6. Acid Additives (60 Min)

8/10/2019 6. Acid Additives (60 Min)

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Carbonate Acidizing Design

Acid Additives

By: Dr. M. Pournik


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Treatment may be a failure if proper additives are not used

Additives in treating fluid used to

Prevent excessive corrosion

Prevent sludging and emulsions

Prevent iron precipitation Prevent precipitation of reaction products

Improve cleanup

Improve coverage of zones

Additives in preflushes & postflushes used to Stabilize clays

Disperse parafins & asphaltenes

Introduction


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H2S scavengers

Chelating agents

Corrosion inhibitors

Scale inhibitors

Drag reducers

Anti-sludge agents surfactants

Main Additive Types


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Stable @ BHT

Compatible with other additives

Minimum impact on acid reaction

Do not adversely affect the performance

of other additives

Minimum impact of wettability

Additives Requirements


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Dont over use

Amount can be determined from

stoichmetry

Expensive

They can cause damage

Additives Recommendations


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Acid Additive Types

Family Function/Examples

Surfactants

Mutual solvents

Water wet formation

Nonionic//fluorocarbon

Cationic

Remove oil, accelerate clean-

up EGMBE

Complex surfactants


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Acid Additive Types


Anti-

sludge/emulsion

agent

Iron control

additives

Prevent emulsions and sludge

Anionics

SDS

Prevent ppt of Fe(OH)3 EDTA

Citric acid

NTA

Reducing agents


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Acid Additive Types


Corrosion Inhibitors

Sulfide suppressors

Control acid corrosion

Aromatic quats Unsaturated oxygen

Prevent sulfide reactions

Aldehydes Chelants/reducing agents


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Most important

Slows attack of corrosion on drillpipe, tubing or anyother metal

Effectiveness depends on the metal

Wide range of responses observed, hence mustmatch properly

Could still get pitting of metal surfaces as a result of

Inhibitor breakdown

Insufficient inhibitor Metal impurities

Corrosion Inhibitors


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Two basic types:

Inorganic corrosion inhibitors

Salts of zinc, nickel, copper, arsenic, antimony, and various other metals

Work effectively at high temperatures for long contact time

Cheap

Tend to lose effectiveness in acids stronger than about 17% HCl

Poison refinery catalysts

May liberate toxic arsine gas

Difficult to mix and unsafe to handle

Organic corrosion inhibitors

Composed of polar organic compounds with one or more polar groups made ofsulfur, oxygen or nitrogen

Do not poison refinery catalysts

Work effectively in all acid concentrations Chemically degrade with time and do not readily provide long-term protection at

temperatures above 200 oF

Expensive

May have inhibitor aids such as potassium iodide, cuprous iodide, cuprouschloride, and formic acid to increase effectiveness of inhibitor

Types of Corrosion Inhibitors


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Comparison of Corrosion Inhibitor

Types

Effectiveness of Corrosion Inhibitors at High

Temperatures in 15% HCl


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Some other additives reduce effectiveness of inhibitorsby altering the tendency of inhibitor to adsorb

Should properly test with representative metal samplesusing the precise acid formulation at most adverse

conditions of temperature and pressure Could reduce tendency for corrosion by:

Precooling tubing by injecting water preflush

Using formic acid rather than HCl

Minimizing contact time

Corrosion Inhibitors Application


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Used to break undesirable emulsions, reduce surface orinterfacial tension, alter wettability, speed cleanup,disperse additives and prevent sludge formation

Requires selection of appropriate molecule

Owe their properties to their dipolar composition

Surfactants


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Classified into 5 groups according to ionic charge carried bywater-soluble group:

Anionic: used primarily as nonemulsifying agents,retarding agents, and cleaning agents

Cationic: consist of long-chain primary, secondary, andtertiary amines or are quaternary ammoniumcompounds

Nonionic: used as nonemulsifiers and foaming agents

Amphoteric: have hydrophilic group that changes fromcationic to nonionic to anionic with increasing pH

Fluorocarbons: lower surface tension of solutions tomuch greater extent than hydrocarbon surfactants

Types of Surfactants


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Main properties of fluid or mineral affected by surfactants are:

Surface tension: adsorbs to surfaces and changes surfacetension

Emulsification tendency: can lead to development of

emulsions Wettability: adsorb at interfaces between solids and liquids

and alters wettability of solids

Micelle formation: form micelles in liquids when presentabove a specific concentration for each molecule, solvent, and

temperature

Dispersibility: wets the dispersed phase with the liquid phasewhich greatly improves dispersibility

Properties of Surfactants


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Some Types of Surfactants

Silicate Particle Wettability

CharacteristicsExamples of Surfactant Micelles


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De-emulsifiers:

Break oil-water emulsions Action depends on how quickly can concentrate at

oil/water interface

Usually are oil-soluble

Nonemulsifiers: Prevent formation of emulsions with reservoir fluids

Mixtures of surfactants and solvents blended toobtain a final composition with broader applications

Emulsifiers:

Ability to isolate internal phase so that is not asreactive

Common example is emulsified acid

Can also act as efficient scale removal systems

Application of Surfactants


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Silt-suspending Agents:

Remove acid-insoluble clay and silt by adsorbingonto them and keeping them suspended byelectrostatic repulsion

Antisludge Agents:

Adsorb and provide a continuous layer of protectionat acid/oil interface to prevent sludge formation fromacid/oil contact

Surface Tension Reducers:

Lower surface tension of treating fluids whichreduces capillary pressure, aiding in cleanup of wells

Corrosion Inhibitors:

Quarternary amines and acetylenic nonionics



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Bactericides:

Eliminate contaminating bacteria

Mostly cationic surfactants with biocidal property,used in conjunction with other wetting surfactants

Clay Treaters:

Reduce swelling of clays by cation-exchange process

Inhibit flocculation of clays by dispersing clays

Foaming Agents:

Generate a stable foam

Can improve foam stability by gelling the liquid



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Stabilize clays by adsorbing through electrostatic attraction or ion

exchange on clays Common types:

1) Highly charged cations:

- Inexpensive

-Treat for both migration and swelling damage & treat large area of rock

2) Quaternary surfactants:

- Used widely for dry gas wells

- Neutralizes charges, hence reduces ion-exchange capacity of clays

3) Polyamines:

- Promote water-wetting of silicates & also polymeric bridging betweensilicate particles

4) Polyquaternary amines- Stabilized by charge neutralization, water-wetting, and polymeric bridging

- Can be used in any water-base fluid

5) Organosilane

- Well suited for formations containing nonclay fines as well as clay fines

Clay Stabilizers


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Soluble in both hydrocarbons and water

Examples: glycol ethers, reaction product of alcohols, and ethylene oxide

Applications:

Reduce water saturation by lowering surface tension of water toprevent water blocks

Solubilize a portion of water into a hydrocarbon phase to reduce

water saturation Maintain a water-wet formation as is to keep best relativepermeability to oil

Prevent insoluble fines from becoming oil-wet

Maintain concentration of surfactants and inhibitors by reducingadsorption of materials

Dissolve both adsorbed inhibitor and acid-insoluble residue

Dissolve any oil on the formation pore surface

Serves as de-emulsifier

Improves cleanup of spent acid

Mutual Solvents


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- Iron, ferric, is introduced during acidtreatments

- It is also present in the reservoir rocks

- It will ppt in spent acids as Fe(OH)3 or FeS(H

2S)

- Both can cause damage

Precipitation of Iron Compounds


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Iron Contamination

Acid A

(1 wt% FeCl3)

Phase separation

Acid C

(1 wt%

FeCl3)

Acid B

(1 wt% FeCl3)

Phase separation Phase separation

In the field, it is a must to minimize the iron contamination inlive acids by Cleaning the mixing tank

Pickling well tubulars or coiled tubing before pumping theacid.


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- Added to acids to keep iron in solution

- Limited solubility

- Not environmentally safe- Don't work if there is H2S

- What is the solution?

Iron Control Agents


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Main source of iron is tubing

Ferric is more damaging than ferrous

Minimize iron in live acids

One acid contains Fe(III)

Use ICA, but

Iron Control


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ICA include NTA, EDTA, lactic acid, citric

acid, ..etc

EDTA has limited solubility in 15 wt% HCl

Hydroxy EDTA has better solubility

Dont use in sour environment

Watch for Na or K salts with HF

Iron Control (2)


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Comparison of Various Iron Control


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Comparison of Various Iron Control

Agents


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Applications: Remove water blocks

Enhance fluid recovery

Retard acid reactivity

Decrease water content

Most common types: isopropanol and methanol

Major disadvantages:

Require large concentration

Costly

Low flash point

Increases corrosiveness

Adverse reactions & side reactions

Incompatibility with crude oils

Alcohols


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Alcohols Limitations

Effect of Various Concentrations of Methanol

on Acid Strength at Increasing Temperatures


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Use dispersant surfactant with xylene

Penetrate and loosen organic deposits which are thendissolves by xylene

Concentrations range from 1% to 10% volume/volume

Concentration depends on deposit type, hardness andadhesion and bottomhole temperature

Soaking time of several hours recommended for matrixacidizing, wellbore and tubing cleanup treatments

Organic Dispersants


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Remove water blocks and solids like damaging particlesand organic deposits

Examples: alcohols, xylene, toluene, and diesel

Used alone or in combination with acid

For inorganic scales with asphaltenes and paraffins:combine organic solvent with acid

For mixed deposits: an oil-external emulsion with acid asthe internal phase is best

Organic Solvents


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Summary Additives to be Used


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Effects of Additives on FeS Dissolution

Function Type Effect

Corrosion inhibitors

Quaternary amines

Or

Unsat. Oxygen derivatives

Negative

surfactants Nonionic mixed

Mutual SolventsAlcohols

Glycols

Small

none

Anti-sludge Additives Anionic Positive

Sulfide scavengers Aldehyde Negative

Iron Control Additives Organic acids Small


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FeS dissolution is inhabited by additives

that adsorb/interact with scale

Corrosion inhibition is impeded by

additives that dissolve or emulsify the

inhibitor film

The two effects can be opposing, so

careful testing under use conditions oftemperature and additives is mandatory

Conclusions

Documents

6. Acid Additives (60 Min)