Development of the Guyed Tower: A Case History

Abstract

Abstract Development of the guyed tower to support deepwater oil and gas production operations has been underway for about two decades. In the summer of 1983, a major milestone was reached with the installation of the first guyed tower production platform on the Lena field in the Gulf of Mexico. The authors trace the history of the development of this concept within their companies from the seed ideas in the early 1960s, through a major offshore test, to the installation of the Lena guyed tower. Possible future developments are also discussed. Introduction The installation last summer of the world's first guyed tower production platform in 1000 ft (305 m) of water in the Gulf of production platform in 1000 ft (305 m) of water in the Gulf of Mexico marked a major milestone in the development of this concept for deepwater petroleum production. The evolution of the guyed tower has been the result of the imagination, dedication and foresight of a large number of research, engineering and management personnel over two decades. personnel over two decades. Exxon Production Research Company and Exxon Company, U.S.A. have had major and continuous roles in the development of this concept. The history of guyed tower development within these companies constitutes an excellent example of the effort and time required to develop a major new offshore production system. The purpose of this paper is to outline the steps taken by these purpose of this paper is to outline the steps taken by these companies in the development of the guyed tower and to show how it evolved as the technical understanding of its characteristics and perception of its applicability improved. THE EARLY DAYS Ever since its beginnings in the late 1940s, the offshore petroleum industry has been searching for economic means of petroleum industry has been searching for economic means of developing reserves in progressively deeper waters. As water depths of interest increased, the size and cost of conventional, pilefounded steel jacket platforms (Fig. 1) increased at an pilefounded steel jacket platforms (Fig. 1) increased at an ever-greater rate. Two factors influenced this size growth:the increasing lever arm over which the environmental forces act to create moments at the base of the structure andthe tendency of the natural period of vibration of the structure to increase into the range of period of vibration of the structure to increase into the range of wave periods. Both of these factors create the need for a stiffer, wider structure and more extensive foundation if the platform is to remain rigidly based on the seafloor. It is not surprising that guyed structures have been considered for offshore use as a potential solution to this problem. These types of structures have been used for many years to resist horizontal loads with a minimum of structural material. As far back as 1894, A. W. Palmer was awarded a U.S. patent for a guyed platform for "making borings at the bottom of deep waters and in platform for "making borings at the bottom of deep waters and in tideways." In the early 1960s, an Exxon engineer proposed that cable-stayed single well conductors be used for drilling and producing in the waters off the coast of Venezuela. This was producing in the waters off the coast of Venezuela. This was basically an extension of the techniques being used in the shallower waters of Lake Maracaibo where tripod-supported wells were drilled using a derrick cantilevered from a drilling barge. By the mid-1960s, this concept had evolved into a multi-well structure held together by a lattice of trusses (Fig. 2). The wells were to be drilled from a floating rig. The only production facilities on the structure were the wellheads: flowlines would carry production to shallower water for processing. The base was supported by a bearing-type foundation called a spud can. This idea was borrowed from jackup drilling rigs. In fact, the concept was essentially a jackup leg containing wells and supported by guylines. A buoyancy can near the top was to be used to aid installation. The guying system at this time was a conventional marine mooring system using drag anchors.