Offshore Platform Construction Extended To 400-foot Water Depths

Abstract

LEE, GRIFF C., MEMBER AIME, J. RAY McDERMOTT and CO., INC., NEW ORLEANS, LA. Abstract Platforms have been installed in water depths slightly over 200 ft. At the present time there are over one-quarter of a million acres under lease in water depths greater than 200 ft in the Gulf of Mexico. To develop and produce oil found in these leases, platforms will be required. This paper presents the major problems involved in platform construction and discusses possible methods of installation.Since offshore platform construction began in 1947, over 1,000 platforms have been completed in the Gulf of Mexico. Platforms existing in approximately 200 ft of water have been built by lifting the jacket in place with two derrick barges, by launching the jacket from a cargo barge and by installing buoyant jacket with controlled flotation. These same methods are practical and can be extended to deeper water. Present technology and construction equipment are adequate to build platforms in the 400-ft depth range; however, considerable engineering will be required to plan the best suitable platform for a specific requirement. Introduction Offshore platforms have been installed in open water in depths slightly over 200 ft. The lease sale of March, 1962, awarded 246,700 acres in water depths between 200 and 600 ft. Drilling in the Gulf of Mexico is currently underway from floating vessels in water depths of approximately 300 ft. Even with the recent developments in floating drilling and underwater completion techniques, platforms are necessary for development of offshore oil fields and will remain necessary for the foreseeable future. Platforms provide the safest and most dependable means of drilling offshore wells. Any deep-water oil production found in the Gulf will be located far from shore. Only a large oil field could justify a pipeline to shore. Quarters, production and storage facilities will be required in the field whether the drilling was done from floating vessels or from fixed platforms.The purpose of this paper is to present general problems involved in construction of platforms in deeper water and to discuss possible means of installation. Installation techniques or design procedures will not be discussed in detail. Rather, discussion will be limited to the construction of fixed platforms similar to those currently being installed in the Gulf of Mexico. Historical Background In 1946 the petroleum industry looked longingly at the submerged lands in the Gulf of Mexico which were beyond the reach of drilling from timber trestles and platforms. The beginning of modern platform construction came in 1947 with the installation of the first jacket or template-type platform in approximately 50 ft of water. Eight years later, in 1955, the first platform was installed in water 100-ft deep, and by 1959 this had been extended to 200 ft.During the early days of offshore construction, many types of structures were erected. The first platforms were installed by small equipment and required a long installation time. These were supported by a large number of small piles and required considerable bracing, which offered high resistance to wave action. The designs were based on limited data, since very little information was available on the wave forces of hurricanes. As more information became available, platforms were built stronger and more wave-resistant. Larger construction equipment has been built to allow handling heavier units. Designs and construction techniques have been improved and streamlined to yield the present-day platform which utilizes a few large-diameter piling with a minimum of bracing.After 15 years, over 1,000 platforms have been constructed in the Gulf of Mexico. Only a few structural failures have occurred, and there has been no loss of life due to these failures. Most platforms have been installed in water depths up to 150 ft, but four drilling platforms have been installed in water deeper than 180 ft. In other areas, two platforms were built in similar depths Argus Island, a research platform installed for the U. S. Navy, off Bermuda, and Texas Tower No. 4, a radar station built in the North Atlantic. Platform Requirements A platform designed for deeper water must satisfy the following basic requirements..1. The intended purpose must be fulfilled. JPT P. 383^