High performance age-hardenable nickel alloys solve problems in sour oil and gas service

The new frontier of oil and gas exploration will be with deep wells, particularly in deepwater. Most of the “easy-to-pick” fruit have been taken with shallow field development. Compared to shallow wells, deep wells generally require more high-performance, nickel-base alloys. Wells are categorized as being either “sweet” or “sour.” Sweet wells are only mildly corrosive, while sour wells are very corrosive. Sour wells can contain hydrogen sulfide, carbon dioxide, chlorides, and free sulfur. There are different levels of corrosive conditions that are compounded by temperatures up to 500 F (260 C) and pressures up to 25,000 psi (172 MPa). Deep wells generally have higher temperatures and pressures. Material selection is especially critical for sour gas wells. The materials of choice must be corrosion-resistant, cost-effective, reliable, and have the required strength for the well conditions. As these conditions become more severe, material selection changes from carbon steels for “sweet” wells, to duplex (austenitic-ferritic) stainless steel, to INCOLOY alloys 825 or 925TM, to INCONEL alloys 725HS and 725TM for sour well service. The limiting chemical compositions of the nickel-base alloys are displayed in Table 1.