Latest Progress in Floatover Technologies for Offshore Installations and Decommissioning Alan M. Wang, Xizhao Jiang, Changsheng Yu, Shaohua Zhu, Huailiang Li, Yungang Wei
Installation Division, Offshore Oil Engineering Co., Ltd.,
Tanggu, Tianjin, China
ABSTRACT
This paper prents a comprehensive overview of various floatover technologies bad on the latest advancements in offshore installation and decommissioning technology. Each floatover methodology is briefed and categorized into specifically defined divisions in a system of classification, including mechanical and non-mechanical schemes, single-barge, catamaran-barge and twin-barge schemes, etc. The prentation of the various floatover technologies will reveal the floatover history and evolution, the advantages and disadvantages of different methods, as well as the promising prospect of their wide applications in installation and decommissioning of integrated topsides onto and from various fixed and floating substructures.
KEY WORDS: Floatover technology; Hi-Deck, Smart-Leg®; Strand Jack Lifting; TML®; Unideck®; Versa-Truss®. NOMENCLATURE
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AHTS = Anchor Handling Tow Supply (tug)学生校服
小快板DP = Dynamic Positioning
DSF = Deck Support Frame
DSU = Deck Support Unit
FPSO = Floating Production Storage Offloading
GBS = Gravity Ba Substructure
GPS = Global Positioning System
LMU = Leg Mating Unit
LSF = Loadout Support Frame
TLP = Tension Leg Platform
TML = Twin Marine Lifter
INTRODUCTION
Various floatover technologies have been developed and successfully applied to offshore installations of integrated topsides onto different fixed and floating platform substructures since the first floatover installation was successfully adapted for the production platform topsides of 18,600 tonnes on the Phillips Maureen Project in 1983. A string of offshore facilities using the floatover concept followed, including jackets, gravity ba platforms, tension leg platforms, misubmersible platforms, and even spars lately.
动身去英语The floatover technology is an offshore topsides installation method that lets large platform topsides be installed as a single integrated package without the u of a heavy lift crane vesl, i.e. modular lifting installation. This allows the integrated topsides to be completed and pre-commissioned onshore prior to loadout, thus eliminating the substantial costs associated with offshore hook-up and commissioning. For the past two decades, the floatover technology has advanced so much from the conventional “Hi-Deck” scheme with leg mating units to numerous floatover techniques with active/passive load transfer systems and different configuration of floatover barge(s), thus providing an installation solution that can accommodate a wide range of topsides sizes and astate conditions. The floatover techniques of every hue include the u of the smart-leg technology with
active hydraulic devices to neutralize vertical impact, the versa-truss boom technology with A-frame booms and multi-winching operations, the strand jack lifting technology, or the hydraulic jack lifting technology to rai floatover decks to the required in-place elevation at offshore sites. In addition, single floatover barge, catamaran barge, or twin barges have been ud to meet the different configuration of substructures, which include future floatover technology of SeaMetric’s TML technique with twin-barge configuration using TML lifting beams with ballast tanks and buoyancy tanks and Pieter Schelte’s single lifting technique with catamaran configuration using hydraulically operated lifting clamps, and so forth.
A comprehensive overview of prent floatover technologies bad on the latest advancements in offshore installation and decommissioning technology is prented hereinafter. The systematic category of various floatover technologies defines the two major flaotover methods, that is, the mechanical method when using active load transfer system and/or paration system and the non-mechanical method when using passive load transfer system and/or paration system. In addition, the floatover technologies can be categorized into specifically defined divisions bad on the configuration of floatover barge(s), namely single barge scheme, catamaran barge scheme, and twin barge scheme, respectively. The advantages and disadvantages of different floatover technologies are also addresd here.
印的成语>钢笔抠图
PAST, PRESENT & PERSPECTIVE
For the past 27 years, many different kinds of floatover technologies have been developed and successfully applied to offshore installations. The conventional "High-Deck" or topsides floatover methodology was initially introduced by KBR, then Brown & Root, in 1977 at the BP's Magnus Field in the North Sea. The first floatover installation was successfully applied to the 18,600Te integrated topsides on the Maureen Project in 1983, who mating operation was engineered and performed by KBR UK. Following the Maureen Project's success, floatover technologies, as an effective installation method, have been widely applied to heavier integrated topsides, such as the world-record 28,800Te PA-B gas production topsides offshore Sakhalin Island, and swell dominant conditions and harsher environments, such as West Africa, West Austria, South China Sea, etc. However, a combination of deep water, rough open a, or swell conditions still po a challenge to provide a cost effective solution in offshore installations. A dozen of mechanical or non-mechanical floatover technologies with different configurations of single barge, twin barges, or catamaran barge have been developed for various fixed and floating substructures in challenging environments.
There are a number of reasons why the floatover method is becoming the preferred installation method for integrated topsides, rather than using heavy lift vesls. The availability of such heavy lift
vesls is very limited. Waiting for one suitable crane vesl to come online can cau significant project delays. Since the majority of heavy lift vesls are typically home-bad in European waters, the mobilization and demobilization costs can be too costly for projects in Asian-Pacific waters. Only a handful of crane vesls have the capacity to carry out large heavy lifts, and their day rates are very high. In addition, different from modular installations, the primary objective with floatover installations is to minimize costly hook-up and commissioning periods offshore. This allows freedom of equipment layout within the deck compared to modular lifting designs, and also completion of testing and pre-commissioning onshore. The result is a significant reduction in overall development cost through a shorter offshore commissioning pha without using expensive, heavy lift crane vesls.
Fig. 1: Floatover Installation of Lun-A Topsides with T-Shaped Barge Traditionally the floatover method is particularly suited to conditions found in the shallow and benign water area, such as Bohai Bay, China, refer to Liu et al. (2006), and offshore Sakhalin Island, Russia. Therefore, the substructure design tends to be a conventional jacket type or GBS type that favors the conventional floatover method. In 2009 four floatover installations were successfully carried out in Bohai Bay alone where three integrated topsides ranging from 6500Te to 11,000Te were installed onto jacket substructure by a conventional “Hi-Deck” installation and one 3000Te topsides was installed directly onto pre-installed piles in an extremely shallow water by the strand-jack lifting floatover scheme. The 21,800Te Lunskoye-A (LUN-A) gas production topsides and 28,800Te Piltun-Astokhskoye (PA-B) gas production topsides were successfully installed onto concrete GBS structures in the Sea of Okhotsk, northeast of Sakhalin Island in June 2006 and July 2007, respectively, tting a new record as the industry's heaviest floatover deck installation, although a 39,000Te Hibernia topsides was installed onto a GBS using a twin-barge configuration in protected waters offshore Newfoundland in early 1997. Nowadays the topsides weight does not significantly affect the floatover procedures or systems. See Fig. 1 for an example.
In the early of 1980s two North Sea projects, i.e. Phillip's Maureen and Conoco's Hutton, placed inte
grated topsides on steel GBS and TLP substructures in relatively sheltered areas and inshore shallow locations. Recently floatover technology can be employed from shallow water to deep water in swell conditions or harsher random waves. Moreover, the floatover substructures can cover almost all types of existing fixed and floating systems, including jackets, GBSs, TLPs, SEMIs, compliant towers, and spars, except FPSOs.
The primary design concerns are fixed platforms or floating platforms with a condary emphasis on shallow water or deep water, as well as benign environments and harsh a conditions. The installation engineering scope-of-work comprid conceptual design, engineering and planning the entire operation, including loadout, afastening, transportation and installation. Perhaps even more important in terms of ultimate cost savings for the client is early involvement during the conceptual design pha. Early design decisions for the float-over method can generate considerable savings further down the line. By being involved during the conceptual and detailed design phas, naval architects and structural engineers can provide invaluable input before construction begins. This minimizes the need for costly changes later on. Detailed planning for topsides transportation and subquent installation also enables hook-up and commission operations to begin earlier.
Originally conceived to address the problem of making heavy lifts in remote locations, floatover tech
niques are increasingly being applied to smaller and smaller topsides. Even in regions where suitable crane vesls are available, specifying an integrated topsides for a floatover installation opens the market to tho contractors without access to such crane vesls, thereby providing a degree of additional competition during project tendering. The state-of-the-art technology of floatover installations will be further developed to improve workability, reduce structural requirements, as well as standardize to avoid the early commitment. Refer to Seij (2007) and O’Neill (2000) for details. FLOATOVER PROCEDURES
Typical floatover operations may be divided into the following major stages:
Loadout: Upon weighing, the integrated topsides will be jacked up by a mega jacking system of hydraulic cylinders or lifted by strand jacks before a tall DSF/LSF can be inrted under the topsides prior to loadout operation. Topsides may be skidded onto pre-lected floatover barge longitudinally, or laterally if longitudinal strength is limited, via a pulling system of strand jacks or Self Propelled Modular Transporter (SPMT) trailers with a sophisticated ballast spread.
Transportation: Once completing the afastening and floatover preparations, and most of all meeting the sailaway criteria, the barge laden with the topsides sails from fabrication yard to offshore
site. The floatover tiedown design is unique and usually consists of two different ctions, i.e. the first ction connecting the topsides and DSF around DSUs, which will be removed prior to mating, and the cond ction connecting DSF and barge deck, which will remain until deck cleaning. Where a twin-barge configuration of transportation is required, such as for spar platforms and narrow compliant towers, special transportation and afastening design should be developed to meet different requirements of rigid, flexible, and even hinged connections between twin barge and the topsides.
Pre-Floatover Preparations: Upon arrival at site, the barge is connected with a pre-installed docking/positioning mooring system via AHTS tugs. While in stand-off position, pre-floatover preparations are performed including t up and function test of GPS positioning monitoring system, motion monitoring system, environmental measure system, soft-line rigging preparations, barge and substructure preparations, and so on.
Docking Operation: By operating mooring winches and/or positioning AHTS tugs, the barge will be positioned and aligned with the substructure slot. For a configuration of twin barges or a catamaran barge, the barge(s) will be positioned and aligned with the substructure in middle. With the help of soft-line rigging arrangement, the barge(s) will be docked inside the substructure slot or around the s
ubstructure when twin barges or a catamaran barge is adopted. One main towing tug can be ud for docking operation while workboats or zodiacs may be ud for soft-line handling.
Mating Operation: Upon aligning stabbing cones with support receptacles, the barge will be ballasted or active hydraulic devices will be ud to transfer the topsides load from the barge onto the substructure. The load transfer system generally compris different ts of multi-stiffness, multi-stage LMUs, which are lf-contained and designed for each leg with different stiffness bad on the leg load transfer at different stage. The load transfer systems are basically same for fixed or floating substructures. The major difference is that the stiffness required for floating substructures is dominated by small relatively small water-plane area of substructure and their free floating motion characteristics. Special multi-stiffness, multi-stage units may be required when large relative motions between deck and substructure are predicted. Many different kinds of mechanical devices have been invented to facilitate the load transfer system, thus minimizing the impact load during mating. Depending on the site condition and installation window requirement, typical limiting a states for floatover operation are given as follows:
Head Seas Beam Seas Quartering Seas Wave Height (Hs) 1.5m 0.8m 1.2m
Wave Period (Tp) 5 - 10 c 4 - 7 c 5 - 8 c
1-Min Mean Wind公司值日表
Speed at EL(+) 10m
10m/c 10m/c 10m/c Surface Current 1.5m/c 1.5m/c 1.5m/c
Separation & Undocking Operation: Having transferred the topsides load, the barge continues ballasting until safe clearance between the topsides structure underside and the DSF upside has been achieved. Then the barge will be withdrawn from the substructure slot. DSU is a conventional passive elastomeric paration unit which is designed to provide an increasing gap between DSF and topsides through the load transfer process until paration occurs. There is no steel to steel contact during paration while the elastomeric units absorb incidental vertical and lateral contact energy. Active paration devices may be employed. Some of the active paration devices may provide exciting paration event, or even explosive paration event. The basic paration system is the same whether for fixed or floating structures, subject to the same multi-stiffness usage as LMUs.
PRIMARY EQUIPMENT SYSTEMS
The equipment systems required for the floatover operations have varied functions and applications. Each equipment system provided is designed to ensure that the overall operation is executed in a safe, timely and efficient manner, while complying with all contractual obligations. The design of the critical installation devices plays a crucial role in ensuring successful floatover operations. The following provides a summary overview of the primary systems:
Floatover Barge(s): Upon loadout, the barge will transport the topsides to site and floatover install the topsides onto a pre-installed fixed substructure offshore or a floating substructure in place or inshore. AHTS/Harbor Tugs: The positioning tugs including AHTS and harbor tugs work with a mooring system and a soft-line winching system to form a positioning spread, thus providing longitudinal and lateral pull control during docking and undocking. AHTS tugs are also ud to pre-install the mooring system and to hook up the pre-installed mooring lines with mooring winches upon arrival of floatover barge(s). AHTS can also work as a positioning spread to position floating substructure during floatover installation.
DSF/LSF: The topsides will be placed on a high transportation frame, normally a truss frame, for its journey to the offshore site. This frame together with the existing height of the barge, i.e. freeboard, will allow the stabbing legs of the topsides to clear the top of the LMUs, if pre-installed on the substru
cture, immediately prior to mating the two structures.
Docking/Positioning System: In shallow water a spread mooring system equipped mooring winches on barge deck, in combination with soft line positioning winches also on barge deck and positioning AHTS tugs, can function adequately to perform barge approach, initial entry, docking and undocking operations. In deep water preci positioning AHTS tugs in combination with soft line winches may be adequate. The soft line positioning winching system is mainly ud to suppress surge and sway motions within the slot. When DP vesl(s) are ud in floatover installation, such docking system may be eliminated.
LMU & DSU: LMUs are designed to buffer the impact load between the support receptacles and the mating cones during mating while DSUs are ud to buffer the impact load between the DSF and the integrated topside during paration. LMU makes soft initial contact and reduces relative motions before engaging to increa stiffness for final load transfer. LMUs are specialized leg and deck mating units that act as shock absorbers as the vesl is ballasted down and the topsides load transfers from the deck support structures onto the substructure. The units are custom designed for each leg of the deck to balance deck load through load transfer and motion compensation. The heave stiffness of each leg is designed to meet the exacting stiffness and deflection characteristics r
equired. Additionally, the load transfer units are designed to have the proper stiffness to absorb initial impact energy and any unsuppresd surge and sway energy due to environmental forces. The design of the units has been developed over two decades of experience and employs exacting elastomer mixing, molding, and
bonding techniques in the fabrication.
Fendering System: In general three types of fendering systems should be provided for docking and undocking operations, i.e., sway fenders, surge fenders, and stern guide fenders. The sway fenders can be installed along the barge sides or on the substructure slot insides to protect barge and substructure from direct impact while a minimum transver clearance may be ud to limit lateral movement of the barge and align the LMU mating cones and support receptacles transverly. The surge fenders work as longitudinal stoppers to align the LMU mating cones and support receptacles longitudinally and also ud to prevent direct impact between support legs and fender system at final position. The stern guide fenders are constructed to assist the initial docking of the barge into the structure slot to smooth the initial entry and also protect the structure legs.
Positioning Monitoring System: A DGPS positioning monitoring system shall be t up in the operatio
n control room located on barge deck. Throughout docking, mating and undocking operations the relative position between barge and substructure shall be continuously monitored by a GPS positioning system and visual obrvation.
Motion Monitoring System: Throughout the floatover operation the barge motions will influence the ability to complete the floatover activities, in particular, the air gap between stabbing cones and support legs, and the mating load during transfer operation. The six-degrees-of-freedom motions, i.e. roll, pitch, heave, sway, surge and yaw, should be continuously monitored, especially the motions of the stabbing cones and the deck support points throughout the floatover operation.刘寄奴草
Environmental Measure System: An environmental measure system will be employed to continuously measure wind, waves, currents, as well as tidal elevation throughout the entire operation.
Rapid Ballast System: During mating, a rapid ballast system may be required to transfer topsides load and ballast barge down to achieve safe clearance between DSF and deck in a timely fashion, normally in four to six hours, depending on tidal cycle and range. A preci ballast monitor and control system may also be located on barge deck.
CLASSIFICATION OF FLOATOVER TECHNOLOGIES
The floatover technologies have become more and more common in recent years. However, so far there is no strict definition and clear categorization of various existing floatover technologies. This paper intends to categorize the technologies into specifically defined divisions in a system of classification to clarify basic concepts of floatover techniques, thus benefiting further development and applications. In general, all the floatover technologies can be divided into two large systematic categories, namely, mechanical methods and non-mechanical methods. The mechanical method is defined as when mechanical devices are employed as active load transfer systems and/or active paration systems. The non-mechanical method is defined as when passive LMUs and DSUs are ud as passive load transfer systems and passive paration systems, where the passive load transfer systems are actuated mainly by ballasting down floatover barge(s) and/or via falling tides. According to the floatover barges, the floatover technologies can be also classified as single-barge methods, catamaran-barge methods, and twin-barge methods bad on the configuration of barge(s) ud in floatover installations. In addition, the twin-barge methods can be further divided into the rigid connection method, the flexible connection method, and the hinged connection method bad on the connection types of the deck support frame supporting astride on the twin barges. Vers
atile and forgiving floatover technologies have been employed to install integrated topsides onto various fixed or floating substructures from shallow water to deep water in benign environment, swell conditions, or harsh random waves. Each combination of the conditions may cau different challenges and concerns in development of applicable floatover techniques. Up to now more than a dozen of floatover techniques have been developed for various fixed and floating substructures, in shallow water and deep water with benign a state or harsher a state. Each of the floatover methodologies will be briefed while their advantages and disadvantages will be addresd hereinafter. The various existing floatover technologies can be systematically categorized into the following techniques.
Conventional Hi-Deck Technique
So-called conventional Hi-Deck technique is a non-mechanical method with a single large barge configuration, which was originally developed by KBR in 1983. The topsides will be placed on a high DSF for its voyage to the offshore site. Upon arrival at the site the floatover barge will be ballasted to a minimum draft with even keel and even heel. The topsides situated high on the top of DSF, together with the existing freeboard height of the barge, will allow the stabbing legs of the topsides to clear the top of the LMUs, if pre-installed on the substructure, immediately prior to mating the two str
uctures.
The floatover barge will be brought between the substructure slot with a combination of positioning tugs, mooring lines, and soft-line winches at an approaching speed of 3-5m/min. As Fig. 2 shows, the concrete GBS has been designed to allow 4 meters clearance between the barge sides and the GBS shafts. Eight mooring lines are attached to the barge as the barge progress through the GBS. With the aid of fendering system and soft-line winching system, the mooring lines will be ud to hold the barge steady in its final lowering position.
Fig. 2: Illustrative Mating between 11,500Te Malampaya Topsides and CGBS in 90m water depth offshore Philippines, South China Sea Upon aligning the stabbing cones with the leg receptors and removing all the tiedowns around DSUs, ballasting operations will commence. The weight of the topsides will be progressively transferred onto the LMUs by lowering the barge away from the topsides. To reduce the initial impact between the deck and the substructure, elastomeric pads will be included in the LMUs. Ballasting of the barge will continue with the u of a rapid ballast system, say to produce a peak load transfer rate of 30,000 tonnes per hour for the 11,500Te Malampaya Topsides. When the deck weight transfer has been completed the barge will be towed from between the shafts of the GBS.
When the transportation barge, together with the DSF, are clear from the substructure slot the final mating operation will commence. Sand jacks located in the LMUs will be activated to lower the deck and allow the deck legs to come into steel-to-steel contact with the substructure legs if non steel-to-steel LMUs are employed. The contact points will then be welded together to form the one permanent structure of the platform. Before departing from the platform, the construction support vesl will perform post installation surveys including the deployment of a ROV for underwater surveys.
Smart-Leg Technique
The first successful shockless Smart-Leg System was completed offshore Nigeria in June 1997 by McDermott-ETPM for the 4,100Te topsides of Ekpe Gas Compression Platform located in a water depth of 50 meters. The barge preparations were done in 3 days while the floatover operation only lasted about 6 hours. The Smart-Leg Technique is a mechanical method with a single barge configuration. This technology was successfully ud in November 1996 to position a 192m long and 8000Te heavy bridge spans crossing the strait between Prince Edward Island and New Brunswick in Canada.
Fig. 3a: Hydraulic Jack Asmblies Accommodated
in Deck Legs right above Jacket Legs
Fig. 3b: Smart Shoes with Explosive Collapsible Mechanism ETPM developed and patented the Smart-Leg System, refer to Labbé (1998) and Seij (2007) for details, which us active hydraulic jacks to neutralize the vertical movements of the barge and to transfer the deck weight from the cargo barge to the piled jacket structure. Upon docking, the jacks activate the mating of each deck le
g onto the corresponding jacket pile by deploying extension pipes. The activation mechanism is controlled by non-return check valves located between each jack and gas accumulator. The action of activating the valves only during rising period of the deck legs will smoothly lock the deck at the peak height of the motion and take place at the preci time when the deck leg vertical speed is zero, therefore eliminating the kinetic energy and the risk of impact. The deck mating is completed in just a few conds, less than the swell period. Rather than using LMUs to absorb the shocks, retrievable jacks are ud to progressively freeze the motion of the cargo barge. This allows a deck to be installed in significant swell conditions common to offshore West Africa. The acceptable swell limit is usually no more than 2.8 meters high in a long period of 15 conds. Smart Fins and Smart Fenders are also developed to restrict the motion of the barge in sway, surge, and yaw. The Smart Fins and Smart Fenders are deployed and recovered by hydraulic rams installed on barge deck. Smart Fins are equipped with hydraulic shock absorbers to establish contact at the four corner legs, thus reducing the surge to under 25mm excursion. Then the Smart Fenders will be activated to progressively eliminate the sway. Upon aligning, the Smart Leg System can be activated to start the deck mating. After partial load transfer occurs as a result of locking of Smart-Leg Jacks, say 50% load transfer, the remaining load transfer can be achieved by ballasting the barge and further jacking up the deck to the point where the Smart Shoes can be actuated to collap with explosive split nuts,
thus yielding a 2.7m undocking clearance. The Smart Shoes are special deck support two A-Frames with sliding bearing pads adapted to fit onto skid rails. Refer to Figs. 3a and 3b for details.
The major disadvantage of this scheme is lack of controlling the final elevation of the topsides and its levelness since the Smart Leg is activated by the vertical motion of the barge when the deck leg ris to its highest position before falling in the swell. In addition the Smart technology is bad on complex active mechanism and do not allow single failure, less reliable compared with passive LMUs and DSUs. Strand-Jack Lifting Technique
The strand jack lifting installation was first developed by JGP in July 2000 to jack up a 300Te topsides more than 30m for installation of Millom West gas platform in the Irish Sea. Following the successful installation, this strand jack lifting technique was successfully applied to installations of four integrated topsides ranging from 2,000Te to 6,200Te in 2002, 2003, 2008, and 2009, respectively, for the Apache /PetroChina Zhaodong Project. The field site is in extremely shallow near-shore waters in western Bohai Bay with a water depth of 1.78 m as per chart datum and 4.2 m referenced to the local mean a level.
This mechanical lifting method can position topsides at a very low level on barge deck, which only de
pends on fabrication requirement, thus improving the barge stability and reducing the size of floatover barge significantly. Therefore no jacking up of the topsides is required prior to loadout. During deck mating, the supporting legs will be first lowered to make initial contact with the pre-installed piles. This requires less or no ballasting for deck mating, eliminates rapid ballast system, and also eas the dredging requirement of the installation basins. Most importantly, the u of strand jack lifting scheme reduces the initial contact impact significantly, just in the magnitude of the weight of the support leg. This eliminates the u of passive LMUs and
