Hydrogen-induced-cracking resistant and sulphide-stress-cracking resistant steel alloy

Abstract

A steel alloy, for use in casing for oil and gas wells in low pH environments. The steel alloy has a carbon range by weight of 0.15% to 0.35%, a manganese range by weight of 0.60% to 1.10%, a molybdenum range by weight of 0.15% to 0.65%, a calcium range by weight of 0.0045% and a sulfur range by weight of less than 0.002%. The steel alloy also has, by weight, a chromium range of less than 0.50%, and an aluminum range of 0.010% to 0.080%.

Description

[0001] The present application is a continuation application of U.S. application Ser. No. 09 / 036,545, which is a continuation application of application Ser. No. 09 / 036,545 filed on Mar. 6, 1998. The '545 application is a continuation-in-part application of U.S. application Ser. No. 08 / 813,374 filed on Mar. 7, 1997. The present application incorporates by reference the entire contents of all of these parent applications.[0002] This invention relates in general to a steel alloy and more particularly to a steel alloy that resists hydrogen-induced cracking and sulfide stress cracking. This alloy is particularly suitable for use in casing for use with sour oil and gas wells. The invention also comprises casing made from such alloy.BACKGROUND TO THE INVENTION[0003] In a number of different industries including the oil and gas industry, there is a need for steel alloys that can resist severe mechanical stresses, hydrogen-induced cracking (HIC), and sulfide stress cracking (SSC).[0004] Oil...

AI Technical Summary

Problems solved by technology

Many new wells contain significant fractions of H.sub.2S while older wells become increasingly sour over their production lifetime.

However, the casing is unable to expand due to the physical constraints placed on the casing by the environment.

At the conclusion of the stimulation cycle, the well cools and the resultant thermal contraction of the material results in a tensile load.

This cycling will be repeated several times through the life of the well and places severe fatigue stresses on the casing.

Unfortunately, seamless casing is very expensive to manufacture.

To be effective, boron must be retained in solid solution throughout the processing schedule; however, boron interacts strongly with nitrogen to form boron nitrides which render boron additions ineffective.

However, even alloys that demonstrate good HIC resistance in laboratory trials may perform poorly when stress is applied.

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