Coping with Nature Offshore An SPE-AIME Distinguished Lecture

Abstract

Introduction The distinguishing feature of development for offshore petroleum is the need to provide a dry, stable working space from which personnel can operate in the conduct of conventional petroleum drilling and production. The industry has devoted substantial production. The industry has devoted substantial effort and money to meet the need for working platforms, in the form of either fixed or floating platforms, in the form of either fixed or floating structures. The design of these structures obviously requites expertise in structural engineering. Moreover, there is an accompanying need for competence in oceanography to understand the environmental forces in the ocean. Both structural engineering and oceanography are outside the traditional petroleum or mining engineering activity. Nevertheless, the offshore industry must employ, and in many cases contribute to advancements in, these technologies. Consequently, petroleum engineers are increasingly being called upon to direct work in these unfamiliar subjects. This conceptual introduction to offshore structures and the governing ocean environment is directed at those engineers. Fixed Platforms The basic element of offshore development is the fixed, bottom-supported structure or platform. While some platforms afford only minimal walkway area around a single well, many platforms support all the equipment and needs for both the drilling and the production operations. Early offshore platforms were production operations. Early offshore platforms were ordinarily pile-supported piers, such as are commonly observed in harbor installations. However, to meet the special needs of the offshore conditions, the industry has developed a "template" or "jacket-type" structure. There are three distinct components to these structures: the jacket itself, the piling, and the deck structure. The cross-braced jacket must extend from the ocean floor to above the water surface. It is generally assembled from tubular structural members in a fabrication yard. Subsequently, the jacket is moved onto a barge and transported to the off shore location. There it is launched or lifted into the water for placement at the prescribed site. (See Fig. 1.) Once the jacket is prescribed site. (See Fig. 1.) Once the jacket is in place, piling are lowered down through the tubular legs of the jacket and driven or otherwise installed deep into the ocean floor. The jacket and piling are then secured together, and the deck is raised to rest on top of the piles. (See Fig. 2.) Platform concepts and installation are discussed in Refs. 1 and 2. To install offshore platforms, which are very large structures, special construction equipment is necessary. Most impressive is the fleet of derrick barges serving mainly the offshore industry. JPT P. 257