Design Of The Hondo Platform For B50-Feet Water Depth In The Santa Barbara Channel

ABSTRACT Exxon Company, U.S.A. has recently installed a drilling and production platform in the Santa Barbara channel off California in a water depth of 850 ft. Man of the design problems associated with this effort were especially challenging because of the water depth and seism city of the area. Exxon solved these problems with a concentrated effort to extend Gulf of Mexico technology thus minimizing the need for new methods and equipment. This paper presents a description of the platform and the criteria governing its in-place design. The background of these criteria are discussed as are the analyses performed, to assure that each criterion was satisfied. Earthquake, severe storm, and operating loads were considered as well as the platform's fatigue resistance and structural ductility. The results of these analyses are discussed. INTRODUCTION In February, 1968, Exxon Company, U.S.A. leased more than 360 square miles in the Santa Barbara Channel off Southern California. In the fall of 1970, 18 leases were unitized into the Santa Inez Unit, located approximately 23 miles west of Santa Barbara and 5 miles south of Gaviota (Fig. 1). The drilling and production platform is in Federal block OCS-P-0188, which varies in water depth from 300 feet to 1300 feet. The platform is in 850 feet of water at latitude 34 ? 23' 26.6", longitude 120 ? 7' 13.9" (Fig. 2). Because of the water depth, a single integrated platform capable of performing all the basic functions is essential. This means that production and drilling facilities are combined with living quarters on the three-level modular deck. In the development of the integrated deck, safety was a particularly important consideration because the living quarters are close to producing facilities. The structural concept of the deck was determined by drilling and production, operating, environmental (earthquake and storm), transportation, installation, and removal loads. To satisfy all requirements, modular, multiple deck units composed of deep trusses were utilized. Design of the platform was essentially done by Exxon Company, U.S.A. and its research affiliate, Exxon Production Research Company. However, fifteen consultants participated in specialized aspects of the overall design. This paper discusses the design of the "in-place" structure, not the installation; however, platform areas (e.g. launch trusses, launch leg joints, etc.) controlled by installation loads will be discussed. PRELIMINARY JACKET DESIGN Various concepts were studied, and it was determined that a conventional jacket platform was advantageous for this application in 850 feet water depth. The jacket's length did create a transportation problem since a single launch of an 850-foot-long jacket would not be practical. A scheme of launching the jacket in sections and joining them at sea was pursued and resulted in the chosen design (Fig. 3). The jacket is composed of four east-west trusses (column rows A, B, C, D) and two north-south trusses (column rows 1 and 2).