GT Scale Presentation Alok Dwivedi

Inorganic Scale Management in Oil FieldBy: Alok Dwivedi

AEE(P)Corrosion & Scale Management Deparatment-IOGPT

Objective

Concept of Scale in oil field

Identifying the scale

Causes of Scale Deposition

Commonly Encountered form of Scale

Mechanism of scale deposition

Chemistry of CaCO3 Scale

Chemistry of SrSO4 Scale

Various Scale Removal Techniques

Inorganic & Organic Deposits

Before the well is drilled & Completed, the fluids in the formation are in equilibrium.

As soon as flow starts, equilibrium gets disturbed.

Solid precipitation starts.

Inorganic deposits are “SCALE”

Organic deposits areWaxes (Saturated Hydrocarbons)Asphaltenes (Unsaturated & Cyclic hydrocarbons)Gas Hydrates etc.

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SCALE

Scale is a deposit that plugs or fouls equipments & systems.

Inorganic mineral constituents of water that precipitate to form hard, adhere deposits.

Scale begins to form when the state of any natural fluid is perturbed in such a way that solubility limit for one or more component is exceeded

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SCALE

Scale formation is a dynamic process and changes in magnitude during the life cycle of a field as the composition of produced water changes.

Produced water changes and life-cycle trends may differ well to wells because of differences in production zone and stratigraphic heterogeneities.

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Restricts Flow

Reduce Production

Reduce Injectivity

Catastrophic Failure

Can Be Radioactive

Problems due to Scale

Types of Waters

Formation Water: Water present in hydrocarbon-producing formation or related rock layers and is found in the pore spaces of rock.

Produced Water: Formation or condensed waters, or both, in various combinations and salinities that are received topside with the oil and gas being produced.

Injection Water: Supplied from surface sources and used to maintain formation pressure

Produced/Formation water is analyzed to determine the concentration of following species (In General)

Major Ions: Na+ , Ca+2, Mg+2, Ba+2, Sr+2, Cl-, HCO3-, SO4

2-, OH-

Minor Ions: Li+, Fe2+, Zn2+, Pb2+, SiO44-, Br-, F-

Dissolved Gases: O2, CO2, H2S, CH4, C2H6 etc..

Water Chemistry

Units:Milligrams per Litre: Temp. Dependent Unitppm: Temp. Independent Unit = 1 mg of solute in 1000 g of solution ppm=(mg/L)/(Sp.Gr)

The equilibrium constants for saturated solution and solid formation (precipitate) are called solubility product, Ksp. For unsaturated and supersaturated solutions, the system is not at equilibrium, and ion products, Qsp, which have the same expression as Ksp is used.

Equilibrium Expression for Ksp and Qsp

AgCl(s) = Ag+(aq) + Cl-(aq) [Ag+] [Cl-] CaCO3(s) = Ca2+(aq) + CO3

2-(aq) [Ca2+] [CO3-]

Li2CO3(s) = 2 Li+(aq) + CO32-(aq) [Li+]2 [CO3

-]

Qsp < Ksp Unsaturated solution Qsp = Ksp Saturated solution

Qsp > Ksp Oversaturated solution

Concept of Solubility Product

Diagnosing Scale

Scale formation can be predicted from water chemistry and system physical conditions.

Diagnosing ScaleDiagnosing scale in Surface Equipments

Diagnosing Scale

Down hole tubing or Production formation

Suspended scale

particles in water

Scale In tubing

Well stimulatio

ns not effective

Prediction from water

chemistry

Evidence of

Production Decline

Well or field

history

Diagnosing scale in Down hole tubing or Production formation

Diagnosing scale in Down hole tubing or Production formation

Diagnosing Scale

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Types of Inorganic Scales:

Types Of Scales

Water Soluble Deposits

Acid Soluble Deposits

Acid Insoluble Deposits

Salt Calcium Carbonate Calcium Sulfate

Calcium Chloride Dolomite Barium Sulfate

Chemical Deposits Iron Sulfide Strontium Sulfate

Iron Oxide

Iron Carbonate

Scale IdentificationStart

Organic Soluble in H2O

NaCl(Probably)

Soluble in HCl

Odor of rotten

egg

FeS(Probably)

CaCO3FeCO3MgCO3

Soluble in hot

HCl

Iron Oxide

Magnetite (Fe3O4)

Magnetic

Soluble in

Na4EDTA

SrSO4CaSO4BaSO4

Floats in

Water

No Yes

No

Yes

Yes

Yes

No

No

Yes

No

Yes

Yes

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• Scales are formed by change in water chemistry causing super saturation

Causes for Scale Deposition

Change in pH,

Temperature Pressure etc.

Mixing Incompatible

Waters

Poor or No Inhibitor

Treatment

Water Evaporation

Flashing

Cause of Scale Deposition

Scale Mechanism

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• Reactions involved• Effect of CO2

CO2 + H2O H2CO3 H2CO3 H+ + HCO3

- HCO3

- H+ + CO3- -

Ca+2 + CO3- - = CaCO3 ---------------------------- (1)

Ca+2 + 2HCO3- = CaCO3 + CO2 + H2O ------- (2)

Chemistry of Scale Formation

Chemistry of Scale Formation

The Equilibrium will shift to right if:

• An increase in temperature• Decrease in pressure• Loss of dissolved CO2

• An increase in pH

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• CO2 partial pressure• Operating temperature• Operating pressure• pH• Calcium & Bicarbonate concentration• Total Dissolved solids

Parameters Affecting Carbonate Scaling

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• Effect of CO2

– pH of water increases with decrease in CO2 concentration

– Decrease in CO2 partial pressure gas over water results in CaCO3 precipitation.

– Partial Pressure = Total Pressure*Mole Fraction


Contd…


Contd…Effect of Operating Temperature Solubility of CaCO3 decreases with increase in temperature

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• Effect of Operating Pressure– Solubility of CaCO3 decreases with decrease in

pressure– Solution pH increases with decrease in pressure– Calcite is very sensitive to pressure changes


Contd…

Effect of pH– Precipitation of CaCO3 increases with increase in pH


Contd…

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• Effect of Ca+2 & HCO32- concentration

– Formation of solid CaCO3 from aqueous phase increases with increase in Ca and HCO3 concentration.

• Effect of TDS– Solubility of CaCO3 increases with increase in

salt content.


Contd…

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• CaCO3 precipitation increases as

– the operating temperature, pH, Ca++ and HCO3

- concentration increase

– the Pressure (partial pressure of CO2) & TDS decrease

In Summary…

No precipitation of CaCO3 occurs in the Reservoiras brine remains saturated at reservoir conditions.

SrSO4

• Occurs as Mineral Celestine or Celestite

• Poorly soluble in water ( 1 part in 8,800 part of water)

Ion Species Formation Water Sea Water

Sodium 31,275 10,890

Potassium 654 460

Magnesium 379 1368

Barium 269 0

Strontium 771 0

Sulfate 0 2960

Chloride 60,412 19,766

Calcium 5038 428

Why SrSO4 Scale Forms??

•Mixing of Incompatible water

Software/EmpiricalTech. to predict Scaling

Link

Scale Management

•Change/Optimize Process Parameters

•Prevent deposition by using scale-inhibitors etc

•Allow scale to form, but periodically remove it.

•Use pretreatments that remove dissolved & suspended solids.

Combating Scale

Combating Calcium Carbonate Scales

Combating Scale

Combating Sulphate Scales.

Scale Inhibitors

•Inorganic Polyphosphates•Organic phosphate esters•Organic phosphonates•Organic polymers

•phosphonates, •polyacrylic acids (PAA) •phosphinopolycarboxylic acids (PCA) and polyvinylsulphonic acids (PVS).

How do Antiscalants Work

Three Predominant Mechanims• Threshold Inhibition• Dispersion• Crystal Modification

How do Antiscalants Work

Antiscalants Mechanisms

Popular Scale Inhibitors

•HEDP, AMP, PBTC = Phosphonate HEDP= 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid

Scale Inhibitors

An ideal Scale Inhibitor should have following properties

•Effective scale control at low inhibitor concentration•Compatibility with sea water & formation water•High thermal stability•Low toxicity & high biodegradability •Low Cost

Scale RemovalSequestration using Co-ordinate complex

SrSO4 = Sr+2 + SO4-2

Sr+2 + L = SrL

L=chelating agent

Co-ordination Complex

• A co-ordinate complex is the product of Lewis acid-base reaction in which neutral molecules or anions (Ligands) bonds to a central metal atom by coordinate covalent bonds.

• Ligands are Lewis base.• Metal atoms/ions are Lewis acids.• Coordination complexes are distinct chemical species: Their

properties and behaviour are different from the metal atom/ion and Ligands from which they are composed.

• Typical examples: [Ag(NH3)2]+ , [Zn(CN)4]2- etc….

• EDTA , Ethylenediaminetetraacetic acid.• A Polyamino carboxylic acid• Colorless, water-soluble solid• Hexadentate ligand• Chelating agent• Used to sequester metal ions, Ca++, Fe++

EDTA

DTPA

• DTPA , Diethylene triamine pentaacetic acid.• A Polyamino carboxylic acid• 8-active metal-complexing sites, octadentate ligand• Chelating agent• Used to sequester metal ions, Ba++, Sr++

• Oxallic acid can be added as a synergists

Srskill

DTPA Vs. EDTA

0510152025303540

0 60 120 180 240 300 360 420

Time Min

Dis

solv

ed c

eles

tite

g/l

EDTA DTPA-Oxalate

Srskill

Celestite dissolution test

0

10

20

30

40

50

60

0 60 120 180 240 300 360 420

Time min

Cele

stite

dis

solv

ed g

/l

DTPA DTPA-Salicylate DTPA-Oxalate

Effect of Oxallic Acid additive

IOGPT developed & Patented Recepie, “Srkill is an effective and fast way to remove SrSO4 scales.”

DTPA+KOH+Oxallic acid at a pH>12

•Implemented in many wells of MH Asset.•Increased liquid production•Minimize tubing intervention•Minimize the production loss•Increased safety

Srskill

[email protected]

Any Questions???

mailto:[email protected]

Thank You

GT Scale Presentation Alok Dwivedi

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