Design and Construction of a Two-Piece Lifted Jack& for the Enchilada Development
Authors: Dorgant Paul L. , Hansen Mark C. , Sgouros G.E. , Sezer Fuat , ter Steege Guus 
Published: October 2008

A new type of jacket design was developed for Shell Offshore Inc.'s Enchilada platform located in the Gulf of Mexico in 630 feet of water. The design was developed by an integrated team representing the operator and contractors and was based on utilizing specific contractor equipment and procedures in order to lower costs and reduce cycle time. The jacket was designed for installation in two sections that were joined underwater with a grouted connection. Both jacket sections were lifted from transport barges and installed on location with HeereMac's SSCV Balder. The installation method avoided the typical launch framing required for jackets in this water depth. Launch framing accounts for as much as 25% of a typical launched jacket weight. This paper describes the unique features and important aspects of the project, including contracting, design approach, fabrication, and installation. The development of this platform concept has added an alternative to conventional single piece launched jacket designs for water depths in the 500 to 700 foot range. Results are presented showing the steel weight savings and the schedule reduction enabled by the design. Information provided in this paper will allow designers and planners to evaluate this alternative design concept.

Introduction

The Enchilada platform was designed as a fixed structure in 630 feet of water in the Gulf of Mexico. The overall field development strategy in Garden Banks Blocks 128 and 172 is described in Reference 1. The primary challenges of the platform design and construction were to reduce costs and lower design to construction cycle time. The design practice for fixed offshore structures is well established. In recent years, designs have steadily produced significant cost and schedule improvements. The challenge of producing further improvements on the established fixed platform design practice requires innovation, risk taking, and new design approaches. During predesign studies for the Enchilada development, a novel design approach and design concept were identified by a team consisting of engineers from Shell, Aker Omega, Aker Gulf Marine and Heere Mac. The design approach utilized an integrated design team to develop a new type of design taking advantage of existing contractor equipment and procedures. The design concept included a two-piece lifted jacket that was joined underwater with a grouted connection.

Platform Functional Requirements

The Enchilada platform was designed for topside facilities capable of processing 60,000 barrels of oil per day and 400 million cubic feet of gas per day. The total topside operating weight is approximately 9,000 tons with an initial dry lift weight of 4,000 tons. The platform will support 15 production wells and 17 import/export pipeline risers. The export pipelines will be capable of transporting over 1 billion cubic feet of gas per day and 250,000 barrels of oil per day (some of the pipelines import production from nearby fields).

Predesign Studies

Preliminary design activities were initiated in November of 1994. With substantial contractor involvement, preliminary designs were developed for both a single piece launched jacket and for the two-piece design that was ultimately chosen. In addition to the preliminary structural design, cost and schedule estimates were developed. At the same time, a preliminary design was developed for the deck and facility.