This peper wes selected for presentetion by the OTC progrem Commillee following review of informetion conteined in en ebstract submilled by the euthor(s). Contents of the peper, es presented, have not been nsviewed by the Offshore Technology Conference end ere subject to correction by the euthor(s). The meteriel, es presented, does not necesserily reflect eny posnion of the Offshore Technology ConIensnce or ns off'lC8I'8, Electronic reproduction, distribution, or storage of eny part of this peper for commerciel purposes without the wriIIen consent of the Offshora Technology ConIensnce is prohibned. Permission to nsproduce in print is nsstricled to en ebstrect of not mora then 300 words; illustrations mey not be copied. The ebstract must contein conspicuous ecknowledgment of whens end by whom the paper wes presented. AbstractNeptune marks the fIrst use of this type of structure to support production operations. The paper will discuss existing spar type structures and the development of the Spar design for the Neptune project. Design considerations for hull sizing and mooring system are discussed. Motion analyses and con-fIrming model tests are presented. The well system design is introduced, which allows for the use of surface type trees providing economical well bore intervention capability. The topsides facility layouts are described. The Spar's capability of future drilling operations, using a semisubmersible drilling rig moored alongside the Spar, is discussed.

The DeepStar Program has sponsored a series of tasks to evaluate the current industry capability in predicting the responses of deepwater theme structures (FPSO, TLP and SPAR). In its Phase IV program, model tests of the FPSO, TLP and SPAR were conducted, and in the Phase V program, engineering companies as well as test basins were invited to evaluate the correlations between the tests and analyses. This paper presents an overview of DeepStar's effort with emphasis on Spar responses. It covers the following areas of response predictions:Model test setup and test conditionsThe state-of-art analytical tools available to the industryEvaluation approachKey results of comparisons - tests vs. analysesSensitivities and uncertainties in predicting Spar responsesAssessment of current industry capabilitiesAreas of future effort Introduction Model tests were conducted November 2000 in the new offshore basin of the Maritime Research Institute Netherlands (MARIN). The objective of the tests was to assess global responses of floaters, with emphasis on the effect of mooring line and riser dynamics in deeper water. These tests included a TLP, Spar and FPSO. During the early part of last year, industry participants of the DeepStar Program were contracted by Det Norske Veritas (DNV) to analytically model the tests using their in-house programs. This paper presents results of that effort for the spar platform conducted by the authors. Modeling particulars and applied computer programs are presented. Test results and predictions are tabulated and shown graphically. Overall, there is good to excellent agreement between predictions and test measurements. Model Tests A brief description of the applied test facility, model and test particulars are given herein. Details may be found in references 1 and 2. Test Facility The MARIN deepwater test basin is 10.5m deep and 45m × 36m in cross section. Multi-flap wave generators on two sides can produce long-crested or short crested waves up to 0.4m with periods of 0.3 to 3.0 seconds, model scale. Current can be generated over the full basin depth with a vertical profile. Wind spectra are produced with electrical fans on a free moving and position-controlled platform. Spar Model Spar tests were conducted with length scale factor 1:87. This simulated a water depth of 913.5m. The spar model was a "classic" spar which is a vertical steel cylinder supporting topside facilities and a centerwell for top tensioned risers. The full-scale hull depth was 214.9m with a 198.1m draft and 37.2m diameter. The deck length, width and height were 65m, 65m, and 27.1m, respectively, with a vertical cg 241.7m above the spar keel. Mass properties, including adjustments to KG and GM for entrained centerwell water are given in Table 1. A sketch of the spar with mooring and risers is given in Figure 1. Table 1 Spar Mass Properties (Available in full paper)

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore Engineering developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for the Benguela Belize (BBT) project. The BBT project consists of a compliant tower supporting a 25,401 metric ton (28,000 s. ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.

The Buoyancy Can Riser Tensioner (BCRT) systems are designed to provide tension to Top-Tensioned Risers (TTRs). BCRT systems do not transfer the riser weight to the floater and they minimize the interaction between the floating platform and the riser system. For deepwater field developments, this attractive feature allows efficient design of the floaters as well as the riser systems. Although, the vertical riser load is not transferred to the hull, the BCRT system makes lateral contact with the hull at several locations. During the past 3 years, analytical models have been developed to characterize mechanics of the contact between two large floating bodies (buoyancy can and hull) and compliant guide hardware has been developed. Placement of a compliant guide between the hull and the BCRT has become the current practice for design of Spar floaters. The initial development of the analytical models and the compliant guide hardware coincided with the Horn Mountain project. The project team placed extensive instrumentation on the hull and compliant guides with a vision to confirm robustness of the guides and to calibrate analytical models used during the design phase. This paper presents a summary of the data collected on the performance of the Spar hull, compliant guides, and the riser systems for storms up to 25 ft of significant wave height. Analytical methods and predictions are presented to characterize the dynamic interaction between the BCRT system and Spar hull.

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore, Inc. developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for a West Africa project. The project consists of a compliant tower supporting a 25,401metricton(28,000s.ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.