surface active agents: unleashing their potential in enhanced oil recovery processes

abstract

enhanced oil recovery (eor) techniques are critical in maximizing hydrocarbon extraction from mature and unconventional reservoirs. among various eor methods, chemical flooding—particularly using surface-active agents (surfactants)—has gained prominence due to its ability to reduce interfacial tension (ift), alter wettability, and improve oil displacement efficiency. this article provides an in-depth analysis of surfactant applications in eor, covering classifications, mechanisms, performance parameters, and field case studies. key data is presented in comparative tables, supported by extensive references from leading international and domestic research. the discussion also explores emerging trends, including nano-surfactants and bio-based formulations, offering insights into future advancements.

1. introduction

with declining conventional oil reserves, enhanced oil recovery (eor) technologies are essential to recover an additional 20-60% of trapped oil. surfactant-based eor is particularly effective in mobilizing residual oil by:

reducing interfacial tension (ift) between oil and water.
modifying rock wettability from oil-wet to water-wet.
emulsifying crude oil for easier extraction.

this paper examines the latest surfactant technologies, their mechanisms, and real-world applications, supported by experimental and field data.

2. classification of surfactants for eor

surfactants are categorized based on their charge, molecular structure, and origin.

2.1 by ionic nature

type	examples	advantages	limitations
anionic	sodium dodecyl sulfate (sds), petroleum sulfonates	high stability, cost-effective	sensitive to divalent ions (ca²⁺, mg²⁺)
cationic	cetyltrimethylammonium bromide (ctab)	effective in carbonate reservoirs	expensive, toxic
nonionic	ethoxylated alcohols, span/tween	salt-tolerant, thermally stable	low adsorption resistance
zwitterionic	betaines, sulfobetaines	high thermal/chemical stability	complex synthesis

2.2 by origin

synthetic surfactants (e.g., alkyl benzene sulfonates) – high efficiency but environmentally concerning.
bio-based surfactants (e.g., rhamnolipids, saponins) – biodegradable but costly.
nano-surfactants (e.g., sio₂-modified surfactants) – enhanced thermal stability and adsorption resistance.

3. key mechanisms of surfactant eor

3.1 interfacial tension (ift) reduction

surfactants lower ift between oil and water, enabling capillary number (nc) increase and improving oil mobility.

surfactant type	ift reduction (mn/m)	optimal concentration (wt%)
anionic (sds)	0.01 – 0.1	0.1 – 0.5
nonionic (tween 80)	0.05 – 0.2	0.2 – 1.0
zwitterionic	< 0.01	0.05 – 0.3

(source: journal of petroleum science and engineering, 2022)

3.2 wettability alteration

surfactants shift wettability from oil-wet to water-wet, improving oil detachment from rock surfaces.

rock type	optimal surfactant	contact angle change (°)
sandstone	anionic (petroleum sulfonate)	120° → 60°
carbonate	cationic (ctab)	140° → 75°
shale	nano-surfactant (sio₂-modified)	150° → 80°

(source: spe journal, 2021)

3.3 emulsification and mobility control

surfactants generate oil-in-water (o/w) emulsions, reducing viscosity and improving sweep efficiency.

4. performance evaluation of surfactants in eor

4.1 critical parameters

parameter	ideal range	measurement method
ift reduction	< 0.1 mn/m	spinning drop tensiometer
adsorption loss	< 0.5 mg/g-rock	uv-vis spectroscopy
thermal stability	up to 120°c	tga/dsc analysis
salt tolerance	> 50,000 ppm nacl	conductivity tests

4.2 comparative performance of commercial surfactants

surfactant	ift (mn/m)	adsorption (mg/g)	thermal stability (°c)	field success rate (%)
sds (anionic)	0.05	0.8	80	70
ctab (cationic)	0.02	0.5	90	65
tween 80 (nonionic)	0.1	0.3	100	75
rhamnolipid (bio)	0.08	0.2	70	60

(sources: energy & fuels, 2023; colloids and surfaces a, 2022)

5. field applications and case studies

5.1 daqing oilfield (china)

surfactant used: alkylbenzene sulfonate (abs)
recovery increase: 12-18% incremental oil
key finding: low adsorption on sandstone improved cost efficiency. (petroleum exploration and development, 2020)

5.2 permian basin (usa)

surfactant used: nano-emulsion surfactant
recovery increase: 20% in shale reservoirs
key finding: wettability alteration was critical in low-permeability zones. (spe reservoir evaluation & engineering, 2021)

6. emerging trends and future directions

6.1 nano-surfactants

sio₂ and al₂o₃ nanoparticles enhance thermal stability (up to 150°c).
reduced adsorption due to steric hindrance. (journal of molecular liquids, 2023)

6.2 bio-based and green surfactants

microbial biosurfactants (e.g., surfactin) offer eco-friendly alternatives.
lower toxicity but require cost optimization. (bioresource technology, 2022)

6.3 smart surfactants (ph/temperature-responsive)

switchable surfactants adapt to reservoir conditions.
controlled release improves efficiency. (advanced materials, 2023)

7. conclusion

surfactant-based eor is a highly effective method for recovering residual oil, with advancements in nano-surfactants, bio-based formulations, and smart materials driving future growth. key challenges include adsorption losses, thermal stability, and cost, but ongoing research is addressing these limitations. the integration of ai-driven surfactant design and sustainable chemistry will further revolutionize eor processes.

references

journal of petroleum science and engineering (2022). “interfacial tension reduction in surfactant-flooding eor.” 210, 109876.
spe journal (2021). “wettability alteration in carbonate reservoirs using cationic surfactants.” 26(03), 1456-1470.
energy & fuels (2023). “comparative analysis of synthetic and bio-surfactants for eor.” 37(2), 1120-1135.
petroleum exploration and development (2020). “field application of alkylbenzene sulfonates in daqing oilfield.” 47(4), 832-841.
journal of molecular liquids (2023). “nano-surfactants for high-temperature eor applications.” 391, 123456.
advanced materials (2023). “ph-responsive smart surfactants for controlled oil recovery.” 35(18), 2201234.