Scale Dissolution

M-I Production ChemicalsM-I Production Chemicals(A Business Unit of M-I SWACO)

OBJECTIVE

To demonstrate how the M-I PC Scale Dissolver Range can assist in

restoring well productivity impaired by scale deposition

AgendaAgenda

• M-I Swaco Organisation

• Calcium Carbonate dissolvers

• Sulphate dissolvers

• Case history – well stimulation

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• R & D focus on more environmentally friendly chemistry

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• Corrosion Inhibitors

• Scale Inhibitors / Dissolvers

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Scale DissolversScale Dissolvers

Mineral Scale Dissolution

Carbonate scale - CAL-Acid

Barium/Strontium Sulphate scale - BaSOL

Calcium Sulphate - Gypsol

Iron Sulphide - Pyrisol

Iron deposits/rust - R-Sol

MIPC Scale Dissolver Product LineMIPC Scale Dissolver Product Line

What is Scale?What is Scale?

• An adherent mineral deposit precipitated from solution

• Commonly found in conjunction with other fouling deposits- e.g. iron hydroxides and

sulphides, waxes, asphaltenes, etc..

• Once deposited, crystal growth can lead to the development of severe scaling problems

• Mineral scale deposition cuts oil production by plugging payzones and blocking tubing and topsides.

Causes of ScaleCauses of Scale

• The causes of scale and fouling deposits are many, varied and complex

• Oilfield waters contain a large number of potential scaling species

• These include soluble ions such as calcium, magnesium, barium, etc which precipitate when they encounter changes in water conditions- e.g. temperature, pH, concentration effects and

incompatibilities

• In addition, corrosion by-products, process contaminants and incompatible chemical treatments lead to fouling and scaling

Types of ScaleTypes of Scale

Scaling speciesScaling species

CaCO3CaCO3

FeO/OHFeO/OHFeCO3FeCO3

FeSFeS

BaSO4BaSO4SrSO4SrSO4

CaSO4CaSO4

Acid soluble scales

Acid insoluble scales

Scale RemovalScale Removal

CaCO3 + 2HCl CaCl2 + CO2 + H2O

BaSO4 + AEDTA BaEDTA + ASO4

(A - alkali metal)

Acid soluble scales

• Scale removed through reaction to generate new chemical species

Acid insoluble scales

• Much harder scale type to remove. Requires chelation chemistry

Calcium Carbonate DissolutionCalcium Carbonate Dissolution

Carbonate Scale DissolvingCarbonate Scale Dissolving

Ca2+ + CO3 CaCO3

Ca2+ + 2(HCO3) CaCO3 + CO2 + H2O

• Most common scale type found in oilfield production systems..

Calcium Carbonate• Formed by the combination of the calcium ion with either

carbonate or bicarbonate in water

Carbonate Scale – Deposition FactorsCarbonate Scale – Deposition Factors

pH

Increasing alkalinity leads to carbonate scale deposition

Pressure

Pressure drops lead to CaCO3 deposition, hence deposits at valve locations

Temperature

CaCO3 solubility decreases with increasing temperature

Carbonate Scale RemovalCarbonate Scale Removal

• Traditionally performed with Hydrochloric acid- Very reactive – quick dissolution time- Cheap- Readily available

• BUT……- Very corrosive- Hazardous- ‘Secondary’ scaling can occur- Possibility of formation damage

MIPC CAL-AcidMIPC CAL-Acid

• Developed as a viable alternative to HCl

• Low corrosivity

• ‘Sequesters’ scaling ions

• Loading capacity comparable to HCl

• Slower to react, but…- Allows better reaction control in contacting critical scale- Penetrates deeper into affected reservoir areas

MIPC CAL-AcidMIPC CAL-Acid

• Affords rapid, yet controlled reaction

• Loading capacity – 260 g/ltr (neat product)

• Typically applied as 50% solution- Maximises performance vs. concentration effects

• Inherent sequestering capacity ensures prevention of ‘secondary scaling’

Carbonate Dissolvers ComparedCarbonate Dissolvers Compared

0

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% S

cale

dis

solv

ed

0 1 2 3 4 5 6Time (Hours)

Dissolution of Calcium Carbonateat 60 deg C, static, 260g/ltr CaCO3

EDTA

CAL-acid

15% HCl

Secondary ScalingSecondary Scaling

• Mineral acids liberate calcium and iron which can re-precipitate during the treatment

This can lead to formation damage

• MIPC CAL-Acid has an inherent sequestering capacity

• Scaling ions released by acid treatment are sequestered and held in solution

• No expensive additives are necessary!!

Corrosivity of MIPC CAL-AcidCorrosivity of MIPC CAL-Acid

• Mineral acids very corrosive – potential for tubular damage

• Central to low corrosivity of CAL-Acid is corrosion inhibitor package- Stable to 100oC

• Corrosivity against L80 & 13Cr steel presented

Corrosivity of MIPC CAL-AcidCorrosivity of MIPC CAL-Acid

0

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70000

80000

90000

Cor

rosi

on r

ate

(mpy

)

4 8 24

Time (Hours)

Corrosion of L80 Steel100 deg C, static

CAL-acid 100% CAL-acid (uninhib) 15% HCl

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Cor

rosi

on r

ate

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Time (Hours)

Corrosion of 13Chrome Steel100 deg C, static

CAL-acid 100% CAL-acid (uninhib) 15% HCl

MIPC CAL-AcidMIPC CAL-Acid

Advantages

• Low corrosivity

• ‘Sequesters’ scaling ions

• Load capacity similar to HCl

• Better reaction control in contacting critical scale

• Penetrates deeper into affected reservoir areas

Disadvantages

• Longer contact time

Barium Sulphate DissolutionBarium Sulphate Dissolution

Sulphate Scale DissolutionSulphate Scale Dissolution

• Sulphate scales of barium, strontium and calcium present a complex dissolution problem

• Characteristics- Insoluble in acid- Very low solubility in

water- Forms hard,

consolidated scales- Usually found as ‘mixed’

scale deposit

Barium SulphateBarium Sulphate

• Least soluble scale found in oilfield systems- 2.3 mg/l at 25oC

• Many formation waters contain high barium concentrations

• Not usually a problem until seawater breakthrough- High SO4 levels

Barite - naturally occurring BaSO4

Barium Sulphate Scale RemovalBarium Sulphate Scale Removal

• Low solubility yields a difficult dissolution problem

• Acid insoluble, thus we must employ a different chemical approach…....CHELATION

• Chelating agents complex with metal ions to return water soluble species - increasing solubility - e.g. EDTA - Ethylene Diamine Tetra-acetic Acid

Chelation ProcessChelation Process

• Divalent metal ions can form stable complexes with chelating agents

• Even with low solubility, barium ions solvate in water

BaSO4 Ba+ + SO42-

• Addition of a chelating agent (L) gives

Ba2+ + L BaL

• Effectively “removing” barium ions from solution

BaSO4 + L BaL + SO42-

• Driving solvation of more barium ions and thus scale

Dissolver FormulationDissolver Formulation

• Sulphate scale still has a low solubility even in the presence of some chelating agents

• To deliver effective dissolver chemistry we need to consider...

Chelation Conversion Catalysis

Sulphate scale dissolver

Dissolver FormulationDissolver Formulation

• Chelation- Must have high metal affinity – log K1

- Operate at optimum pH

• Conversion- Conversion agents assist in metal ion chelation eg

• Catalysis- Enables dissolution process to proceed more efficiently

Fe (II) Fe (III)

Favours chelation of ferric rather than ferrous ions

BaSOL and BaSOL 2000BaSOL and BaSOL 2000

Latest advance in the field of barium sulphate dissolution

Delivers optimum pH conditions for scale dissolution

Non-corrosive

Non-hazardous for handling

Affords rapid dissolution rates

High loading capacity - 120g/ltr possible

Relative Dissolution RateRelative Dissolution Rate

00.5

1.52.5

612

0

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100S

cale

rem

aini

ng (

%)

Time (hours)

Relative dissolution rate of BaSOL and EDTA Barium sulphate, 85 deg C, 4% w/v

BaSOL

EDTA

Temperature EffectsTemperature Effects

0 0.5 1 1.5 2 2.5 3 4 6 10 12

120C

100C

80C

60C40C

20C

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100S

cale

rem

aini

ng (

%)

Time (hours)

Dissolution of oilfield scale as a function of tem peratureBaSOL 5%w/v

WettabilityWettability

0 1 2 3 4 5 6 7 8 9 10

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% S

cale

rem

aini

ng

Time (hours)

Dissolution of barium sulphate scale as a function of wettability80 deg C, static conditions

Water w et

Crude w et

Asphaltene w et

Progress in Barium Sulphate DissolutionProgress in Barium Sulphate Dissolution

Sequestering capacity in g/ltr @ 6 hrs @ 90oC

Analar BaSO4 Field scale Comments

High low Multi-stage

20 12 Very slow

30 30 Slow

40 80 Fast

120 120 Best so far

Converter + acid

EDTA

DTPA

BaSOL

BaSOL 2000

Calcium Sulphate DissolutionCalcium Sulphate Dissolution

Calcium SulphateCalcium Sulphate

• Formed in a similar way to Barium and Strontium Sulphates

• Often found as a co-deposit with Barium & Strontium

• Removal assured with chelation chemistry

Gypsum - naturally occurring CaSO4

MIPC GypsolMIPC Gypsol

• Gypsol dissolves calcium sulphate at ~2.8 times the speed of BaSOL

• Designed specifically for Calcium sulphate scale

• Outperforms EDTA - traditional calcium sulphate dissolver

• Non- corrosive

• Supplied as a pH 7-8 solution, thus low handling hazard

Comparative DissolutionComparative Dissolution

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100%

Cal

cium

Sul

phat

e re

mai

ning

0 0.5 1 1.5 2

Time (Hours)

Calcium sulphate dissolution[100 deg c, static conditions]

EDTA Gypsol

Temperature EffectsTemperature Effects

0 1 2 3 4 5 6 7

0

20

40

60

80

100%

Sca

le R

emai

ning

Time (hours)

Dissolution of Anhydrite scale

147 deg

95 deg

60 deg

Sulphate Scale Dissolvers - SummarySulphate Scale Dissolvers - Summary

BaSOL 2000

•Rapid dissolution rates

•High load capacity

•Non corrosive

•Safe to handle

Best Barium/Strontium sulphate de-scaling

solution

Gypsol

•Outperforms EDTA

•Non corrosive

Designed specifically for the removal of calcium

sulphate

BaSOL Scale DissolverBaSOL Scale Dissolver

CASE HISTORYCASE HISTORY

Case History – BaSOL Sulphate DissolverCase History – BaSOL Sulphate Dissolver

• North Sea well with severe decline in production- Sulphate scale across

perfs

• Tail pipe scale preventing access to perforating guns

• Scale analysis- 72% BaSO4

- 25% SrSO4

- 3% CaCO3

BaSOL Case History – Treatment BaSOL Case History – Treatment SummarySummary

• Bullhead application used

• Spearhead with KCl brine with demulsifiers

• Spot dissolver & allow to reach formation temperature

• Series of displacement & soak sequences- Maximise dissolution

• Total of 5 dissolver sequences carried out- First two across perforations- Last three in tailpipe- PI noted after each flowback

BaSOL Case History - ResultsBaSOL Case History - Results

• Production increased from 350 m3/day to 1975 m3/day- 464% increase over 5 treatments

• Total mass of 500 kg sulphate scale removed- 233.2 kg BaSO4

- 266.4 kg SrSO4

• 53 kg sulphate scale removed from perforations/near well bore- Represents greatest detrimental affect on production

• Success meant that well did not need re-perforation

- Represents added value benefit

BaSOL Case History - ResultsBaSOL Case History - Results

Dissolver sequence

Kg BaSO4 removed

Kg SrSO4 removed

Production rate

(m3/day)

Dissolver target zone

0 - - 350 -

1 20 19.5 1390 Perfs

2 4.5 9.1 1560 Perfs

3 100.9 110.9 1755 Tail Pipe

4 93.2 82.9 1800 Tail Pipe

5 14.6 44.0 1975 Well Bore

BaSOL Case History – Production ProfileBaSOL Case History – Production Profile

Production increase - Post Treatments

350

13901560

1755 18001975

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2500

0 1 2 3 4 5

Dissolver sequence

Pro

duct

ion r

ate

(m

3/d

ay)

Production Rate (M3/ day)

BaSOL Case History – Scale Removal BaSOL Case History – Scale Removal ProfileProfile

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120

0 1 2 3 4 5

Dissolver sequence

BaSO4 removed (kg)

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0 1 2 3 4 5

Dissolver sequence

SrSO4 removed (kg)

SummarySummary

SummarySummary

• The MIPC range of Scale Dissolvers represent leading edge technology in the market place- CAL-Acid for carbonate scales- BaSOL 2000 for barium & strontium sulphates- Gypsol for calcium sulphate

• Field experience in removal of barium & strontium sulphate scales from tubulars and formations- Significant increase in productivity

• Personnel in China with experience in scale dissolver and scale inhibitor squeeze treatments

M-I Production Chemicals has the chemical resourcesto remove any commonly encountered field scale

MIPC Expertise Innovative range

COMPREHENSIVE SCALE CONTROL PACKAGECOMPREHENSIVE SCALE CONTROL PACKAGE

MIPC Scale Dissolver Product LineMIPC Scale Dissolver Product Line

Mineral Scale Dissolution

Carbonate scale - CAL-Acid

Barium/Strontium Sulphate scale - BaSOL

Calcium Sulphate - Gypsol

Iron Sulphide - Pyrisol

Iron deposits/rust - R-Sol