Polydadmac (poly diallyldimethylammonium chloride) is a highly effective cationic organic polymer widely used in oilfield produced water clarification. Produced water is one of the largest waste streams in oil and gas operations, generated during crude oil extraction and natural gas production. It typically contains oil droplets, suspended solids, dissolved salts, organic compounds, and chemical additives from production processes. Due to its complex composition and high stability of emulsions, produced water requires efficient chemical treatment. Polydadmac plays a key role in destabilizing oil droplets, aggregating fine solids, and improving separation efficiency.

1. Characteristics of oilfield produced water

Produced water composition varies depending on reservoir type and production conditions, but generally includes:

• Dispersed and emulsified oil droplets
• Suspended solids (sand, clay, corrosion products)
• Dissolved salts (high salinity brine)
• Organic compounds (BTEX, phenols, hydrocarbons)
• Production chemicals (corrosion inhibitors, scale inhibitors)
• High turbidity and COD

These components are often stabilized by surface-active agents and fine particle size, making separation difficult without chemical conditioning.

2. Properties of Polydadmac for produced water treatment

Polydadmac is a water-soluble quaternary ammonium polymer synthesized from diallyldimethylammonium chloride monomers.

Key properties include:

• Very high cationic charge density: Strong interaction with negatively charged oil droplets and solids
• Excellent water solubility: Rapid dispersion in high-salinity water
• Stable performance in wide pH and salinity conditions
• Low to medium molecular weight (or customized grades): Suitable for rapid coagulation
• Fast adsorption kinetics: Immediate destabilization of emulsions

These properties make Polydadmac highly effective in oilfield wastewater environments, which often contain high salt and complex emulsions.

3. Mechanism of action

Polydadmac improves produced water clarification through several mechanisms:

(1) Charge neutralization of oil droplets
Oil droplets in produced water are often stabilized by negative surface charges. Polydadmac neutralizes these charges, reducing repulsion and allowing droplets to coalesce.

(2) Emulsion destabilization
It breaks oil-in-water emulsions by adsorbing onto surfactant-stabilized interfaces, weakening interfacial films.

(3) Floc formation and aggregation
Once destabilized, oil droplets and fine solids aggregate into larger flocs that can be separated easily.

(4) Bridging and enmeshment (in higher MW grades)
Polymer chains connect multiple particles, forming larger flocs that trap oil and solids.

4. Application process in produced water treatment

(1) Primary separation (gravity or API separator)

Large oil droplets are removed by gravity separation, but fine emulsified oil remains.

(2) Chemical coagulation (Polydadmac dosing)

Polydadmac is injected into produced water to destabilize remaining emulsions and fine suspended solids.

(3) Flocculation stage

Gentle mixing allows microflocs to form and grow into larger aggregates.

(4) Dissolved air flotation (DAF)

Air bubbles attach to flocs, lifting oil and solids to the surface for removal.

(5) Filtration or polishing

Remaining fine particles are removed using media filters or membrane systems.

5. Applications in oilfield operations

(1) Onshore produced water treatment

Used in large-scale treatment facilities to enable water reuse or safe discharge.

(2) Offshore platforms

Applied in compact systems such as hydrocyclones and flotation units for space-limited environments.

(3) Enhanced oil recovery (EOR) water recycling

Helps clarify injection water to prevent reservoir damage.

(4) Refinery wastewater treatment

Used for emulsified oil and solids removal in downstream processing units.

6. Advantages of Polydadmac in produced water clarification

(1) Strong emulsion breaking ability
Effectively destabilizes stable oil-water emulsions.

(2) High efficiency in high salinity water
Performs well in brine-rich environments typical of oilfields.

(3) Fast reaction speed
Immediate coagulation reduces retention time.

(4) Improved oil removal efficiency
Enhances separation of fine oil droplets not removed by mechanical systems.

(5) Reduced sludge volume
Produces denser and more compact oil-solid sludge.

(6) Operational flexibility
Works across varying production water qualities.

7. Dosage and influencing factors

Typical dosage ranges:

• 5–30 mg/L for low oil content produced water
• 20–100 mg/L for medium contamination levels
• 50–200 mg/L for heavily emulsified systems

Key influencing factors include:

• Oil concentration and droplet size
• Salinity and ionic strength
• Temperature of produced water
• Presence of natural surfactants or chemicals
• Mixing conditions and residence time

Jar testing or field pilot testing is essential for optimization.

8. Combination with other treatment chemicals

Polydadmac is often used together with other chemicals in produced water treatment:

(1) Cationic polyacrylamide (CPAM):
Enhances floc size and improves flotation efficiency.

(2) Demulsifiers (nonionic surfactants):
Assist in breaking strong oil emulsions before coagulation.

(3) Ferric salts or PAC:
Improve removal of suspended solids and reduce COD.

(4) pH adjusters:
Optimize conditions for emulsion destabilization.

This multi-chemical approach ensures high removal efficiency.

9. Limitations and considerations

(1) Highly stable emulsions
Some produced waters with strong surfactants may require additional demulsifiers.

(2) Overdosing risk
Excess polymer can restabilize emulsions or increase residual COD.

(3) Variability of produced water
Composition changes frequently with reservoir conditions.

(4) Cost considerations
More expensive than simple inorganic coagulants but more effective in complex systems.

10. Operational best practices

To maximize performance:

• Conduct regular jar tests or field trials
• Optimize injection point for best mixing
• Adjust dosage based on oil content fluctuations
• Combine with flotation systems for best results
• Monitor effluent oil content and turbidity continuously

11. Future trends

The use of Polydadmac in produced water treatment is expected to expand due to:

• Increasing water reuse in oilfield operations
• Stricter environmental discharge regulations
• Development of compact offshore treatment systems
• Integration with membrane and advanced separation technologies
• Demand for high-efficiency low-dosage chemicals

Future formulations will focus on improved emulsion-breaking efficiency and better performance in extreme salinity conditions.