Overview

Petroleum is a natural oil mixture. Because of its high energy density and convenient transportation, petroleum is used as an important fuel in industry and transportation. It has a role that other materials cannot replace. In our lives, petroleum is used as fuel for automobiles, ships, and airplanes; in industrial production, it is the raw material for many industrial chemical products, so it is one of the most important commodities in the world.

However, petroleum is a limited energy source, it is non-renewable, and it takes 2 million years for pure natural formation. Therefore, people can only extract natural oil from several kilometers deep underground for people to use. In this article, we will introduce the principle of petroleum exploitation and the selection of nickel alloys in petroleum exploitation.

The Principle of Oil Drilling

Most of the oil nowadays is generally buried several kilometers underground. Therefore, people must first detect whether there is oil underground in a certain place through technical means. After the exploration is completed, people can start oil extraction. The equipment that goes deep into the ground in the process of extracting oil is called oil well pipe. The oil well pipe is divided into three parts: drill string, casing and tubing.

Drill String

The drill string is a long strip of drill bit that can destroy the rock underground and dig to the depth of the oil. The well dug is a circular hole with a depth of several kilometers, and the oil is extracted from this hole. The working principle of the drill string is shown in the figure below:

Casing

Since the oil well dug by the drill string is several kilometers deep, such a deep oil well can easily lead to the collapse of the formation. Therefore, during the drilling process, a pipe needs to be placed in time. This pipe is called a casing, and its role is to fix the oil well. The structure increases the stability of the oil well and prevents the collapse of the formation. The working principle of the casing is shown in the figure below:

Tubing

After the oil well is excavated and fixed, a nickel alloy capillary tube needs to be inserted into the casing. The role of the tubing is to transport underground oil to the surface. The following figure shows the working principle of the tubing:

The Environment and Requirements of Oil Drilling

Before exploiting oil, we must clarify the environment of the oil layer and make targeted selection of materials according to different mining environments.

Temperature Environment

The ambient temperature of the oil layer mainly depends on the depth of the oil layer. The deeper the oil layer, the closer the mining environment is to the mantle, and the higher the mining temperature. In the early stage of oil exploitation, the depth of the oil wells that people exploited was only about 1,000 meters.

At this depth, the ambient temperature is not high, so ordinary stainless steel (such as 316) can be well qualified for the work of oil exploitation. But now as the depth of the oil well reaches 6000 meters, the ambient temperature can reach more than 200°C. In this high temperature environment, the use of nickel alloys has become inevitable.

Corrosive Environment

With the development of oil more and more to the later stage, the environment of many oil layers has become more and more severe. There are often high concentrations of corrosive elements such as H2S, CO2, S, and Cl-. In this environment, commonly used stainless steel is no longer competent. People are increasingly using nickel alloy pipes with better corrosion resistance to manufacture oil well pipes.

Stressful Environment

Many oil layers are buried in underground with high pressure. These oil fields do not require manual pumping. As long as the valve is opened, the oil will be ejected under its own pressure. In this process, the oil well pipe will be subjected to very large stress.

Coupled with higher temperature, the steel pipe of general material is prone to fracture. The nickel alloy has very large high-temperature strength and stress corrosion resistance, and it can easily handle various high-temperature, high-pressure and high-corrosion environments.

Material Introduction and Selection Basis

Nickel alloys commonly used in petroleum drilling engineering are: Inconel 625, Incoloy 825, Incoloy 028, Hastelloy G-3 and Hastelloy C-276. Their chemical compositions are as follows:

NICKEL

As nickel has a significant tendency to passivation, pure nickel itself has good corrosion resistance. In dilute non-oxidizing acids, especially in neutral and alkaline solutions, the corrosion process is significantly slowed down. In addition, nickel can dissolve a large amount of chromium, copper, molybdenum and other elements, and maintain a stable FCC (Face Centered Cubic) structure, so nickel is an important matrix for all nickel alloys.

Chromium

Chromium is easier to passivate than nickel. It can endow the alloy with anti-corrosion ability in oxidizing medium, as well as anti-oxidation and anti-sulfurization ability at high temperature. After adding chromium element to the alloy, a Cr2O3 film is formed on the surface, which can improve the oxidation resistance and corrosion resistance of the alloy. All the above nickel alloys have a lot of chromium content to resist oxidizing elements in oil wells, especially Incoloy 028 and Hastelloy G-3.

Molybdenum

The addition of molybdenum can significantly improve the corrosion resistance of the alloy in reducing media (such as hydrochloric acid and sulfuric acid). In addition, the addition of molybdenum can significantly improve the alloy's resistance to local corrosion (such as pitting and crevice corrosion) and resistance to chloride intergranular. Therefore, adding chromium and molybdenum elements to the alloy at the same time can improve the corrosion resistance of the alloy in the oxidizing medium and the reducing medium, and improve the local corrosion resistance of the alloy. Inconel 625 and Hastelloy C-276 contain more molybdenum elements, so they are more suitable for oil wells in reducing environments.

Copper

The addition of Copper is mainly to improve the corrosion resistance of the alloy in reducing media, and the alloy has excellent corrosion resistance in fluid seawater, salt water, and solutions containing HF acid. Therefore, if you are mining oil in the sea, you can choose Incoloy 825, Incoloy 028 or Hastelloy G-3.

Tungsten

As an important solid solution strengthening element, tungsten can increase the strength of single crystal alloys, so that Hastelloy G-3 and Hastelloy C-276 have better local corrosion resistance and creep resistance in high-pressure environments.

Aluminum

As an important precipitation strengthening element, aluminum can significantly increase the strength of the alloy. Therefore, in extremely high-pressure oilfield environments, high-strength Inconel 625 and Incoloy 825 alloys are recommended.

Cobalt

The addition of cobalt can significantly increase the creep strength of the material. In long-term engineering, Hastelloy G-3 and Hastelloy C-276 with high cobalt and tungsten content have greater advantages.

Niobium

The high niobium content of Inconel 625 makes it have very high strength in an environment above 200°C. With the aluminum element in the composition, it can be competent for any extreme high temperature and high pressure oil field environment.

Iron

Iron can improve the compatibility of alloying elements with the matrix, and at the same time can reduce costs. In the case of meeting the conditions of use, Incoloy 825, Incoloy 028 or Hastelloy G-3 can be used as much as possible to reduce the cost of the project.

Conclusion

• 1. Oil drilling is a technology for extracting oil by using oil well pipe systems to dig oil wells and transport oil from the underground to the ground.
• 2. As the depth of the oil well increases, the environment of the oil layer becomes more and more severe. It is necessary to use high temperature nickel alloy to replace ordinary steel for mining.
• 3. The environment of the oil field must be probed before mining. Depending on the oilfield environment and budget, different nickel alloy materials can be selected to meet different needs.

AEETHER CO., LIMITED produce nickel alloys for Oil & Gas applications. If you have any requirements, you can send inquiry to our E-mail: