1、Surfactants used for heavy oil extraction
Due to the high viscosity and poor fluidity of heavy oil, it brings many difficulties to exploitation. To extract such heavy oil, aqueous solutions of surfactants are sometimes injected into the wellbore to convert the high-viscosity heavy oil into low-viscosity oil-in-water emulsions, which are then 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 polyene polyamine, sodium polyoxyethylene alkyl alcohol ether sulfate, etc. For the produced oil-in-water emulsions, it is necessary to separate the water, and some industrial surfactants are also used as demulsifiers for dehydration. These demulsifiers are water-in-oil emulsifiers. Commonly used ones are cationic surfactants, or naphthenic acids, asphaltic acids and their polyvalent metal salts. Special heavy oil cannot be exploited by conventional pumping units and requires steam injection for thermal recovery. To improve the effect of thermal recovery, surfactants need to be used. Injecting foam into the steam injection well, that is, injecting high-temperature resistant foaming agents and non-condensable gases, is one of the commonly used preparation methods. Commonly used foaming agents are alkylbenzene sulfonates, α-olefin sulfonates, petroleum sulfonates, sulfoalkylated polyoxyethylene alkyl alcohol ethers, and sulfoalkylated polyoxyethylene alkyl phenol ethers, etc. Since fluorinated surfactants have high surface activity and are stable to acids, alkalis, oxygen, heat and oil, they are ideal high-temperature foaming agents. In order to make the dispersed oil easily pass through the pore-throat structure of the formation or to make the oil on the formation surface easily displaced, surfactants called film diffusing agents are needed, and the commonly used ones are oxyalkylated phenolic resin polymer surfactants.
2、Surfactants for extracting waxy crude oil
When extracting waxy crude oil, it is necessary to frequently carry out wax prevention and wax removal. Surfactants are used as wax inhibitors and wax removers. The surfactants used for wax prevention include oil-soluble surfactants and water-soluble surfactants. The former exerts a wax prevention effect by changing the properties of the wax crystal surface. Commonly used oil-soluble surfactants are petroleum sulfonates and amine-type surfactants. Water-soluble surfactants play a role in preventing wax by altering the properties of wax-depositing surfaces (such as the surfaces of oil pipes, sucker rods, and equipment). Available surfactants include sodium alkyl sulfonates, quaternary ammonium salts, alkane polyoxyethylene ethers, aromatic hydrocarbon polyoxyethylene ethers, and their sodium sulfonate salts, etc. Surfactants used for wax removal also fall into two categories: oil-soluble ones are used in oil-based wax removers, and water-soluble ones such as sulfonate-type, quaternary ammonium salt-type, polyether-type, Tween-type, OP-type surfactants, as well as sulfate-esterified or sulfoalkylated Peregal-type and OP-type surfactants, are used in water-based wax removers. In recent years, both domestically and internationally, wax removal and prevention have been organically combined, and oil-based wax removers and water-based wax removers have also been organically combined to produce mixed-type wax removers. This type of wax remover uses aromatic hydrocarbons and mixed aromatic hydrocarbons as the oil phase, and emulsifiers with wax removal effects as the water phase. When the selected emulsifier is a non-ionic surfactant with an appropriate cloud point, it can reach or exceed its cloud point at the temperature below the wax-depositing section of the oil well, thereby causing the mixed-type wax remover to demulsify before entering the wax-depositing section, separating into two types of wax removers, which exert the wax removal effect simultaneously.
3、Surfactants used in stable clay
Stabilizing clay involves two aspects: preventing the swelling of clay minerals and preventing the migration of clay mineral particles. For preventing clay swelling, cationic surfactants such as amine salt type, quaternary ammonium salt type, pyridine salt type, and imidazoline salt can be used. For preventing the migration of clay mineral particles, fluorine-containing nonionic-cationic surfactants can be used.
4、Surfactants used in acidizing measures
To enhance the acidizing effect, it is generally necessary to add various additives to the acid solution. Any surfactant that is compatible with the acid solution and easily adsorbed by the formation can be used as an acidizing retarder. Examples include fatty amine hydrochlorides, quaternary ammonium salts, and pyridinium salts among cationic surfactants, as well as sulfonated, carboxymethylated, phosphate-esterified, or sulfate-esterified polyoxyethylene alkylphenol ethers among amphoteric surfactants. Some surfactants, such as dodecyl sulfonic acid and its alkylamine salts, can emulsify the acid solution in oil to form an acid-in-oil emulsion, which, when used as an acidizing working fluid, also functions as a retarder.
Some surfactants can act as demulsifiers for acidizing fluids. Surfactants with branched structures, such as polyoxyethylene-polyoxypropylene propylene glycol ether and polyoxyethylene-polyoxypropylene pentaethylenehexamine, can serve as acidizing demulsifiers.
Certain surfactants can be used as spent acid cleanup additives, including amine salt-type, quaternary ammonium salt-type, pyridinium salt-type, non-ionic, amphoteric, and fluorinated surfactants.
Some surfactants function as acidizing sludge inhibitors, such as oil-soluble surfactants like alkylphenols, fatty acids, alkylbenzenesulfonic acids, and quaternary ammonium salts. Due to their poor acid solubility, non-ionic surfactants can be used to disperse them in the acid solution.
To improve the acidizing effect, wettability modifiers need to be added to the acid solution to reverse the wettability of the near-wellbore zone from oil-wet to water-wet. Mixtures such as polyoxyethylene-polyoxypropylene alkyl alcohol ether and phosphate-esterified polyoxyethylene-polyoxypropylene alkyl alcohol ether are adsorbed by the formation as the primary adsorption layer, thereby achieving wettability reversal.
In addition, some surfactants, such as fatty amine hydrochlorides, quaternary ammonium salts, or non-ionic-anionic surfactants, are used as foaming agents to prepare foam acid working fluids, which achieve the purposes of retarding reaction, inhibiting corrosion, and acidizing deep formations. Alternatively, such foams can be used as pre-pads for acidizing: after being injected into the formation, acid solution is injected subsequently. The Jamin effect generated by bubbles in the foam can divert the acid solution, forcing it to mainly dissolve low-permeability layers and thus improving the acidizing effect.
5、Surfactants used in fracturing measures
Fracturing measures are often applied in low-permeability oilfields. They involve using pressure to fracture the formation, creating cracks, and propping up the cracks with proppants to reduce fluid flow resistance, thereby achieving the goal of increasing production and injection. Some fracturing fluids are formulated with surfactants as one of their components. Oil-in-water fracturing fluids are prepared from water, oil, and emulsifiers. The emulsifiers used include ionic, non-ionic, and amphoteric surfactants. If thickened water is used as the external phase and oil as the internal phase, a thickened oil-in-water fracturing fluid (polymer emulsion) can be formulated. This type of fracturing fluid can be used at temperatures below 160°C and can automatically demulsify and discharge fluids. Foam fracturing fluids are those with water as the dispersion medium and gas as the dispersed phase, whose main components are water, gas, and foaming agents. Alkyl sulfonates, alkyl benzene sulfonates, alkyl sulfate esters, quaternary ammonium salts, and OP-type surfactants can all be used as foaming agents. The concentration of foaming agents in water is generally 0.5–2%, and the ratio of gas phase volume to foam volume ranges from 0.5 to 0.9. Oil-based fracturing fluids are formulated using oil as the solvent or dispersion medium. The most commonly used oils in field applications are crude oil or its heavy fractions. To improve their viscosity-temperature performance, oil-soluble petroleum sulfonates (with a molecular weight of 300–750) need to be added. Oil-based fracturing fluids also include water-in-oil fracturing fluids and oil foam fracturing fluids. The former uses oil-soluble anionic surfactants, cationic surfactants, and non-ionic surfactants as emulsifiers, while the latter uses fluorine-containing polymeric surfactants as foam stabilizers. Fracturing fluids for water-sensitive formations are emulsions or foams formulated using a mixture of alcohols (such as ethylene glycol) and oils (such as kerosene) as the dispersion medium, liquid carbon dioxide as the dispersed phase, and sulfated polyoxyethylene alkyl alcohol ethers as emulsifiers or foaming agents, used for fracturing water-sensitive formations. Fracturing fluids for fracture acidizing serve as both fracturing fluids and acidizing fluids, used in carbonate formations where both measures are carried out simultaneously. Those related to surfactants are acid foams and acid emulsions; the former uses alkyl sulfonates or alkyl benzene sulfonates as foaming agents, and the latter uses sulfonate-type surfactants as emulsifiers. Like acidizing fluids, fracturing fluids also use surfactants as demulsifiers, cleanup additives, and wettability reversal agents, which will not be elaborated on here.
6、Surfactants used in profile control and water plugging measures
To improve the effectiveness of waterflooding development and inhibit the rate of increase in crude oil water cut, it is necessary to adjust the water absorption profile in injection wells and implement water plugging measures in production wells as stimulation methods. Some of these profile control and water plugging methods often use certain surfactants. The HPC/SDS gel profile control agent is prepared by mixing hydroxypropyl cellulose (HPC) and sodium dodecyl sulfate (SDS) in fresh water. Sodium alkyl sulfonate and alkyl trimethyl ammonium chloride are respectively dissolved in water to prepare two working fluids, which are injected into the formation successively. The two working fluids meet in the formation, producing alkyl sulfite precipitates of alkyl trimethyl amine, which block the high-permeability layers. Polyoxyethylene alkyl phenol ether, alkyl aryl sulfonate, etc., can be used as foaming agents. They are dissolved in water to prepare a working fluid, which is then alternately injected into the formation with a liquid carbon dioxide working fluid. This forms foam in the formation (mainly in high-permeability layers), causing blockage and achieving the profile control effect. A quaternary ammonium salt-type surfactant is used as a foaming agent, dissolved in a silica sol prepared from ammonium sulfate and water glass, and injected into the formation. Then, non-condensable gas (natural gas or chlorine gas) is injected, which first generates foam with liquid as the dispersion medium in the formation, and then the silica sol gels to produce foam with solid as the dispersion medium, thereby blocking high-permeability layers and achieving profile control. Using sulfonate-type surfactants as foaming agents and high molecular compounds as thickening and foam-stabilizing agents, followed by injecting gas or gas-generating substances, water-based foam is generated on the surface or in the formation. In the oil layer, a large amount of the surfactant moves to the oil-water interface, causing the foam to break, so it does not block the oil layer and is a selective oil well water plugging agent. Oil-based cement water plugging agent is a suspension of cement in oil. The surface of cement is hydrophilic. When it enters the water-producing layer, water displaces the oil on the cement surface and reacts with the cement, causing the cement to solidify and block the water-producing layer. To improve the fluidity of this plugging agent, carboxylate-type and sulfonate-type surfactants are usually added. Water-based micellar fluid plugging agent is a micellar solution mainly composed of ammonium petroleum sulfonate, hydrocarbons, alcohols, etc. When it encounters highly saline water in the formation, it can become viscous to achieve the water plugging effect. Water-based or oil-based cationic surfactant solution plugging agents, which are mainly composed of alkyl carboxylate and alkyl ammonium chloride surfactants, are only applicable to sandstone formations. Active heavy oil plugging agent is a heavy oil dissolved with water-in-oil emulsifiers. When it encounters water in the formation, it produces a high-viscosity water-in-oil emulsion to achieve water plugging. Oil-in-water plugging agent is prepared by emulsifying heavy oil in water using cationic surfactants as oil-in-water emulsifiers.
7、Surfactants for sand control measures
Before sand control operations, a certain amount of active water prepared with surfactants needs to be injected as a preflush fluid to pre-clean the formation, so as to improve the sand control effect. Most of the surfactants commonly used at present are anionic surfactants.
8、Surfactants for crude oil dehydration
In the primary and secondary oil recovery stages, water-in-oil demulsifiers are mostly used for the produced crude oil. Three generations of products have been developed. The first generation includes carboxylates, sulfates, and sulfonates. The second generation consists of low-molecular-weight nonionic surfactants such as OP, Pegosperse, and sulfonated castor oil. The third generation is high-molecular-weight nonionic surfactants. In the late secondary oil recovery stage and the tertiary oil recovery stage, the produced crude oil mostly exists in the form of oil-in-water emulsions. There are four types of demulsifiers used, such as tetradecyltrimethylammonium chloride and didecyldimethylammonium chloride. These can react with anionic emulsifiers to change their hydrophilic-lipophilic balance value, or adsorb on the surface of water-wet clay particles to change their wettability and break the oil-in-water emulsion. In addition, some anionic surfactants that can act as water-in-oil emulsifiers and oil-soluble nonionic surfactants can also be used as demulsifiers for oil-in-water emulsions.
9、Surfactants for water treatment
After crude oil is separated from the produced fluid of an oil well, the produced water needs to be treated to meet the requirements for reinjection. The purposes of water treatment include six aspects: corrosion inhibition, scale prevention, sterilization, deoxygenation, oil removal, and removal of solid suspended solids. Therefore, corrosion inhibitors, scale inhibitors, bactericides, deoxidizers, oil removers, flocculants, etc., are used. The industrial surfactants involved are as follows:
Industrial surfactants used as corrosion inhibitors include salts of alkyl sulfonic acids, alkyl benzene sulfonic acids, perfluoroalkyl sulfonic acids, straight-chain alkyl amine salts, quaternary ammonium salts, alkyl pyridinium salts, salts of imidazolines and their derivatives, polyoxyethylene alkyl alcohol ethers, polyoxyethylene dialkyl propynols, polyoxyethylene rosin amines, polyoxyethylene stearyl amines, polyoxyethylene alkyl alcohol ether alkyl sulfonates, various quaternary amino inner salts, and inner salts of bis(polyoxyethylene) alkyls and their derivatives. Surfactants used as scale inhibitors include phosphate esters, sulfate esters, acetates, carboxylates, and their polyoxyethylene compounds. The thermal stability of sulfonate esters and carboxylates is significantly better than that of phosphate esters and sulfate esters. Industrial surfactants used as bactericides include straight-chain alkyl amine salts, quaternary ammonium salts, alkyl pyridinium salts, salts of imidazolines and their derivatives, various quaternary ammonium inner salts, and inner salts of bis(polyoxyethylene) alkyls and their derivatives. Industrial surfactants used as oil removers are mainly those with a branched structure and containing sodium dithiocarboxylate groups.
10、Surfactants for chemical flooding in oil recovery
Primary and secondary oil recovery can extract 25% – 50% of the underground crude oil, with a large amount of crude oil remaining underground and unable to be extracted. Tertiary oil recovery can improve oil recovery efficiency. Tertiary oil recovery mostly adopts chemical flooding methods, that is, adding some chemicals to the injected water to improve water flooding efficiency. Among the chemicals used, some belong to industrial surfactants, and their conditions are briefly introduced as follows: The chemical flooding method with surfactant as the main agent is called surfactant flooding. Surfactants mainly play a role in improving oil recovery by reducing the oil-water interfacial tension and increasing the capillary number. Since the surface of sandstone formations is negatively charged, the surfactants used are mainly anionic surfactants, and most of them are sulfonate surfactants. It is made by sulfonating petroleum fractions with high aromatic hydrocarbon content using sulfonating agents (such as sulfur trioxide) and then neutralizing with alkali. Its specifications: active ingredient 50% – 80%, mineral oil 5% – 30%, water 2% – 20%, sodium sulfate 1% – 6%. Petroleum sulfonates are resistant to high temperatures but not to salt and high-valent metal ions. Synthetic sulfonates are prepared from corresponding hydrocarbons using corresponding synthesis methods. Among them, α-olefin sulfonates are particularly resistant to salt and high-valent metal ions. In addition, some anionic-nonionic surfactants and carboxylate surfactants can also be used for oil flooding. Surfactant flooding requires two types of additives: one is cosurfactants, such as isobutanol, diethylene glycol butyl ether, urea, sulfolane, alkenyl benzene sulfonates, etc.; the other is electrolytes, including acids, alkalis, and salts, mainly salts. They can reduce the hydrophilicity of surfactants, relatively increase lipophilicity, and also function by changing the hydrophilic-lipophilic balance value of surfactants. In order to reduce the loss of surfactants and improve economic efficiency, surfactant flooding also uses chemical substances called sacrificial agents. Substances that can be used as sacrificial agents include alkaline substances, polycarboxylic acids and their salts, oligomers and polymers can also be used as sacrificial agents, and lignosulfonates and their modified products are a type of sacrificial agent. The oil flooding method that uses two or more main agents for chemical oil flooding is called composite flooding. Such oil flooding methods related to surfactants include: surfactant + polymer for thickened surfactant flooding; alkali + surfactant for alkali-enhanced surfactant flooding or surfactant-enhanced alkali flooding; alkali + surfactant + polymer for ternary composite flooding. Composite flooding usually has higher oil recovery than single flooding. According to the analysis of current development trends at home and abroad, ternary composite flooding has higher advantages than binary composite flooding. The surfactants used in ternary composite flooding are mainly petroleum sulfonates, and they are usually compounded with sulfuric acid, phosphoric acid and carboxylate of polyoxyethylene alkyl alcohol ether, sodium polyoxyethylene alkyl alcohol alkyl sulfonate, etc., to improve their salt resistance. Recently, both domestic and foreign countries have attached importance to the research and use of biosurfactants, such as rhamnolipids, sophorolipid fermentation broths, as well as natural mixed carboxylates and papermaking by-product alkali lignin, etc., which have achieved good oil flooding effects in field and laboratory tests.
Post time: Mar-26-2026