8 Chemical Contaminations and Treatments

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1Agip KCO Well Area Operations

Drilling Supervisors Training CourseDrilling Muds RPW2021A

CHEMICAL CONTAMINATIONS AND TREATMENTS





INTRODUCTION

A contaminating agent can be a material either solid, gaseous or liquid, with

a damaging effect on chemical and physical properties of mud.

Low gravity reactive solids are the most common contaminants in a mud.





The most common types of contaminations of water-based muds are:

1. Anhydrite (CaSO4) or gypsum (CaSO4• 2H2O).

2. Cement (silicate complex of Ca(OH)2.

3. Salt (salt, sea water, magnesium, calcium, sodium chloride and nativewater).

4. Acid gas as CO2 and H2S.

INTRODUCTION





The main aims of this chapter are:

• Discover the origin of each chemical contaminant.

• Identify the chemical contaminant.

• Understand which effect can have each contaminant on mud.

• Understand how to handle changing characteristics.

• Correct the mud and give it its original properties.

INTRODUCTION





ANHYDRITE OR GYPSUM CONTAMINATIONS

Anhydrites and calcium are either calcium sulphate with a very similar chemical

composition.

The gypsum (CaSO4•2H2O), has attached water and is more soluble than

anhydrite (CaSO4).

If in small quantities, the contaminants can be tolerated by the precipitation of

the calcium ion. If in large quantities, it could be necessary to transform the

original mud in a calcium-based system





The initial effect of the calcium contamination in a bentonitic mud,

determines the increase in viscosity, gel strength and fluid loss.

These properties are influenced by the concentration of the

contaminant, the concentration of reactive solids and the deflocculant

products in the mud.






The CaSO4 solubility is controlled by th pH, the salinity and temperature. The

increase in the pH and temperature causes a decrease in the gypsum

solubility and as the chlorides in the mud increase, the solubility increases.The solubility of the calcium sulphate is reversible and will reach an

equilibrium with the chemical ambient.






Warning Factors

The first indication of this contamination is an increase in physical properties:

• Yield point

• Funnel viscosity

• Gel strength






From a chemical aspect, the main symptoms of anhydrite or gypsum contamination are:

1) An increase in the calcium filtrate, not easily detectable at the beginning, if an

excess in carbonate, bicarbonate or phosphate ions exists in the mud.

When the gypsum, once dissolved, inactivates these chemical products, there willbe a decrease in the pH because the pH of the gypsum (6 to 6.5) is very low. Such

pH reduction will cause a significant increase in the calcium filtrate since the

calcium solubility is inversely proportional to its pH.

So the reduction of pH and alkalinity and increase in Ca++ in the filtrate are the

most reliable indicators.






2) Due to limited solubility of anhydrite and gypsum, the drillling cuttings can have

traces of mineral. This is often underlined by the presence in the cuttings of small

white balls which are soluble in the acid.

3) The qualitative test for the sulphate ion should indicate an increase. However,

tthrough this test the ion of the sulphonate can be detected. The test would not

make sense if lignosulphonate was used as the primary deflocculant, unless it was

compared with non.contaminated mud.






Treatment of mud for gyp/anhydrite contamination

1. Increase the concentration of deflocculant in the system. Both lignosulphonates

and lignite are very effective deflocculants in presence of calcium. This

treatment must be proportional to the quantity of anhydrite and gypsum in the

drilling. The lignite holds the ions of calcium so removing them If there’s toomuch calcium it will be necessary to use calcium carbonate (soda ash) (Na2

CO3) to cause its precipitation.

Na2CO3 + CaSO4 Na2SO4+CaCO3






2. Manintain the pH between 9.5 and 10.5 with caustic soda (NaOH) or caustic potash

(KOH). This maintains the gypsum solubility and improves the property of the

lignosulfonate.

3. One of the following chemical prducts may precipitate an increase in filtrate calcium.

The efficiency of precipitation of calcium by carbonate ions is high. Due to the low pH

of the anhydrite and gypsum, 6 – 6.5 it is preferable to use soda ash (sodium

carbonate) because of the high pH, 11 – 11.4, then sodium bicarbonate (pH 8-8.5).

When soda ash is mixed in water, there is an increase in pH caused by the formation

of the hydroxyl.






If there are calcium ions, these precipitate in CaCO3

insoluble (limestone).

This is the reaction of the soda ash (sodium carbonate) with the gypsum.

4. 2 Na2CO3 + H2O HCO3-+CO3

2-+ 4Na+ +OH – (pH <11.3)

Phosphate also may complex filtrate calcium

The following reaction gives rise to an insoluble calcium phosphate.

The most common materials of this type are:

Sodium Acid Pyrophosphate (SAPP) - Na2H2P2O7 (pH 4.8)

Sodium Tetraphosphate (STP or PHOS) – Na6P4O13 (pH 8.0)

Phosphates are limited by their relatively low temperature stability 200°F (93°C)

Na2CO3 + CaSO4 Na2SO4 + CaCO3 (pH >11.3)






Calcium-based mud conversion

When drilling takes place through higher formations of anhydrite or gypsum the

contamination is high. As a consequence, it is impossible to maintain the rheological

properties and an optimal control of fluid-loss. Therefore, it is necessary to add clacium

sulphate to convert the original mud into calcium-based mud.

It is possible to convert to a gypsum-based mud, by treating with caustic soda,

lignosulfonate and additional gypsum. pH must be maintained in a range of 9.5-10.5. At

the beginning, an increase in viscosity will occur, but when the correct amount of

gypsum and NaOH were added, the system will break-over and the viscosity willdecrease.






It is possible to convert to a lime-based mud. Some procedure as before, but adding

lime instead of gypsum and maintain lime excess in the mud. The pH also will be

maintained over 11.5 by caustic soda.

2NaOH + CaSO4 ⇋ Ca(OH)2 + Na2SO4

Both systems require the addition of a fluid loss control agent, as polymers with

Calcium resistance properties.






CEMENT CONTAMINATION

The cement contamination is initially indicated by the increase in viscosity, gel

strength and loss of fluid-loss control.

The cement is a complex silicate of Ca(OH)2 and once dissolved in the water phase

of the mud, hydroxyl ions (OH−) are generated in large quantities.

Ca(OH)2 Ca 2+ + 2OH – (pH <11.7)

This is a reversible reaction and represents an equilibrium between the concentration

of the cement and the pH of the mud. The solubility of the lime decreases as the pH

increases and when the pH reaches 11.7, lime precipitates. Therefore, lime becomes

insoluble.





The first sign of cement contamination is an increase in the pH, Pm and the

excess of lime measured by the Pm and the Pf.

If the amount of cement is small, there is no problem: treatment with deflocculants

and precipitants will be enough to go ahead in drilling.







In those cases in which it will be necessary to drill large quantites of cement, it will

be necessary to apply the following rules:

1) If the drilling is in an intermediate or final phase, it is often preferable to use water

instead of mud to drill out the cement. Obviously, only in cased hole, without

communication with below pressure.

2) If on the contrary, it is necessary to use mud, the contaminations problems can be

resolved if the drilling is in an intermesiate state. In this case, there is sufficient

time to treat the mud diluting it gradually.

3) If the well is already in the completion phase, it is essential to allow the necessary

time to treat the cementing contamination to prevent problems caused by gelation.





HOW TOLERATE CONTAMINANTS

How treat the mud contaminated by cement:

1. Increasing the concentration of deflocculants. Lignosulphonate and lignite work well in

presence of calcium in a wide range of pH. Most cement contamiantion problems can be

adequately tolerated in this manner. However, if an excessive amount of cement is

drilled, the mud can be converted to a low-lime system, if temperatures allow.

2. The cement increases alkalinity when becomes soluble. The addition of deflocculants

with low pH reduces the pH and Pm of the system which increases the solubility of the

calcium (from cement) allowing the precipitation.






3. The calcium in solution can be precipitated by sodium bicarbonate. Sodium

bicarbonate is an excellent product to treat for precipitation of Calcium and reduction

of the pH, the cement contamination. Depending on the pH of the mud, the sodium

bicarbonate will form carbonate (CO3--) and bicarbonate (HCO3

-) ions which will

precipitate calcium forming calcium carbonate as follows:

NaHCO3 + Ca(OH)2 ⇋ NaOH + H2O + CaCO3 ↓







4. Many of the polymers may be hydrolized by the high pH and then precipitated by

Ca++, as shown in the following figures.

For this reason, the treatment to reduce the pH and precipitate Ca++, has to be fast

and adequate. In this case, the critic acid is also an ideal additive for both these

actions.

5. The improvement in the efficiency of the solids removal euqipment is another way

to reduce the contamination. The cement particles removed, cannot be later

dissolved in solution as Ca(OH)2





Polyacrylamide polyacrylate hydrolisis at high pH, freeing ammonium gas






Precipitation of the polyacrylate calcium






CARBONATE CONTAMINATION

Carbonate and bicarbonate contamination is one of the most complicated

concepts in drilling fluids chemistry. They both progressively increase the mud

viscosity, yield gels to the extreme point of solidifcation of the mud.






The possible sources of carbonates and biarbonates are:

1) Carbon Dioxide (CO2) is absorbed from the air by the mud through mud mixer in

the pits and through some solids removal equipment discharge. The CO2,

dissolving, becomes carbonic acid (H2CO3)which converts in bicarbonate (HCO3-)

and/or carbonate (CO32-) according to the pH of the mud.

2) An excessive use of calcium carbonate or sodium bicarbonate during the

treatment of gypsum or cement contaminations.

3) CO2 gas coming from the formation or the formation water.

4) Bicarbonates and/or carbonates caused by thermal degradation of the

lignosulphonates and lignite at very high temperatures.

5) Impurity in barite.

C O CO O





The following equations show the CO2 dissolution which causes a formation of carbonic

acid (H2CO3) and/or carbonate depending on the pH of the mud. These equations

illustrate that the chemical reactions are reversible as a function of the pH. Therefore, the

CO3-can revert back to HCO3

CO2 + H2O ⇋ H2CO3

H2CO3 + OH -⇋ HCO3

- + H2O and

HCO3

- +OH -⇋ CO

3

2– + H2

O







Equilibrium carbonate bicarbonate

P e r c e n t


H2CO3






IDENTIFICATION OF CRBONATE/BICARBONATE WITH CHEMICAL ANALYSIS

The pH/Pf method for the carbonate/bicarbonate analysis, is based on the quantity (ml)

of 0.02 N Sulphuric Acid (H2SO4) necessary to reduce the pH of the filtrate, from the

existent pH at a 8.3pH that is the pH range in which hydroxyls and carbonates exist .

If carbonates are not present, very little NaOH is required to achieve the correspondent

pH range of common drilling fluids. The relative Pf is also low. A very small concentration

of H+ (from H2CO

4) is required to convert the OH- in water and reduce to Pf end point

(pH=8.3).








If carbonates ions exist, they must be converted to bicarbonate ion by addition of

H2SO4 to reach the Pf end point.

This makes the Pf higher (for an equivalent pH) in a filtrate that contains carbonates

compared to a filtrate that does not. This difference make it possible to calculate the

concentration of carbonates and bicarbonates and the equivalent conc. of calcium to

precipitate it.






Relationship of pH and alkalinity for pure water

17000501414

170051.413

1700.50.1412

170.050.0411

1.70.0050.001410

0.170.00050.000149

0.0170.000050.0000148

0.00170.0000050.00000147

OH–

(ppm)

Pf

(cc 0.02N H2SO4)

NaOH

(lb/bbl)pH







The Pf/Mf method of the carbonate/bicarbonate analysis is based on the quantity

(ml) of sulphuric acid 0.02 N necessary to reduce the pH of a filtrate from a known

pH to a pH 8.3 and to a pH 4.3 respectively. This covers the pH range in which

carbonates, bicarbonates and carboinc acid exist.

If carbonates/bicarbonates concentration is high, the Mg will also be much higherthan the Pf.







Due to the fact that it will not be a qualitaitve analysis, it is necessary to make

sure that:

• Normally, If Mf is less than 5 ml of 0.02 N sulphuric acid, there is no carbonate

problem.

• If Mf > 5 ml of 0.02 N sulphuric acid, and the ratio Mf/Pf tends to increase,

there are strong possibilities of the presence of carbonates and an in-depth

analysis is necessary, for instance, with the pH/Pf or Garrett Gas Train (GGT).







CARBONATE/BICARBONATE TREATMENT

This treatment is rather complicated, because the ions of HCO3- and CO3

2- can

coexist at different pH degrees. Only the CO32- can be treated with calcium to allow

the CaCO3 to precipitate.

Their coexistence, form a buffer solution that remains at the same pH value but at

increasing Pf or Mp levels.

Treatment with lime:

(CO3

2–) + Ca(OH)2

⇋CaCO

3 ↓+ 2(OH –)

Treatment with gypsum:

(CO32–) + CaSO4 ⇋ CaCO3 ↓+ (SO4

2–)







It may take several applications of Lime or Gypsum over several circulations to treat

out completely the carbonates.

If the pH of the mud drops to less than 10, carbonates are converted to bicarbonates.

It develops high viscosity and gels.

Adding deflocculants and caustic in large concentration, there will be a deflocculation

but what is really important is that the addition of caustic soda converts the

bicarbonates to carbonates. When it happens, there will be a large reduction in

viscosity as it is shown in the next figure.







Effect of the concentrations of carbonate and bicarbonate on the yield point.






Lime Method

Find on diagram the Pf value and then proceed horizontally until intercept the line of

the pH. From this point, descend vertically until intercepting the horizontal axis and

read the concentration of carbonate in millimoles/litres. Then, go up to the top of the

graph and read the ppb of lime required to precipitate the carbonates.

The diagram II indicates the concentration and treatment of the bicarbonate and it is

used in the same way. Find on the vertical axis the Pf value, run until the pH line and

go up at the top of the diagram to determine lb/bbl of lime necessary. Sum the

quantity of lime obtained by either the diagrams and multiply for the water fraction. Fw

to determine the treatment necessary.







Diagram I: Concentration and treatments for carbonates







Diagram II: Concentrations and treatments for bicarbonates.







Example:

pH = 10.7; Pf = 1.7; FW = 0.80From Diagram I:

CO3 = 33.5 millimoles/litre

Lime needed = 0.34 lb/bbl

From Diagram II:

HCO3 = 3.3 millimoles/litre

Lime needed = 0 lb/bbl

Total treatment =

(0.34 lb/bbl + 0 lb/bbl)(.80) = 0.27 lb/bbl lime







METHOD B (lime and gypsum for a constant pH)

Find the Pf value on diagram I, and proceed horizontally up to intercept the pH

line. Move donwards until the horizontal axis and read the concentration of

carbonate in millimoles/litre. Continue downwards and read lb/bbl of gypsum

necessary for the precipitation of the carbonates. Diagram II is for the bicarbonateand it is used in the same manner.







Example:

pH = 10.7; Pf = 1.7; FW = 0.80

From diagram I:

CO3 = 33.5 millimoles/litre

Gypsum needed = 0.8 lb/bbl

From Diagram II:

HCO3 = 3.3 millimoles/litro

Gypsum needed = 0.1 lb/bbl

Lime needed = 0 lb/bbl

Total treatment with lime = (0 lb/bbl)(0.80) = 0 lb/bbl(0.8 lb/bbl + 0.1 lb/bbl)(0.80) = 0.72 lb/bbl gypsum

Sum the quantity of lime and gypsum and multiply for water fraction, in this way the

needed treatment is obtained.

SALT CONTAMINATION





SALT CONTAMINATION

The three types of salt that it is possible to encounter during the drilling are:

Halites (NaCl), sylvite (KCl) and carnallite (KMgCl3• 6H2O). Other salts are

magnesium (MgCl2) and calcium chloride (CaCl2), often mixed or with other

dissolved salts, in the formation water. The underground salt water

presence can cause significant contamiantions to the mud.

The salt contamination mechanism is based on a cationic exchange with

the clays, the mass action of the predominant cations and sometimes the

pH.

The initial effect is high viscosity, gel strength fluid loss and a large

increase in the chloride content. Also an increase of the hardness in the

filtrate is observed in presence of clays intervals. This is due to the salt-

based exchange flushing out the calcium ions from the clay particles.

.

SALT CONTAMINATION





Halite (NaCl)

Halite is the most common drilled salt and the major constituent of the flowing meter

Halite causes clays flocculation when in large amount in contact with the mud

The increase in chlorides confirm the contamination.

Other sympthoms are funnel viscosity, yield point, gel strength, fluid loss increase

The mud treatment for this contamination, consists in dilution with fresh water and

addition of deflocculant to maintain acceptable rheological characteristic. When the

clays have been deflocculated, additional caustic soda is required to rinse the pH.

SALT CONTAMINATION





Pure halite has a pH of 7 and as a consequence, the thicher the halite layer, the

higher the caustic soda additions in order to maintain the pH>9.5.

Moreover, halite falsifies the reading of the pH with the pH papers, due to the

chlorides. In this case, the increase in the obtained value of 1 unit is suggested.

If available, the use of a pH metre is recommended.

There are not convenient treatments to precipitate Na+ and Cl- from the system so

until it is tolerable, dilution with fresh water is the recommended solution. If

masssive salt must be drilled, it is preferable to saturate the mud with salt to avoid

wash out and collapsed hole.

Important to remember that in these circumstances dry bentonite is not effective if

directly added in the system, but it is possible the addition after pre-hydration.

SALT CONTAMINATION





SYLVITE (KCl)

Do the same type of contamination of halite.

Sylvite is more soluble than halite. For this reason, a mud salt saturated with NaCl

would still wash out the sylvite formation.

SALT CONTAMINATION





CARNALLITE (KMgCl3 • 6H2O)

Carnallite is a complex rare salt.

Problems caused by carnallite in the mud are quite serious:

1. There are two strong cations (calcium and magnesium) which act on clays

causing flocculation and dehydration. If this is the only problem, the corrective

interventions are rather simple.

2. In presence of hydroxile ions (OH –) magnesium from the dissolved carnallite

precipitates as magnesium hydroxide (Mg(OH)2) a thick, jelly substance that

causes increase of viscosity. Magnesium can only be precipitated by caustic.

SALT CONTAMINATION





Most of the muds are run in an alkaline ambient both to maximise the clays

performance with the other additives and to minimize the corrosive effect.

The sodium sulphate (Na2SO4) controls the calcium filtrate in high magnesium

content fluids.

Na2SO4 + Ca2+ 2 Na+ + CaSO4

SALT WATER FLOWS





Influx water can have a wide range of salts.

The solubility of the most common salts is directly proportional to the temperature.

As the temperature increases the salt solubility increases.

The waters enriched in calcium and magnesium are the most detrimental. There are thecommon indicators of the contamination from Mg++:

• Rapid pH fall.

• Mud viscosity increase with the addition of caustic soda or sodium carbonate.

• Titrate for magnesium ions concentration.

With no or limited calcium presence, the indicators of a high content of calcium in the water will

be:

1. Minor effect on pH.

2. Positive reaction of the mud at the caustic soda or calcium carbonate additions.

3. Titration for concentration of calcium ions.

H2S CONTAMINATION





H2S (Hydrogen Sulphide) is the most corrosive and dangerous contaminant. It is

a destructive gas for metals and lethal for the man.

In presence of H2S, drilling crews must be prepared to use detection equipmentand personal protective equipment.

H2S is generated by:

1. Thermal deposits

2. As formation gas

3. Biological degradation

H2S CONTAMINATION





H2S can be identified by:

• Reduction of the pH in the mud.

• Mud colour changing to dark colour caused by FeS.

• Odor of rotten eggs (only for low percentage, after odourless).

• Viscosity and fluid loss increase caused by pH reduction.

• Formation of a black deposit (FeS) on the drill pipes.

2

H2S CONTAMINATION





Due to the fact that H2S is an acid gas, the pH is dramatically reduced so to neutralize

the harmfuls effects of the H2S gas, the pH has to be increased up to 11 or 12 with the

addition of caustic soda or lime. The following chemical reaction describes the alkaline

application of the H2S.

H2S + OH –⇋ HS- + H2O

H2S + OH –⇋ HS – + H2O

HS – + OH –⇋ S2

– + H2O

2

H2S CONTAMINATION





Sulphur distribution with pH

H2S CONTAMINATION





The bisulohite ion (S2--) may be removed by a reaction with zinc oxide (2nO) to form

the insoluble Zinc Sulfide ½ S2 – + Zn2+ ZnS.

A treatment with 1-lb/bbl of zinc oxide removes approximately 1,100 mg/l of

sulphures.

For a preventive treatment against H2S, 2 lb/bbl of zinc oxide are needed. The

addition of 1 or 2 lb/bbl of chrome lignosulfonate is recommended.

For the protection of the tubulars against H2S, an oil-based mud is recommended.

Infact, the patina left by the oil on the tubular surface protect it. The H2S molecules

penetrate in the porosity of the metal. Without an adequate protection, the expansion

of the molecules will cause cracks in the metal. However, this does not mean that H2Sis less toxic using oil-based mud. On the contrary, the H2S is much more soluble in an

oil-based mud than in a water-based mud.

H2S CONTAMINATION





The H2S presence can be detected in two ways:

1) Garrett Gas Train (GGT).

2) Hach test.

The H2S detection in the mud takes place through the GGT. If the presence is

detected, you must intervene as follows:

1) Immediately increase the pH to at least 11.5 to 12 with caustic soda.

2) Buffer the pH with lime.

3) Begin treatment with zinc oxid to remove from mud solubles sulphures.

CONTAMINANTS IDENTIFICATION ANDTREATMENT





CEMENT

Symptoms :

1) Viscosity and gels strengths increase.

2) pH, Pm and Pf (in particular Pm).

3) Fluid loss increase.

4) Lime and soluble calcium increase.






Treatment:

1) It depends on the system used, “acid sodium pirophosphate” or “lignite” and

sodium bicarbonate can be used to lower the pH and make soluble calcium

precipitate. Citric acid is also recommended.

2) Voluminous treatments with water and lignosulphonate to control the flow

properties. Bentonite additions can help control the fluid loss.






MAGNESIUM CONTAMINATION

Symptoms:

1) Yield point and fluid loss instability.

2) High hardness levels after the treatment with calcium and sodium carbonate.






Treatment:

1) Increase the mud pH at 11 with caustic soda or causitc potash (KOH) to

remove the magnesium.

2) Maintain the pH at these levels to prevent the re-solubilization of Magnesium

from Mg (OH)2.






GYPSUM OR ANHYDRITE CONTAMINATION

Symptoms:

1) Viscosity and Gel Strength increase.


3) Soluble calcium increase.

4) Probable Pf and pH decrease.






Treatment:

1) Precipitation of soluble calcium using phosphate or sodium carbonate. Reduce

viscosity with lignosulfonates and caustic soda treatment. Lower the fluid loss

with bentonite, polianionic cellulose or lignite.2) Stabilize level of the gypsum or anhydrite in the mud around a level higher than

600 mg/l as soluble calcium. Control the viscosity with lignosulfonates, pH with

caustic soda and the fluid loss with bentonite and polianionic cellulose.






SALT CONTAMINATION

Symptoms:

1) Viscosity increase.


3) Chlorides and soluble calcium increase.

4) Pf and pH decrease.






Treatment:

1. If the salt formation is to be cased off shortly after drilling, dilute the NaCl using

water. Use lignosulfonates to control the viscosity, caustic soda and lime,

proiportion 1:2 for pH and Pf control; polianionic, bentonite for fluid loss.

2. If the salt formation must not be cased and the formation must be exposed for a long period, sature the mud with salt to avoid further hole enlargements.

Control the viscosity with lignosulfonates plus caustic soda and lime. Control

fluid loss by starch, poliamic polymers and prehydrated bentonite. If starch isused and the salinity is depleting below 190,000 mg/l (NaCl), biocide must be

used to prevent fermentation.

CONTAMINANTS IDENTIFICATIONS ANDTREATMENTS





Contamination done by salt water

Symptoms:

1) Mud flow return increase.

2) Mud tank increase.

CONTAMINANTS IDEMTIFICATIONS ANDTREATMENTS





Treatment:

1) Control the kicking situation using the right method of well control.

2) Caustic Soda to maintain the adequate pH.







Symptoms:

1) Gel Strength increase.

2) Pf increase with constant pH.

3) Difference between Pf and Mf increase.

4) Carbonate or bicarbonate levels increase.






Treatment:

1) The pH increases to at least 10.3 to 11.3

2) Add lime gypsum to remove carbonates as CaCO3-

Ch i l t t t (A l S ) t






Chemical treatments (Anglo-Saxon) systems

mg/l x Fw x 0.00091Zinc OxidePlu+ caustic soda

to raise pH > 10.5

Sulphur (H2S, HS –, S2 –)H2S

mg/l x Fw x 0.00116Caustic SodaCalcium and

magnesium

Salt and industrial

water

lb/bbl gypsum excess x 1lb/bbl gupsum excess x 1.150

lb/bbl gypsum excessx 1.893

Sodium bicarbonateCitric Acid

Calcium and hydroxileLime and cement

mg/l x Fw x 0.000928

mg/l x Fw x 0.000971

mg/l x Fw x 0.00735

Calcium carbonate

Sodium bicarbonate

CalciumGypsum and

Anhydrite

mg/l x Fw x 0.00100

mg/l x Fw x 0.000432mg/l x Fw x 0.00424

Gypsum reduces pH

Lime increases pH

Carbonate

Bicarbonate

Carbon Dioxide

Concentrazione Trattamento

(lb/bbl)TreatmentContaminant IonContaminant






Chemical Treatments (metric system)

mg/l x Fw x 0.002596

Zinc Oxide

Plu+ caustic soda to

raise pH > 10.5

Sulphur (H2S, HS –, S2 –)H2S

mg/l x Fw x 0.00285Caustic SodaCalcium andmagnesiumSalt and industrialwater

Kg/m3 gypsum excess x3.161

Kg/m3 gypsum excess x

3.281

Kg/m3 gypsum excess x 5.4

Sodium BicarbonateCalcium and HydroxileLime and cement

mg/l x Fw x 0.00265

mg/l x Fw x 0.00277

mg/l x Fw x 0.002097

Calcium carbonateCalciumGypsum and Anhydrite

mg/l x Fw x 0.00285mg/l x Fw x 0.00121Gypsum reduces pHLime increases pHCarbonate BicarbonateCarbon Dioxide

Treatment Concentration

(lb/bbl)TreatmentContaminant IonContaminant






References contaminating contaminants treatment

Caustic, dilution

water, thinner

and fluid-loss

polymer

__ __ __

Salt

Caustic, dilution

water and

thinner, or sodaash (plus fluidloss

polymer)

__

__ __ __ Gypsum or anhydrite

Bicarb,or thinner, bicarb

and citric acid

PH

11.5

__ __ __ Cement

TreatmentSolid

sCa2+Cl –Mf Pf PmpH

F

L

Gel

sYPPVFVWTContaminant






Increase Decrease No change Slight increase Slight decrease

TreatmentSolidsCa2+Cl –Mf Pf PmpHFLGelsYPPVFVWTContaminant

References treatments contaminanting contaminants

Dilution water,

solids-removalequipment and

thinner

New

Dilution

water and

solids-removal

equipment

__ __ __ __ __ __ __ __old

solids

Caustic, lime

and

zinc source

__

__

__ __

H2S

pH <10.3: lime

pH 10.3 to 11.3:

lime and gyp

pH >11.3: gyp __ __ __ __

Carbonate or

bicarbonate

Date post:	03-Jun-2018
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8 Chemical Contaminations and Treatments

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