Application of surfactants in oil field production

Application of surfactants in oil field production

1. Surfactants used for mining heavy oil

Due to the high viscosity and poor fluidity of heavy oil, it brings many difficulties to mining. In order to extract these heavy oils, it is sometimes necessary to inject an aqueous solution of surfactant downhole to convert the high-viscosity heavy oil into a low-viscosity oil-in-water emulsion and extract it 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, polyoxyethylene Vinyl alkyl alcohol ether sulfate sodium salt, etc. The oil-in-water emulsion produced needs to separate the water and use some industrial surfactants as demulsifiers for dehydration. These demulsifiers are water-in-oil emulsifiers. Commonly used are cationic surfactants or naphthenic acids, asphaltonic acids and their multivalent metal salts.

Special heavy oil cannot be mined by conventional pumping units and requires steam injection for thermal recovery. To improve the thermal recovery effect, surfactants need to be used. Injecting foam into the steam injection well, that is, injecting high-temperature resistant foaming agent and non-condensable gas, is one of the commonly used modulation methods.

Commonly used foaming agents are alkyl benzene sulfonates, α-olefin sulfonates, petroleum sulfonates, sulfohydrocarbylated polyoxyethylene alkyl alcohol ethers and sulfohydrocarbylated polyoxyethylene alkyl phenol ethers, etc. Because 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 surface of the formation easy to be driven out, it is necessary to use a surfactant called a film diffusing agent. The commonly used one is oxyalkylated phenolic resin polymer surface activity. agent.

​

1. Surfactants for mining waxy crude oil

Exploitation of waxy crude oil requires frequent wax prevention and wax removal. Surfactants act as wax inhibitors and wax removers. There are oil-soluble surfactants and water-soluble surfactants used for anti-wax. The former plays an anti-wax role by changing the properties of the wax crystal surface. Commonly used oil-soluble surfactants are petroleum sulfonates and amine surfactants. Water-soluble surfactants play an anti-wax role by changing the properties of wax-formed surfaces (such as oil pipes, sucker rods and equipment surfaces). Available surfactants include sodium alkyl sulfonates, quaternary ammonium salts, alkane polyoxyethylene ethers, aromatic hydrocarbon polyoxyethylene ethers and their sulfonate sodium salts, etc. Surfactants used for wax removal are also divided into two aspects. Oil-soluble surfactants are used for oil-based wax removers, and water-soluble sulfonate type, quaternary ammonium salt type, polyether type, Tween type, OP type surfactants, Sulfate-based or sulfo-alkylated flat-type and OP-type surfactants are used in water-based wax removers. In recent years, domestic and foreign wax removers have been organically combined, and oil-based wax removers and water-based wax removers have been organically combined to produce hybrid wax removers. This wax remover uses aromatic hydrocarbons and mixed aromatic hydrocarbons as the oil phase, and uses an emulsifier with wax clearing effect as the water phase. When the selected emulsifier is a nonionic surfactant with an appropriate cloud point, the temperature below the waxing section of the oil well can reach or exceed its cloud point, so that the mixed wax remover can The emulsification is broken before entering the wax-forming section, and two wax-clearing agents are separated, which simultaneously play the role of wax-clearing.

3. Surfactants used to stabilize clay

Stabilizing clay is divided into two aspects: preventing the expansion of clay minerals and preventing the migration of clay mineral particles. Cationic surfactants such as amine salt type, quaternary ammonium salt type, pyridinium salt type, and imidazoline salt can be used to prevent clay swelling. Fluorine-containing nonionic-cationic surfactants are available to prevent clay mineral particle migration.

4. Surfactants used in acidification measures

In order to improve the acidification effect, a variety of additives are generally added to the acid solution. Any surfactant that is compatible with the acid solution and is easily adsorbed by the formation can be used as an acidification retardant. Such as fatty amine hydrochloride, quaternary ammonium salt, pyridine salt in cationic surfactants and sulfonated, carboxymethylated, phosphate ester salted or sulfate ester salted polyoxyethylene alkanes in amphoteric surfactants base phenol ether, etc. Some surfactants, such as dodecyl sulfonic acid and its alkylamine salts, can emulsify acid liquid in oil to produce an acid-in-oil emulsion. This emulsion can be used as an acidified industrial liquid and also plays a retarding role.

Some surfactants can be used as anti-emulsifiers for acidifying liquids. Surfactants with branched structures such as polyoxyethylene polyoxypropylene propylene glycol ether and polyoxyethylene polyoxypropylene pentaethylene hexaamine can be used as acidifying anti-emulsifiers.

Some surfactants can be used as acid-deficient drainage aids. Surfactants that can be used as drainage aids include amine salt type, quaternary ammonium salt type, pyridinium salt type, nonionic, amphoteric and fluorine-containing surfactants.

Some surfactants can be used as acidifying anti-sludge agents, such as oil-soluble surfactants, such as alkylphenols, fatty acids, alkylbenzenesulfonic acids, quaternary ammonium salts, etc. Because they have poor acid solubility, nonionic surfactants can be used to disperse them in the acid solution.

In order to improve the acidification effect, a wetting reversal agent needs to be added to the acid solution to reverse the wettability of the near-wellbore zone from lipophilic to hydrophilic. Mixtures of polyoxyethylene polyoxypropylene alkyl alcohol ethers and phosphate-salted polyoxyethylene polyoxypropylene alkyl alcohol ethers are adsorbed by the formation to form the third adsorption layer, which plays a role in wetting and reversal.

In addition, there are some surfactants, such as fatty amine hydrochloride, quaternary ammonium salt or nonionic-anionic surfactant, which are used as foaming agents to make foam acid working fluid to achieve the purpose of slowing corrosion and deep acidification, or Foams are made from this and used as pre-fluid for acidification. After they are injected into the formation, the acid solution is injected. The Jamin effect produced by the bubbles in the foam can divert the acid liquid, forcing the acid liquid to mainly dissolve the low permeability layer, thereby improving the acidification effect.

5. Surfactants used in fracturing measures

Fracturing measures are often used in low-permeability oil fields. They use pressure to open the formation to form fractures, and use proppant to support the fractures to reduce fluid flow resistance and achieve the purpose of increasing production and attention. Some fracturing fluids are formulated with surfactants as one of the ingredients.

Oil-in-water fracturing fluids are formulated with water, oil and emulsifiers. Emulsifiers used are ionic, nonionic and amphoteric surfactants. If thickened water is used as the external phase and oil is used as the internal phase, a thickened oil-in-water fracturing fluid (polymer emulsion) can be prepared. This fracturing fluid can be used at temperatures below 160°C and can automatically break emulsions and drain fluids.

Foam fracturing fluid is a fracturing fluid that uses water as the dispersion medium and gas as the dispersed phase. Its main components are water, gas and foaming agent. Alkyl sulfonates, alkyl benzene sulfonates, alkyl sulfate ester salts, quaternary ammonium salts and OP surfactants can all be used as foaming agents. The concentration of foaming agent in water is generally 0.5-2%, and the ratio of gas phase volume to foam volume is in the range of 0.5-0.9.

Oil-based fracturing fluid is a fracturing fluid formulated with oil as solvent or dispersion medium. The most commonly used oil on site is crude oil or its heavy fraction. In order to improve its viscosity and temperature properties, oil-soluble petroleum sulfonate (molecular weight 300-750) needs to be added. Oil-based fracturing fluids also include water-in-oil fracturing fluids and oil foam fracturing fluids. The emulsifiers used in the former are oil-soluble anionic surfactants, cationic surfactants and nonionic surfactants, while the foam stabilizers used in the latter are fluorine-containing polymer surfactants.

Water-sensitive formation fracturing fluid uses a mixture of alcohol (such as ethylene glycol) and oil (such as kerosene) as the dispersion medium, liquid carbon dioxide as the dispersed phase, and sulfate-salted polyoxyethylene alkyl alcohol ether as the emulsifier. Or emulsion or foam formulated with foaming agent to fracture water-sensitive formations.

The fracturing fluid used for fracturing and acidification is both a fracturing fluid and an acidifying fluid. It is used in carbonate formations, and the two measures are carried out simultaneously. Related to surfactants are acid foam and acid emulsion. The former uses alkyl sulfonate or alkyl benzene sulfonate as a foaming agent, and the latter uses a sulfonate surfactant as an emulsifier. Like acidifying fluids, fracturing fluids also use surfactants as anti-emulsifiers, drainage aids and wetting reversal agents, which will not be discussed here.

6. Use surfactants for profile control and water blocking measures

In order to improve the water injection development effect and suppress the rising rate of crude oil water content, it is necessary to adjust the water absorption profile on the water injection wells and to increase production by blocking water on the production wells. Some of the profile control and water blocking methods often use some surfactants.

HPC/SDS gel profile control agent is composed of 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 liquids, which are injected into the formation one after another. The two working liquids interact with each other in the formation to produce alkyl trimethylamine. The sulfite precipitates and blocks the high permeability layer.

Polyoxyethylene alkyl phenol ethers, alkyl aryl sulfonates, etc. can be used as foaming agents, dissolved in water to prepare a working fluid, and then injected into the formation alternately with liquid carbon dioxide working fluid, just in the formation (mainly high The permeable layer) forms foam, produces blockage, and plays a role in profile control.

Using a quaternary ammonium surfactant as a foaming agent dissolved in a silicic acid sol composed of ammonium sulfate and water glass and injected into the formation, and then injecting non-condensable gas (natural gas or chlorine), a liquid-based form can be generated in the formation first. The foam in the dispersion interlayer, followed by the gelation of the silicic acid sol, produces a foam with solid as the dispersion medium, which plays the role of plugging the high permeability layer and controlling the profile.

Using sulfonate surfactants as foaming agents and polymer compounds as thickening foam stabilizers, and then injecting gas or gas-generating substances, a water-based foam is generated on the ground or in the formation. This foam is surface-active in the oil layer. A large amount of the agent moves to the oil-water interface, causing foam destruction, so it does not block the oil layer. It is a selective and oil well water-blocking agent.

Oil-based cement water-blocking agent is a suspension of cement in oil. The surface of the cement is hydrophilic. When it enters the water-producing layer, water displaces the interaction between the oil well and the cement on the surface of the cement, causing the cement to solidify and block the water-producing layer. In order to improve the fluidity of this plugging agent, carboxylate and sulfonate surfactants are usually added.

Water-based micellar liquid-soluble water-blocking agent is a micellar solution mainly composed of petroleum ammonium sulfonate, hydrocarbons and alcohols. It contains high salt water in the formation and becomes viscous to achieve water-blocking effect. .

Water-based or oil-based cationic surfactant solution water-blocking agent is based on alkyl carboxylate and alkyl ammonium chloride salt active agents and is only suitable for sandstone formations.

Active heavy oil water-blocking agent is a kind of heavy oil dissolved with water-in-oil emulsifier. It produces a highly viscous water-in-oil emulsion after the formation is dewatered to achieve the purpose of blocking water.

Oil-in-water water-blocking agent is prepared by emulsifying heavy oil in water using a cationic surfactant as an oil-in-water emulsifier.

7. Use surfactants for sand control measures

Before sand control operations, a certain amount of activated water prepared with surfactants needs to be injected as a pre-fluid to pre-clean the formation to improve the sand control effect. Currently, most commonly used surfactants are anionic surfactants.

8. Surfactant for crude oil dehydration

In the primary and secondary oil recovery stages, water-in-oil demulsifiers are often used for the extracted crude oil. Three generations of products have been developed. The first generation is carboxylate, sulfate and sulfonate. The second generation is low-molecular nonionic surfactants such as OP, Pingpingjia and sulfonated castor oil. The third generation is polymer nonionic surfactant.

In the later stages of secondary oil recovery and tertiary oil recovery, the produced crude oil mostly exists in the form of oil-in-water emulsion. There are four types of demulsifiers used, such as tetradecyltrimethyloxyammonium chloride and didecyldimethylammonium chloride. They can react with anionic emulsifiers to change their hydrophilic oil balance value, or Adsorbed on the surface of water-wet clay particles, changing their wettability and destroying oil-in-water emulsions. In addition, some anionic surfactants and oil-soluble nonionic surfactants that can be used as water-in-oil emulsifiers can also be used as demulsifiers for oil-in-water emulsions.

1. Surfactants for water treatment

After the oil well production fluid is separated from the crude oil, the produced water needs to be treated to meet the reinjection requirements. There are six purposes of water treatment, namely corrosion inhibition, scale prevention, sterilization, oxygen removal, oil removal and solid suspended matter removal. Therefore, it is necessary to use corrosion inhibitors, anti-scaling agents, bactericides, oxygen scavengers, degreasers and flocculants, etc. The following aspects involve industrial surfactants:

Industrial surfactants used as corrosion inhibitors include salts of alkyl sulfonic acid, alkyl benzene sulfonic acid, perfluoroalkyl sulfonic acid, linear alkyl amine salts, quaternary ammonium salts, and alkyl pyridine salts. , salts of imidazoline and its derivatives, polyoxyethylene alkyl alcohol ethers, polyoxyethylene dialkyl propargyl alcohol, polyoxyethylene rosin amine, polyoxyethylene stearylamine and polyoxyethylene alkyl alcohol ethers Alkyl sulfonate, various quaternary ammonium internal salts, di(polyoxyethylene)alkyl internal salts and their derivatives.

Surfactants used as antifouling agents include phosphate ester salts, sulfate ester salts, acetates, carboxylates and their polyoxyethylene compounds. The thermal stability of sulfonate ester salts and carboxylate salts is significantly better than that of phosphate ester salts and sulfate ester salts.

Industrial surfactants used in fungicides include linear alkylamine salts, quaternary ammonium salts, alkylpyridinium salts, salts of imidazoline and its derivatives, various quaternary ammonium salts, di(polyoxy) Vinyl) alkyl and internal salts of its derivatives.

Industrial surfactants used in degreasers are mainly surfactants with branched structures and sodium dithiocarboxylate groups.

10. Surfactant for chemical oil flooding

Primary and secondary oil recovery can recover 25%-50% of the underground crude oil, but there is still a lot of crude oil that remains underground and cannot be recovered. Performing tertiary oil recovery can improve crude oil recovery. Tertiary oil recovery mostly uses chemical flooding method, that is, adding some chemical agents to the injected water to improve water flooding efficiency. Among the chemicals used, some are industrial surfactants. A brief introduction to them is as follows:

The chemical oil flooding method using 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 number of capillaries. Since the surface of the sandstone formation is negatively charged, the surfactants used are mainly anionic surfactants, and most of them are sulfonate surfactants. It is made by using a sulfonating agent (such as sulfur trioxide) to sulfonate petroleum fractions with high aromatic hydrocarbon content, and then neutralizing them with alkali. Its specifications: active substance 50%-80%, mineral oil 5%-30%, water 2%-20%, sodium sulfate 1%-6%. Petroleum sulfonate is not resistant to temperature, salt, or high-priced metal ions. Synthetic sulfonates are prepared from corresponding hydrocarbons using corresponding synthetic methods. Among them, α-olefin sulfonate is particularly resistant to salt and high-valent metal ions. Other anionic-nonionic surfactants and carboxylate surfactants can also be used for oil displacement. Surfactant oil displacement requires two kinds of additives: one is co-surfactant, such as isobutanol, diethylene glycol butyl ether, urea, sulfolane, alkenylene benzene sulfonate, etc., and the other is dielectric , including acid and alkali salts, mainly salts, which can reduce the hydrophilicity of the surfactant and relatively increase the lipophilicity, and also change the hydrophilic-lipophilic balance value of the active agent. In order to reduce the loss of surfactant and improve economic effects, surfactant flooding also uses chemicals called sacrificial agents. Substances that can be used as sacrificial agents include alkaline substances and polycarboxylic acids and their salts. Oligomers and polymers can also be used as sacrificial agents. Lignosulfonates and their modifications are sacrificial agents.

The oil displacement method using two or more chemical oil displacement main agents is called composite flooding. This oil displacement method related to surfactants includes: surfactant and polymer thickened surfactant flooding; Alkali-enhanced surfactant flooding with alkali + surfactant or surfactant-enhanced alkali flooding; element-based composite flooding with alkali + surfactant + polymer. Composite flooding generally has higher recovery factors than a single drive. According to the current analysis of development trends at home and abroad, ternary compound flooding has higher advantages than binary compound flooding. The surfactants used in ternary composite flooding are mainly petroleum sulfonates, usually also used in combination with sulfuric acid, phosphoric acid and carboxylates of polyoxyethylene alkyl alcohol ethers, and polyoxyethylene alkyl alcohol alkyl sulfonate sodium salts. etc. to improve its salt tolerance. Recently, both at home and abroad have attached great importance to the research and use of biosurfactants, such as rhamnolipid, sophorolipid fermentation broth, etc., as well as natural mixed carboxylates and papermaking by-product alkali lignin, etc., and have achieved great results in field and indoor tests. Good oil displacing effect.