Oilfield Scale

47
SPE DISTINGUISHED LECTURER SERIES is funded principally through a grant of the SPE FOUNDATION The Society gratefully acknowledges those companies that support the program by allowing their professionals to participate as Lecturers. And special thanks to The American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) for their contribution to the program.

Transcript of Oilfield Scale

Page 1: Oilfield Scale

SPE DISTINGUISHED LECTURER SERIESis funded principally

through a grant of the

SPE FOUNDATIONThe Society gratefully acknowledges

those companies that support the programby allowing their professionals

to participate as Lecturers.

And special thanks to The American Institute of Mining, Metallurgical,and Petroleum Engineers (AIME) for their contribution to the program.

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Oilfield Scale:A New Integrated Approach to Tackle an Old Foe

Dr Eric J. Mackay

Society of Petroleum EngineersDistinguished Lecturer 2007-08 Lecture Season

Flow Assurance and Scale Team (FAST)Institute of Petroleum EngineeringHeriot-Watt UniversityEdinburgh, [email protected]

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Outline

1) The Old Foea) Definition of scaleb) Problems causedc) Common oilfield scalesd) Mechanisms of scale formation

2) The New Approacha) The new challengesb) Proactive rather than reactive scale managementc) Effect of reservoir processes

3) Conclusions

FormationWater (Ba)

• •••

• ••••••

Injection Water(SO4)

Ba2+ + SO42- BaSO4(s)

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Outline

1) The Old Foea) Definition of scaleb) Problems causedc) Common oilfield scalesd) Mechanisms of scale formation

2) The New Approacha) The new challengesb) Proactive rather than reactive scale managementc) Effect of reservoir processes

3) Conclusions

FormationWater (Ba)

• •••

• ••••••

Injection Water(SO4)

Ba2+ + SO42- BaSO4(s)

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1a) Definition of ScaleScale is any crystalline deposit (salt) resulting from the precipitation of mineral compounds present in water

Oilfield scales typically consist of one or more types of inorganic deposit along with other debris (organic precipitates, sand, corrosion products, etc.)

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1b) Problems CausedScale deposits

formation damage (near wellbore)blockages in perforations or gravel packrestrict/block flow linessafety valve & choke failurepump wearcorrosion underneath depositssome scales are radioactive (NORM)

Suspended particlesplug formation & filtration equipmentreduce oil/water separator efficiency

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Examples - Formation Damage

quartz grainsquartz grains

scale crystals block scale crystals block pore throatspore throats

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Examples - Flow Restrictions

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Examples - Facilities

separator scaled up

and aftercleaning

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1c) Common Oilfield Scales

Iron Scales: Fe2O3, FeS, FeCO3

Some Other Scales

Sand GrainsHF solubleinsoluble2.65SiO2silicon dioxide

Exotic Scales: ZnS, PbS

(insoluble in HCl)357,0002.16NaClsodium chlorideacid soluble2,4102.32CaSO4.2H2Ocalcium sulphateacid soluble2,0902.96CaSO4calcium sulphate

slightly acid soluble1133.96SrSO4strontium sulphateacid soluble142.71CaCO3calcium carbonate

60 mg/l in 3% HCl2.24.50BaSO4barium sulphateCommon Scales

(mg/l)othercold waterGravity

SolubilitySpecificFormulaName

SPE 87459

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1d) Mechanisms of Scale Formation

Carbonate scales precipitate due to ΔP (and/or ΔT)wellbore & production facilities

Sulphate scales form due to mixing of incompatible brinesinjected (SO4) & formation (Ba, Sr and/or Ca)near wellbore area, wellbore & production facilities

Concentration of salts due to dehydrationwellbore & production facilities

Ca2+(aq) + 2HCO-

3(aq) = CaCO3(s) + CO2(aq) + H2O(l)

Ba2+(aq) (Sr2+or Ca2+) + SO4

2-(aq) = BaSO4(s) (SrSO4 or CaSO4)

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Slide 12 of 40

Outline

1) The Old Foea) Definition of scaleb) Problems causedc) Common oilfield scalesd) Mechanisms of scale formation

2) The New Approacha) The new challengesb) Proactive rather than reactive scale managementc) Effect of reservoir processes

3) Conclusions

FormationWater (Ba)

• •••

• ••••••

Injection Water(SO4)

Ba2+ + SO42- BaSO4(s)

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2a) The New Challenges

Deepwater and other harsh environmentsLow temperature and high pressureLong residence timesAccess to well difficultCompatibility with other production chemicals

Inhibitor placementComplex wells (eg deviated, multiple pay zones)

Well value & scale management costs

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Access to Well

Subsea wellsdifficult to monitor brine chemistrydeferred oil during squeezeswell interventions expensive (rig hire)squeeze campaigns and/or pre-emptive squeezes

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Inhibitor Placement in Complex Wells

Where is scaling brine being produced?

Can we get inhibitor where needed?

wellbore frictionpressure zones(layers / fault blocks)damaged zones

Options:Bullheadbullhead + divertorCoiled Tubing from rigInhibitor in proppant / gravel pack / rat hole

Ptubing head

Fault

Shale

Pcomp 1

Pcomp N

Presv 1

Presv N

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Well Value & Scale Management Costs

Deepwater wells costing US$10-100 million (eg GOM)

Interval Control Valves (ICVs) costing US$0.5–1 millioneach to install

good for inhibitor placement controlsusceptible to scale damage

Rig hire for treatments US$100-400 thousand / daynecessary if using CTdeepwater may require 1-2 weeks / treatmentcf. other typical treatment costs of US$50-150 thousand / treatment

Sulphate Reduction Plant (SRP), installation and operation may cost US$20-100 million

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Number of SRP per Year and Total Capacity

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2b) Proactive Rather Than ReactiveScale Management

Scale management considered during CAPEX Absolute must:

good quality brine samples and analysisPredict

water production history and profiles well by wellbrine chemistry evolution during well life cycleimpact of reservoir interactions on brine chemistryability to perform bullhead squeezes:

• flow lines from surface facilities• correct placement

Monitor and review strategy during OPEX

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2c) Effect of Reservoir Processes

EXAMPLE 1 Management of waterflood leading to extended brine mixing at producers(increased scale risk)

EXAMPLE 2 In situ mixing and BaSO4 precipitation leading to barium stripping(reduced scale risk)

EXAMPLE 3 Ion exchange and CaSO4 precipitation leading to sulphate stripping(reduced scale risk)

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SPE 80252

Extended Brine Mixing at Producers

EXAMPLE 1

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SPE 80252

Field M (streamline model)

This well has been treated > 220 times!

Extended Brine Mixing at Producers

EXAMPLE 1

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Barium Stripping (Field A)

% injection water

Bar

ium

(mg/

l)

Dilution line

SPE 60193EXAMPLE 2

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Barium Stripping (Theory)

Injection water (containing SO4) mixes with formation water (containing Ba) leading to BaSO4 precipitation in the reservoirMinimal impact on permeability in the reservoirReduces BaSO4 scaling tendency at production wells

SPE 94052EXAMPLE 2

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Barium Stripping (Theory)

Ba2+

Rock

SO42-

1) Formation water (FW): [Ba2+] but negligible [SO42-]

FW

(hot)

EXAMPLE 2

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Barium Stripping (Theory)

Ba2+ SO42-

2) Waterflood: SO42- rich injection water

displaces Ba2+ rich FW

Rock

FWIW

(cold) (hot)

EXAMPLE 2

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Barium Stripping (Theory)

Ba2+ SO42-

Rock

3) Reaction: In mixing zone Ba2+ + SO42- → BaSO4

FWIW

(cold) (hot)

BaSO4

EXAMPLE 2

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Barium Stripping (Theory)

0

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0 20 40 60 80 100seawater fraction (%)

[Ba]

(mg/

l)

0

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[SO

4] (m

g/l)

BaBa (mixing)SO4SO4 (mixing)

•Large reduction in [Ba]

•Small reduction in [SO4](SO4 in excess)

•Typical behaviour observed in many fields

EXAMPLE 2

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Barium Stripping (Model & Field Data)

0

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bariu

m c

once

ntra

tion

(ppm

)

Field A - actualField A - dilution lineField A - modelled

EXAMPLE 2

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Sulphate Stripping (Theory)

Injection water (with high Mg/Ca ratio) mixes with formation water (with low Mg/Ca ratio) leading to Mg and Ca exchange with rock to re-equilibrateIncrease in Ca in Injection water leads to CaSO4 precipitation in hotter zones in reservoirMinimal impact on permeability in the reservoirReduces BaSO4 scaling tendency at production wells

SPE 100516EXAMPLE 3

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Ion Exchange

Ca

Mg

Ca

Mg

CC

0.50 CC

=FW: 0.077

IW: 3.2

Rock: 0.038

Mg on rockĈMg

Ca on rockĈCa

Mg in solutionCMg

Ca in solutionCCa

2,32530,185

Gyda FW (mg/l)

1,368426

IW (mg/l)

EXAMPLE 3

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Sulphate Stripping (Theory)

Ba2+

Rock

SO42- Ca2+ Mg2+

1) Formation water: [Ca2+] and [Mg2+] in equilibrium with rock

FW

(hot)

EXAMPLE 3

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Sulphate Stripping (Theory)

Ba2+ SO42- Ca2+ Mg2+

2) Waterflood: [Ca2+] and [Mg2+] no longer in equilibrium

Rock

FWIW

(cold) (hot)

EXAMPLE 3

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Sulphate Stripping (Theory)

Ba2+ SO42- Ca2+ Mg2+

3) Reaction 1: Ca2+ and Mg2+ ion exchange with rock

Rock

FWIW

(cold) (hot)

EXAMPLE 3

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Sulphate Stripping (Theory)

Ba2+ SO42- Ca2+ Mg2+

4) Reaction 2: In hotter zones Ca2+ + SO42- → CaSO4

Rock

FWIW

(cold) (hot)

CaSO4

EXAMPLE 3

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Modelling Prediction: [Ca] and [Mg]

0

5,000

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[Ca]

(mg/

l)

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[Mg]

(mg/

l)

CaCa (mixing)MgMg (mixing)

•Large reduction in [Mg]

•No apparent change in [Ca]

EXAMPLE 3

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Observed Field Data: [Ca] and [Mg]

•Large reduction in [Mg]

•No apparent change in [Ca]

EXAMPLE 3

0

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Modelling Prediction: [Ba] and [SO4]

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[Ba]

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l)

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[SO

4] (m

g/l)

BaBa (mixing)SO4SO4 (mixing)

EXAMPLE 3

•Small reduction in [Ba]

•Large reduction in [SO4](No SO4 at < 40% SW)

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Observed Field Data: [Ba] and [SO4]

•Small reduction in [Ba]

•Large reduction in [SO4](No SO4 at < 40% SW)

EXAMPLE 3

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seawater fraction (%)

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[SO

4] (m

g/l)

BaBa (mixing)SO4lSO4 (mixing)

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3) Conclusions

Modelling tools may assist with understanding of where scale is forming and what is best scale management option…

identify location and impact of scalingevaluate feasibility of chemical options

… thus providing input for economic model.

Particularly important in deepwater & harsh environments, where intervention may be difficult & expensive

But – must be aware of uncertainties…..reservoir descriptionnumerical errorschanges to production schedule, etc.

… so monitoring essential.

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Acknowledgements

Sponsors of Flow Assurance and Scale Team (FAST) at Heriot-Watt University:

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Extra Slides

Barium stripping example (Field G)Placement example (Field X)

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Barium Stripping (Field G)

a) water saturation b) mixing zone

c) BaSO4 deposition (lb/ft3)

SPE 80252

Field G (model)

EXAMPLE G

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Barium Stripping (Field G)

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time (days)

bariu

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sulp

hate

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cent

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Ba Ba (no precip)SO4SO4 (no precip)

[Ba] at well when noreactions in reservoir

[Ba] at well when reactions in reservoir

Field G (model)

EXAMPLE G

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Barium Stripping (Field G)

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% seawater

bariu

m c

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ntra

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(ppm

Field B - observedFiled B - dilution lineField B - modelled

deep reservoir + well/near well mixing

deep reservoir mixing

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% seawater

bariu

m c

once

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Field B - observedFiled B - dilution lineField B - modelled

deep reservoir + well/near well mixingdeep reservoir + well/near well mixing

deep reservoir mixingdeep reservoir mixing

Field G (model & field data)

EXAMPLE G

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Impact of Reservoir Pressures on Placement

Question for new subsea field under development:

Can adequate placement be achieved without using expensive rig operations?

EXAMPLE X

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Placement (Field D)

-200

-100

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well length (m)

flow

rate

(m3/

d) prior to squeezeshut-inINJ 1 bbl/mINJ 5 bbl/mINJ 10 bbl/m1 year after squeeze

production

injection(squeeze)

• Good placement along length of well during treatment (> 5 bbls/min)• Can squeeze this well

SPE 87459EXAMPLE X

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Placement (Field D)production

injection(squeeze)

• Cannot place into toe of well by bullhead treatment, even at 10 bbl/min• Must use coiled tubing (from rig - cost), or sulphate removal

-600

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flow

rate

(m3/

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SPE 87459EXAMPLE X