injection well problems

WELL INTERVENTION PRODUCTIVITY SCHOOL Nov 2001

CORROSION

Production Related Problems• Are numerous (!) and included:

– water

– corrosion

– wax precipitation

– asphaltene precipitation

– hydrates

– Hydrogen sulphide

– fines migration

– phase-related permeability reduction

– stress-induced permeability change

– scale

– emulsions

– gas production

REMEMBER

PREVENTIONIS

BETTERTHANCURE


CORROSION

• How can we handle produced water more effectively?

• Water Production and its effects on profitability

Production Related Problems - Water

How to recognise production related damage

Rapid decline due to production related damage - productivity might be restored by regular stimulation treatments (not always successful, dependent on interval length and cause of damage).

Years of Production

Production Rate, stb/day 6000

4000

2000

0 0 1 2 3 4

Production Rate, stb/day

Years of Production

6000

4000

2000

0 0 1 2 3 4

Natural decline due to drop in reservoir pressure - no production related damage.


CORROSION

Production Related Problems - Water• Main culprit of production related damage

Some or all of the above problems may occur at the same time!

P r o d u c t i o n W e l l

WATERPRODUCTION

It causes loss of lift energyextra treatment expensecorrosion scale formationhydratesemulsionswells to be choked back

due to facilities constraints


CORROSION

Production Related Problems - Water• Corrosion considerably increases the cost to well productivity

Increased roughness, hence bigger friction drops and lower rates.

Potential for formation/screens/perforationplugging during bullheading or injection.

Difficulty in running intervention tools(especially in ERD wells).

Difficult to set reliable plugs for gas/water/sand control.

Well has to be shut-in/loss of production/injection until workover.

May be impossible to plug tubing and isolatereservoir, therefore well may require killingby bullheading with potential for permanent formation damage.

Water/gas/sand production loss in oilproduction.

May require well abandonment or a sidetrack.

Limited corrosion of tubing

Corrosion of injection pipework,pumping equipment etc.

Extensive corrosion downhole

e.g. Holes in production tubing

e.g. Parting of tubing

e.g. Failure of liner

e.g. Failure of casing

Incr

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CORROSION

Not normally a problem with the right metallurgy

Not normally a problem with

the right completion metallurgy

Production Related Problems - Corrosion• CO2

– Combines with water to form Carbonic Acid– Pitting

• H2S– Sulphide stress cracking – Hydrogen embrittlement

• Completion and Intervention fluids– Oxygen – Microbiologically induced corrosion.

• Acids– Severe corrosion without inhibitor – May also react with sulphides to form H2S– may require sulphide scavenger

• Solids– Erosion – Or erosion-corrosion– Monitor rates and if need be choke back


CORROSION

Water Injection - Source• Seawater

– Quality varies with location, depth and time (e.g. algal blooms)). – Monitoring may be required.

• River water - – clearly the water quality will vary with location and time.

• Aquifer water - many fields use dedicated water production wells. – The water may be fresh (with or without oxygen) – Saline (again with or without oxygen). – Contaminants may be introduced by extraction (e.g. if gas lift is used to lift the

water).

• Produced water - – Oxygen free at the wellhead. – The water may also contain dissolved salts, oil carryover, dissolved gas or

produced solids. – Once separated from the oil, the water may also pick up oxygen.


CORROSION

Water Injection Treatment• Bacteria

– beware of bugs in your water

– can plug pore throats

– can cause H2S

• Corrosion (oxygen control)– major problem for

many injectors

– maintain O2 levels below 30 ppb

– many workovers required because of this

Injectionpump(s)

Water injection wells

Oxygen removal(eg. gas stripper)

Ineffective removal e.g.inadequate gas rate

Oxygen introducedthrough seals

Oxygenintroducedthrough leakyflanges

Corrosion byoverdosingoxygen scavengeror poordeployment


CORROSION

Corrosion - Water Injectors


CORROSION

Oxygen Control - The Reality

Any oxygen above threshold - even for very short durations causes corrosion -

and over long time period1 2 3 4 5 6

Time (days)


CORROSION

Corrosion Monitoring

• Examination of recovered intervention toolstrings

• Detection of dissolved iron

• Finding a leak! (beware!)

• Corrosion probes (at surface)

• Corrosion logs (beware!)


CORROSION

Intervention In Water Injectors

• Avoid?

• Wireline or toolstrings can score semi-protective

films

• Wireline or toolstrings can damage plastic coatings -

especially at connections

• Coil?

• Use nylon roller stem

• Avoid burrs and sharp edges

run at normal rather than reduced speeds - for slickline - reduced speed for braided cable - why?


CORROSION

corrosion in tubing exacerbated by erosion from wireline operators.

REMOVAL OF “PROTECTIVE” FILM

Corrosion - Best Practices• Adopt corrosion management strategy

• Be aware of corrosion

• Involve contractors in planning

• Develop maintenance programs, measure corrosion

• Consider dedicated corrosion engineer

• Read relevant literature

• Use your eyes! - report corrosion

• Design your completion to minimise corrosion

• Ensure inhibitors are compatible with materials and the reservoir!

• If tubing corrosion is suspected, DO NOT bullhead fluids in the formation

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