1.Surfactants for Heavy Oil Extraction
Due to the high viscosity and poor fluidity of heavy oil, its extraction poses significant challenges. To recover such heavy oil, an aqueous solution of surfactants is sometimes injected into the wellbore to transform the highly viscous crude into a low-viscosity oil-in-water emulsion, which can then be pumped to the surface.
The surfactants used in this heavy oil emulsification and viscosity reduction method include sodium alkyl sulfonate, polyoxyethylene alkyl alcohol ether, polyoxyethylene alkyl phenol ether, polyoxyethylene-polyoxypropylene polyamine, and sodium polyoxyethylene alkyl alcohol ether sulfate.
The extracted oil-in-water emulsion requires water separation, for which industrial surfactants are also employed as demulsifiers. These demulsifiers are water-in-oil emulsifiers. Commonly used ones include cationic surfactants or naphthenic acids, asphaltic acids, and their polyvalent metal salts.
For particularly viscous crudes that cannot be extracted using conventional pumping methods, steam injection for thermal recovery is required. To enhance thermal recovery efficiency, surfactants are necessary. One common approach is injecting foam into the steam injection well—specifically, high-temperature-resistant foaming agents along with non-condensable gases.
Commonly used foaming agents include alkyl benzene sulfonates, α-olefin sulfonates, petroleum sulfonates, sulfonated polyoxyethylene alkyl alcohol ethers, and sulfonated polyoxyethylene alkyl phenol ethers. Due to their high surface activity and stability against acids, bases, oxygen, heat, and oil, fluorinated surfactants are ideal high-temperature foaming agents.
To facilitate the passage of dispersed oil through the pore-throat structure of the formation or to make oil on the formation surface easier to displace, surfactants known as thin-film spreading agents are used. A common example is oxyalkylated phenolic resin polymer surfactants.
2.Surfactants for Waxy Crude Oil Extraction
Extracting waxy crude oil requires regular wax prevention and removal. Surfactants serve as both wax inhibitors and paraffin dispersants.
For wax inhibition, there are oil-soluble surfactants (which alter the surface properties of wax crystals) and water-soluble surfactants (which modify the properties of wax-deposition surfaces like tubing, sucker rods, and equipment). Common oil-soluble surfactants include petroleum sulfonates and amine-type surfactants. Water-soluble options include sodium alkyl sulfonate, quaternary ammonium salts, alkyl polyoxyethylene ethers, aromatic polyoxyethylene ethers, and their sodium sulfonate derivatives.
For paraffin removal, surfactants are also categorized into oil-soluble (used in oil-based paraffin removers) and water-soluble (such as sulfonate-type, quaternary ammonium-type, polyether-type, Tween-type, OP-type surfactants, and sulfate/sulfonated PEG-type or OP-type surfactants).
In recent years, domestic and international practices have integrated wax prevention and removal, combining oil-based and water-based removers into hybrid paraffin dispersants. These use aromatic hydrocarbons as the oil phase and emulsifiers with paraffin-dissolving properties as the water phase. When the emulsifier has an appropriate cloud point (the temperature at which it becomes cloudy), it demulsifies below the wax deposition zone, releasing both components to work simultaneously.
3.Surfactants for Crude Oil Dehydration
In primary and secondary oil recovery, oil-in-water demulsifiers are predominantly used. Three generations of products have been developed:
1.First generation: Carboxylates, sulfates, and sulfonates.
2.Second generation: Low-molecular-weight nonionic surfactants (e.g., OP, PEG, and sulfonated castor oil).
3.Third generation: High-molecular-weight nonionic surfactants.
In late-stage secondary recovery and tertiary recovery, crude oil often exists as water-in-oil emulsions. Demulsifiers fall into four categories:
·Quaternary ammonium salts (e.g., tetradecyl trimethyl ammonium chloride, dicetyl dimethyl ammonium chloride), which react with anionic emulsifiers to alter their HLB (hydrophilic-lipophilic balance) or adsorb onto water-wet clay particles, changing wettability.
·Anionic surfactants (acting as oil-in-water emulsifiers) and oil-soluble nonionic surfactants, also effective for breaking water-in-oil emulsions.
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