AU773396B2 - Satellite separator platform (SSP) - Google Patents

Abstract

A floating platform with motion characteristics for offshore deepwater developments with vertical axial symmetry and decoupling of hydrodynamic design features. A motion-damping skirt (120) is provided around the base of the hull (1), which is configured to provide ease of installation for various umbilicals and risers. A retractable center assembly (300) is used in a lowered position to adjust the center of gravity and metacentric height, reducing wind loads and moments on the structure, providing lateral areas for damping and volume for added mass for roll resistance. The center assembly (300) is used to tune system response in conjunction with the hull damping skirt (120) and fins (121). The center assembly (300) also includes separators (350) below the floating platform deck which serve to add stability to the floating structure by shifting the center of gravity downward, the separators (350) capable of being raised and lowered vertical separators alone or as a unit.

Description

APPLICATION FOR PATENT INVENTOR: Richard David Haun TITLE: SATELLITE SEPARATOR PLATFORM (SSP)

SPECIFICATION

FIELD OF THE INVENTION The invention relates to a moored offshore or self-propelled floating platform with improved motion characteristics for economic offshore deepwater developments. The floating platform of the present invention is capable of being self propelled in mild environments or moored for use in extreme depths and severe wind and wave conditions.

BACKGROUND

In the development of offshore energy systems such as deepwater oil and/or gas production, long flowlines, power cables and control umbilicals are frequently required between subsea wells and a host platform. The extended lengths pose energy loss, pressure drop and production difficulties.

Costs of structures for deepwater applications are high and costs are frequently increased due to the foreign locations at which they are fabricated. Other difficulties, associated with deepwater offshore operations, result from floating vessel motions which affect personnel and efficiencies especially when related to liquid dynamics in tanks. The primary motion related problem, associated with offshore petrochemical operations, occurs with large horizontal vessels in which the liquid level oscillates and provides erroneous signals to the liquid level instruments causing shutdown of processing and overall inefficiency for the operation.

Prior art for deepwater has generally resulted in facili- -'i1 or.' i or an 1/20 A MM"ET offshore oil field development. Such prior art includes tension leg platforms (TLP's), which may incorporate well drilling capabilities to several mini-TLP designs that perform simplified functions; SPARS which are configured much the same as a spar buoy and have dry wellheads, as opposed to subsea trees; deepwater floating production storage facilities (FPSO's) and their several variations.

Present tendon technology limits the common TLPs to approximately 5,000-ft water depths, which causes them to be stationed long distances from planned deepwater fields and the subsea wells. Systems that are moored by catenary lines can be placed within the deepwater fields within fairly close proximity to the subsea wells.

IPEAS 25 JAN 2001 References Cited: US PATENT DOCUMENTS Patent Number Issue Date Inventor US Class RE32119 April 22, 1986 Abbott, Philip A. 405/227 5722797 February 21, 1996 Horton, Edward E. III 405/224 5704731 May 10 1996 Huang, Yen T. 405/223.1 5588387 March 14, 1995 Tellington, Wentworth J. 114/261 5536117 July 16, 1996 Frame, Malcolm B. 405/202 5525011 June 11, 1996 Huang, Yen T. 405/223.1 5375550 December 27, 1994 Innis, Donald A. 114/267 5363788 November 15, 1994 Delrieu, Jean-Luc 114/125 5215028 June 1, 1993 Hayakawa, Yasuhiro 114/267 5213447 May 25, 1993 Srock, Brian J. 405/219 5129347 July 14, 1992 Hill, Anthony E. 114/266 4987846 January 29, 1991 Yamashita, Seiya 114/265 4987846 January 29, 1991 Yamashita, Seiya 114/265 4913591 April 3, 1990 Steele, James E. 405/196 4906139 March 6, 1990 Chiu, Hin 405/224 4886398 December 12, 1989 Sparks, Charles 405/224 4834014 May 30, 1989 Olsen, Fred 114/265 4746245 May 24, 1989 Mork, Harald J. 405/224 4716972 January 5, 1988 Makinen, Eero 175/008 4692065 September 8, 1987 Suzuki, Yoshio 405/211 4685833 August 11, 1987 Iwamoto, William T. 405/195 4674919 June 23, 1987 Olsen, Olav 405/226 4626137 December 2, 1986 Willemsz, John R. 405/224 4606673 August 19, 1986 Daniell, Alan F. 405/210 4604962 August 12, 1986 Guibault, Denis 114/266 4596291 June 24, 1986 Makinen, Eero 175/005 4576520 March 18, 1986 Suh, Sung L. 405/224 4576520 March 18, 1986 Suh, Sung L. 405/224 4576517 March 18, 1986 McCann, James 405/195 'tr YS5 JAN 2001 Inventor US Class Patent Number Issue Date 4565150 January 21, 1986 Liden, Hadar 114/265 4554883 November 26, 1985 Lane, Wallace W. 114/266 4519728 May 28, 1985 Oshima, Masanao 405/224 4498412 February 12, 1985 Liden, Hadar 114/264 4482274 November 13, 1984 Brandi, Roberto 405/224 4481899 November 13, 1984 Einstabland, Tomas B. 114/265 4457250 July 3, 1984 Oshima, Masanao 114/265 4452165 June 5, 1984 Bergman, Gunnar B. 114/125 4433941 February 28, 1984 Gerwick, Jr., Ben C. 405/211 4409921 October 18, 1983 Carroll, James P. 114/264 4406243 September 27, 1983 Kim, Chung U. 114/264 4378178 March 29, 1983 Roach, Richard T. 405/224 4310052 January 12, 1982 Rivertz, Johan A. 166/362 4286538 September 1, 1981 Matsui, Atsushi 114/266 4281613 August 4, 1981 Ray, Donald R. 14/230 4239417 December 16, 1980 Slatten, Arvid 405/195 4217848 August 19, 1980 Meyer-Haake, Gerhard D. 114/264 4170186 October 9, 1979 Shaw, Clarence W. 114/264 4168673 September 25, 1979 Poeppel, Fritz O. 114/265 4168556 September 25, 1979 Fink, Charles R. 009/008.R 4167147 September 11, 1979 Bergman, Gunnar B. 114/122 4155674 May 22, 1979 Martin, Yves 405/224 4155673 May 22, 1979 Yashima, Nobuyoshi 405/224 4155323 May 22, 1979 Finsterwalder, Klemens 114/264 4117691 October 3, 1978 Spray, Claude 405/205 4108102 August 22, 1978 Linstrom, Karl Olof 114/264 4087984 May 9, 1978 Mo, Olav 061/094 4067285 January 10, 1978 Jones, Robert M. 114/266 3982492 September 28, 1976 Steddum, Riddle E. 114/000.5D 3978805 September 7, 1976 Thomas, David G. 114/000.5F 3975784 August 24, 1976 Whitaker, Charles T. 009/008.R 3951086 April 20, 1976 Lown, Eldon C. 114/000.5D 4/20 Patent Number Issue Date Inventor US Class 3951085 April 20, 1976 Johnson, Don E. 114/000.5F 3949693 April 13, 1976 Bauer, Peter 114/000.5D 3885511 May 27, 1975 Wipkink, Johannes 114/000.5D 3870010 March 11, 1975 Wright, Everald V. 114/230 3788254 January 29, 1975 Shell, John E. 114/000.5F 3768463 October 16, 1973 Gassett, Paul L. 141/388 3739737 June 19, 1973 Baier, Robert J. 114/000.5D 3673975 July 4, 1972 Strauss, Erwin S. 114/043.5 3635182 January 18, 1972 Paffett, James Arthur Haines 114/000.5 The principal elements which can be modified for improving the motion characteristics of a moored floating vessel are the draft, the water plane area and its draft rate of change, location of the center of gravity the metacentric height about which small amplitude roll and pitching motions occur, the frontal area and shape on which winds, current and waves act, the system response of pipe and cables contacting the seabed acting as mooring elements, and the hydrodynamic parameters of added mass and damping. The latter values are determined by complex solutions of the potential flow equations integrated over the floating vessel's detailed features and appendages and then simultaneously solved for the potential source strengths. It is only significant to note herein that the addition of features which allow the added mass and/or damping to be 'tuned' for a certain condition requires that several features can be modified in combination, or more preferably independently, to provide the desired properties. The optimization is greatly simplified if the vessel possesses vertical axial symmetry as in the present invention which reduces the 6 degrees of motion freedom to 4, roll=pitch=pendular motion, sway=surge=lateral motion, yaw=rotational motion, and heave=vertical motion). It is further simplified if hydrodynamic design features may be de-coupled to linearize the process and ease the ideal solution search.

An object of the present invention is a floating platform which contains features which allow the platform motions to be optimized for size and weight to specified hydrodynamic environments and to include features which reduce offshore oil and gas processing operations and field development costs It is also desirable to provide a platform which allows the roll hydrodynamics to be determined and optimized and by other features allows tuning of the frequency response for the vertical heave.

It is also desirable to provide a more efficient self propelled or severe weather moored deepwater floating platform called an SSP with focus upon providing improved vessel motions in wind and wave conditions while exhibiting features which reduce offshore gas/oil field development and operation costs.

It is the object of the present invention to substantially overcome or at least ameliorate one or more of the prior art disadvantages or to achieve at least one of the io above desires.

SUMMARY OF THE INVENTION The present invention provides a floating structure for use in water floating above a seabed, the floating structure having a floating hull with ballast/storage tanks set S: within, the floating structure having: a. a hollow central section defined by the hull; b. a center assembly mounted in said hollow central section and being S: retractable and extendable below the hull, and c. a fixed ballast damping skirt affixed proximate a lower portion of the center assembly to provide heave damping and added mass for the 20 center assembly.

The preferred embodiment of the present invention provides for an offshore floating facility with improved hydrodynamic characteristics and the ability to moor in ••co extended depths thereby providing a satellite platform in deep water resulting in shorter flowlines, cables an umbilicals from the subsea trees to the platform facilities. The design 25 incorporates a retractable center assembly which contains features to enhance the hydrodynamics and allows for the integral use of vertical separators in a quantity and size providing opportunity for individual full time well flow monitoring and extended retention times.

The floating platform of the preferred embodiment is capable of being self-propelled in mild environments or moored for use in extreme depths and severe wind and wave conditions. The floating platform may be configured to perform the functions of a well-gathering platform, an offshore utility work platform; a remote power or communication transmission hub or relay platform or a satellite separator platform (SSP).

The floating platform is hereafter referred to as an SSP despite its adapted use.

6/20 [R:\LIB LL] I 5388.doc:TCW A principal feature of the SSP is a retractable center assembly within the hull, which may be raised or lowered in the field to allow transit in shallow areas. The retractable center assembly provides a means of pitch motion damping, a large volumetric space for the incorporation of optional ballast, storage, vertical pressure or storage vessels, or a centrally located moon pool for deploying diving or remote operated vehicle (ROV) video operations without the need for added support vessels.

Hydrodynamic motion improvements are provided by: the basic hull configuration; extended 0 0 IOo :00 *00* **000 0 0 6a*20 [R:\LIBLL] 15388.doc:TCW iB1~~Li5SN 010 skirt and radial fins at the hull base; a (lowered at site) center assembly extending the retractable center section with base and mid-mounted hydrodynamic skirts and fins; the mass of the separators below the hull deck of the SSP favorably lowering the center of gravity; and attachment of the steel catenary risers, cables, umbilicals and mooring lines near the center of gravity at the hull base. The noted features improve vessel stability and provide increased added mass and damping which improves the overall response of the system under environmental loading.

Key field production items that are satisfied by the invention are: housing large and efficient vertical high-pressure separators with extended 'retention times which can minimize multiphase flow with upstream primary separation closer to subsea wells which also improves reservoir recovery ratios; providing vertical separators of such dimension that multiple sensors can be used to optimize the liquid gas interface level; providing more economical full pigging ability with individual control of well flowlines; providing individual well flowline chemical injection without added subsea manifolding; simplification of operations and maintenance requirements; and providing for reduced inspection costs below water by the incorporation of a moon pool on the SSP centerline.

The principal cost reductions evolve from: the ability to perform fabrication in relatively shallow water sites; elimination of the necessity of costly offshore deck installation which is typical of certain deepwater alternatives; allowing for short transportation routes to the offshore field by minimizing draft and allowing use of domestic coastal fabrication facilities; providing duplicate functions for structural appendages to minimize fabricated weight and maximize the available flotation per ton of fabrication; and providing pressure control as close to the field as practical for improved economics of pipeline and flowline steel tonnage and installation cost reduction.

The prior art does not disclose methods for: the use of retractable center sections which by their position, structure, appendages, and contents improve the in-place hvdrodynamic characteristics while allowing shallow water access when fully rais.: 1re art also Jr-ln.1-,U iu YU o does not disclose .,,einods of providing increased extendt.,uration vertcal vessels or separators below the floating platform deck that serve to add stability of the floating structure by favorably shifting the center of gravity downward while also increasing the roll and heaveadded mass and damping of the floating structure for reduced platform motions in wind and waves. The prior art also does not disclose methods of raising and lowering vertical separators alone or as a unit within a center assembly to allow passage to or from shallow waters. The prior art does not disclose methods of providing a one-atmosphere access zone around the operational components of separators suspended from a floating platform. The prior art does not disclose methods of optimizing a vertical separator's performance by a nearly continuous array of sensors that allow a variable liquid level. The prior art does not disclose extending a skirt at the base of a hull with a diameter and configuration to ease the offshore attachment of steel catenary risers, umbilicals, and cables.

Because of the features which may be provided for, when utilized in the capacity of a floating deepwater oil and/or gas primary separation platform, the SSP performs bulk separation and yields full time test capabilities of each attached well via the flowlines and well control umbilicals. The hull features of the SSP include objects of the invention such as the vertical columns which provide hull-stiffening while serving as mooring line conduits for above water mooring line tensioning, and tension monitoring; facilities for the installation addition maintenance of the long vertical separators offshore; benefits afforded by the hydrodynamic hull damping skirt that doubles as a submerged towing rim and a load ring that distributes the transverse mooring loads and provides a foundation for steel catenary risers; umbilicals and cables; the separator supported damping skirt which doubles as separator spacing restraints; and the separator raising and lowering frame systems allowing shallow water fabrication yard access.

Due to the size of the individual first stage vertical separators and slug catchers afforded by the center assembly space and the available extended residence times which can be accommodated, efficient high-pressilUe separatior; car be accomplished for the purposes of minimizing transportation of produ: .ed re~ o .v ;r v; (stances. Vertical, as 8/20 Ulil. LiW~. 'J AN 2001 opposed to horizunital, separators minimize motion effec- 'due to the reduced overall elevation significance of internal separator fluid waves without the need for baffles and utilize the nearly unlimited available space within the water column without wasting deck space.

Other functions provided by the SSP, while in the role of an oil/gas platform, are pigging of the flowlines and outgoing gas/oil lines; metering of multiple wells; chemical injection of the incoming and outgoing lines; manifolding to perform the required functions; quarters facilities for the limited crew required for operations; instrument gas generation and controls; satellite and other information transmissions to the host platform(s); electric power transmission; and umbilical control of the satellite wells.

While Individual prior art includes several of the above features, none have addressed the aspect of extended oil gas separation residence times in vertical separators and variable elevations control of the liquid gas interface by numerous vertically-spaced sensors, which are a solution to the issue of improved high-pressure separation without excessive treatments. Prior art does not address the issue of minimizing the floating structure draft beyond normal ballasting for fabrication yard and tow conditions to site provided by the SSP.

The SSP may therefore be fabricated and/or outfitted at common shipyards. Once lowered, the separators and associated equipment increase the draft beyond normal port access and while doing so, improves the floating vessel stability by lowering the center of gravity and Sincreasing roll and heave-added mass and damping.

The manner of achieving improved hydrodynamic motion improvements within the present invention involves the incorporation of the following features: Use of the vertical reactions of the mooring system and the steel catenary and other risers to achieve an operating draft for the facility which is sufficient for reduced motions with minimal conventional ballast; providing a hull water plane area vs. draft ratio which, when tuned to the heaveadded mass and damping, provides sufficient free board in design storms and 9/20 Alk, nc. l 01 DB oH U provides adequate vertical heave damping to resist high-frequency response to normal wind and waves; making use of the difference of the vertical wave particle velocities at the surface and at the base of the center assembly to damp out the storm-induced heave motions; use of the retractable center section weight and its content in the full lowered position to decrease the overall system center of gravity; use of the center section in its lowered position to improve the lateral damping in order to offset lateral motion of the primary hull section and minimize roll and sway motions; use of the trapped hydrodynamic added mass due to the center assembly and its contents as well as enhanced damping and added mass features of spaced segments and the lower center section 'skirts'; use of the skirt extending around the lower circumference of the main hull to decrease the floating roll response by added mass and damping; use of vertical gussets supporting the hull 'skirt' as fins to provide added mass and damping and to reduce yaw rotational motions.

providing the opportunity to separately tune roll and heave response frequencies by designing the hull skirt to control roll damping and the hull plus center section hull skirts to control heave added mass and damping, thereby allowing the system to be finely tuned for a drier deck in a design limit seastate.

BRIEF DESCRIPTION OF THE DRAWINGS For further understanding of the nature and objects of the present invention, reference should be had to the following drawings in which like parts are given like reference numerals and wherein: 10/20 Figure 1 presents the plan and elevation view of the preferred embodiment of the present invention; Figure 2 presents a more detailed plan view of the deck 120; Figure 3a presents the SSP with the retractable section item 300 extended for shallow water being towed by a boat 500 in an un-powercd SSP configuration for transferred to/from a site; Figure 3b presents the SSP in a partially ballasted position as the retractable center assembly 300 is partially lowered as may be the case of a tow during heavy seas or unexpected storm; Figure 3c presents the SSP in an installed position with center section 300 fully deployed below the waterline 400 and mooring lines 200 and risers 160 extending to the seabed (not shown); Figure 4 is a plan view of the lowest portion separators 350 contained within the center assembly 300; Figure 5.A is a side view, partly in phantom line, of a separator of the preferred embodiment of the present invention; Figure 5.2 is an enlarged side view of the bottom of the separator of Figure 5.1A; Figure 5.3 is an englarged view of the center of the separator of Figure 5.1A; Figure 5.4 is a side view of the top of the separator of Figure 5.1A; and Figure 5.5 is a plan view of the separator of Figure 5.1A.

l DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS

The embodiments of the present invention provide for an offshore floating structure (as shown in Fig. 1) with augmented added mass damping and mooring tensioning features which provides a moored platform for the functions of primary process oil gas water separation, pigging of well flowlines and downstream pipelines, chemical injection and control of satellite well functions, pressure control for outgoing gas and oil lines to the host(s), and communication links to other locations. Other features associated with the object of the invention includes a floating hull 1 with low draft for convenience of domestic construction, su'Ltably broad beam for a stable tow, deep set ballast tanks to augment the tow to site, elimination for the need of deck installation offshore, and the capability of lowering 11/20 A 0 OM' the center assembly with features for improved motion. IPEAIS 25 JAN 200 A portion of hull 1 is the hull segment 100 that is above the water line 400. Hull segment 100 includes a top deck 110, having a helideck 120 to allow helicopter traffic. Top deck 110 further includes a crane 112 for allowing materials to be transported to and from the deck 110 and cargo boats (not shown). A plurality of piping and pigging elements 113, 114 which connect the process elements in the central section 300 to the attached wells on the seabed are also located on top deck 110. A control umbilical and/or power cable 115 is also routed to the attached wells on the seabed from deck 110. Piping and pigging elements 116, 117 are also provided on deck 110 to transfer liquids and gases away from the SSP to distant pipeline or platform connections.

A second portion of hull 1 below water line 400 includes a hull skirt 120. Elements 121, 122, 123 act as a stiffener 130 which also provides rotational damping.

Hull 1 has a central section 140 which is hollow and contains a retractable section 300. The hull 1 further includes radial mooring lines 200 depending from the hull 1. Catenary risers 160 are attached to the hull skirt 120. A riser guard 170 is provided for the risers 160 as they are routed from the hull skirt 120 to the top deck 110. Hull 1 also has a boat bumper 180 for allowing small vessels (not shown) to berth during loading and unloading of equipment or personnel.

The naval architectural and marine engineering aspects of the SSP floating platform differ from prior art in that reliance of the upper hull 100 of the floating structure 1 is augmented by the center assembly 300, which provides a dual service by providing a large space for various payloads and/or equipment and providing a lower center of gravity when in a lowered position to add to the stability as discussed above. Mooring attachment port 210 penetrates the upper hull 100 and acts as a restraint, thus allowing tensioning of the mooring system lines 200. The mooring system follows prior art in the use of a compound or alternate mooring system to minimize vertical reactions while providing lateral restoring force for station keeping.

Figure 4 shows a preferred embodiment of the separators 350 included within the center 12/20 AM7T assembly 300. Separators 350 may be much larger in volume and retention time, due to their length, compared to prior art. Further, separators 350 can make up a more significant portion of the platform mass than the prior art, and provide extended retention duration for improved separation at higher pressures for separation of gas and liquids. The extended vertical length of separators extends below the water line 400, and one such separator may be provided for each well. The separators may be provided with a multitude of sensors 360 (as shown in Figure which detect the state of the fluids at each elevation and that each separator may be equipped with several outlets for gas 395, oil I condensate and water 380.

Each separator 350 may be equipped with several, inlet valves 390 for optimization of the incoming well stream, and the overall control system (now shown) can determine the required opening and closing of the respective valving with the object of optimizing the separation process with the available constraints of inflow and retention volume of the separators.

The economy of the design is enhanced by the fact that, if desired, limited equipment is necessary on the top deck of the facility 110, as shown in Fig. 2, with the exception of the well control panels, emergency quarters 111, and helideck 190. The well flowline and outgoing gas, oil lines, pig launcher 116 (as shown in Figure associated manifolding, and chemical injection system are on the hull segment 100. The hull segment 100 also contains the normal offshore elements of boat landings 180 and safety devices typical of floating structures.

Preferred embodiments of the process function are: to allow primary well separation by long efficient vertical separators within the center assembly that may comprise a far more significant portion of the weight system than prior art, assisting the marine vessel stability; to utilize vertical separators to minimize the variation of liquid surface variations relative to level settings and minimize the overall dynamic motion problems due to floating marine vesse- mtions; 13/20 IPE '.US V- to provide individual separators for continual well monitoring of gas and liquid well production and satisfy the test separation requirements for any well; to allow signal transfer simultaneously of multiple individual wells with the liquid and gas rates plus temperature and pressure allowing remote control capability to a host location by satellite communication; to provide improved quality gas and oil condensate pipelines at reduced energy consumption to the shallow water host platform(s) by improved moderate to high pressure primary separation reducing pumping and compression and minimizing multi-phase conditions; to provide smaller diameter pipeline from the SSP to the host platform(s) due to water removal nearer the subsea well field and improving flow characteristics by minimizing multiphase flow and slugging and reducing the viscosity increase associates with oil and water flow.

Preferred embodiments of the marine engineering aspects are: As shown in Fig. 3d., an embodiment to enhance the hydrodynamic damping of the system is a hull, skirt 120, which extends below the boat level draft around the circumference of the hull and also acts to provide reinforcement for the mooring attachment points and ease of 4Mo attachment of steel catenary and umbilical risers 160 while offshore. The skirt 120 is modified at the outer rim 123 to increase the added mass and damping in roll. The skirt is stiffened by large gussets 121, 122, which provide yaw damping and "pockets" for added roll mass. Such duplicity of features tends to reduce the needs for excess weight and increased fabrication costs.

The lowest portion of the separator 350 shown on Fig. 4 is contained within the center assembly 300. The center assembly 300 incorporates a damping skirt 301 (as shown in Figure 3c) which, being well below the wave action of the surface, provides heave-damping and added mass and transmits the reaction to t'e hull via the cenier assembly. Other skirts 302 not previously identified, serving as reinforc;c;iiei.i. a.i yguidcs i r iiie center assembly, 14/20 11M j3 I' i U V 2 9 A IPEA5 JAN 2001 add to the damping and added mass in heave.

Thus, the SSP contains physical design features which facilitate: fabrication; transfer to the final site; field mounting of elements which are to be suspended from the platform to the seabed during offshore construction; mounting of specialized equipment in manners to minimize contamination from marine environments; improvement of offshore gas/oil processing field development costs; mooring in the field; and underwater video inspection of the suspended components and mooring attachments while in operation on site.

The floating facility allows the use of naval architectural features which improve the hydrodynamic motion characteristics while allowing the overall weight of the structure to be reduced for fabrication economics.

When used in the role of a moored oil/gas satellite separator platform the center assembly is 0 used to contain hydrocarbon gas/oil separators, utility storage, and ballast. Due to the available space, separators can be measurably larger in their capacity with resulting higher retention times for improved separation of gas and liquids than normally achievable in the present offshore practice which provides much value and operational flexibility for offshore operators. Due to the large allowable vertical dimension in the center assembly, vertical separators may be implemented which are less affected by marine motions and, with the benefits of larger allowable size, offset any inefficiencies of the reduced liquid-gas contact area within the separator. Due to the space within the center assembly, a large number of 2-2 vertical separators may be installed permitting individual wells to be continually monitored for their independent properties. Continual well monitoring greatly benefits the evaluation of the field production conditions by reservoir engineers. In other applications, vessels within the center assembly may provide opportunity for temporary bulk or liquid storage.

The central assembly, when fully raised, allows for the fabrication and outfitting of the SSP at numerous coastal shallow water fabrication facilities providing cost and transportation savings opportunities to nearby offshore fields. When the central assembly is fully lowered Sto its operational position, the center assembly enhances the motion characteristics of the floating facility by sevcra! means.

15/20 Ir 84~fi rytvii~J~J/ 1 U V29 S"US 5 JAN 2001 The main hull of the SSP includes hydrodynamic features sAch as a hull damping skirt for improved roll damping and increased roll added mass; radial plate hull damping skirt stiffeners acting as fins which provide yaw damping and increased yaw added mass; and a variable water plane area to provide nonlinear heave stiffness. These features provide benefit in storm conditions. Other features include options for a clear deck to reduce wind force and moments, locating heavy mooring and other equipment well below the top deck, and a bilge/ballast area at the hull base which all add to improve shallow water towing stability when the center assembly would be elevated for seabed clearance.

To provide benefit in storm conditions, the center assembly, in its fully lowered position, extends well below the normal water level of the floating facility providing significant improvement in the center of gravity and metacentric height; and the reduction of tall vertical separators above the hull deck further reduces wind loads and moments on the structure.

The center assembly may contain vessels provided strictly for ballast or by their operations, contain production liquids that provide natural ballast. The center assembly, when lowered, provides lateral area for damping and volume for added mass for roll resistance. The damping and added mass of the center assembly differs in yaw and heave motion. The center assembly contains skirts and fins oriented to provide the degree of hydrodynamic characteristics in either of the motions and be used to tune the final system response following the hull design. The use of the center assembly to tune response in conjunction with the hull form and hull damping skirt and fins is central to this invention.

Thus, the floating platform termed an 'SSP' that may be moored or self-propelled which may be used as an offshore facility for communications and/or power generation or utility platform or work platform or to gather seabed products from outlying sources and contains a means to individually "tune" the heave added mass and damping motions separately from motions of roll and yaw.

Further, the floating platform utilizes a centrally located assembly that can be raised and lowered or installed offshore to the base of the hull, having sufficient size and volume to favorably affect the sea-keeping motions in wind and wave conditions by shifting the center 16/20 A~Eri~?

~~CET

of gravity and providing added mass and damping to reduce the floating structure motions in waves and wind.

Such a floating platform may utilize high pressure vertical separators providing individual well monitoring that may extend significantly below the normal water line and which may be retractable for shallow water access, or maintenance.

Such a floating platform may utilize a damping skirt at the base of the structure, which doubles as structural reinforcement for a retractable center assembly. It may also utilize a damping skirt at the base of the structure, containing upturned and/or downtumrned edge appurtenances, yielding pockets to improve added mass and damping characteristics.

L Such a floating platform has provision for steel catenary riser (SCR) receptacles and connections which attach to the damping skirt at the base of the structure.

Such a floating platform incorporates a skirt continuous or segmented, extending laterally from the hull base to improve riser, umbilical, and cable installation ease by providing sufficient hull clearance for installation vessels and clearance for the installation rigging.

Such a floating platform utilizes mooring lines which extend from the interior dry space above the water line through vertical or near vertical hull supporting columns to vertically/or near vertically mounted fairleads.

Such a floating platform provides a central moon pool for ROV and diver operations which doubles as a structural stiffening of a centralized raising and lowering assembly.

Such a floating platform utilizes a series of sensors in submerged or in one atmospheric environment impervious to submerged service, to identify the phase and product at various levels within separators providing information for the optimization of the system operations for valving gas, oil or condensate, or water while avoiding excess separator height.

Such a floating platform with a retractable center assembly utilizes vertical rotational symmetry to avoid the need to weathervane and reducing its overall mass requirements for acceptable motions by implementing rotationally symmetric added mass and damping appurtenances.

The best mode and preferred embodiments of the invention ha e beern cescribed. it is to be understood that the invention is not limited, thereto, but ratiC .0 Le asuied by the 17/20 wsrcnn/2dMos scope and spirit of appended claims.

18/20 AMENDED EFT

Claims (11)

1. A floating structure for use in water floating above a seabed, the floating structure having a floating hull with ballast/storage tanks set within, the floating structure having: a. a hollow central section defined by the hull; b. a center assembly mounted in said hollow central section and being retractable and extendable below the hull, and c. a fixed ballast damping skirt affixed proximate a lower portion of the center assembly to provide heave damping and added mass for the center assembly.

2. The floating structure of Claim 1, further comprising a hull skirt extending about the circumference of the hull to be disposed below the water during flotation, the hull skirt providing an anchorage in combination with catenary risers.

3. The floating structure of Claim 1, wherein said center assembly includes at least one vertically-oriented hydrocarbon gas/oil separator extending below the water.

4. The floating structure of Claim 3, wherein each separator includes an inlet valve.

5. The floating structure of Claim 1, wherein the hull further includes a hull segment that is disposed above the water during flotation, the hull segment further including a top deck.

6. The floating structure of Claim 2, wherein said hull skirt has an outer Srim portion of added mass to increase stability of the floating structure.

7. The floating structure of Claim 2, wherein said hull skirt is straightened by gussets to provide yaw damping and pockets for added roll mass. o* 25

8. The floating structure of Claim 1, wherein said damping skirt has upturned edge appurtenances.

9. The floating structure of Claim 1, wherein said damping skirt has downturned edge appurtenances.

The floating structure of Claim 1, wherein said hollow central section includes structural stiffening. 19/20 [R:\LIBLL] 15388.doc:TCW

11. A floating structure substantially as hereinbefore described with reference to the accompanying drawings. Dated 15 March, 2004 OPE, Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 20/20 [R:\LBLL] 15388.doc:TCW