Introduction
Quaternary ammonium salt, [R4N+]X-, is formed by the nucleophilic substitution reaction of tertiary amines with hydrocarbons with active halogen atoms, such as haloalkanes and aromatic halides. The special structure of quaternary ammonium salt makes it salt-like, soluble in aqueous solution and has positive charge, easy to adsorb on the solid-liquid and solid-gas interfaces. In addition to good water solubility, quaternary ammonium salt is widely used in oilfield chemicals due to its simple synthesis process, safety, low toxicity, stable performance and strong biological activity.
Application
- Corrosion Inhibitor
During oilfield exploitation and water injection, quaternary ammonium salts are used as corrosion inhibitors to protect metals. The corrosion inhibitor is adsorbed on the steel surface through molecules to form a dense hydrophobic adsorption film to isolate the corrosion medium. The greater the adsorption performance, the more compact and stable the formed adsorption film and the better the corrosion inhibition effect. The quaternary ammonium salt corrosion inhibitor was prepared by reacting imidazoline compound with sodium chloroacetate. The corrosion inhibitor made the iron and steel corrosion product film (Fe2CO3) dense in CO2-containing oil field water, thereby achieving the corrosion inhibition effect.
- Fungicide
There are many kinds of bacteria in oil field water, among which the life activity reduction products of sulfate reducing bacteria (SRB) contain S2-, which is easy to cause metal corrosion. The most efficient and convenient way to solve this problem is to add fungicides. Quaternary ammonium salt has good solubility, strong biological activity and low toxicity. It is often prepared from nitrogen heterocyclic compounds with high activity and low toxicity and long-chain alkyl benzyl halides as raw materials, so that it has surface activity, can peel off slime and Inhibits the growth of SRB.
- Shale Inhibitor
Shale reservoirs account for a high proportion in oil and gas exploitation. Shale illite and montmorillonite have high clay content. Shale forms silicate layer through the intermolecular force of clay and electrostatic attraction, which is easy to absorb water to produce expansion pressure and causes serious peeling. The positive charge of the quaternary ammonium salt inhibitor and the negative charge on the surface of the clay crystal layer stabilize the shale through electrostatic interaction. The diameter of the silicon-oxygen tetrahedral network is similar to that of the ammonium ion, which can solidify the clay and prevent water molecules from entering the clay crystal layer. The hydrophobicity of long carbon chain in quaternary ammonium salt reverses the wetting of clay surface and inhibits the hydration of clay surface.
- Organic Soil Modifier
Quaternary ammonium salt is used as organic soil modifier to prepare organic soil for oil-based drilling fluid by ion exchange with nano-bentonite. The strong inhibition, lubricity and wall protection properties of oil-based drilling fluids make them widely used in drilling in various oil fields. The viscosity-increasing and cutting-increasing performance, fluid loss reduction performance and wall protection performance of oil-based drilling fluids are mainly realized by organic soil. The most common organic modifiers are quaternary ammonium salt surfactants. Many scholars improve the temperature resistance and viscosity-shearing ability of organic soils by changing the alkyl chains on quaternary ammonium salts.
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Reference
- Wang, X.; et al. Adsorption of imidazoline quaternary ammonium salt on N80 steel surface in saturated CO2 oilfield water and its relationship with its corrosion inhibition performance. Material protection. 2014, 47(2):4.