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Copyright 2013, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 6-9 May 2013. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any p art of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright. Abstract 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.
- Summary/Review (0.68)
- Research Report (0.48)
- Well Drilling > Drilling Equipment (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Risers (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (1.00)
Abstract 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.
- North America > Cuba > Gulf of Mexico (0.89)
- Africa > West Africa (0.89)
Abstract 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. Introduction Significant new discoveries in offshore West Africa, offshore Brazil, and the Gulf of Mexico are currently attracting a lot of attention. The larger finds, however, are in ultra-deep locations with water depths of 3000 ft to 6000 ft. Ultra-deep discoveries around the world have much of the same challenges i.e. frontier drilling/wells technology, unconsolidated sediments, and flow assurance problems. Economic exploitation of the large finds may be troubled by extreme water depths, lack of pipeline or other off-take infrastructures, and distance to terminals and refineries from consumer market. While WA has favorable weather conditions its location imposes some special boundary conditions, which includes lack of local contractors of a sufficient size to handle major projects, limited local yard capacities and skilled work force and few harbors to provide operational service. Lack of offshore infrastructure implies that an FPSO concept may be more attractive, as some form of storage vessel will be required. A storage vessel will offer a large deck surface thus emerging as a kind of "free issue property" for a process plant for which one would otherwise have to build a separate platform. The "first wave" of WA projects of this type has homed in on large (or rather gigantic) stand alone FPSO's The "next wave" will show some preference for field developments that includes "on-board" drilling and workover functions. In addition, some reshuffling in the target fields queue has taken place.
- Africa (1.00)
- North America > United States > Montana > Roosevelt County (0.24)
- South America > Brazil > Brazil > South Atlantic Ocean (0.93)
- North America > Cuba > Gulf of Mexico (0.93)
Abstract The paper describes an FPDSO (Floating Production Drilling Storage and Offloading unit) equipped with a drilling plant and a near surface disconnectable drilling riser ("free-standing riser"). Drilling operation takes place through a dedicated moonpool, which is located just aft of the turret area. This allows a 100% clean split between the drilling and station keeping functions with minimum interfaces between two systems, which is a novelty for concepts based on turret moored drilling vessels. The relatively small internal turret makes use of taut leg mooring system and provides a number of slots for import/export risers as well as a swivel/drag chain transfer system. The mooring legs are configured in clusters, typically 120° apart. The vessel may change its translatory position by adjusting top chain sections using winches at the turret, while simple weathervaning or thruster systems perform heading control. The subsea wells are located in the "down wind" sector of the mooring leg clusters, whereas the import/export risers are laid out in the remaining sectors which are normally observed "upwind". The paper describes the operational procedures for the drilling (or well work over) from the vessel. Drilling/work over may take place under conditions when weathervaning is required; featuring the novelty that the drilling/work over riser may stay connected as long as the weathervaning takes place within approximately a 180° sector (+/-90° from prevailing heading). The weathervaning, naturally, has to take place about the axis, which runs through the well/centre and drilling riser. This means that the vessel has to change heading (weathervane) at the same time as it performs a translatory adjustment of its turret position. This is made possible through stepwise, predetermined manipulations of the chain section and some thruster control, if necessary. If weather forecast suggests heading beyond the 180° sector, a disconnection of the drilling riser system is planned for (upper portion only - the rest remains free-standing in the water), and executed if necessary. After disconnect of the riser the vessel may rotate around the turret in normal FPSO manner and a full n × 360° weathervaning capability is achieved. Drilling has in this situation been suspended, however, kill and choke lines and BOP controls may still be connected as these may be routed through the turret/swivel arrangement and connected to the top of the submerged free-standing drilling riser. This allows for continuos mud circulation and well control while disconnected. The paper also outlines the subsea wells and seabed arrangement, riser configuration, turret swivel solution, the mooring leg configuration, the drilling plant and the overall FPDSO layout. The potential of the proposed FPDSO design carried out by Kvaerner will be briefly discussed in the paper, like the main features of the FPDSO unit, the status of the technology, and the areas which may need further studies. Introduction As the industry is increasingly expanding exploration activities in deepwater blocks, demand for competitive solutions based on stand-alone field development emerges. Besides being subjected to deepwater challenges these prospects are often characterised by great distances to existing infrastructure.
Abstract 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. Introduction Traditionally the industry has been capable to follow up with production unit solutions as the exploration rigs moved into new deepwater frontiers. The current deep-water regime is no exception. Looking at the pace of exploration and interest for future deepwater acreage is a clear signal that decision makers are judging the risk for running into technical "show stoppers" sufficiently low. However, speaking of the deep- to ultra- deep water depth range, 2000 to 10 000 feet, some real challenging technical aspects are evoked:Flow assurance Sea bottom and formation stability Carrier water depth sensitivity Station keeping /Mooring system Riser systems Carrier Concept Selection - Discussion All concepts have to solve the a) Flow assurance problem, but it is implicit that carriers that offer dry well solutions will be preferred in most cases (temperature control/rapid well intervention) The b) Sea bottom and formation stability aspects favor surface solutions that are not vulnerable to sea bottom or foundation failures, which disfavors the TLPs The TLP is further troubled by the c) issue water depth sensitivity.