Demulsifiers for Oil Production: Types, Selection, and Dosage Optimization

Why Crude Oil Always Contains Water

No oil field in the world yields “clean” oil. From the moment of extraction to delivery for refining, oil is a mixture of hydrocarbons, formation water, dissolved gases, mechanical impurities, and salts. The water content in produced fluid (water cut) ranges from 5% in new wells to 90%+ in depleted fields.

Water in oil is not just ballast. Calcium and magnesium chlorides dissolved in formation water hydrolyze upon heating in a rectification column, forming hydrochloric acid (HCl), which causes intense corrosion of refinery equipment. Salts contaminate cracking catalysts. Water increases transportation costs – pumping unnecessary tons of liquid that has no commercial value.

Standards for commercial oil are strict: water content – no more than 0.5% (ДСТУ 3437), chloride salt content – up to 100 mg/l for the first quality group.

In the Poltava fields, we selected a demulsifier for oil with API 28° and a water cut of 65%. Out of 8 tested formulas, only 2 showed >90% water separation in 30 minutes at 55 °C. This is a clear example of why a bottle test with a specific sample is the only reliable selection method. To achieve these indicators from raw production with a water cut of 30–70%, effective demulsification is required.

Water-Oil Emulsion: Why It Forms and Why It's So Stable

Formation Mechanism

An emulsion is a dispersed system where one liquid is distributed in another in the form of droplets with a diameter of 0.1–100 µm. In oil production, emulsion forms at several stages.

At the bottom of the well, oil and formation water pass through casing perforations, chokes, valves, and pumping equipment. Each flow constriction with a pressure drop is mechanical dispersion: water is broken into fine droplets and mixed with oil. The more intense the turbulence, the smaller the droplets and the more stable the emulsion.

Natural Stabilizers

Mechanical mixing alone is not enough to form a stable emulsion – pure water and pure hydrocarbon quickly separate under gravity. The stability of oil emulsions is provided by natural surface-active substances (surfactants) present in the oil.

Asphaltenes are high-molecular-weight polar compounds that migrate to the oil-water interface and form a strong, elastic film around water droplets. This film has solid-like properties: it does not rupture upon droplet collision but deforms elastically, preventing their coalescence.

Resins act as co-surfactants – they enhance the adsorption of asphaltenes at the interfacial surface, increasing the thickness and mechanical strength of the protective film.

Naphthenic acids are another class of natural surfactants. Their effect depends on the pH of the formation water: at pH > 6, naphthenates ionize and become effective emulsifiers.

Solid particles – clay, sand, corrosion products (iron sulfide, oxides) – accumulate at the interfacial surface and create an additional mechanical barrier (Pickering emulsions).

Emulsion Types

W/O (water-in-oil) – the most common type in oil production. Water droplets are dispersed in a continuous oil phase. Forms at water cut < 60–70%. This type requires demulsifier treatment.

O/W (oil-in-water) – oil droplets in a continuous water phase. Forms at high water cut (> 70–80%) or in wastewater systems. Requires other reagents – flocculants and reverse demulsifiers.

Multiple emulsions (W/O/W) – water droplets in oil, inside which there are even smaller oil droplets. The most complex case, occurs with demulsifier overdose or when incompatible reagents are mixed.

How Demulsifiers Work

A demulsifier is a synthetic surface-active substance that destroys the protective film around water droplets and ensures their coalescence. The process occurs in three stages.

Stage 1: Interfacial Film Destruction

Demulsifier molecules have higher surface activity than natural oil surfactants. They migrate to the oil-water interface and displace asphaltenes and resins from the interfacial film. The film becomes thin, loses elasticity, and mechanical strength.

Key parameter – the rate of demulsifier adsorption at the interfacial surface. An effective demulsifier reaches the interface in seconds, while a slow reagent may require minutes – during this time, some droplets may re-stabilize.

Stage 2: Droplet Coalescence

After the protective film is destroyed, water droplets begin to merge upon collision – coalesce. Small droplets combine into large ones: thousands of droplets with a diameter of 1–5 µm form droplets of 100–500 µm. The rate of coalescence depends on temperature (higher temperature – lower oil viscosity – faster droplet movement) and mixing intensity.

Stage 3: Gravitational Separation

Large water droplets settle under gravity. The settling rate is described by Stokes' Law and is proportional to the square of the droplet diameter – therefore, coalescence is critical: doubling the droplet diameter accelerates settling fourfold. Separation occurs in settling tanks, electrostatic dehydrators, or separators.

Types of Demulsifiers

Ethylene Oxide and Propylene Oxide Block Copolymers (EO/PO)

The most common class of demulsifiers. The polymer chain consists of alternating hydrophilic blocks (polyethylene oxide, PEO) and hydrophobic blocks (polypropylene oxide, PPO). The EO/PO ratio determines the hydrophilic-lipophilic balance (HLB) of the molecule and, accordingly, its effectiveness for a specific emulsion type.

Advantages: wide HLB range (4–18), possibility of fine-tuning for specific oil, effectiveness at low dosages.

Alkylphenol Formaldehyde Resins (Oxyalkylated)

Resins based on nonylphenol or dodecylphenol, modified with ethylene oxide. Characterized by high adsorption rate at the interfacial surface and the ability to effectively displace asphaltenes. Work at elevated temperatures.

Limitations: nonylphenol is an endocrine-disrupting substance, restricted by EU REACH Regulation (EC) No 1907/2006 in accordance with ECHA recommendations on SVHC. For oil export or work on international projects, alternative formulas are required. More details on REACH requirements – in the article “UA-REACH: What Manufacturers Need to Know”.

Polyesters (Polyolefins)

Products of condensation of polyhydric alcohols (glycerin, pentaerythritol, sorbitol) with fatty acids, additionally modified with EO/PO blocks. The branched molecular structure provides multiple contact points with the interfacial film.

Effective for heavy viscous oils with high asphaltene content (>5%). Work in a wide temperature range.

Comparative Table

Demulsifier Selection Criteria

Oil Density (API gravity)

Light oils (API > 35°) with low asphaltene content form less stable emulsions – for them, high HLB block copolymers are effective at minimal dosages of 5–15 ppm. Heavy oils (API < 25°) with a large amount of natural surfactants require polyester or composite demulsifiers at dosages of 20–50 ppm.

Water Cut

At a water cut of 10–30%, standard demulsifiers work effectively. At 50–70%, increased dosages and often two-stage treatment are required. At a water cut > 70%, emulsion inversion (W/O → O/W) may occur, requiring a change in reagent type.

Formation Water Mineralization

High mineralization (> 100 g/l) stabilizes the emulsion by reducing the thickness of the electrical double layer at the phase interface. Demulsifiers for highly mineralized systems require higher concentrations and a specially selected HLB.

Temperature

Temperature at the well bottom (60–120 °C) and at the oil treatment facility (40–70 °C) differ significantly. A demulsifier effective at 80 °C may be inactive at 30 °C – and vice versa. The optimal approach is to inject the demulsifier at the highest possible flow temperature (as close to the well as possible).

Emulsion Stability

Evaluated by laboratory bottle test – a key tool for demulsifier selection.

Bottle Test: Laboratory Selection Protocol

The bottle test is a standard method for screening demulsifiers under laboratory conditions. Procedure.

1. Sample Collection. A fresh water-oil emulsion sample is collected as close as possible to the reagent injection point at the field. Volume – 100 ml per test tube. Critical: the sample must be fresh (up to 24 hours), as emulsion aging changes its stability.

2. Dosing. Demulsifier is added to a series of graduated test tubes (6–10 pieces) in increasing concentrations: 5, 10, 15, 20, 30, 50 ppm. One test tube is a control (without reagent).

3. Mixing. Test tubes are shaken 100–200 times (or on a mechanical shaker for 5 minutes) for uniform demulsifier distribution in the emulsion.

4. Thermostating. Test tubes are placed in a water bath at a temperature corresponding to actual field conditions (usually 50–70 °C).

5. Observation. The volume of separated water is recorded after 5, 10, 15, 30, 60, and 120 minutes. The quality of separation is assessed: transparency of the oil phase, clarity of the interface, presence of an intermediate (rag) layer.

6. Selection Criteria. The optimal demulsifier ensures: >90% water separation in 30 minutes, a clean interface without a rag layer, a clear aqueous phase (absence of oil droplets), and minimal dosage to achieve the target result.

Dosage Optimization

The working dosage range for demulsifiers is 5–50 ppm. Optimal dosage is determined by the bottle test and adjusted based on field trial results.

Insufficient dosage – incomplete emulsion separation, residual water content in oil exceeds the standard, a stable intermediate layer forms in settling tanks.

Optimal dosage – maximum water separation with minimal reagent consumption. The typical “dosage – efficiency” relationship has an S-shaped curve with a plateau.

Overdosing – a critical error. Excess surfactant does not improve separation but causes the opposite effect: the formation of stable reverse emulsions (O/W or multiple W/O/W), stabilized by excess surfactant molecules. Such an emulsion is much harder to break than the original one. Rule: if increasing the dosage from 20 to 30 ppm does not improve the result – the problem is not in the quantity, but in the type of demulsifier.

When production parameters change (increased water cut, connection of new wells, seasonal temperature drop), the dosage needs to be reviewed. Regular bottle tests on fresh samples – quarterly or with every change in operating mode – ensure stable effectiveness.

Integration with Other Reagents

A demulsifier is just one element of a chemical program at the field. A typical oil treatment system includes 4–6 reagents, and their mutual compatibility is a critical factor.

Corrosion inhibitors. Film-forming inhibitors (imidazolines, quaternary ammonium compounds) are cationic surfactants and can interact with anionic components of the demulsifier, reducing the effectiveness of both reagents. Solution: spatial separation of injection points (inhibitor – at the wellhead, demulsifier – before the separator) or use of compatible formulas. More details on inhibitor types – in the article “Corrosion Inhibitors for Oil and Gas Pipelines”.

Scale inhibitors. Phosphonates and polycarboxylates are usually compatible with demulsifiers, but at high concentrations (> 50 ppm) they can affect interfacial tension. Compatibility is checked by bottle test with a combination of reagents.

H₂S scavengers. Triazine scavengers (MEA-triazine) interact minimally with demulsifiers. However, amine scavengers at high dosages (> 500 ppm) increase the pH of the aqueous phase, which can change emulsion stability and demulsifier effectiveness.

Paraffin inhibitors (ASPV). Paraffin depressants and dispersants are predominantly non-ionic surfactants, like most demulsifiers. Competition for adsorption at the interfacial surface is possible but usually not critical. General principles of chemical reagent compatibility are described in the glossary of industrial chemistry.

FAQ

What is the typical demulsifier dosage for oil production?

The working range is 5–50 ppm depending on oil density, water cut, and emulsion stability. For light oils (API > 35°), 5–15 ppm is usually sufficient. For heavy oils with high asphaltene content – 20–50 ppm. Optimal dosage is determined by bottle test and field trials.

What happens if a demulsifier is overdosed?

Overdosing is a common and expensive mistake. Excess surfactant stabilizes reverse emulsions (O/W or multiple W/O/W), which are significantly harder to separate than the original water-oil emulsion. If increasing the dosage does not improve the result, the type of demulsifier should be changed, not the concentration increased.

How often should a bottle test be performed?

Recommended frequency – quarterly under stable production parameters. In case of changing conditions (increased water cut, connection of new wells, seasonal temperature fluctuations, changes in formation pressure) – immediately. A bottle test on a fresh sample takes 2–3 hours and costs significantly less than working with an ineffective demulsifier.

Can one demulsifier be used for different fields?

No. Each field has a unique oil composition: different content of asphaltenes, resins, naphthenic acids, different formation water mineralization, and temperature regime. A demulsifier that works perfectly at one site may be ineffective at another. Selection is always individual – through bottle test and field trials. More details on chemical reagents for water systems – in the article “Reagents for Industrial Water Treatment”.

SVK Demulsifier Line

SVK develops and manufactures demulsifiers for oil treatment in various types of fields. Our laboratory performs a full selection cycle: bottle test on customer samples, dosage optimization, compatibility check with other reagents in the chemical program.

We provide technical support from laboratory testing to field trials and continuous optimization of the chemical regime at the site. Request a technical consultation – we will select a demulsifier for your production parameters.

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Read also:

• Corrosion Inhibitors for Oil and Gas Pipelines
• Glossary of Industrial Chemistry: 30 Terms
• Reagents for Industrial Water Treatment
• UA-REACH: What Manufacturers Need to Know