A Review of Gemini Surfactants: Potential Application in Enhanced Oil Recovery

Gemini surfactants are a group of novel surfactants with more than one hydrophilic head group and hydrophobic tail group linked by a spacer at or near the head groups. Unique properties of gemini surfactants, such as low critical micelle concentration, good water solubility, unusual micelle structures and aggregation behavior, high efficiency in reducing oil/water interfacial tension, and interesting rheological properties have attracted the attention of academic researchers and field experts. Rheological characterization and determination of the interfacial tension are two of the most important screening techniques for the evaluation and selection of chemicals for enhanced oil recovery (EOR). This review deals with rheology, wettability alteration, adsorption and interfacial properties of gemini surfactants and various factors affecting their performance. The review highlights the current research activities on the application of gemini surfactants in EOR.     

Salt-Induced Constructions of Gemini-like Surfactants at the Interface and Their Effects on the Interfacial Tension of a Water/Model Oil System

It is an urgent issue to enhance oil recovery for unconventional reservoirs with high salinity. Focused on this topic, salt addition is a powerful tool to motivate the surfactant assembly at the water/oil interface and improve the interfacial activity. We used a cationic surfactant cetyltrimethylammonium bromide (CTAB) and an anionic salt dicarboxylic acid sodium (CnDNa) to construct gemini-like surfactants at the interface and evaluated their ability to reduce the interfacial tension (IFT) between model oil (toluene and n-decane, v:v = 1:1) and water. Interestingly, the fabrication of a (CTAB)₂/C4DNa gemini-like surfactant was hardly achieved at the fresh water/model oil interface, but accomplished at the brine/model oil interface. At a high NaCl concentration (100,000 mg L⁻¹), the IFT value is reduced to 10⁻³ mN m⁻¹ order of magnitude, which is generally desired in practical applications. The control experiments displacing the surfactant type and the spacer length further confirmed the NaCl effects on the interfacial assembly.     

A New Series of Double-Chain Single-Head Sulfobetaine Surfactants Derived from 1,3-Dialkyl Glyceryl Ether for Reducing Crude Oil/Water Interfacial Tension

A new series of sulfobetaine surfactants with double-chain single-head structure were derived from 1,3-dialkyl glyceryl ethers and their performances in reducing Daqing crude oil/connate water interfacial tension (IFT) in the absence of alkali were studied. With a large hydrophilic head group and double hydrophobic chains, these surfactants are efficient at reducing crude oil/connate water IFT. Those with didecyl and dioctyl are good hydrophobic surfactants that can reduce Daqing crude oil/connate water to ultra-low IFT by mixing with a small molar fraction of various conventional single-chain hydrophilic surfactants, such as α-olefin sulfonates, dodecyl polyoxyethylene (10) ether, and cetyl dimethyl hydroxypropyl sulfobetaine. The asymmetric double-chain sulfobetaine derived from 1-decyl-3-hexyl glyceryl ether can reduce Daqing crude oil/connate water IFT to ultra-low solely over a wide concentration range (0.03–10 mM or 0.0017–0.58 wt.%), which allows for use of an individual surfactant instead of mixed surfactants to avoid chromatographic separation in the reservoir. In addition, formulations rich in sulfobetaine surfactants show low adsorption on sandstone, keeping the negatively charged solid surface water-wet, and forming crude oil-in-water emulsions. These new sulfobetaine surfactants are, therefore, good candidates for surfactant-polymer flooding free of alkali.