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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
Family Function/Examples
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
Family Function/Examples
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
Application of Surfactants
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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
Application of Surfactants
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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
Recommended