Current and future flow streams from HTHP wells usually have to contend with H2S, CO2, and chlorides at high temperatures. At wells with temperatures of over 350F this hostile environment requires selecting Nickel-based alloys for tubing/casing that are corrosion resistant alloys (CRA). Unfortunately, these Nickel-based or high chrome corrosion resistant alloys (CRA's) can be expensive particularly considering that some HPHT wells are being considered for completion depths of over 30,000 feet. In addition, CRA mill capacities are at their limits with deliveries projected of up to 2 to 3 years. It is imperative for HPHT well projects to be able to move forward by providing alternative alloys that can help to alleviate these issues with Nickel-based CRAs. Titanium alloys can potentially provide for an alternative opportunity. The price for Titanium alloys has historically been higher than that for Nickel-based alloys. However, Titanium alloys are approximately half as dense as Nickel-base alloys so a pound of Titanium can provide twice as much tubing. This test program has shown that Ti-6246 is competitive and complimentary to the Nickel-based alloys traditionally used for production tubing in corrosive and highly sour wells. The Ti-6246 shows excellent resistance to environmental stress cracking in production, workover and completion environments that may occur in severe HPHT and deepwater fields. Burst strength and connection performance have also been documented. This test program has pointed out some limitations of the Ti-6246 alloy that will be resolved with appropriate project planning, tubing design, and field operations practices, which take into account the unique properties of the metal. As with any CRA materials selection, project-specific testing should always be considered to define material performance with respect to the environments and stresses assumed for the completion. After redesigning a 4.5' tubing connection to take into account titanium's unique properties, a premium metal to metal seal can perform well under the high temperature and high pressure conditions in Chevron's sour service fields.
Titanium alloy tubing for HPHT applications
Rohrleitung aus Titanlegierung für HPHT-Anwendungen
2008
17 Seiten, 6 Bilder, 3 Tabellen
Conference paper
English
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