The paper provides laboratory test data that was used to select high strength, nickel base alloy, production tubing for Mobil's 823 field. The application is of critical importance because of the large quantity of H2S (0.5 to 5 mole percent at 20,000 psi BHP) present in Mobile Bay wells. A rigorous test and evaluation program was required to ensure that the selected tubulars are immune to stress corrosion cracking and localized corrosion. New test methods consisting of slow strain rate experiments and critical pitting temperature tests were employed to diagnose temperature limitations and alloy class suitability.

The data suggest that some alloy types may exhibit an localized corrosion and stress corrosion cracking at intermediate temperatures (250 – 350 F). The intermediate region of temperature in which cracking is seen for cold worked high alloy tubing is a novel observation for sour gas well environments and is associated with situations in which the normally protective chromium oxide on the metal is transformed to a predominantly sulfide film. Elemental sulfur was found to have a major influence on cracking susceptibility.

This research supports the economic selection of high alloy tubing for critical applications such that the alloy content is matched to the actual field requirements this resulting in significant cost savings. Reliability of production equipment is maximized by a firm understanding of degradation mechanisms and temperatures.

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