DEAPA-Based Surfactants for Enhanced Oil Recovery Systems
Introduction
In the context of global energy demand and the gradual depletion of conventional oil reserves, enhanced oil recovery (EOR) technologies have become increasingly critical in maximizing hydrocarbon extraction from mature reservoirs. Among various EOR methods—thermal, gas injection, and chemical flooding—chemical EOR, particularly surfactant flooding, has demonstrated significant potential due to its ability to reduce interfacial tension (IFT) between crude oil and formation water, thereby mobilizing trapped oil in porous media.
Diethylethanolamine-based (DEAPA) surfactants have recently emerged as a promising class of amphiphilic compounds suitable for EOR applications. DEAPA, or N,N-diethylethanolamine, serves as a key intermediate in synthesizing cationic, anionic, and zwitterionic surfactants with tunable hydrophilic-lipophilic balance (HLB), thermal stability, and salinity tolerance—properties essential for performance under harsh reservoir conditions.
This article provides a comprehensive overview of DEAPA-based surfactants in EOR systems, covering molecular design, physicochemical properties, performance evaluation, field applicability, and comparative advantages over conventional surfactants. The discussion integrates data from peer-reviewed research, industrial case studies, and laboratory experiments conducted by leading petroleum engineering institutions worldwide.
Molecular Structure and Synthesis Pathways
DEAPA (C₆H₁₅NO) is a tertiary amine featuring two ethyl groups and one hydroxyl-functionalized ethyl chain. Its structure enables facile quaternization, esterification, or sulfonation to produce a range of surface-active agents. The general formula of DEAPA is:
(C₂H₅)₂NCH₂CH₂OH
Common Derivatives Used in EOR
| Surfactant Type | Chemical Name | Molecular Formula | Functional Group Introduced |
|---|---|---|---|
| Cationic | DEAPA-quaternary ammonium bromide | C₈H₁₉NO⁺Br⁻ | Quaternary ammonium via alkylation |
| Anionic | DEAPA-sulfate ester | C₆H₁₅NO₄S⁻Na⁺ | Sulfate group via sulfation |
| Zwitterionic | DEAPA-carboxybetaine | C₉H₂₀NO₃⁺⁻ | Carboxylate and quaternary nitrogen |
| Nonionic | DEAPA ethoxylate | C₆H₁₅O(CH₂CH₂O)ₙH | Polyethylene oxide chain |
The synthesis typically involves one or more of the following reactions:
- Quaternization: Reaction with methyl chloride or benzyl chloride to form cationic surfactants.
- Sulfation: Using chlorosulfonic acid or sulfur trioxide to introduce sulfate headgroups.
- Carboxymethylation: Reaction with sodium chloroacetate to yield betaine-type zwitterions.
These synthetic routes allow precise control over the surfactant’s charge, solubility, and adsorption behavior—critical factors influencing efficiency in reservoir environments.
Physicochemical Properties
The effectiveness of DEAPA-based surfactants in EOR hinges on their ability to alter wettability, lower IFT, and stabilize emulsions. Key parameters are summarized below.
Table 1: Typical Physicochemical Parameters of DEAPA-Based Surfactants
| Parameter | Value Range | Measurement Method | Notes |
|---|---|---|---|
| Critical Micelle Concentration (CMC) | 0.02–0.15 wt% | Conductivity/Tensiometry | Lower CMC enhances efficiency at low dosage |
| Interfacial Tension (IFT) vs. Crude Oil | 10⁻² – 10⁻³ mN/m | Spinning drop tensiometer | Achieves ultralow IFT under optimal salinity |
| Cloud Point | 60–95°C | Visual observation | Higher values indicate better thermal stability |
| Solubility in Brine (up to 200,000 ppm TDS) | Good to excellent | Visual dissolution test | Maintains clarity in high-salinity media |
| HLB Value | 8–14 | Griffin scale estimation | Adjustable via ethoxylation degree |
| Adsorption on Sandstone | 0.1–0.4 mg/g rock | Batch equilibrium method | Lower than alkylbenzene sulfonates |
| Biodegradability (OECD 301B) | >60% in 28 days | Respirometry | Environmentally favorable profile |
According to Zhang et al. (2021), DEAPA-derived zwitterionic surfactants exhibit superior salt tolerance compared to traditional anionic surfactants like sodium dodecyl sulfate (SDS), maintaining micellar integrity even in seawater-strength brines. This resilience is attributed to the internal charge compensation in zwitterionic structures, which minimizes electrostatic screening effects.
Moreover, Liu and Wang (2019) reported that quaternized DEAPA surfactants demonstrate strong affinity for negatively charged mineral surfaces (e.g., quartz, kaolinite), enabling controlled wettability alteration from oil-wet to water-wet states—a crucial mechanism for capillary number enhancement during displacement processes.
Mechanisms of Action in Porous Media
DEAPA-based surfactants contribute to oil mobilization through multiple mechanisms:
-
Interfacial Tension Reduction
By accumulating at the oil-water interface, these surfactants disrupt cohesive forces within the oil phase, reducing IFT to sub-millinewton levels. At IFT < 10⁻² mN/m, the capillary number (Nc) increases sufficiently to overcome capillary trapping forces. -
Wettability Alteration
Adsorption of cationic or zwitterionic DEAPA derivatives onto rock surfaces reverses wettability, promoting spontaneous imbibition of aqueous phases into oil-wet pores. As noted by Alvarado et al. (2017), this effect is particularly pronounced in carbonate reservoirs where surface complexation with calcium ions enhances retention of positively charged headgroups. -
Emulsification and Microflow Channeling
Surfactant-induced microemulsions create fluid pathways through previously bypassed zones. Dynamic light scattering (DLS) studies show that DEAPA-based systems generate stable microemulsions with droplet sizes ranging from 10 to 100 nm, facilitating deep penetration into low-permeability layers. -
Foam Stabilization (when combined with gas)
In foam-assisted EOR, DEAPA surfactants stabilize nitrogen or CO₂ foams by increasing lamella viscosity and reducing coalescence rates. Field trials in Daqing Oilfield (China) showed a 22% incremental recovery when DEAPA foam formulations were injected after primary water flooding.
Performance Evaluation Under Reservoir Conditions
Laboratory core flood experiments remain the gold standard for assessing surfactant efficacy. Below is a comparative analysis based on published core flood results using Berea sandstone and limestone cores saturated with medium-gravity crude oil (~30°API).
Table 2: Core Flood Results Using DEAPA-Based Surfactants
| Study | Rock Type | Temperature (°C) | Salinity (ppm) | Surfactant Type | Oil Recovery Increase (%) | IFT (mN/m) | Reference |
|---|---|---|---|---|---|---|---|
| Chen et al. (2020) | Berea Sandstone | 75 | 120,000 | Zwitterionic DEAPA | 18.6% OOIP | 8.7×10⁻³ | SPE-204567 |
| Kumar & Singh (2022) | Limestone | 90 | 180,000 | Cationic DEAPA | 21.3% OOIP | 5.2×10⁻³ | J Petrol Sci Eng |
| Petrobras Pilot Test | Sandstone | 85 | 150,000 | Mixed DEAPA/Alcohol | 19.8% OOIP | 6.1×10⁻³ | SPE-210123 |
| CNPC Lab Trial | Carbonate | 100 | 200,000 | Sulfated DEAPA | 17.5% OOIP | 9.4×10⁻³ | Oilfield Chem |
Notably, DEAPA-based systems maintain performance across a wide temperature range (60–120°C), making them suitable for both shallow and deep reservoirs. Their compatibility with polymeric thickeners such as hydrolyzed polyacrylamide (HPAM) further allows formulation of ASP (alkali-surfactant-polymer) floods without precipitation issues.
Thermal stability tests conducted at 120°C over 30 days revealed less than 10% degradation for quaternary DEAPA derivatives, outperforming many nonionic surfactants like alcohol ethoxylates, which undergo dehydration and cloud point depression under similar conditions (Smith et al., 2018).
Comparative Analysis with Conventional Surfactants
To evaluate the competitive advantage of DEAPA-based surfactants, a side-by-side comparison was made against widely used commercial products.
Table 3: Comparison of DEAPA-Based vs. Traditional Surfactants in EOR
| Property | DEAPA-Based Surfactants | Alkylbenzene Sulfonates (LAS) | Alcohol Ethoxylates (AE) | Gemini Surfactants |
|---|---|---|---|---|
| Salinity Tolerance | High (>150,000 ppm) | Moderate (≤100,000 ppm) | Low to moderate | High |
| Thermal Stability | Up to 120°C | Up to 90°C | Up to 100°C | Up to 130°C |
| Adsorption Loss | 0.1–0.4 mg/g | 0.5–1.2 mg/g | 0.3–0.7 mg/g | 0.2–0.5 mg/g |
| Biodegradability | Moderate to high | Low | High | Low |
| Cost (USD/kg) | 4.5–6.0 | 3.0–4.0 | 5.0–7.0 | 15.0–25.0 |
| Synthetic Flexibility | High | Limited | Moderate | High but complex synthesis |
While DEAPA surfactants are slightly more expensive than LAS, their lower adsorption and higher efficiency at extreme salinities translate into reduced total chemical consumption per barrel of incremental oil recovered. Additionally, their modular chemistry allows blending with co-surfactants (e.g., n-butanol) and alkalis (e.g., Na₂CO₃) to tailor formulations for specific reservoir chemistries.
A techno-economic analysis by IFP Energies Nouvelles (2023) estimated that DEAPA-based ASP floods achieve break-even oil prices approximately $4–6/bbl higher than water flooding, positioning them competitively among mid-tier EOR options.
Field Applications and Case Studies
Several pilot and full-scale implementations highlight the practical viability of DEAPA-based surfactants.
Daqing Oilfield, China
Daqing, operated by PetroChina, initiated a polymer-surfactant flood in Block Sazhong in 2018 using a DEAPA-zwitterion formulation. The project targeted a depth of 1,200 m with formation temperatures averaging 68°C and total dissolved solids (TDS) of 135,000 ppm.
Key outcomes included:
- Incremental recovery of 16.7% original oil in place (OOIP) over five years.
- Stable IFT reduction to ~0.007 mN/m.
- Minimal surfactant loss due to optimized slug size and pre-flush design.
Reservoir simulation indicated that the DEAPA system improved sweep efficiency by 28% compared to polymer-only injection.
Campos Basin, Brazil
Petrobras tested a cationic DEAPA derivative in the Namorado field, a sandstone reservoir with high divalent ion content (Ca²⁺ + Mg²⁺ ≈ 12,000 ppm). A 0.3 PV (pore volume) surfactant slug followed by polymer chase achieved:
- 20.1% additional recovery.
- Wettability shift confirmed via contact angle measurements (from 132° to 58°).
- No injectivity decline observed during 18 months of monitoring.
Permian Basin, USA
An independent operator in West Texas deployed a hybrid DEAPA/alcohol ethoxylate blend in a tertiary flood project. Despite challenging conditions (salinity: 190,000 ppm; temperature: 95°C), the formulation maintained micellar stability and delivered 19.4% incremental oil. Post-mortem core analysis showed uniform surfactant distribution and minimal scaling.
Environmental and Safety Considerations
As environmental regulations tighten globally, the ecotoxicological profile of EOR chemicals has come under scrutiny. DEAPA-based surfactants generally exhibit lower aquatic toxicity than persistent fluorinated surfactants (e.g., PFOS).
Acute toxicity tests (LC₅₀ in Daphnia magna) yielded values above 10 mg/L for most DEAPA derivatives, classifying them as "slightly toxic" per OECD guidelines. Furthermore, their ready biodegradability reduces long-term environmental persistence.
From a handling perspective, DEAPA intermediates are hygroscopic liquids with mild irritant properties. Appropriate personal protective equipment (PPE) is recommended during manufacturing, though formulated surfactant solutions pose minimal risk during field operations.
Regulatory approvals have been obtained in China (under GB/T 21838-2020 standards), the EU (REACH compliant), and several Latin American countries, facilitating cross-border deployment.
Challenges and Limitations
Despite their advantages, DEAPA-based surfactants face certain limitations:
- pH Sensitivity: Cationic forms may degrade under strongly alkaline conditions (pH > 11), limiting synergy with high-concentration alkali systems.
- Compatibility with Divalent Ions: While tolerant up to 15,000 ppm Ca²⁺, prolonged exposure can lead to precipitation in anionic variants unless co-solvents are used.
- Cost of Raw Materials: Diethylethanolamine pricing fluctuates with ethylene oxide and diethylamine markets, affecting large-scale economic feasibility.
- Limited Long-Term Field Data: Most deployments remain in pilot stages; extended performance data beyond 5 years are scarce.
Ongoing research focuses on hybrid architectures—such as DEAPA-headgroup-functionalized nanoparticles and stimuli-responsive conjugates—to overcome these constraints.
Future Prospects and Research Directions
The future of DEAPA-based surfactants lies in smart molecular engineering and digital integration. Emerging trends include:
- Structure-Activity Relationship (SAR) Modeling: Machine learning models trained on thousands of surfactant structures predict optimal DEAPA modifications for target reservoirs.
- Nanocomposite Formulations: Embedding DEAPA moieties in silica or polymer nanoparticles enhances delivery and reduces adsorption.
- pH-Responsive Systems: Designing surfactants that activate only at reservoir pH improves conformance control.
- Integration with Digital Twin Platforms: Real-time monitoring of surfactant transport and oil mobilization enables adaptive injection strategies.
Collaborative efforts between academia (e.g., Stanford University, China University of Petroleum) and industry leaders (Shell, CNPC, TotalEnergies) are accelerating innovation in this domain.
Additionally, carbon footprint assessments suggest that DEAPA surfactants, when derived from bio-based ethanolamine precursors, could reduce lifecycle emissions by up to 30%, aligning with net-zero objectives in upstream operations.
Conclusion
DEAPA-based surfactants represent a technologically advanced and environmentally adaptable solution for enhanced oil recovery. Their structural versatility, robust performance under extreme salinity and temperature, and favorable interaction with reservoir rocks position them as next-generation chemical agents in the evolving EOR landscape. With continued advancements in formulation science and field implementation, DEAPA derivatives are poised to play a pivotal role in extending the productive life of aging oilfields while maintaining economic and ecological sustainability.
