Evaluating Deepwater Development Concepts

Abstract

Summary This paper provides an overview of the current state of deepwater technology. It discusses the major factors that must be considered when evaluating potential deepwater development concepts, presents proven deepwater development concepts, and provides insight into the applicability of each. Two unproven "dry tree" concepts are presented to illustrate proposed new concepts. Approximate costs are included, leading up to general conclusions with respect to the evaluation process. The focus is primarily on the Gulf of Mexico. The Deepwater Market The incentives for developing deepwater fields are clear. World oil demand is expected to rise annually by an average of 890,000 B/D between 1993 and 1995. The U.S. has a serious balance of payments problem that is aggravated by the fact that it is importing more than half of its oil. The east and west coasts of the U.S., plus the section of the Gulf of Mexico east of Alabama, are restricted from drilling. Total deepwater discovered and potential reserves in the Gulf of Mexico are estimated to be 2 to 4 billion bbl and 10 to 12 billion bbl, respectively. More than 20 undeveloped discoveries exist in the Gulf of Mexico in water depths ranging from 2,400 to 7,520 ft. Development Options and Critical Issues Development Options. Deepwater fields can sometimes be developed with subsea tieback techniques without requiring a deepwater platform at the field itself. If a deepwater platform at the field is required, a wide choice of type exists. The list of proven and unproven (but highly developed) deepwater platform concepts includes (1) steel and concrete tension leg platforms (TLP's); (2) semi- and monohull, steel and concrete floating production systems (FPS's); (3) steel and concrete spars; (4) concrete deep draft floaters (DDF's); and (5) compliant towers (primarily steel). Some critical issues to consider when selecting concepts to include in a detailed evaluation study will be presented before describing the various deepwater development concepts and discussing the pros and cons of each. The pros and cons of the use of DDF's will not be included because the 45-ft draft limitation along the U.S. gulf coast will probably prohibit their use unless and until suitable techniques for mating an integrated deck to an already-moored hull are developed.