The importance of corrosion inhibitors in oil production

Corrosion prevention is a very important subject in the petroleum industry. Corrosion is an important factor restricting the development of the petroleum industry. Therefore, the research and application of corrosion prevention technology is of great significance. In this paper, the causes of corrosion and the factors affecting corrosion in oil production are reviewed. The application status of corrosion inhibitors as an important anti-corrosion technology in oil production is summarized, and the development trend of corrosion inhibitors is prospected.

Corrosion in crude oil production

(1) Corrosion in the drilling system

The corrosive media in the drilling process are mainly hydrogen sulfide and carbon dioxide from the formation fluid, hydrogen sulfide generated by the action of microorganisms in the drilling fluid on sulfate, and oxygen dissolved in the drilling fluid. The presence of these corrosive media makes the equipment used in the drilling process prone to electrochemical corrosion.

(2) Corrosion in oil production and gathering and transportation systems

Oil well corrosion: Oil well corrosion refers to the corrosion of oil and well tubing, casing and downhole tools caused by harmful components such as carbon dioxide, hydrogen sulfide and produced water contained in the produced fluid and associated gas.

Corrosion of gathering system: When the crude oil transported in the gathering pipeline contains more water and the water contains oxygen, carbon dioxide or sulfate reducing bacteria, serious electrochemical corrosion will occur inside the gathering pipeline

2. Common corrosion types in crude oil production

(1) Electrochemical corrosion

There are differences in the type, concentration, temperature and flow rate of the electrolyte in contact with different parts of the metal, and there will be cathode and anode regions on the metal surface, and the cathode and anode will form corrosion batteries through the metal itself.

(2) hydrogen sulfide corrosion

Part of H2S in oil field production water comes from oil reservoir and associated gas, and the other part is transformed from crude oil and sulfur-containing substances in water through the action of microorganisms. When the oil field water contains both dissolved hydrogen sulfide and dissolved oxygen, the corrosion will be more serious.

(3) carbon dioxide corrosion

Carbon dioxide, as the associated gas in oil field production fluid, dissolves in water to form carbonic acid, which makes the pH of hydrogen ions in the solution acidic and causes electrochemical corrosion.

Fe2+ +CO32- →FeCO3

Fe2+ +2HCO3- →Fe (HCO3) 2

Fe (HCO3) 2 →FeCO3+CO2+H2O

(4) Dissolved oxygen corrosion

Oxygen corrosion is the most common type of corrosion and occurs whenever air and water are present.

8 h2o – oh – 8 + 8 h +

4Fe→4Fe2+ +8e-

8H++e-→8H adsorption

Fe2+ +8H2O→4Fe (OH) 2+8H adsorption

(5) Salt corrosion

Ca2+ and Mg2+ ions will increase the salinity of oil field produced water and make local corrosion more serious.

(6) Microbial corrosion

There are a variety of microbial communities in the oilfield production system, which cause great losses to the corrosion of oilfield equipment and pipelines.

Third, the application of corrosion inhibitors in the corrosion protection of crude oil production

A corrosion inhibitor is “a chemical or mixture of several chemical substances that, when present in the environment (medium) in an appropriate concentration and form, can prevent or slow the corrosion of a material.” The addition of corrosion inhibitor is a simple, cheap and applicable means of corrosion prevention. This method is widely used in many petroleum production units because of its convenient operation and remarkable effect.

(1) Application of imidazoline corrosion inhibitors

Imidazoline is generally composed of three parts: a five-membered heterocyclic ring containing nitrogen, a branch chain on the heterocyclic ring that bonds with nitrogen (amide functional group, amine functional group, hydroxyl group, etc.) and a long hydrocarbon branch chain (generally alkyl).

(2) Application of organic phosphoric acid corrosion inhibitors

Organic phosphoric acid molecules contain phosphoryl groups, which can interact with metal ions such as calcium, magnesium, aluminum, iron, steel and zinc to form insoluble complexes covering the metal surface and playing an anti-corrosion effect.

(3) The application of heterocyclic corrosion inhibitors

Heterocyclic corrosion inhibitor contains O, N, S, P and other atoms, has a number of active adsorption centers, carbon steel, copper, aluminum alloy and other metals have a strong adsorption effect and can form a stable chelate on the metal surface. Hydrogen bonds can be formed within or between molecules to thicken the adsorption layer and have better anti-corrosion effect.

(4) The application of triazole corrosion inhibitors

The molecules of triazole corrosion inhibitors contain different active adsorption groups such as triazole ring, amino group, hydrophobic group, aromatic ring group and pyridyl group of three nitrogen atoms, which can be centrally adsorbed on the surface of the metal, thereby increasing the coverage of the corrosion inhibitor.

(5) The application of quaternary ammonium salt corrosion inhibitors

Corrosion problem is very serious when acidizing with high concentration hydrochloric acid at high temperature. Quaternary ammonium salt is an important component of corrosion inhibitor for high temperature acidification. Quaternary ammonium cation has high surface activity and can form a dense and complete covering film on metal surface. This kind of corrosion inhibitor has been widely used in oil and gas well protection.

(6) The application of alkynyl alcohol corrosion inhibitors

The three bonds in the alkynyl compound have a strong binding force with the metal, which makes the three bonds easy to break, and then polymerization occurs, resulting in multilayer polymerized film. Long chain nitrogen-containing compounds have good shielding effect, so the corrosion inhibition effect is better when alkynyl compounds and long chain nitrogen-containing compounds are used together.

(7) The application of Schiff base corrosion inhibitors

Schiff base refers to a class of organic compounds containing RC = N which are easy to synthesize, and the RC = N group contained in the molecule is easy to form complexes with metals.

Fourth, the research trend of corrosion inhibitors in petroleum industry

(1) Research on corrosion inhibitors for refinery processes and corrosion inhibitors for acidification at high temperature (above 200℃). Under the condition of high temperature and concentrated acid, the combination of various corrosion inhibitors can greatly improve the anti-corrosion effect.

(2) Local corrosion (pitting corrosion, underscale corrosion, stress corrosion) of equipment in oil and gas Wells is very serious, and local corrosion is the main reason for the failure of production equipment. However, there are few researches on corrosion inhibitors to prevent local corrosion. Specific corrosion inhibitors should be studied for uniform corrosion and local corrosion respectively.

(3) The use of modern advanced analysis and testing instruments and computers, from the molecular and atomic level to study the behavior of corrosion inhibitor molecules on the metal surface and the mechanism of action, the synergistic mechanism between corrosion inhibitors, to guide the research and application development of corrosion inhibitors.