Design of the Harmony and Heritage Platforms for Offshore California

Abstract

Abstract The Harmony and Heritage platforms are planned by Exxon Company, U.S.A., for installation planned by Exxon Company, U.S.A., for installation offshore California, in 1200 feet (366 m) and 1075 feet (328 m) of water, respectively. The design criteria and analysis procedures are an extension of the technology used for the 850-foot (259 m) water depth Hondo platform, about ten years ago. Each of various in-place (environmental) and installation loadings are discussed, and their relative impacts on jacket weight are evaluated. Introduction Exxon Company, U.S.A.'s Hondo platform was installed in the Santa Ynez Unit in the Santa Barbara Channel in 1976. The design and construction procedures of this 850-foot (259 m) water depth platform (which are described in References 1 and 2) have evolved to meet the additional challenges presented by the Harmony and Heritage platforms, the next developments for the Santa Ynez Unit. As shown in Figure 1, the Harmony platform will be located about 3 miles (4.8 km) west of the Hondo platform, and the Heritage platform will be located about 7 (11.3 km) miles west of Harmony. Pipelines are planned to extend from Heritage to Harmony, to Hondo, to a terminal. Like Hondo, both platforms were designed by Exxon Company, U.S.A., with extensive support by its research affiliate, Exxon Production Research Company. Designs for a one-and two-piece option and for a Far East and West Coast jacket assembly are essentially complete. The anticipated schedule for the platform jacket design and construction is shown in Figure 2. To capture economies of scale, design and fabrication of the Heritage platform is planned to be simultaneous with that for Harmony, and water phase construction will be sequential. phase construction will be sequential. PHYSICAL FEATURES PHYSICAL FEATURES As shown in Figure 3, the Harmony and the Heritage platforms are similar to the Hondo platform. They are all 8-legged, pile founded platform. They are all 8-legged, pile founded structures for the support of drilling rigs, production equipment, and personnel quarters. production equipment, and personnel quarters. The size of the new platforms prohibits the use of any existing fabrication yards on the U.S. West Coast. Also, no existing barge is capable of carrying either jacket as a single unit across the Pacific. Thus, to encourage competitive bidding and launch barge development, both one-piece and two-piece (like Hondo) jackets were designed and offered to potential fabricators. potential fabricators. The deck structures on Harmony and Heritage are essentially identical. They are three-level modular decks, atop a module support frame. The deck plan is 180 feet by 145 feet (55 m by 44 m) with a total area of about 78,000 square feet (7300 m2). Two drill rigs and 60 well conductors are planned for each platform. The total topside weights above the module support frame is about 40,000 kips (mass 18,100 Mg) for each platform.