Anionic surfactants, that is, ionic surfactants that can ionize into anions when dissolved in water, are called anionic surfactants. It is also divided into two categories: first, salt anionic surfactants, such as carboxylate type (R-COONa) and sulfonate type (R-SO3Na) active agents, which are composed of organic acids and metal ions. The second is the ester salt type anionic surfactant, such as sulfate salt type (R-OSO3Na) and phosphate salt type (R-OPO3Na2) active agent, their molecules have the structure of ester, but also have the structure of salt. The application of anionic surfactants in oilfield, like its application in other industrial sectors, is the earliest application time, the most used, and the most widely used industrial surfactants. Anionic surfactants are widely used in the process of oil drilling, oil production and oil gathering and transportation.
1.1 Application and development in drilling process
Anionic surfactants have been applied to various degrees in the whole process of drilling, cementing and completion in oilfield drilling.
In the drilling process, in order to improve the wettability, stability and high temperature resistance of the drilling fluid, reduce the density, filtration loss and friction resistance of the drilling fluid, and prevent the sticking of the drilling fluid, mixed oil drilling fluid is widely used, generally mixed with 5% to 20% oil, such as crude oil, diesel or oil, etc., to form an oil-in-water emulsion. When drilling Wells within 3000M to prepare mixed oil drilling fluid, carboxymethyl cellulose sodium salt, sodium tannate and iron chromium lignosulfonate and other drilling fluid treatment agents can be directly used. Because their hydrophilicity is slightly greater than lipophilicity, they belong to anionic active agents; The oil contains naphthenic acid, which is treated by alkali in drilling fluid and becomes sodium naphthenate, which is also an anionic oil-coated emulsifier, so there is no need to add other emulsifiers. Other emulsifiers must be added when drilling deep and inclined Wells to prepare oil-mixed drilling fluids. The commonly used emulsifiers for oil-in-water drilling fluids include normal alkyl (C10 ~ C20) sodium sulfonate, sodium alkyl phenyl sulfonate, etc. In order to resist high temperature, leakage and salt, water-in-oil drilling fluid is often used. The commonly used emulsifiers are anionic surfactants such as calcium stearate, aluminum stearate and calcium oleate.
In low pressure oil and gas reservoir drilling, foam drilling fluid is generally prepared and used to reduce drilling fluid density and protect oil and gas reservoir. The anionic surfactants used as foaming agents include sodium salt of fatty acids, alkyl sulfonates, alkyl sulfonates, etc. On the contrary, during the drilling process, the density of drilling fluid is reduced by gas invasion. Due to the presence of natural emulsifiers and additional emulsifiers or the use of sulfonated product treatment agents in the drilling fluid, the density of the drilling fluid will be reduced by foaming. These situations should be timely defoaming, the use of defoaming agents, anionic surfactants in the defoaming agents such as aluminum stearate.