In continued pursuit of safe and economic field development solutions in deep and ultra-deep waters, the authors in this paper present a project oriented and technology robust dry tree semi-submersible floater concept. The proposed dry tree floating production and drilling system is based on the proven technology of a conventional four-column deep draft semi-submersible and comprises topside facilities, hull and mooring system, top-tensioned risers, and steel catenary risers.The paper discusses engineering analysis, computer simulation, and model test validation carried out in the investigation of the proposed concept. Sample design cases for ultra-deep water fields in the Gulf of Mexico are presented, where the authors discuss design philosophy, global configuration, and coupled responses of the dry tree semi-submersible hull with mooring and riser system. Safe design and layout of the wellbay hosting the top-tensioned riser system and its interfaces with hull and topsides are addressed as the core of the concept technology. In addition, constructability of the proposed dry tree semi concept is discussed by outlining project execution options under realistic infrastructure and facilities constraints during project construction, integration, and installation phases. Through engineering design, analysis and verification, the authors demonstrate robust performance and cost-effectiveness of the proposed concept, particularly the attractive quayside integration and commissioning. In summary, this paper presents a project oriented dry tree semi-submersible floating system concept with potential improved cost efficiency and reliability over current technology.

The paper presents the results from a feasibility study carried out by Kvaerner for a top tensioned riser system adapted for its deep-water Deep Draft Floater production unit, which often is referred to as a multileg SPAR. The study addressed allimportant aspects of a multi-riser system (array), including effective drilling/ work-over arrangements for a GOM deepwater application. The presented paper demonstrates the proposed two tier well and work-over riser top tensioning system has several attractive features and advances the capabilities of the mechanically tensioned systems considerably. Hydralift USA has been the co-operating partner on the hardware side. The introductory part of the paper addresses the present art systems (as used in the SPARs) as opposed to the principles of the proposed "two-tier well riser tensioning system". The nature of riser strokes is discussed on a general level along with a proposed approach to develop the basis for functional requirements for the two-tier system, being a mechanical top tensioning system. Two case studies, based on 1500 and 5000 feet water depth respectively, are used to illustrate the stroke demand. The paper puts the main emphasis on the justification of the new philosophy of splitting the tensioning system duties into two parts, based on certain observations made in the frequency domain. In short the split duty philosophy involves separation of the low frequency and steady stroke motions from the wave induced stroke frequency (high frequency). It is believed that this philosophy is a step forward for the mechanically tensioned systems. The configuration of the proposed system has inspired the use of the term "two tier tensioning system", as the proposed system is analogue to hydraulic cylinders working in series. It is concluded that the proposed system can be designed and developed from present state of the art mechanical tensioning equipment components. The two-tier system is especially attractive when used in conjunction with dry tree solutions.

In Systems Engineering CTR 6901, DeepStar developed a process to identify technologies that have good economic impact on 3 typical deepwater tie-back marginal reservoirs. This is accomplished with a life-cycle economic analysis which establishes benchmark economics using standard technologies. New technologies were then incorporated into these scenarios and the economic impact was compared to the benchmark field development results. Use of this process provides insights, for the conditions studied, into new technologies' ability to have commercial impact on deepwater marginal fields. This paper provides an overview of this work and findings. Introduction: DeepStar System Engineering CTR 6901 evaluated the life cycle economic aspects of three long offset marginal tie-back fields identified as Cottontail, Coyote and Hyena (all are scavenger names). The characteristics of these fields are given in Table 1. The evaluation was performed in two parts. The first part applied currently available technology to these 3 fields to establish the current industry capability and related commercial performance. Four of these "base cases" were established for each of the three reservoirs. The development scenario alternatives used in this evaluation were:Subsea tiebacks with heated flowlinesVertical well access (Dry Tree in 5,000 fsw)In-field processing system on structure.Subsea Processing System. Graphically, these 12 scenarios are illustrated in Figure 1. Each scenario was evaluated using a typical project economics approach which accounts for all CAPEX, OPEX, production profile, etc over the life of the field. An Excel spreadsheet developed by AkerKvaerner was used for this purpose to make all data visible and easy to understand. This is an important feature since this work only has value to a large and diverse group if the details can be understood, challenged & ultimately believed. This evaluation identified the "benchmark" scenario for each field with the most avorable economics from the Operator's perspective. These were:Cottontail - Case 1: A standard 4-well tie-back using an electrically heated flowline for flow assurance in 5,000 fsw with a 30 mile offset to the Host facility.Coyote - Case 14: This 10,000 fsw 50 mile offset field performed best with a 3-phase subsea processing system.Hyena - Case 6: For this 5,000 fsw West of Africa Field, a satellite structure with dry tree production wells gave the best economic results. This best economic scenario for each field became the "benchmark" example against which all other development alternatives and technologies may be compared. The second part of CTR 6901 evaluated the 10 selected technologies listed in Table 2 as if they were commercially mature and technically viable as projected by their sponsors. Each emerging technology was individually evaluated in the respective benchmark development scenario (or other scenario where appropriate) and the economic results were evaluated. None of these technologies generated an economic step change in the field life cycle economics for the tie-back field conditions evaluated. The technologies yielding (small) positive economics were consolidated together to determine their collective impact on these marginal tie-back field economics. The result identified a combination of emerging technologies, which together, have potential to improve the field's life-cycle economics.

Depletion of deep-water reservoirs by means of dry completion units (for short: DCUs) have been confined to TLPs, Spars, and Deep Draft Floaters (DDF). The preference for DCUs is well motivated as they give maximum well access with ample well and riser condition monitoring and flow assurance control. This paper proposes another step forward and that is, to exploit the potential of semisubmersible hulls as carriers of dry tree solutions. The paper describes the findings from a development study by Kvaerner Oil & Gas Field Development (KOG FD). The proposed solution may be seen as an extension of the classic semisubmersible/top tensioned riser combination technology, with which the industry has several thousand rig-years of experience. This paper demonstrates that a DCU semisubmersible hull can be arranged and operated more or less similarly to present art TLPs, in terms of overall, structural, and drilling layout, favourable construction as well as operational and safety procedures. The enabling technology is connected to the recently developed large stroke multi-riser tensioning system, which takes away the need for tension legs and floater vertical motion suppression. Additionally the freely ventilated wellbay and riser area of the DCU semisubmersible has several safety advantages in mitigating the risks from riser leaks/explosions/fire within the platform or its vicinity. The reduced consequential damages lead to less onerous riser specifications relaxing barrier/weight requirements and cost. The DCU semisubmersible will be a competitive alternative to Spar/ DDF solutions, and will fill the shortcomings of the TLPs beyond present waterdepth limitations.

The paper presents the main findings from an internal verification study on motions of the Aker Kvaerner Deep draft Floater (DDF). The study employed traditional linear analysis techniques as well as coupled and uncoupled time domain analyses. The coupled analysis is carried out utilizing state of the art software belonging to the Norwegian Marine Technology Research Institute (Marintek) program portfolio and developed further in the DEEPER Joint Industry Program organized by Marintek and Det Norske Veritas (DnV) (ref /1/). The analysis case is based on the functional requirements of a DDF with 56 000 Mt displacement and up to 30 rigid risers. The DDF has been analyzed at 1400 m water depth both in a West Africa and a Gulf of Mexico natural environment. By investigating the effect of including keel plates at large depths below the SWL, the heave response of the DDF can be controlled without significantly increasing the heave excitation on the structure. The 100-year return heave response has been found to be less than 1 m and 2 m for, respectively, the West Africa and the Gulf of Mexico Environment. By comparing coupled and uncoupled analyses of the DDF motions it is concluded that the effect of coupling is slight at 1400 m water depth. With 30 rigid risers present, the fully coupled model will predict approximately 10 % smaller motions than the uncoupled time domain analysis model. Introduction Aker Kvaerner have taken part in the DEEPER JIP development project. As a part of the breaking-in exercise of new deep water time domain analysis software and in order to thoroughly investigate the scope for optimization of the DDF motion behavior, Aker Kvaerner decided to run an advanced verification study on motions of the Aker Kvaerner DDF. The scope of the analysis was as follows:Investigate and optimize first order heave motion of the Deep Draft Floater (DDF) using first order radiationdiffraction analysis. This is carried out employing the WADAM program which is based on WAMIT5 /2/.Investigate the motion of the DDF using the time domain analysis program SIMO developed by Marintek /3/.Investigate the motion of the DDF using SIMO coupled with RIFLEX as described in /1/Verify and optimize mooring line, riser and tensioner design.develop a DDF sizing tool which calculates stability and gives an accurate estimate of first order heave response. The three first points above are addressed in the present paper. The Aker Kvaerner Deep Draft Floater General. The Aker Kvaerner DDF is a general-purpose marine facility for deep water environments. The design is focused on minimal vertical (heave) motions in order to facilitate rigid marine risers with dry trees. This type of design is very little affected by a change in water depth making the DDF ideal for use in deep waters. The DDF as shown in figure 1 can functionally be described as a multi-leg Spar or Truss Spar.