Principle of Enhanced Oil Recovery
Chapter 6 Surfactant Flooding
SUN Yongpeng
（孙永鹏）
School of Petroleum Engineering
1
Oil distribution in ideal micromodel
Oil distribution before Oil distribution after
water flooding water flooding
Capillary Number Correlation
The capillary number (Ca) represents the relative effect of viscous forces versus surface tension
acting across an interface between a liquid and a gas, or between two immiscible liquids.
Outline
1. Surfactants
2. Concepts and types of surfactant flooding
3. Surfactants used in surfactant flooding
4. Active water flooding
5. Micelle solution flooding
6. Screening Criteria of Surfactant Flooding for
Oilfield
7. Problems in Surfactant Flooding
Section 1. Surfactants
Anionic: sodium dodecyl sulfate (C12H25SO4-Na+).
Cationic: dodecyltrimethylammonium bromide.
Zwitterionic: 3-dimethyldodecylamine propane sulfonate
Section 1. Surfactants
Representative Anionic surfactants
Sodium dodecyl sulfate
Texas No. 1 sulfonate
Commercial petroleum sulfonates
Section 2. Concepts and types of surfactant
flooding
Type Component State of Surfactant Feature
active water the simplest surfactant
surfactant single surfactant
flooding flooding
micellar solution surfactant, single surfactant and low concentration
flooding alcohol, salt micelle surfactant
Foam water, gas, foam agent single surfactant and low concentration
flooding (polymer, salt, alcohol) micelle surfactant
Microemulsion water, oil, surfactant, high concentration
micelle
flooding salt, cosurfactant system
Section 3. Surfactants used for surfactant flooding
1. Sulfonate surfactant
Alkyl sulfonate
Synthesis sulfonate is another important sulfonate
surfactant. It can be synthesized from
Petroleum sulfonate
corresponding hydrocarbons (such as alkane,
alkylbenzene, alkyl toluene alkylxylene) by
corresponding methods. Alkyl sulfonate, alkylaryl
sulfonates, naphthalene sulfonate belong to this Alkylaryl sulfonate
type sulfonate.
Alkyl sulfonate
2. Carboxylate surfactant
Tallate
Petroleum carboxylate Peregal surfactant
3. Nonionic surfactant OP surfactant
Tween surfactant
4. Nonionic-anionic amphoteric surfactant
Good salt tolerance, good high value metal
ions tolerance
Section 4. Active water flooding
2. The EOR principle of active water
（1）mechanism of low interfacial tension
– Surfactant adsorption at the interface of water and
oil can decrease the interfacial tension;
– Decrease the rock’s adhesion to the oil ;
• Increase the capillary number;
• Decrease the capillary resistance of the lipophilic
W 1 cos
Reservoir.
（2） Mechanism of wettability reversal
The natural surfactant The surfactant
in the oil in the injected water
oil
water
water oil
Rock surface Interject active water Rock surface
Wettability reversal because of the surfactant
Hydrophilic surfactant →reverse the hydrophobic interface to
hydrophilic interface →the oil’s wetting angle to the formation
increases →adhesive work decreases →displacement efficiency
increases
（3） Mechanism of emulsification
• The HLB of the surfactant used in displacement is between 7 to
18, and stable oil in water emulsion can be formed.
• The oil in the emulsion cannot adhere to the formation again, this
can increase the displacement efficiency.
• Emulsified oil form superimposed Jamin effect in the high
permeability layer. So the water can transport evenly in the
formation, and the sweep efficiency is increased.
Surfactant→ form oil in water emulsion →the oil in the emulsion
cannot adhere to the formation again→ the displacement efficiency
increases；Jamin effection in the high permeability layer→ sweep
efficiency is increased.
（4）Mechanism of improving the surface charge density
oil
sand
sand
oil
sand
The adsorption of anionic surfactant increases the surface charge
density, the electrostatic repulsion between oil droplet and the rock
becomes higher. The oil droplet can be brought out easily and the
displacement efficiency increases.
（5）Mechanism of coalescence and forming oil zone
Disperse oil
Oil zone
Active water
Displaced oil forming oil zone
Disperse oil
Active water Oil zone
Expanding of the oil zone during moving award
The surfactant concentration of the active water is
low, the adsorption may also bring certain
consumption and cause lose of surfactant. So we
must increase the dosage and the slug to achieve
better effects.
Using sacrificial agent can reduce the adsorption of
surfactant. Sacrificial agent is the cheap agent
whose depletion can reduce other agent’s depletion
in return.
Available sacrificial agent :
1) Alkaline matters;
2) Polycarboxylic acid and its salt;
3) Oligomer and polymer;
4) Lignosulfonate.
Section 5. Micelles solution flooding
Formation of micelles Various models of micelle structures
Section 5. Micelle solution flooding
Preparation of micelle solution
•Surfactant
•Alcohol (isopropanol, normal butanol) or salt (sodium chloride)
The additive such as alcohol and salt can adjust the polarity of oil
and water, and can fully balance the lipophilicity and
hydrophilicity of the surfactant, then the surfactant can furthest
adsorb at the interface, which can cause ultra-low interfacial
tension (<10-2 mN•m-1), and this enhances the low interfacial
tension mechanism of micelle solution.
3. The EOR mechanism of micelle solution flooding
Possesses all the mechanisms of active
flooding.
Micelle solubilization of oil mechanism.
Because of the high concentration of surfactant
and the existence of alcohol and salt, the
interfacial tension is ultra-low, which
enhances the low interfacial tension
mechanism.
W(petroleum sulfonate)*10-2
A classical relation curve of the interfacial tension of oil and water
versus mass fraction of surfactant
Conditions: surfactant (petroleum sulfonate); alcohol: isobutanol; oil phase: dodecane;
Water phase: TR10-410+IBA+NaCl=0.015; m(TR10-410)/m(IBA)=5/3
Active water Micellar solution Microemulsion
flooding flooding flooding
The cost becomes higher.
The mechanism becomes more complicated.
The range of enhanced recovery becomes greater.
Mechanism of active water flooding
Increasing
Low IFT surface charge
density
Surfactant
Wetting concentration is
conversion less than critical
micelle
concentration
Coalescence into
oil bank
Emulsification
1 Low interfacial tension is base and effect the displacement efficiency.
2 Emulsion entrainment can enhance displacement efficiency. Emulsion
entrapment can enhance sweep efficiency.
3 The absorption of surfactant could make the oil wet surface reserved into
water wet surface and affect the displacement efficiency.
Micelle solution flooding
Mechanism of
active water
flooding
Intensify low Solubilization of oil
interfacial tension capacity
Component in system: Micelle appears because of the
Surfactant, salt, alcohol high surfactant concentration.
Section 6 Screening Criteria of Surfactant Flooding
for Oilfield
Density/(g•cm-3) <0.934
Crude oil Viscosity/(mPa•s) <35
component High light dydrocarbon content
Mineralization/(mg•L-1)
<4×104
Water Ca2+, Mg2+ content
<500
/(mg•L-1)
Oil saturation/Vp >0.35
Thickness/m Unlimited
Permeability×103/μm2 >10
Reservior
Burial depth/m <2740
Temperature/℃ <93
lithology Sandstone
Section 7 Problems in Surfactant Flooding
Surfactant Cause loss of surfactant
retention
Form of retention
(1)absorption；
(2)dissolved in oil and water；
(3)anionic surfactant would react with
multivalence metal ion to produce sediment；
Emulsification （4）incompatible with polymer
to produce flocculation
Methods
Fluid mobility (1)use sacrificial agent;
(2)prerinse the formation by water；
control (3)choose surfactant with strong salt tolerance；
Section 7 Problems in Surfactant Flooding
Surfactant
Emulsion break problem
retention of produced fluid
Methods
(1)electric Demulsification
Emulsification (high frequency alternating
current )
(2) demulsifier
Fluid mobility
control
Section 7 Problems in Surfactant Flooding
Surfactant
retention
Surfactant is easy
Emulsification fingerring along high
permeability layer
Fluid mobility (1)profile control
control (2)Use mobility control agent；
（polymer slug）
