Reverse Circulating With Coiled Tubing

7/31/2019 Reverse Circulating With Coiled Tubing

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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.



3/21

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????



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Reverse Circulating Above

the reservoir with no losses.

1.5

bpm

1.5

bpm



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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



7/21

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



8/21

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



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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



10/21

Baker Oil ToolsReversing/Jetting Nozzle



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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).



12/21

RC&J ToolCaptured Ball Concept



13/21

Barriers

Two Barriers Required:

Mechanical

Stuffing box

Contingent

BOP (CT BOP and/or Drilling BOP depends on set-up)

Others?

Circulating fluid (kill weight?)



14/21

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


15/21

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



16/21

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



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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.



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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.



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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.



20/21

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.



21/21

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.


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Reverse Circulating With Coiled Tubing