Regulatory Considerations in the Design of Tension-Leg Platforms

Abstract

Summary The tension-leg platform (TLP) is an accepted development option indeepwater Gulf of Mexico projects. The first TLP installed in projects. Thefirst TLP installed in U.S. coastal waters is now in operation. Thecertification of TLP's under current U.S. regulations is a new experience forthe platform operators accustomed to operating in the Gulf of Mexico and forthe regulatory bodies with platform-design jurisdiction. Introduction Operators in the Gulf of Mexico introduced two unique deepwater floatingproduction developments in 1987 and 1988. The Placid Green Canyon floatingproduction unit is based on a converted semisubmersible drilling unit in1,450-ft [440-m] -deep water. Conoco's Jolliet tension-leg well platform(TLWP), in 1,760-ft [535-m] -deep water, is based on the original TLP conceptdeveloped in the North Sea (Fig. 1). Other operators have proposed TLP's forGulf of Mexico sites because TLP technology is now established and the economicadvantages of TLP's are comparable to those of fixed or floating platforms. Of particular interest to operators are the hidden costs of design, construction, and installation for these new deepwater developmentalternatives. This paper addresses a fairly narrow aspect of the overalleconomics of the TLP concept: the design certification process and its impacton costs. Factors unique to TLP certification are discussed. This paper alsobriefly explains the background of TLP regulations in U.S. coastal waters andcompares the basic philosophies of maritime and oilfield philosophies ofmaritime and oilfield practices on which current regulations are based.practices on which current regulations are based. OCS Regulatory Approach Regulatory requirements for TLP's evolved from existing regulations forfixed platforms and mobile offshore drilling units (MODU's). The currentregulatory approach is the result of combining fixed-production platformrequirements developed by platform requirements developed by the MineralsManagement Service (MMS) and MODU requirements developed by the U.S. CoastGuard. Ref. 1 provides background on the evolution of the rules; Refs. 2through 4 give information on actual regulations. Two main areas of interest to TLP operators are the division of authoritybetween the Coast Guard and the MMS concerning process facilities and technicalstandards to process facilities and technical standards to be applied for theremaining TLP systems. Specific technical requirements for TLP's do not existtoday within Coast Guard or MMS regulations. This paper explains thesignificant differences in philosophy between these two agencies. Background of Coast Guard Regulations. The Coast Guard's main interest ispreserving the safety of life at sea. Its requirements derive from 150 years'experience in the marine environment. The Coast Guard's extensive regulations, found in the Code of Federal Regulations, cover all types of vessels, includingpassenger, cargo, and fishing vessels and MODU'S. While based largely onconventional merchant-vessel practices, Coast Guard requirements for MODU'S, developed with the assistance of the oil industry, are "in tune" withthe offshore workplace environment and are supported by the offshoreindustry. In formulating its strategy for reviewing TLP designs, the Coast Guarddetermined that MODU regulations would form a good basis for TLP safetyregulations. It recognized the need to remain flexible in setting specificrequirements for the TLP. Rather than generating specific requirements forTLP's, the Coast Guard chose to work with the industry and the API indeveloping design standards for TLP'S. API RP2T provides general guidance forthe design, provides general guidance for the design, construction, andoperation of TLP'S, liberally incorporating the practices and requirements ofthe Coast Guard and the American Bureau of Shipping. The initial application ofRP2T was on the Jolliet TLWP project. Background of MMS Regulations. The MMS is responsible for E and P on theU.S. Outer Continental Shelf (OCS). MMS requirements are based onfixed-platform practices in the Gulf of Mexico, southern practices in the Gulfof Mexico, southern California, and Atlantic coast. MMS' interest is preserving and protecting the environment and geology inareas protecting the environment and geology in areas of petroleum E and P. Itis interested mainly in drilling and production systems, including well-baysafety and fire protection, hazardous-area classification, blowout prevention, subsea equipment design, prevention, subsea equipment design, emergencyshutdown procedures, and platform fire protection. JPT June 1990 P. 764