A Review of the Offshore Environment - 25 Years of Progress

Abstract

Offshore operations and JPT have grown up together. A quarter of a century has seen platforms evolve from a drilling deck prayerfully supported on 22 piles sunk in soft mud under 20 feet of water to an 8-pile structure rising confidently through more than 300 feet of water. Introduction In 1947, the Kerr McGee-Phillips-Stanolind group supported a drilling deck on 22 piles driven into the soft mud floor of Ship Shoal Block 32. This move into 20 ft of water in the hurricane-plagued Gulf of Mexico opened a new chapter in the story of marine oil operations that had begun in the lake, marsh, and tide zone fields of earlier times. Today, however, an operator of a field in water more than 300 ft deep typically supports his equipment on an eight-pile structure, and with the confidence that the platform will withstand storm forces. Behind that dramatic expansion of technical capability is a growth of knowledge about the ocean environment and the forces it can generate. This paper will trace that growth of knowledge by examining the technical literature. Environmental forces are, of course, only one of the factors in successful operations in the ocean today. Great advances have been made in the design of huge drilling barges, subsea systems, producing equipment and oil transfer and storage systems; each has a story by itself. Although the environmental studies have important applications in all those developments, the tremendous investment in fixed platforms has been a prime motivation for increasing our knowledge of the ocean environment. For that reason, this paper is mainly about the technology developed for fixed platforms. The Journal of Petroleum Technology was established at about the same time offshore operations began in growth, and JPT has been an important vehicle for disseminating the technical advances that mark that era. More than 100 papers on all phases of offshore activity have been published in the Society's journals and many of these papers defined the advances in knowledge of the offshore environment Wave Heights The location of early activity in the Gulf of Mexico, where hurricane waves of great height and force were encountered, focused attention on improving knowledge of wave heights. This wave-height information is the starting point for platform design. From it the elevation of the platform deck and the basis for wave forces is determined. The piling structure exposed to wave action is relatively transparent to waves, whereas the deck structure has much more surface area and would receive a massive force if struck by a wave. The bottom of the deck structure, therefore, is placed above the highest wave the platform is expected to experience. An important question arises: What is the highest wave a platform will experience? This question is difficult to answer. The general literature on this subject is extensive, and the offshore industry has drawn upon important contributions by many persons. This section is confined, however, to work on waves generated by wind blowing across ocean areas and particularly to engineering applications to offshore platform design. JPT P. 1355