(1) The surface activity on the oil-water interface is high, which reduces the oil-water interfacial tension to below (0.01-0.001) × 10-5N/cm, and has suitable solubility, cloud point and pH value, and reduces the adsorption of crude oil by the rock formation.
(2) The amount of adsorption on the rock surface is small.
(3) There should be a larger diffusion rate in the formation medium.
(4) When the concentration in water is low, it should have strong oil displacement capacity.
(5) It should have the ability to prevent the occurrence of side reactions of other chemical agents, that is, the so-called "resistance property".
(6) The surfactant for water injection should consider its relationship with formation mineral composition, formation water injection water composition, formation temperature and depletion degree of reservoir.
(7) It should have the ability to resist formation high temperature and high salt concentration.
(8) It has high economic value, and the input-output ratio has advantages.
(1) Nonionic surfactants
Commonly used varieties are fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyoxyethylene oleate, etc. The advantages are strong salt resistance, low critical micelle concentration, but low cloud point, and cannot be used in formations beyond its cloud point. At present, through modification, it not only has the above advantages, but also has a high cloud point and stronger salt resistance, which is suitable for high-salt and high-temperature formations.
(2) Anionic surfactants
Commonly used varieties are petroleum sulfonate, alkylbenzene sulfonate, lignosulfonate, etc. The advantages are high cloud point, less adsorption on sandstone surface, but poor salt resistance and high critical micelle concentration.
(3) Other surfactants and pharmaceuticals
Cationic surfactants have poor ability to reduce oil-water interfacial tension because they are easily adsorbed or precipitated by the formation, and are generally not suitable for the preparation of micelles for secondary or tertiary oil recovery. Under some specific conditions, quaternary ammonium amphoteric surfactants, quaternary ammonium sulfonates, etc. can be used. Other commonly used agents are: water-soluble high molecular polymers (such as polyacrylamide), low-carbon fatty alcohols, etc.
In oil exploration, surfactant flooding often does not use a surfactant, but a complex system composed of composite surfactants, polymers, additives, etc., only by cooperating with each other can the oil recovery rate be improved. For example, using water-soluble petroleum sulfonate to flood oil, which can be mixed with a small amount of solubilizer such as dialkylbenzene polyoxyethylene alkyl sulfonate, can improve the oil displacement efficiency. Because the dialkyl group on the surfactant can be straight chain or branched chain, and each alkyl group has 6 to 14 carbon atoms, the dialkyl structure has sufficient lipophilicity, while the alkyl sulfonate has sufficient lipophilicity. The structure has good compatibility with petroleum sulfonate and brine, thereby reducing the oil-water interfacial tension and improving the oil displacement effect.