Lena Guyed Tower Project Overview

ABSTRACT The installation of the Lena guyed tower was one of the industry's most significant accomplishments of 1983. This paper serves as an introduction to a series of papers to be presented at the 1984 Offshore Technology Conference concerning the design, fabrication, and installation of the Lena guyed tower. The purpose of the paper is to provide an overview of the entire project, including the evolution of the guyed tower concept and the extent to which this concept may be applicable to other prospects. The most important design features of the Lena guyed tower are briefly discussed in order to prepare the reader for the more detailed treatment provided by the other papers in this series. Particular attention is focused on project management, primarily from the perspective of manpower usage, schedule control, and cost management. Successful techniques that may be of value in the management of future projects are identified. INTRODUCTION Guyed Tower Development Since the offshore petroleum industry began in the 1940's, an economical means of developing reserves in progressively deeper water has been pursued. As water depths of interest increased, the size and cost of conventional, pile-founded, steel-jacket platforms increased at a much greater rate. One approach to the problem of disproportionate increases in the size of the deepwater structures has been the use of guying systems. Exxon Production Research Company first considered the guyed tower in 1965. In 1975 Exxon and 12 other companies built a one-fifth scale model of a tower designed for use in 1500 feet of water. The unmanned, heavily instrumented test tower was installed in 300 feet of water in the Gulf of Mexico near Grand Isle, Louisiana. The foot-square tower had eight 3/4-inch guylines that modeled a full-scale system. Test data from the tower confirmed that the basic guyed tower concept was sound. During 3 1/2 years of operation, the test tower experienced a number of waves that, in full scale, approximated or exceeded North Sea design conditions. Maximum measured guyline tensions and tower .motions matched well with predicted maximum tension and motions. Lena Guyed Tower In mid-1978, a decision was made to design a guyed tower specifically for the 1000-foot. Wterdepth at the Lena Prospect in the Gulf of Mexico. As shown in Figure 1, the Lena Prospect straddles the 1000-foot water depth contour line and consists of four tracts, all of which are in the Mississippi Canyon area. The design of the Lena guyed over. Differed significantly from the test tower con. The use of a spud-can foundation was located to favor of eight centralized main piles to prevent settlement. Torsion piles were added at each of the four corners of the jacket to resist base torque and shear loads.