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Oilfield Production Chemicals - Water Clarifier

Water clarifiers, also known as Reverse Emulsion Breakers (REB) or deoilers, are a class of chemicals used to remove oil and entrapped solids from produced water so that it can be discharged or reused. 

 
Topics

 

Water Clarifier Selection

Theory of Reverse Emulsions and Solids

Reverse Emulsion Breakers

Water Clarifier Selection

 

Water Clarifier Selection

 

A suitable water clarifier for a certain application can be selected by theoretical considerations regarding chemical interferences and compatibilities, engineering and environmental considerations regarding its downstream fates and effects, and empirical consideration regarding its apparent performance in bench scale tests accurately modeling relevant aspects of the process in which it will be used. The basic principles of good practice which apply to this process are outlined below.

 
General Considerations

  • Review system 

  • Samples

    • Untreated, fresh, using low differential pressure

  • Model entire system 

    • Sample composition (including recycle), temperture, timing agitation, etc

  • Test all treatments

    • in total fluids

    • at intended treat rates

  • Select for fastest adequate resolution

 

Sampling

A good sample for water clarifier selection should be:

  • untreated with water clarifiers

  • treated with demulsifier and any other chemicals

  • from proposed injection point

    • Bottom of 2-phase lines

  • without shearing or aeration

    • Minimum pressure drop or use a bomb

  • include free oil, if present

    • Add back in

 

Parameters to Simulate

  • Oil Contents 

  • Temperatures

  • Chemical Dose

  • Agitations

  • Retention Times

  • G-Forces

  • Scale-Up Factors 

  • Aerations

 

Different treatment processes require different test designs. For example, in Mixed Production, test design parameters would include:

  • Oil content

  • Temperature

  • Chemical Doses

  • Agitation

  • Time

 

Test Interpretation

For small particles at long residence times (i.e. in a relatively big Skimmer with small production), removal of oil droplets from water phase depends almost entirely on rate of growth, instead of rate of rise. In this case, Stirred Jar Test should be used which measures mostly rate of growth.


In most cases, fast but not complete resolution looks good at first but may eventually fail to meet expectations. On the contrary, slow but complete resolution looks bad in early process but improves by time.
 

 

Theory of Reverse Emulsions and Solids

 

Contrary to regular water-in-oil emulsions, reverse emulsion is a type of emulsion that:

  • water is the external phase and oil is the internal phase.

  • emulsifying surfactants must be present.

  • the emulsifying surfactants must be chemically altered prior to physical treatment. 

 

Spot tests or solvent tests can be run to determine if it is a regular emulsion or a reverse emulsion.

Theory of  Reverse Emulsions and Solids

Solids in a reverse emulsion can either stablize it or destablize it.

  • Solids can stabilize emulsions

    • by increasing interfacial viscosity

    • by bringing or being emulsifying surfactants 

    • by removing demulsifying surfactants

  • Solids can destabilize emulsions

    • by bringing or being demulsifying surfactants 

    • by removing emulsifying surfactants

 

Solids dispersed in oilfield reverse emulsions could originally come from water phase:

  • Salts (NaCl, CaCl2, etc.)

  • Scales (CaCO3, BaSO4, etc.)

  • Clays (SiOx, Al(SiOx)y, etc.)

  • Rusts (Fe(OH)x, etc.)

  • Some Organics (humic acids, most polymers) 

They could also come from oil phase:

  • Most Organics (C fines, naphthenates, asphaltenes, some polymers)

  • Sulfides (S, FeS, etc.)

 

Reverse Emulsion Breakers

 

Throughout the water clarification process, particle contact, adhesion, and growth can be promoted through the appropriate use of chemical coagulants, flocculants, or coalescence aids, also referred to as reverse (emulsion) breakers, deoilers, or water clarifiers. Dispersed particles generally do not coagulate or coalesce well, due to stabilizing forces that are chemical in nature. The right chemical can convert a repulsive force (such as two like charges) into an attractive force (such as two opposite charges) and create an exponential rate of particle growth.

 

Exponential growth is a powerful driver for separation. Two particles coalescing once per minute will have a diameter a million times larger in an hour—from a micron to a meter. By inducing or accelerating the rate of coalescence, the right chemical can generally accomplish far more at a lower cost than any type of physical improvement. 

 

Since the chemical acts to modify only the surface of the particle, not the bulk water or oil, the amount of chemical needed is proportional to the internal surface area of the emulsion or dispersion. So, for the same volume of a given dispersed phase, the dose requirement for a given chemical is proportional to the mean particle diameter. The specific proportionality constant depends on the nature of the surfaces and the nature of the chemicals, but all other thing being equal, micron particles will require a thousand times more chemical treatment than millimeter particles. Minimizing the degree of emulsification to prevent small particle size can be the most cost effective oily-water mitigation strategy.
 

By mechanism, there are two basic types of water clarifiers to break reverse emulsions:

1.   Known as Coagulants which destabilize dispersions so droplets can stay together on contact, they         eliminate repulsive forces through:

  • Charge neutralization

  • Interface modification

  • Steric hindrance removal 

      They have low MW molecules which are smaller than droplets/solids.

2.   Known as Flocculant which adds attractive forces and brings droplets/solids together, they have             high MW Molecules which are larger than the distance between the particles.

 

Polymeric water clarifiers can be further divided into two groups:

  • SOLUTION POLYMERS - low MW

    • Water based 

  • EMULSION POLYMERS - high MW (5 to 40MM)

    • Oil external emulsion (Invert Emulsion Polymers)

    • Water external emulsion

      • Latex-polymer in water

      • Brine Dispersion Polymer- more compatible in brines 

 

Most water clarifiers are cationic since oil droplets in produced water tend to be anionic. Amphoteric, anionic and nonionic chemicals have been used as water clarifiers as well. A commercial water clarifier could have one or more of the following chemistries:

  • Polyamines

  • Polyalkanolamines

  • Polyvinylamines

  • Polyacrylamides

  • Polyaminoacrylates

  • Quaternary amines

  • Acrylates

  • Metal Salts, zinc, aluminum, zirconium

 

Reverse Emulsion Breakers
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