This paper describes the results of conceptual design studies conducted to develop efficient deepwater fixed platform configurations. This work resulted in the development of the Composite Leg Platform, which has proven to be effective in both compliant (CCLP) and noncompliant (CLP) versions. In these studies, features were integrated into the configuration which offer improved efficiencies for in-place, fabrication and installation phases. The results of a preliminary design for a CCLP in 2600 ft. of water in the Gulf of Mexico are reported, including dynamic response characteristics, design force levels, and steel tonnage requirements. Fabrication and installation requirements and procedures are discussed. Schedules and cost estimates for the construction phases are included in this paper.
The development of viable deepwater drilling and production concepts is a topic of great practical importance today. Discoveries of significant reservoirs in deepwater have been made and are anticipated in several areas of the world including the North Sea, the Mediterranean Sea, the southern Atlantic offshore Brazil and the Gulf of Mexico. However, the current intensity of deepwater activity in the Gulf of Mexico is probably unsurpassed anywhere.
The current price of oil and the increasing development costs in deeper waters are factors which combine to demand more efficient solutions than those used traditionally in shallower water depths. A relatively few, but increasing, number of firms have invested significant amounts of time and resources investigating alternative solutions. Many concepts have been proposed, but relatively few are considered to be viable candidates. In many cases, the proposed concept is found to be effective for in-place conditions, only to be judged after more in-depth investigations to be impractical or too costly to construct. A viable candidate must be technically sound; however, of equal importance is the requirement that the construction of such a structure be practical and economically feasible.
Three classes of deepwater structures have either been installed or are currently under construction which are considered to be viable for development in water depths beyond 2,000 feet; the Tension Leg Platform, Floating Production Systems (semi-submersible or tanker based), and Compliant Towers (Maus, et al, 1986). These concepts have at least one feature in common in that they are all compliant structures. Various combinations of structural elements, buoyancy and inertia are employed to resist gravity and environmental forces. Fabrication and installation requirements are quite different for the space frame construction of the Compliant Tower and the stiffened hull construction required by the TLP and the Floating Production System. The use of subsea completions with the Floating Production System, and use of tethers as primary structural elements with the TLP are examples of key deviations from traditional approaches. The Compliant Tower offers the deepwater mode of operations which most resembles the traditional fixed platform because of the space frame type of construction, and the ability to provide conventional support for drilling and production operations.
