Reverse Circulating With Coiled Tubing

CT Rev Rever erse se Circul Circulat ating ing - Basics Basics Reverse circulating with aqueous fluid to unload frac • Reverse sand from large wellbores – If sufficient annular velocities are possible with normal circulation, usually don’t use reverse reverse circulating. circulating.

Hydraulics for lift are the critical issue • Hydraulics – Low shear shear support support fluids – 2.5 to 3.5 3.5 ppb biopolymer biopolymer – Ability to quickly shift from reverse reverse to normal norm al circulation

• Hydrocarbons are never intentionally reversed up the coil – extreme extreme care care is is require required. d.

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George E. King Engineering

Data from Alaska and North Sea – Sources Sources – Charlie Charlie Michel, Michel, Rodney Rodney 1

Normal Normal Path Path Circulat Circulation ion – Rate Rate and ability to lift depends on CT capacity. 3/ 14/ 200 9


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Solids Transport in Annuli (Conventional Jetting) • Difficult to unload sand from 7” casing even with 13/4” 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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1.5 bpm

1.5 bpm

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Reverse Circulating – Above the reservoir with no losses. George E. King Engineering

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Reverse Circulating – Above Reservoir (no losses) m p b 5 . 1

m p b 5 . 1

4800 psi PRV

1.5 bpm

Disposal 3/14/2009

10 psi

1500 psi

10 psi

1500 psi

2200 psi PRVs

1.5 bpm George E. King Engineering

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Reverse Circulating – 2 bpm losses

m p b 5 . 3

4800 psi PRV

m p b 5 . 1

3.5 bpm 10 psi

1500 psi

2200 psi PRVs

2.0 bpm

10 psi

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1500 psi


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Reverse Circulating – 10 bpm losses

4800 psi PRV

11.5 bpm 10 psi

10 psi

Disposal 3/14/2009

1500 psi

2200 psi PRVs

1500 psi

m p b 5 . 1 1

m p b 5 . 1

10 bpm


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Jetting Bridge

m p b 5 . 2

4800 psi PRV

m p b 5 . 2

2.5 bpm 4000 psi

10 psi

Disposal 3/14/2009

4000 psi

2200 psi PRVs

10 psi


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Baker Oil Tools Reversing/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 normal jetting (prevents erosion of the ports). 3/14/2009


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RC&J Tool Captured Ball Concept

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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?)

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Risks • Elimination of the CT flapper valve – small risk, still two barriers • Sticking the coil – reduced because of higher velocities around solids and clean fluid in the annulus. • Bridging in the coil – just not seen - minimized by: – Control rate of bridge entry - control of particles entering the 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 circulation 3/14/2009


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Coil Collapse Risks • Coil far weaker under collapse than burst. • Precautions and relief considerations needed to keep outside pressure minimized. • Consider increasing pickup weight on the coil (weight of 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

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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

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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 prevent coil collapse. • No more than 10% (volume of coil) solids in the coil at any time. • Model the job. 3/14/2009


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Formation/Well Requirements • All hydrocarbons push out of pipe (3x pipe volume)

• All zones kept overbalanced. • Contingency plans for well flow. • Consider type, shape, density and size of solids lifted.

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Selection of Equipment • CT – largest possible with > ½” clearance between CT • • • • •

and tubing. Large OD nozzle helps prevent bypassing solids in deviated wells. Single large hole in nozzle for reversing (hole smaller than 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.

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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 right equipment.

3.

Circulating fluid must have low shear support.

4.

Must limit the amount of sand in the coil at any time.

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Reverse Circulating With Coiled Tubing

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