Service Experience with Offshore Mobile Drilling Units
Authors: Foley John L. 
Published: December 2007

This paper was prepared for the Second Annual European Meeting of the Society of Petroleum Engineers of AIME, to be held in London, England, April 2–3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
From a successful drilling venture situated in the Gulf of Mexico in 1949, the offshore petroleum industry has evolved into a worldwide, multibillion-dollar operation utilizing various and sophisticated types of mobile drilling units. The American Bureau of Shipping, as an independent classification agency, has been participating in the development of these units from their inception.
Because of the advancements in the design of the structures and their expanded sphere of operations, the necessity of formal standards for self-regulation became apparent. Due to its experience with mobile drilling units through classification services and international affiliates, the Bureau was requested in 1966 to formulate the first standards. Efforts in this regard culminated in the 1968 ABS publication of the Rules for Building and publication of the Rules for Building and Classing Offshore Mobile Drilling Units.
Since then, to keep pace with the improved state of knowledge and to properly reflect industry developments, appropriate changes were effected in the rules, resulting in a 1973 edition.
Through experience, the Bureau has recognized certain problem areas common to the fabrication of mobile drilling units. Of particular concern are those involving particular concern are those involving weldments, since they are of the utmost importance to the integrity of the structure. It is hoped that future weld defects may be minimized by directing attention to their potential occurrences. In this regard, specific welding problems are described and their remedies problems are described and their remedies explained.

EVOLUTION OF OFFSHORE MOBILE DRILLING UNITS
From a revolutionary idea originated in the waters off the Louisiana coast, offshore drilling has grown into an international industry that invests well over $2 billion annually. The petroleum industry's expanding fleet of self-elevating, column-stabilized, and surface-type units now includes 214 rigs in operation and 59 that are under production or in the planning stage. The basis for this ambitious planning stage. The basis for this ambitious drilling rig program is, of course, the soaring demand for energy.
Before the introduction of the first mobile unit, offshore drilling had been limited to stationary platforms standing in shallow water on stilt-like legs. However, the distinct disadvantage of these structures was that it was economically prohibitive to move them to a new site if they did not strike oil.