Design of the Hondo Platform for 850-Ft Water Depth in the Santa Barbara Channel

Abstract

This paper describes the design problems associated with installing the Hondo platform in Santa Barbara Channel in 850 ft (259 m) of water. Earthquake, severe storm, operating loads, and platform criteria, as well as the fatigue resistance and structural ductility, were considered during the design of this platform. Solving the design problems minimized the need for new methods and equipment. Introduction In Feb. 1968, Exxon Co. U.S.A. leased more than 360 sq miles (932 km) in the Santa Barbara Channel off southern California. In the fall of 1970, 18 leases were unitized into the Santa Ynez Unit, located about 23 miles (37 km) west of Santa Barbara and 5 miles (8 km) south of Gaviota (Fig. 1). The drilling and production platform is in Federal Block OCS-P-0188, which varies in water depth from 300 to 1,300 ft (90 to 400 m). The platform is in 850 ft (259 m) of water at latitude 34 deg. 23' 26.6", longitude 120 deg. 7' 13.9" (Fig. 2). Because of the water depth, a single integrated platform capable of performing all basic functions is essential. This means that production and drilling facilities are combined with living production and drilling facilities are combined with living quarters on the three-level modular deck. During the development of the integrated deck, safety was a particularly important consideration because the living particularly important consideration because the living quarters are near the producing facilities. The structural concept of the deck was determined by drilling and producing, operating, environmental (earthquake and producing, operating, environmental (earthquake and storm), transportation, installation, and removal loads. To satisfy all requirements, modular, multiple-deck units composed of deep trusses were used.This paper discusses the design of the "in-place" structure, not the installation; however, platform areas (launch trusses, launch leg joints, etc.) controlled by installation loads will be discussed. Preliminary Jacket Design Preliminary Jacket Design Various concepts were studied, -and Exxon determined that a conventional jacket platform was advantageous for this application in 850 ft (259 m) of water. The jacket's length did create a transportation problem because a single launching of an 850-ft (259-m) long jacket would not be practical. Exxon pursued a plan of launching the jacket in sections and joining them at sea, which resulted in the chosen design (Fig. 3).The jacket is composed of four east-west trusses (Column Rows A, B, C, and D) and two north-south trusses (Column Rows I and 2). These contain 14 horizontal framing levels supported by eight main legs, and cross and diagonal bracings. The structure is anchored to the ocean floor by eight 48-in. (1.2-m) main piles penetrating 340 to 375 ft (104 to 1 14 m) into the piles penetrating 340 to 375 ft (104 to 1 14 m) into the sea floor, and twelve 54-in. (1.37-m) skirt piles penetrating about 255 ft (78 m). The main piles are penetrating about 255 ft (78 m). The main piles are welded to the jacket at the waterline and are grouted to the bottom 200 ft (61 m) of the main legs. Skirt piles are grouted in the skirt pile sleeves for 110 ft (34 m). Twenty-eight 22-in. (56-cm) diameter conductors were driven to a final penetration of 300 ft (91 m). The bottom of the jacket is sloped to match the 4 deg. slope of the ocean floor. The jacket measures 169 x 233 ft (52 x 71 m) at the base, 45 x 125 ft (14 x 38 m) at the waterline; it is 865 ft long (264 m) and weighs 12,000 tons (10.89 Gg) in place. When launched, the upper unit weighed about 5,000 tons (4535 Mg) and the lower unit weighed 7.000 tons (6350 Mg). JPT P. 407