, very low pressure well how to unload several meters of fill????
3/14/2009 3George E. King EngineeringGEKEngineering.com
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Reverse Circulating Above
the reservoir with no losses.
1.5
bpm
1.5
bpm
3/14/2009 4George E. King EngineeringGEKEngineering.com
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3/14/2009 5George E. King EngineeringGEKEngineering.com
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Reverse Circulating Above Reservoir (no losses)
Disposal1.5 bpm
1500 psi10 psi
1500 psi2200 psi
PRVs
1.5
bpm
1.5
bpm
4800 psiPRV
1.5 bpm
10 psi
3/14/2009 6George E. King EngineeringGEKEngineering.com
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Reverse Circulating 2 bpm losses
2.0 bpm
Disposal1.5 bpm
1500 psi10 psi
1500 psi2200 psi
PRVs
1.5
bpm
3.5
bpm4800 psi
PRV
3.5 bpm
10 psi
3/14/2009 7George E. King EngineeringGEKEngineering.com
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Reverse Circulating 10 bpm losses
10 bpm
Disposal1.5 bpm
1500 psi10 psi
1500 psi2200 psi
PRVs
1.5
bpm
11.5bpm
4800 psiPRV
11.5 bpm
10 psi
3/14/2009 8George E. King EngineeringGEKEngineering.com
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Jetting Bridge
Disposal2.5 bpm
10 psi10 psi
4000 psi2200 psi
PRVs
2.5
bpm
2.5
bpm4800 psi
PRV
2.5 bpm
4000 psi
3/14/2009 9George E. King EngineeringGEKEngineering.com
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Baker Oil ToolsReversing/Jetting Nozzle
3/14/2009 10George E. King EngineeringGEKEngineering.com
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Nozzle converts
from a single
large port for
reversing to
multiple ports
for normal
jetting.
Clear string before
switch from
reverse to normaljetting (prevents
erosion of the
ports).
3/14/2009 11George E. King EngineeringGEKEngineering.com
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RC&J ToolCaptured Ball Concept
3/14/2009 12George E. King EngineeringGEKEngineering.com
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Barriers
Two Barriers Required:
Mechanical
Stuffing box
Contingent
BOP (CT BOP and/or Drilling BOP depends on set-up)
Others?
Circulating fluid (kill weight?)
3/14/2009 13George E. King EngineeringGEKEngineering.com
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Risks
Elimination of the CT flapper valve small risk, stilltwo barriers
Sticking the coil reduced because of higher
velocities around solids and clean fluid in theannulus.
Bridging in the coil just not seen - minimized by:
Control rate of bridge entry - control of particles enteringthe coil
Control of type of particles that are reversed
High velocities in the coil
Fluid with high support at low shear
Can quickly move from reverse to forward circulation3/14/2009 14George E. King Engineering
GEKEngineering.com
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Coil Collapse Risks
Coil far weaker under collapse than burst.
Precautions and relief considerations needed to keepoutside pressure minimized.
Consider increasing pickup weight on the coil (weightof solids)
Collapse is function of OD, ID, material strength,ovality, pickup loads (weights and frictions),
buoyancy, coil condition, rate of load increase, etc. The collapse tables are for round pipe, not oval CT
3/14/2009 15George E. King EngineeringGEKEngineering.com
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Typical fluid density increase with sand at 1
lb/gal is about 9%. Sand is 6% of coil volume
at 1 lb/gal.
At 10,000 ft, weight difference between 0.43
and 0.47 psi/ft (1 lb sand) is 0.77 lb/gal or
extra 500 lb
3/14/2009 16George E. King EngineeringGEKEngineering.com
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Higher Risks (Poor Candidates)
Multi-zone oil wells with cross flow
Wells not killed by column of water
Wells that produce but cannot inject Deep or bad dog leg wells where pick-up
near the max allowable for the coil.
HPHT wells no experience.
3/14/2009 17George E. King EngineeringGEKEngineering.com
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Coil Requirements
Less than than 40% fatigue wear.
Less than 4% oval.
No corrosion, pits, welds or damage.
Pressure relief valves on backside to preventcoil collapse.
No more than 10% (volume of coil) solids in
the coil at any time. Model the job.
3/14/2009 18George E. King EngineeringGEKEngineering.com
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Formation/Well Requirements
All hydrocarbons push out of pipe (3x pipevolume)
All zones kept overbalanced.
Contingency plans for well flow.
Consider type, shape, density and size ofsolids lifted.
3/14/2009 19George E. King EngineeringGEKEngineering.com
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Selection of Equipment
CT largest possible with > clearance between CTand tubing.
Large OD nozzle helps prevent bypassing solids indeviated wells.
Single large hole in nozzle for reversing (hole smallerthan minimum anywhere else in the system).
Where frac sand is only fill, nozzle design is simple.
No sharp shoulders on tool oval shape preferred. Venturi junk baskets for large pieces.
3/14/2009 20George E. King EngineeringGEKEngineering.com
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CT Reverse Circulating Conclusions
1. Must have pressure differentials and hydraulics
under control.
2. Frac sand removal is most common target, but
other materials are possible with the rightequipment.
3. Circulating fluid must have low shear support.
4. Must limit the amount of sand in the coil at anytime.
3/14/2009 21George E. King EngineeringGEKEngineering.com