A key imperative to deepwater development is continued technological advances to reduce the development cost while improving reliability. Therefore, composite materials are being considered for several water depth sensitive systems such as risers and tethers. This paper focuses on the application of the composites technology that is being developed through the Conoco/Kværner Composite Alliance as part of the effort to promote the commercialisation of composite risers and tethers. The paper demonstrates the economic impact and the enabling capability of composite tethers and risers for ultra deepwater TLP's. Benchmark cost of conventional TLP solutions with TLP solutions based on composite tethers and risers is being presented. Subjects to be covered in details are:Feasibility of composite tethers and risers for deep and ultra deep water TLP applications,Composite risers and tethers impact on overall TLP design,Design and fabrication of composite tethers. Also presented, are the results of a composite tether prototype development that is being performed as part of a DEMO 2000 project. Introduction For deepwater developments with floating structures, the use of lightweight and high-strength materials has become increasingly important. Increased water depth generally means increased weight and tension from risers and station keeping systems. These effects have to be compensated for with additional buoyancy; which results in increased displacement and dynamic mass of the floating structure. This again requires larger station keeping systems, and the design spiral continues until convergence is achieved. Generally, the use of composites and advanced materials reduces the requirement for increasing the displacement. This effect becomes more important as the water depth increases. The cost benefits gained by introducing composites are dependent on the type of concept and where the substitution takes place. The more weight-sensitive the concept is, the larger the gain will be. The most sensitive floating concepts are the TLP followed by the Semi, and the least sensitive is the FPSO. Through the Conoco/Kværner Composite Alliance, both Kvaerner and Conoco have performed significant work to assess the global impact of the use of composites on overall platform configuration. The costs associated with composite applications, and the cost reduction for the entire system when substituting composites for steel, has also been extensively investigated. The reduction of the system cost is important since the procurement costs for composite components are generally higher than equivalent steel components by a factor of 1.5 to 2.0. Although several studies have shown that the use of composite materials in risers and tethers results in many benefits and that the market potential is large, several hurdles remain before the technology becomes commercially available. One of the main objectives of the Kværner/Conoco Composite Alliance is to overcome these hurdles. The current plan is to complete by the end of 2001 programmes for the demonstration of full scale fabrication and installation of both composite risers (CompRiser?) and composite tether (CompTether?). In addition, systems for certification and quality control will be established according to DNV design guidelines for composites offshore.

The paper summarises the results of a study performed by Kvaerner Oil & Gas Field Development and Smedvig Asia Limited investigating the use of tender assisted drilling (TAD) for floating structures. The paper further discusses the general benefits and challenges associated with the use of tender assisted drilling for floating structures and how the CAPEX and OPEX of field developments can be significantly reduced. Results from a study investigating the use of tender assisted drilling with a wellhead TLP in a benign environment will be used for quantifying the benefits and to describe how the challenge can be solved for a specific development. Focus is put on the following :Overall Tender vessel and TLP configuration.Reduction in size of the TLP due to reduced payload requirement. A conceptual design of a TLP with conventional drilling and tender assisted drilling are presented.The challenge related to stationkeeping of two floating structures in proximity and how to connect them ensuring that the distance between them is controlled. Several different configurations are discussed and results from non-linear time domain analyses of the two connected vessels are presented.Safety and operational aspects related to tender assisted drilling are presented. Typical topics covered are drilling operation, installation of drilling and productionFinally cost and schedule estimates are presented. Introduction For any field development one always faces the question whether to use dry or subsea completed wells. There are many arguments to which dry completion offers the most efficient solution considering total capital and operating expenditure.easy and economical well interventionincreased recoverable reserves as a result of more frequent well stimulationsimple flow assurancesimple well control systems The main challenge for dry well completion lies in the geographical extents of the field and the fact that the reservoir must be drained from preferably one central position to avoid investing in several wellhead platform structures facilitating drilling equipment. For deep water development this challenge is even more apparent considering that an increased topside capacity has significant knock-on effects on the entire platform configuration. Therefore, many of today's deep water hydrocarbons reservoirs have been developed with a subsea solution and the associated operational problems and adverse effect on the overall recoverable reserves. A solution to the challenge is tender assisted drilling, which reduces the functional requirement to the wellhead platform and therefore makes the dry completion more competitive from a CAPEX point of view. Tender assisted drilling with self erecting rig capability is a proven technology which in shallow water areas such as Southeast Asia and West Africa has been in use for more than 25 years. Traditionally, the wellhead platforms for which tender assisted drilling are performed have been jacket structures. The benefits transferred to floating structures are expected to be even more pronounced. In deepwater developments dry completion units such as Tension Leg Wellhead Platforms (TLWP), SPARs or Deep Draft Floaters have been shown to be economically attractive.

The present paper describes the extension of well proven TLP technology to applications in ultra deep waters. It is concluded that the careful optimisation of the TLP hull and topside as well as the use of composite risers and tethers lead to economical and technically feasible TLP solutions at water depths as large as 3000 m.The paper addresses the following subjects: − TLP technology and hydrodynamic optimisation − Composite risers and tethers impact on overall TLP design − Composite riser and tether design and fabrication − Status on the composite tether and riser development program which is ongoing through the Conoco/Kvaerner Composite Alliance − Installation of composite tethers − A case study including cost estimates

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