Installation of the South Pass 52 Platform

Abstract

Installation of the drilling and gas production platform for South Pass 52 required extensive planning and careful consideration of risks brought about by the tripod configuration, economic limitations on exploiting a marginal prospect, soft soils, and potentially significant currents. The jacket, 548 feet long and 2700 tons, relatively light for the water depth, was lifted from the barge at sea. Five foot deep skirts on the mud mats helped mobilize adequate bearing capacity and minimized mat size. Carefully selected ballasting, attention to currents and weather forecasts, and a short exposure time partially compensated for the limited resistance to overturning of the jacket before piles were driven. The jacket made the first use of a new type of pile gripper, shop tested before deployment, which could be used to grip stabbed or partially driven piles for levelling the jacket and minimizing jacket motion during grout set-up. Performance of the plans and systems for installation was generally satisfactory. The risks accepted for the installation were believed to be near the economic optimum. The platform is currently the tallest offshore tripod platform in the world. INTRODUCTION The South Pass 52 platform is a six-slot, pile-supported steel platform in 531 feet of water which supports a drilling rig and production facilities for 60 mmscfd of gas. The combination of relatively low gas production rate and deep water made this prospect a marginal one requiring an economical structure. The general configuration of the jacket and deck is shown in Fig. 1. The jacket is supported by three 72" diameter skirt piles penetrating to depths of 430 to 470 feet below the seafloor. The deck consists of a main deck and a production module. The minimization of weights and areas was accomplished in the deck and module by designing to tightly accommodate a particular drilling rig, by not providing any quarters except those with the rig, by using the space vacated by the drilling rig for compression after the wells are completed, and by using a three-level module for most of the production facilities. The tripod design minimized weight in the jacket. Gas is sold directly to a nearby pipeline and natural gas liquids are piped to ARCO's Mississippi Canyon 148 platform. More details on the design of the platform were given by Whicher et al (1991.) The contract for fabrication and installation of the South Pass 52 jacket and deck was awarded in July 1990. Rolling of tubular members began soon thereafter in a fabrication yard on Bayou Boeuf in Morgan City, Louisiana. The jacket was fabricated in the Harbor Island yard near Aransas Pass, Texas. The deck and production module were fabricated and outfitted at two different yards in New Iberia, Louisiana. The jacket was installed in September 1991 and facilities were started up in early 1992. This paper describes the work done to prepare for and complete the load-out, transportation and installation of the platform.