How to Select Materials for Downhole Tools?

Material selection for downhole tools is influenced by multiple factors. From the perspective of downhole tool types:

Drilling tools, logging tools, and workover tools: These tools have a short service life downhole, so they require high strength but have low corrosion resistance requirements.

Completion tools: They need to work downhole for several years, so downhole temperature and corrosion resistance must be considered.

From the perspective of downhole environments, they are usually classified into four categories:

Standard environment (free of hydrogen sulfide (H₂S), with carbon dioxide (CO₂) content less than 1 psi [approximately 0.0069 MPa]);H₂S corrosion environment;CO₂ corrosion environment;Combined corrosion environment of H₂S and CO₂.

Material Selection for Downhole Tools in Standard Environments

For downhole tools used in standard environments, alloy steels such as 4130, 4140, and 4145 (AISI grades) are usually selected. The chemical compositions and mechanical strengths of these materials are shown in the following tables:

1. Comparison of Chemical Compositions (Mass Fraction)

2.Comparison of Mechanical Strengths

As can be seen from the tables:

The carbon content of these materials increases in sequence (4130 < 4140 < 4145), while the contents of other elements are similar.

Mechanical properties: Strength is positively correlated with carbon content—4145 has the highest strength—while toughness decreases inversely, with 4130 having the highest toughness.

4130, 4140, and 4145 are international material grades, and their domestic equivalents in China are as follows:

• 4130 (AISI) ≡ Domestic grade 30CrMoA;
• 4140 (AISI) ≡ Domestic grade 42CrMo;
• 4145H (AISI) ≡ Domestic grade 45CrMo.

4130 and 4140 are suitable for conventional completion tools, with emphasis on cost-effectiveness and weldability.

4145H is often used in deep-well, high-pressure, or high-load tools (such as drilling tools and workover tools), with priority given to strength and wear resistance.

Material Selection for Completion Tools in Corrosive Environments

For completion tools in corrosive environments, the selection mainly depends on the partial pressure of acidic gases (divided into two types: CO₂ and H₂S).

1. Wells with High CO₂ Content

To resist CO₂ corrosion, the chromium (Cr) content in materials needs to be increased. The following materials (sorted by Cr content) can basically cover wells with CO₂ partial pressure ranging from 0.5 MPa to 14 MPa ：3Cr (Cr content ≈ 3%), 9Cr1Mo (Cr content ≈ 9%), 13Cr, S13Cr, 17Cr (grade S17400), 22Cr (e.g., duplex stainless steel S32205), and 25Cr steel.

2. Wells with High H₂S Content

To reduce sulfide stress cracking (SSC) corrosion, the nickel (Ni) content in materials needs to be increased. When the H₂S partial pressure is higher than 1 MPa and the CO₂ partial pressure is also high, high-temperature alloys such as the following should be used:

Material Selection for Special Components

Main materials of downhole tools (in contact with well fluid and bearing loads): Selected in accordance with the above standards.

Shear components: Generally made of H62 brass or S36600 stainless steel bars.

Anchoring components: Selected from 20CrMoTi or 20CrMnTi. To improve surface hardness, surface carburizing treatment (with a carburized layer thickness of 0.8-1.2 mm) is required, which increases the surface hardness to HRC 58-62.

Other Factors Affecting Material Selection and Reference Standards

In addition to acidic gases, the material selection for downhole oil casings and downhole tools is also related to downhole temperature, water cut, mineralization degree, and pH value. For more specific selection criteria, refer to the industry standard Q/HS 14015 Design Guidelines for Corrosion Prevention of Tubing and Casing in Offshore Oil and Gas Wells.

Landrill also supply 41430、4140、4145 steel material bar.

Feel free to inquire.https://www.landrilloiltools.com/