Betaines as EOR Surfactants: Which Grades Work, Can They Tolerate High Temperature and High Salinity, and Do They Survive Manufacturing?
Starting from the zwitterionic structure, this article maps the carboxybetaine, sulfobetaine and hydroxysultaine grades used in EOR, compares their tolerance limits under high temperature, high salinity, high calcium and magnesium, and wide pH, and separates the four stages a betaine must survive: synthesis, blending, field make-up and reservoir service.
Full Article
“Betaine” is not a single product but a broad class of surfactants with similar structures and markedly different performance. A structural advantage in temperature or salt tolerance does not establish that a specific product will perform under a specific reservoir condition.
Surfactant flooding is one of the important chemical EOR methods in oilfield enhanced-oil-recovery operations. Betaine-type zwitterionic surfactants have attracted increasing attention as EOR surfactants in recent years because their molecules carry both positive and negative charges.
The most common selection error is to see one betaine labeled “temperature- and salt-resistant” and conclude that all betaines suit high-temperature, high-salinity reservoirs. This article follows a structure–tolerance–manufacturing–selection sequence to clarify which betaines can be used, what environments they tolerate, and whether they can survive the production process.
01 Why Are Betaines Suitable as EOR Surfactants?
A betaine molecule contains both a cationic group and an anionic group: typically a quaternary ammonium center as the cation and a carboxylate or sulfonate group as the anion. The more accurate term is “zwitterionic surfactant”: the positive and negative charges coexist within the molecule, and the molecule is overall electrically neutral under neutral and most service conditions. Only under strongly acidic conditions does the carboxylate group of a carboxybetaine protonate, making the molecule cationic and no longer electrically neutral.
This structure offers four potential advantages in EOR, each with a clear boundary:
| Potential advantage | Mechanism | Boundary that must be stated |
|---|---|---|
| Salt and hard-water tolerance | Usually less sensitive than conventional anionic surfactants to Na⁺, Ca²⁺ and Mg²⁺, so it is less likely to precipitate or fail in high-salinity water | Behavior varies widely among structures. Salt can also change interfacial adsorption in ways related to the CMC, aggregation state and phase behavior; this is not a case of “higher salinity is always better” |
| Good interfacial activity | Appropriately structured betaines can reduce oil–water interfacial tension to very low levels; public studies report that hydroxysultaines at 40–100°C can reach the 10⁻³ mN/m range | Interfacial tension is a property of the surfactant–crude oil–formation water system. Quoting a single-product value without the specific crude and brine composition is not rigorous |
| Good blending potential | Can be combined with HPAM, other surfactants or alkali to form surfactant–polymer (SP) or alkali–surfactant–polymer (ASP) systems as the primary or auxiliary surfactant | Compatibility depends on salinity, temperature, concentration, polymer type and molecular weight, and must be verified for the specific formulation |
| Potentially favorable adsorption | On positively charged carbonate surfaces, betaine adsorption is usually lower than that of anionic surfactants; on negatively charged sandstone, adsorption is also lower than that of cationic surfactants | Adsorption must be measured on the target rock; it cannot be inferred from the chemical class |
02 Which Betaines Are Commonly Used in Oilfield EOR Surfactants?
Betaine nomenclature is not fully standardized across industry and literature, and two classification dimensions are often mixed: classification by anionic group (carboxylate, sulfonate, etc.) or by linker structure (alkyl directly attached to the quaternary ammonium, amidopropyl linkage, etc.). A more rigorous approach uses two levels: first the anionic group, then the linker and hydrophobic-chain structure.
Table 1: Carboxybetaines
The anionic group is carboxylate (—COO⁻). The synthesis is mature and raw materials are readily available, making this the most widely used class.
| Subclass | Representative grades and codes | Structural feature | EOR positioning and boundary |
|---|---|---|---|
| Alkyl dimethyl carboxybetaines | Octyl through behenyl series: OB-8, DB-10, LAB (BS-12), CAB, MB-14, CB-16, STAB-18, OB, BB | Hydrophobic chain attached directly to the quaternary ammonium group | Mature manufacturing and relatively low cost; suited to low-to-moderate temperature and conventional salinity, while long-chain grades have lower water solubility |
| Alkyl amidopropyl carboxybetaines | CAPB, LAPB (LAB-35), PAPB, SAPB, OAPB, EAPB, BAPB | Hydrophobic chain connected to the quaternary ammonium group through an amide bond and a propyl bridge | Good foaming and interfacial performance; the amide bond carries a hydrolysis risk under long-term high temperature combined with strong acid or alkali |
Table 2: Sulfobetaines
The anionic group is sulfonate (—SO₃⁻), and this class is a focus of high-temperature, high-salinity EOR research. The three subclasses are defined by whether the propyl bridge carries a hydroxyl group and whether the hydrophobic chain is attached through an amide or directly. A few grades combine both features and are classified by the naming backbone.
| Subclass | Representative grades and codes | Structural feature | EOR positioning and boundary |
|---|---|---|---|
| Alkyl dimethyl sulfopropyl betaines | SB3-8, SB3-10, SB3-12 (DSB), SB3-14, SB3-16, SB3-18 | Sulfonate connected to the quaternary ammonium group through a propyl bridge, with no amide bond | Good temperature and salt-tolerance potential; solubility decreases as the chain lengthens, so grades must be screened by chain length |
| Hydroxysultaines | CHSB, LAHS (LHSB), HSB-12 (DHSB), HSB-16 (MBS16), HSB1214, HSB1618, OHSB, EHSB | A hydroxyl group is introduced on the propyl bridge, improving water solubility | A focus of high-temperature, high-salinity research; the amide-free HSB1214 and HSB1618 receive particular attention for long-term stability |
| Amidosulfobetaines | CASB (CAPS) | Hydrophobic chain attached through an amide bond | Combines sulfonate stability with an amide structure; hydrolysis still requires evaluation under long-term high-temperature and acidic conditions |
Table 3: Other Structures and Modified Grades
| Type | Structural feature | Research and selection notes |
|---|---|---|
| Sulfate-ester amphoteric surfactants | Anionic group is —OSO₃⁻ | Hydrolytic stability is generally weaker than that of sulfonates, EOR studies are scarce, and whether these count as “betaines” varies in the literature |
| Gemini betaines | Two betaine headgroups connected by a linker | Higher interfacial activity and a recent research focus, but mature products and systematic evaluations remain limited |
| Aryl sulfobetaines | An aromatic ring is introduced into the hydrophobic chain | One report states that interfacial activity is retained at 130°C, but aging duration and performance retention are not disclosed; cite with caution |
| Polyether-modified betaines | EO/PO segments are incorporated | Used to adjust hydrophilicity and interfacial behavior; performance varies with the segment structure |
| Long-chain (C16–C22) betaines | The hydrophobic chain is extended | There is no simple rule that a longer chain gives lower interfacial tension; optimization must consider salinity, temperature and crude-oil composition together |
03 What Environments Can These Betaines Tolerate?
The following ranges are commonly reported in public research and product literature. Actual performance varies with manufacturer, structure and purity, and must be verified before application through laboratory aging, interfacial-tension and salt-precipitation tests.
Temperature
| Type | Reported performance in public studies | How to interpret it |
|---|---|---|
| Sulfobetaines and hydroxysultaines | Generally the best temperature tolerance. In one public study, at 95°C and total salinity of about 5.76×10⁴ mg/L, a sulfobetaine system aged for 150 days was clearly more stable long-term than the sulfate and carboxylate systems in the same study | This is a result for a specific system. A foaming study at 130°C, 30 MPa and 2.5×10⁵ mg/L supports foam flooding, not the low interfacial tension required for oil displacement |
| Carboxybetaines | Cannot simply be described as “suitable only for low-to-moderate temperatures.” The thermal decomposition temperature of the pure alkyl-type molecule is not low, and some long-chain grades have been studied at higher temperatures | The limitation in demanding reservoirs comes more from changes in solubility and interfacial performance at high salinity and high calcium/magnesium levels; long-term stability under extreme high temperature and salinity is generally inferior to that of purpose-designed sulfobetaines, and each grade still requires evaluation |
| Amide-based betaines (carboxy or sulfo types) | Quite stable at neutral pH and conventional temperature; CAPB and similar grades can be commodity personal-care products | The risk arises under long-term conditions combining high temperature with strong acid or alkali. HSB1214 and HSB1618 were relatively stable at 110°C, whereas amide-containing LHSB and EHSB degraded markedly faster, especially under acidic conditions; above 130°C, even amide-free structures gradually decompose as aging continues |
Salinity and Divalent Ions
In oilfields, “salt tolerance” cannot be judged by NaCl alone; Ca²⁺ and Mg²⁺ are often the more severe test.
| Type | Reported performance in public studies | How to interpret it |
|---|---|---|
| Sulfobetaines and hydroxysultaines | Generally outstanding salt tolerance. One report gives salt tolerance of 2.0–2.7×10⁵ mg/L, with tolerance to Ca²⁺ and Mg²⁺ of about 1.9×10⁴ mg/L and 2.3×10⁴ mg/L, respectively. Another study verified interfacial activity at 90°C in simulated formation water with total salinity of about 1.15×10⁵ mg/L, 7040 mg/L Ca²⁺ and 614 mg/L Mg²⁺ | These are results for specific products and systems. Salt tolerance varies greatly among hydroxysultaines with different chain lengths and structures and must not be treated as a class-wide specification |
| Carboxybetaines | Good hard-water tolerance | Solubility or performance may decline at very high calcium and magnesium concentrations; each grade must be screened |
| Amide-based betaines | Salt tolerance is usually good | When high salinity coincides with high temperature, the amide hydrolysis risk must be reassessed |
pH Conditions
Two concepts must be distinguished: the pH range over which the charge state is stable, and the pH range over which the chemical structure remains stable long-term.
| Type | Charge state and stability | Application notes |
|---|---|---|
| Sulfobetaines and hydroxysultaines | The sulfonate group is strongly acidic, so the zwitterionic character is maintained over a wide range, commonly cited as about pH 2–12, without marked charge reversal or precipitation as pH changes | Suitable for alkaline ASP systems and also for mildly acidic environments. However, amide-containing grades can still hydrolyze under hot acidic conditions; not every sulfobetaine resists chemical degradation at pH 2–12, high temperature and long exposure |
| Carboxybetaines | Discuss the protonation equilibrium of the carboxyl group rather than applying an amino-acid-style “isoelectric point.” At pH above the carboxyl pKa (generally around pH 2–4), the molecule is zwitterionic; below the pKa, the carboxylate protonates and the molecule becomes overall cationic | The charge change affects interfacial tension, adsorption and solubility; in specific systems, acid precipitation may occur under strongly acidic conditions |
| Amide-based betaines | Relatively stable under neutral to weakly alkaline conditions | Strong acid or strong alkali combined with high temperature accelerates amide hydrolysis, so long-term service at extreme pH is unsuitable |
Other factors: under high temperature and aerobic conditions, surfactants may undergo oxidative degradation. Betaines generally have good chemical stability, but long-term aging evaluations should still account for dissolved oxygen, oxidants and metal ions.
04 What Conditions Are Encountered During EOR Surfactant Manufacturing?
Two easily confused questions must be separated: how the betaine raw material itself is synthesized, and what conditions are encountered when a betaine is blended into an EOR surfactant product. The user’s concern about “manufacturing the EOR surfactant” mainly refers to the latter, but synthesis conditions also reveal the molecule’s tolerance boundary.
| Stage | Typical conditions | Key challenge to the betaine |
|---|---|---|
| Betaine synthesis | Carboxybetaines are commonly made by quaternization of a tertiary amine with sodium chloroacetate, typically at about pH 7–9 with heating. Sulfo- and hydroxysultaines can be made by reacting a tertiary amine with 1,3-propane sultone or with sodium 3-chloro-2-hydroxypropanesulfonate under alkaline conditions; a laboratory two-step process runs at about 80°C for several to tens of hours. Amide-based betaines are made by first preparing an amidopropyl dimethylamine intermediate and then quaternizing it | Short periods of high temperature and alkalinity during reaction; feed rate and temperature must be controlled to suppress side reactions |
| Blending the EOR surfactant product | Mixing, stirring, dissolution and homogenization from room temperature to several tens of degrees Celsius, usually at neutral to weakly alkaline pH and for a short time; products are mostly aqueous solutions with a solids content commonly of 30%–50% | Most betaines are not damaged by these conditions; storage should avoid prolonged high temperature and direct sunlight and maintain a suitable pH |
| Field make-up and injection | Fluids are prepared directly with oilfield reinjection water or formation water, encountering high salinity and Ca²⁺/Mg²⁺, pump shear, and contact with pipelines and residual biocide, scale inhibitor or corrosion inhibitor | Focus on turbidity, precipitation, phase separation and changes in interfacial tension, as well as the effects of shear and compatibility on performance |
| Reservoir service | Tens to 130°C, salinity from tens of thousands to hundreds of thousands of mg/L, pressures of tens of MPa, and residence times measured in months or even years | The real test: thermal stability, salt tolerance, adsorption loss and long-term performance retention |
The real question is therefore not “how many degrees can this betaine withstand,” but: under the target reservoir’s temperature, salinity, calcium and magnesium content, pH, crude oil and rock conditions, how much active component remains after 1, 3, 7, 30, 60 and 90 days of aging? Can the interfacial tension still meet the target? A supplier’s “temperature resistance” figure should also be questioned for its evaluation basis: is it a short-term thermal decomposition temperature or a performance-retention temperature after long-term aging? In oilfield usage, the meaningful temperature rating is the latter.
05 Selection Guidance: Matching Betaines to Reservoir Conditions
Screen by reservoir condition (this is a screening priority, not a performance ranking):
| Reservoir or operating condition | Priority screening direction | Rationale and boundary |
|---|---|---|
| High temperature, high salinity, high calcium and magnesium | Sulfobetaines and hydroxysultaines (long-chain SB3 and HSB grades) | The best structural potential, but variation within the class is large and each grade must be evaluated individually |
| Extreme high temperature of 110–130°C and ultra-high salinity | Purpose-designed hydroxysultaines (amide-free grades such as HSB1214 and HSB1618) | Supported by public aging data at 110–130°C; still requires re-verification with the target water and crude oil |
| Low-to-moderate temperature and conventional salinity | Carboxybetaines and amide-based carboxybetaines (BS-12, CAPB, etc.) | Mature manufacturing, good foaming and interfacial performance, and relatively manageable cost |
| Alkaline EOR systems (e.g., ASP) | Sulfobetaines | Zwitterionic character is maintained over a wide pH range, and compatibility with alkali is usually better |
| Carbonate reservoirs | Betaines as a class are worth testing first | Carbonate surfaces are positively charged and betaine adsorption is usually lower; sandstone reservoirs require measured adsorption data |
| Cost-sensitive projects | Carboxybetaines | Raw materials are readily available, but cost also depends on the synthetic route, scale and purity; specific quotations are required |
Three points require emphasis:
- Screening priority, not a performance ranking
The table above is a screening order, not a performance ranking. Even within hydroxysultaines, amide-containing and amide-free structures differ markedly in temperature tolerance, so the final answer must come from testing.
- Temperature is only one dimension
A complete selection also considers formation lithology (sandstone or carbonate), crude-oil properties, injection-water compatibility and the target interfacial tension; selection cannot be based on temperature alone.
- A recommended direction is not a ready-to-use product
Every betaine product must be evaluated in the laboratory and in core-flood tests under the target reservoir conditions.
06 Conclusion
Betaine-type zwitterionic surfactants are genuinely promising EOR surfactants, especially sulfobetaines and hydroxysultaines, which show good research prospects for high-temperature, high-salinity reservoirs and alkali-free surfactant–polymer (SP) flooding.
In one reported core-flood study, under specific experimental conditions, a 0.3% hydroxysultaine (MBS16) and 0.15% HPAM system, starting from a water-flood recovery of 48.6%, increased recovery by 16.5 percentage points, which was 9.4 percentage points more than the polymer-only system. Note that this is a core-scale laboratory result. From molecular evaluation and formulation evaluation to core flooding, physical simulation, field pilots and commercial application, there is a long validation chain, and the result cannot be extrapolated directly to field performance.
At the same time, beware of the simple equation “betaine = high-temperature and high-salinity resistant.” CAPB, carboxybetaines, sulfobetaines and hydroxysultaines can behave completely differently under high temperature, high salinity, calcium and magnesium ions, acid or alkali, and long-term aging. Even within one class, different carbon chains and the presence or absence of an amide bond can change performance by orders of magnitude.
eMAI New Materials (eMaterial) focuses on products and technical services for oilfield chemicals and EOR surfactants. The data in this article are drawn from publicly published research papers, patents and industrial application reports; actual product performance is subject to test and evaluation results.