BR112019026698B1 - OFFSHORE VESSEL FOR THE PRODUCTION AND STORAGE OF HYDROCARBON PRODUCTS - Google Patents

Abstract

The present invention relates to a vessel anchored in multiple moorings for the production and/or storage of hydrocarbons. The vessel comprises a laterally extending main deck, a symmetrical mooring arrangement for anchoring the vessel to the seabed when the vessel is afloat in a body of water, and a longitudinal hull. The longitudinal hull further comprises a bow, a central body, a stern and a motion suppression element that projects outwards from the longitudinal hull, below the vessel's maximum draft. The ratio between the maximum length (Lwl) and the maximum width (Bwl) of the longitudinal hull, at the vessel's maximum draft, is between 1.1 and 1.5. The specific shape of the hull with the specific length/width ratio and the motion suppression element allows favorable and uniform movements in relation to the wave direction in relation to the vessel's heading.

Description

technical field

[0001] The present invention generally relates to offshore vessels used for the production and/or storage of petroleum products. More specifically, the present invention relates to offshore vessels for connecting a plurality of subsea risers and a deck structure for supporting topside modules, such as a floating production, storage and offloading (FPSO) vessel or a floating liquefied natural gas (FLNG) vessel. The vessel's hull can also be used as a base for a drillship.

Background and prior art

[0002] A floating production, storage and offloading (FPSO) system is a floating facility above or near an offshore oil and/or gas field to receive, process, store and export hydrocarbons.

[0003] The system consists of a float, which can be a purpose-built vessel or a converted tanker, moored at a selected location. The vessel's carrying capacity is used as buffer storage for the produced oil. Process facilities (topsides) and accommodations are installed on the float. Mooring configuration on FPSOs can be either a multi-mooring type or a single-point mooring (SPM) type such as a turret. An anchoring configuration based on dynamic positioning (DP) is also possible, but not recommended due to high complexity and cost.

[0004] The high pressure mixture of fluids produced from the well is delivered to the process facilities on the vessel's deck where oil, gas and water are separated. The water can be reinjected into the reservoir or discharged into the sea after treatment, eliminating hydrocarbons. Stabilized crude oil is stored in the vessel's cargo tanks and subsequently transferred to commercial tankers directly via a buoy, lying side by side/together with the FPSO vessel or using tankers/cargo transfer vessels (CTV).

[0005] The gas can be used to improve the production of liquids by means of gas lift and/or for energy production on board the vessel. Excess gas can be compressed and piped or reinjected into the reservoir.

[0006] A floating liquefied natural gas (FLNG) vessel is conceptually similar to the FPSO. The difference is that the well's hydrocarbon mix is predominantly gas and the purpose of the process facility is to separate, clean and liquefy the gas for storage in dedicated cryogenic tanks within the hull. The offloading of the liquefied gas is done to trading gas (LNG) vessels.

[0007] Conventional ship-shaped FPSOs require weathervaning facilities, such as a tower, when located in adverse environmental areas. A characteristic for these types of FPSOs, however, is a very different pitch and roll behavior, allowing for large waves in offshore conditions, but significantly smaller waves from offshore and 45° seas (beam and quartering seas). Therefore, weathervaning is required for this type of ship.

[0008] Semi-submersible designs can provide favorable and uniform movements. However, storage capacity is limited and sensitivity to topside weight is critical. Therefore, a semi-submersible design is not considered advantageous when a large storage capacity is an important design criterion, such as for an FPSO or FLNG unit. Furthermore, the structural details are more complex in semi-submersibles, resulting in higher weight of steel per ton of payload on the topside, as well as higher manufacturing cost. An early example of a semi-submersible platform is disclosed in WO 02/090177 A1.

[0009] Other designs, such as box-shaped units or cylindrical hulls, can provide uniform motion behavior regardless of wave direction. If equipped with motion suppression elements, favorable motions can also be achieved. The form of such units, however, does not allow the use of standard ship-shaped construction installations. Automatic panel line installations cannot be used without significant modifications, and the shape/dimension offers other limitations. The critical measurements in this regard are width and depth. For the use of cylindrical designs with a storage capacity greater than 1,000,000 bbl, there will be a significant limitation regarding available dry docks and floating cranes. Another disadvantage of the cylindrical design is the low ratio between deck area and storage volume and the maximum distance obtained between the safe and dangerous side, which complicates the topside design. (1 bbl (barrel of oil) is a unit of volume corresponding to 159 liters).

[0010] Document US 2004/0067109 A1 discloses a drilling vessel without storage capacity having an elongated shape, preferably rectangular in shape, and anchored to the seabed in a substantially fixed orientation. The vessel comprises two transverse skirts close to its keel level, with a width such that the vessel's natural pitch period is above a predetermined period. Document US 2004/0067109 A1 states that the length/width ratio of the vessel must be at least 1.5, preferably at least 2, since a length/width ratio of 1.5 or less can be subject to roll instability or Mathieu instability. The design objective of this prior art craft is to control pitch, not the combination of heave, roll and pitch. Similar elongated vessels without a pronounced bow and with length-to-width ratios greater than 1.5 are disclosed in patent publications US 2011/0209655 A1, US 4015552 and US 2002/0083877.

[0011] WO 2015/038003 A1 discloses a platform comprising a hull with a main portion that is substantially axisymmetric around a central axis, without a pronounced bow and a parallel central section. The upper end of the platform supports a deck and the lower end of the platform, located below a nominal waterline, is provided with a non-circular stabilizing member projecting from the main portion.

[0012] WO 2012/104308 A1 discloses a cylindrical platform for the production and storage of hydrocarbons. The vessel's substantially circular hull is configured to permit the suspension of risers in at least one frame arranged in a moon pool in the center of the hull. The structure is placed so that the connection of the risers can be carried out above the waterline when the platform has a minimum draft. The moon pool may comprise a conical shape at its lower end, allowing for static and dynamic angular deflections of the risers. The moon pool extends above the main deck, where the extended vertical moon pool is lowered to increase deck space availability. The hull can also be fitted with a hump to reduce pitching, pitching and pitching.

[0013] Document WO 2014/167591 A1 describes a drillship with a pronounced bow and a parallel central section, where its climbing/descent and pitching behavior has been improved by the addition of a protrusion with a flattened shape, at the bow or at the stern. Due to the lack of roll dampening devices, this vessel will experience significant roll motions if exposed to waves that are side by side. Furthermore, no tower is disclosed in WO 2014/167591 A1. Therefore, it is assumed that the ship's positioning system is based on a DP system, since a dispersed mooring system would not be able to sufficiently suppress wave-induced movements.

[0014] The aforementioned prior art does not disclose vessels with a design that allows safe, easy and effective handling in a hostile environment, at the level offered by the FPSO of the present invention.

[0015] Consequently, the objective of the present invention is to provide a vessel for the production and/or storage of hydrocarbons arranged to float in a body of water, hereinafter referred to in abbreviated form as FPSO, offering beneficial properties in relation to motor behavior, storage capacity and safety, in relation to FPSOs of the prior art. The order is equally relevant for similar purpose vessels such as FSO or FLNG, but only the term FPSO is used below for simplicity.

[0016] A second objective of the invention is to provide a vessel with a non-cylindrical design that has a movement behavior independent of the wave direction in relation to the vessel's orientation. Lifting, pitching and turning movements must be favorable and uniform, regardless of position on the vessel.

[0017] A third object of the invention is to provide an FPSO that is moored at multiple moorings and does not require a turret or turret-like equipment.

[0018] A fourth objective of the invention is to provide an FPSO in which the number and/or size of mooring lines are smaller than the number and/or size used in conventional multi-moored FPSOs with comparable storage capacity.

[0019] A fifth objective of the invention is to provide an FPSO with a bow design that optimizes orientation in the field, both in relation to the protection of the green sea and in relation to anchorage through reduced drag/wave forces on the hull.

[0020] A sixth objective of the invention is to provide an FPSO design that is suitable in both benign and adverse environmental conditions.

[0021] A seventh objective of the invention is to provide an FPSO of scalable size in relation to its oil storage capacity.

[0022] An eighth objective of the invention is to provide an FPSO with a vessel design that allows for greater topside weight capacity compared to conventional FPSO designs.

[0023] A ninth objective of the invention is to provide an FPSO with a vessel design that ensures a large deck area for the placement of modules on the topside and a simple interface, compared to rotational symmetric FPSO designs.

[0024] A tenth objective of the invention is to provide an FPSO with a design and size such that fabrication can be carried out using standard shipbuilding facilities, including existing dry docks, allowing flexibility in the choice of fabrication yard.

[0025] An eleventh objective of the invention is to provide an FPSO with favorable and uniform vertical movements, thus allowing the suspension of the riser in any longitudinal and transverse position.

[0026] A twelfth objective of the invention is to provide an FPSO with a design that, through the adjustment of its suppression element/bilge box, allows the use of free suspended steel catenary risers (SCRs) in a hostile environment for large water depths, for example, between 1,500 meters and 3,000 meters. SCRs can also be applied for shallower water in case of more benign environmental conditions.

[0027] A thirteenth objective of the invention is to provide an FPSO design with significantly reduced fatigue compared to conventional ship-shaped FPSOs.

[0028] In addition to meeting one or more of the objects mentioned above, the FPSO vessel-specific design should preferably comply with international regulations, including class society, MARPOL (international convention for the prevention of pollution from ships), SOLAS (international convention for the safety of life at sea) and/or relevant requirements of new state (shelf-state) of the site. Furthermore, the inventive FPSO should preferably fall under the rules regime associated with conventional ship-shaped vessels.

Summary of the invention

[0029] The aforementioned objectives are achieved by the invention, as established and characterized in the main claims, while the dependent claims describe other embodiments of the invention.

[0030] In particular, the present invention relates to a multi-anchored vessel suitable for production and/or storage of hydrocarbons. The vessel comprises a laterally extending main deck, a mooring arrangement suitable for anchoring the vessel to the seabed when the vessel is floating in the water, and a longitudinal hull. The mooring arrangement is preferably arranged symmetrically to the main deck, i.e. mirroring at least one central plane of the hull directed perpendicularly to the main deck. The longitudinal hull further comprises a bow, a central body, a stern and at least one motion suppression element that projects out of the longitudinal hull, below the vessel's maximum draft, preferably from each of the hull sections. The motion suppression element(s) causes a significant reduction in undesirable vessel motion, especially climb/descent, roll and pitch. The ratio between a maximum length and a maximum width of the longitudinal hull, at the vessel's maximum draft, is between 1.1 and 1.7, more preferably between 1.1 and 1.7, even more preferably between 1.2 and 1.4. The particular ratios, in combination with the motion suppression element(s), have the advantage that the effect that waves have on movements in the vessel relative to longer vessels is reduced, making the vessel more stable during operation. The longitudinal hull, seen from above, may be in the shape of a rectangle with a rounded triangle at the front end.

[0031] As a consequence of the above characteristics, the movement of the vessel will be almost independent of the wave direction and the requirement for mooring systems other than a mooring system in multiple moorings can be eliminated. Furthermore, the total number of mooring lines can be reduced compared to conventional ship-shaped multiple mooring FPSOs, thus reducing the complexity and cost of the vessel mooring arrangement compared to prior art vessels with the same or similar function. It should be noted that the multi-moored arrangement can only be applied to conventional FPSO designs for areas with relatively benign wave climate.

[0032] The term 'laterally extending main deck' means a deck having a surface which extends parallel to the surface of the water when the vessel is afloat on a still body of water. Furthermore, the hull is hereinafter defined as the area of the longitudinal vessel lying below the main deck area of the vessel.

[0033] In an advantageous example, the motion suppression element(s) project laterally from the hull along at least 70% of the lateral extension circumference of the hull, more preferably at least 80%, for example along the entire circumference.

[0034] In another advantageous example, the motion suppression element(s) protrudes laterally from a lower part of the hull. The lowest part may be flat, i.e. parallel to the deck.

[0035] In yet another advantageous example, the length of the lateral protrusion of the motion suppression element(s) is between 5% and 30% of the maximum hull width at the maximum draft of the vessel.

[0036] In yet another advantageous example, the central body comprises a port side portion and a starboard side portion, where at least 30% of the longitudinal length of the central body is flat, i.e. without folds and/or curves, and oriented parallel to a central plane of the hull. The center plane is hereinafter defined as the plane which intersects the hull midway between the center body, i.e. the midway between the port and starboard side portions and aligned perpendicularly to the laterally extending main deck.

[0037] In yet another advantageous example, the transition region between the bow and the central body forms a sudden angle change at the maximum draft of the vessel, in relation to the tangent plane of the central body directed parallel to the central plane, preferably at least 20 degrees.

[0038] In yet another advantageous example, the longitudinal length of the bow at the vessel's maximum draft is at least 25% of the maximum hull length.

[0039] In yet another advantageous example, the mooring arrangement comprising a plurality of mooring lines, wherein at least one mooring line is mooring from a location near or at the center of the bow relative to the hull width, at least one mooring line is mooring from a location adjacent to the stern on the port side of the hull, and at least one mooring line is mooring from a location adjacent to the stern on the port side of the hull starboard. However, in this specific embodiment, additional anchor lines can be arranged at other locations around the lateral periphery of the hull, in order to obtain the required positioning/stability. At the locations of the plurality of anchor lines, the at least one motion suppression member preferably has a suitable recess, or is omitted entirely, to allow the anchor lines to be guided in the body of water closest to the lateral center of the vessel. These recesses can also provide additional control of the vessel's movement.

[0040] In yet another advantageous example, the longitudinal length of the vessel is separated into a loading zone and at least one unloading zone, for example by a wall and/or a safety distance. Furthermore, the longitudinal hull exhibits at least one cargo tank for containing the cargo, wherein the cargo tank, or all cargo tanks in the case of a plurality of cargo tanks, are confined within the vessel's cargo area. Therefore, no cargo tanks are located outside the no-cargo zone. The unloaded zone is preferably located at the bow of the vessel. However, this no-load zone can also be situated aft for specific topside layouts. In addition, the hull may be double-sided around its vessel circumference, having one or more ballast tanks between the hull walls.

[0041] In yet another advantageous example, the longitudinal hull further exhibits at least one waste tank located adjacent to at least one cargo tank, for collecting drains, tank washes and other fluid mixtures. The at least one waste tank is preferably arranged in or adjacent to the center plane of the hull.

[0042] In yet another advantageous example, at least one of the at least one no-load zone is located within the bow.

[0043] In yet another advantageous example, the longitudinal hull comprises at least two walls having a space between them, in which at least one ballast tank is located.

[0044] In yet another advantageous example, the vessel is configured to allow the suspension of an arrangement of multiple risers in the central body, at the bow and/or at the stern.

[0045] In yet another advantageous example, a plurality of riser guide tubes are arranged along at least part of the lateral circumference of the longitudinal hull. Each of the plurality of riser guide tubes is configured to allow at least one riser to be guided therethrough.

[0046] In yet another advantageous example, the area of the projected lateral surface of the hull in the vertical position of the main deck is greater than the area of the projected lateral surface of the hull in the vertical position of the maximum draft of the vessel, preferably at least 10% greater, for example 20% greater. The beginning of the rise preferably starts at or above the maximum draft of the vessel. Full rise from the start can occur abruptly. However, it is preferable that the rise is continuous, for example a linear rise with a 1:2 ratio or a comparable parabolic rise. This vessel design increases the deck area available for placing modules on the topside, while allowing for a simple interface. This, in combination with a rectangular-shaped stern and central body, forms a large space available for topside modules on deck, compared to conventional ship-shaped FPSOs.

[0047] In yet another advantageous example, the ratio between the maximum length of the longitudinal hull and the maximum depth of the longitudinal hull, where the maximum depth is defined as a distance from the vertical position of the main deck to the lowest part of the hull, is between 2 and 6, more preferably between about 2 and about 3. These ratios are considerably lower than conventional ship-shaped FPSOs, typically between 10 and 12. Significantly reduced hull beam bending stress and/or deflection compared to conventional ship-shaped FPSOs, resulting in a streamlined top interface without the need for sliding supports. Considering that the hull beam bending moment is proportional to the length squared (Lwl2) and the capacity is a function of the depth squared (Dwl2), it is clear that a reduction in Lwl/Dw causes a corresponding reduction in the stress of the hull beam. The comparison can also be illustrated in terms of hull beam longitudinal stress at main deck level. While conventional ship-shaped FPSO designs experience around 75% material flow into the deck skin, the inventive design will have less than 25% material flow.

[0048] In yet another advantageous example, the hull of the vessel is dimensioned in size/shape and with the arrangement of the tank so that the hull can support a total weight above the main deck that is greater than the total weight of the hull including the main deck.

[0049] Static loads dominate the load picture for the inventive design of the FPSO, which means that fatigue in general is not the ruler. Therefore, the number of critical details will be significantly less with the above-mentioned inventive vessel compared to conventional ship-shaped FPSO designs.

[0050] The governing static load of the FSO/FPSO design also allows the use of manufacturing materials such as high tensile strength steel (typically 355 MPa) to a greater extent than for conventional vessel designs with length >> width, providing not only lower weight (due to, among others, the use of thinner plates), but can also result in lower cost, since materials such as high tensile strength steel have a lower strength/cost ratio compared to normal strength steel.

[0051] The combination of reduced movement, large deck area, large topside cargo capacity and a large storage volume are important features for FPSOs, vessels and storage units for floating production, cooling and storage of natural gas (FLNG). The combination of a longitudinal vessel with a ratio (Lwl/Bwl) less than 1.7, preferably equal to or less than 1.5, and with motion suppression element(s) projecting from the hull, makes positive contributions to these characteristics.

[0052] As explained above, the specific design of the vessel's hull also allows the use of SCR risers. This is a major advantage over using traditional flexible risers, as the latter solution is generally more expensive, offers a more complex installation and requires more maintenance compared to a steel riser solution. Furthermore, flexible risers are more sensitive to irregularities during operation and have a shorter service life than steel risers. Since repairing a flexible riser has proven to be difficult, they are often exchanged for new ones, thereby increasing costs. SCRs can be hung alongside, aft or through a moon pool within the hull.

[0053] Due to the design of the vessel with a bow, parallel central body and a stern that are familiar features of shipyards, the inventive vessel provides flexibility regarding the fabrication yard and the fabrication method.

[0054] The inclusion of a pronounced bow on the vessel results in several advantages compared to box-shaped and cylindrical vessels of the prior art: - For a given vessel size in terms of storage capacity, the shape of the bow offers a greater overall length than without the bow, allowing for a greater distance between the safe area and the dangerous area on the vessel. The bow shape also provides an area outside the cargo area for the location of living quarters, ensuring that the quarter is not located above the cargo tanks, which again provides complete flexibility in filling cargo tanks without compromising the safety or damage stability of the vessel. - With the bow added, the vessel can be oriented such that drag/wave forces on the hull are reduced. Aligning the vessel with the bow against the direction from which the maximum waves are coming will provide reduced drag forces on the vessel and consequently allow optimization of the mooring system. The small radius curved bow shape also has greater structural capacity than a flat or semi-flat structure and allows adequate strength with a lower steel weight. Resistance during potential wet towing will also be reduced compared to a bowless design which in turn will increase towing speed and reduce towing cost.

[0055] In the following description, numerous specific details are introduced to provide a complete understanding of the embodiments of the claimed longitudinal vessel. One skilled in the relevant art, however, will recognize that these modalities can be practiced without one or more specific details, or with other components, systems, etc. In other cases, known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

Brief description of the drawings

[0056] The invention will now be described with reference to the accompanying drawings, in which:

[0057] Figure 1 is a side view of a vessel according to an embodiment of the present invention,

[0058] Figure 2 is a top view of the vessel, in accordance with figure 1, showing the raised deck and the exemplary positions of the cargo tanks, waste tanks and mooring winch arrangement,

[0059] Figure 3 shows a horizontal section through a vessel in accordance with figures 1 and 2, showing exemplary locations of cargo tanks, waste tanks, fuel tanks and ballast tanks, the horizontal section being within or around the waterline, i.e. between the hull suppression elements and the flared side casing of the hull,

[0060] Figure 4 shows a cross section through the cargo area of the vessel according to figures 1-3,

[0061] Figure 5 is a longitudinal cross section through a central plane of the vessel according to figures 1 - 4,

[0062] Figure 6 is a longitudinal cross-section through a central plane of a vessel according to a second embodiment of the invention, showing an alternative configuration in which a safe area with accommodation is located towards the stern of the vessel,

[0063] Figure 7 is a view of the bottom of the vessel according to the invention, including anchor lines and local recesses in the suppression elements,

[0064] Figures 8 (a) to (d) show representative movement characteristics of a vessel according to the invention compared to conventional ship-shaped designs of comparable storage capacity, plotting the simulated response of the rise/fall movement as a function of the wave period for the inventive FPSO (a) and a conventional FPSO (b) and plotting simulated data of the pitch/swing movement ratio as a function of the wave period for the inventive FPSO (c) and the conventional FPSO ( d).

Detailed description of the invention

[0065] Figures 1-7 show a first embodiment of a longitudinal vessel 1 according to the present invention, having a maximum length and width at the maximum draft location of Lwl and Bwl, respectively (see in particular Figure 2). The vessel 1 comprises a bow 3, a stern 4, a hull 2 with a parallel central body 2a, 2b and a deck structure 5. The latter further comprises a main deck D, a processing deck P and accommodations A resting on a forward deck F. m outside the hull 2, preferably around the entire periphery of the hull 2. The suppression element 6 can extend 10-25% of the width of the vessel 6, depending on the required movement characteristics. The safe area of the FPSO, i.e. the main deck area D which contains living quarters A, is separated from the processing area by distance or a blast wall. The bow area 3 and/or the stern area 4 can be raised to provide improved protection from the green sea. Furthermore, as is more evident in Figure 2, the deck area behind the bow area 3 is preferably rectangular, thus allowing a simple and effective arrangement of the topside modules. The maximum length of vessel 1 (Lwl) is preferably 1.1 to 1.5 times the maximum width of vessel 1 (Bwl), for example 1.3 times the width (Bwl). As best seen in figures 1 and 4, the topside of hull 2, which is the height of hull 2 above the waterline (w(l)) or maximum draft, is enlarged to provide greater deck area.

[0066] The FR flared region typically starts about 1 meter above the waterline (w(l)) and extends to the P process deck or above, depending on the required deck space. The default flare angle of the flare region is typically 1:2 in terms of horizontal versus vertical increment, but can be increased for areas where crashing waves are not an issue. The flare angle can therefore vary around the circumference of vessel 1.

[0067] The elevation of the main deck D in relation to the waterline w(l) is determined for each specific application, but is generally kept as low as possible within the limits established by the international convention of the load line, stability and green sea. A distance (d) from elevation D of the main deck of about 10 to 12 meters above the waterline w(l) is typical for harsh environment areas, and somewhat less for benign conditions. The process deck P is typically located 4-6 meters above the main deck D. For very severe wave conditions, the forward deck F, on which the living quarters and lifeboats will be located, can be raised an additional 4-6 meters.

[0068] The suppression element 6 provides additional mass that influences, among others, the up/down movements, pitch and roll of vessel 1 caused by external forces, such as waves. By adjusting the size of the suppression element, the shape of the vessel, including length/width ratio and waterline area, and the total mass of the vessel, including added mass, it is thus possible to achieve a natural frequency outside the critical wave excitation frequency range. When selecting the actual ship shape and design, the coupling effects between inertia, damping and buoyancy forces need to be considered as these effects have a significant influence on up/down, pitch and roll motions. It is the combination of the increased natural period and the aforementioned coupling effects that provides the favorable motion characteristics of the present invention. This motion behavior has been documented and verified through calculations and model testing.

[0069] Figures 2 and 3 show the top view sections on the main deck D and the waterline w(l), respectively, and provide an overview of the vessel's tank arrangement. The vessel 1 is divided into no-load zones (NCZ) comprising a plurality of ballast tanks 101 and fuel/MDO (marine diesel oil) tanks 102 and a cargo zone (CZ) comprising a plurality of cargo tanks 100a and apparent waste tanks 100b.

[0070] The double hull configuration with the flared outer hull 2 provides a significant area around the circumference of the main deck D in which there is no hydrocarbon content underneath. With a double side of 3-4 meters and the mentioned hull 2 with the flared FR region, the width of the outer deck area above the ballast tanks will be more than 8 meters. Figures 2 and 3 also show the distinctive rectangular shape of the rear part 4 and the central body part 2a, 2b, as well as the triangular bow 3 including the curved forward part (the last one in figure 3 confined in the safety area, i.e. in front of the safety division S).

[0071] The central body of the hull 2 comprises a port side portion 2a and a starboard side portion 2b oriented parallel to a central plane CP of the hull 2, the central plane CP being defined as the plane that intersects the hull 2 midway between the port side portion 2a and the starboard side portion 2b and aligned perpendicularly to the main deck D (see dotted line in Figure 7).

[0072] The wave excitation forces are greater in the waterline area and, therefore, the shape and dimensions of the vessels 1 in this area are decisive to obtain favorable responses and independent of the wave direction. The bow part 3 shown in figures 2 and 3 constitutes about 35% of the waterline length w(l), i.e. 35% of Lwl, and forms a bow angle (BA) between 20 and 60 degrees from the parallel central part. With a slope angle of 40 degrees and with a length/width ratio (Lwl/Bwl) at the waterline w(l) of about 1.3, the length and width range of the inventive design will be Lwl = 50-140 meters and Bwl = 35-100 meters for storage capacities of 100,000 bbl - 2,000,000 bbl, just as an example.

[0073] As an alternative, the distribution of the pump rooms 103 and the fuel tanks 102 can be located in the rear part 4 of the vessel 1.

[0074] The arrangement of ballast tanks 101 around the circumference of hull 2 provides protection to ballast and waste tanks 100a, 100b, fuel tanks 102 and pump room 103. A double bottom 10, as shown in Figures 4-6, provides additional protection for tanks 100a, 100b, 102, 103, in addition to being used as tank space (s ) of additional ballast(s) 101. This tank arrangement, combined with the wide width of vessel 1, results in high vessel stability. The high stability allows the application of large apparatus/process systems on vessel 1, such as FPSOs or FLNGs. If using vessel 1 for natural gas, the ballast and waste tanks must be separate from the tanks for fluid-cooled natural gas.

[0075] An example of an anchoring arrangement M is shown in Figures 2 and 7. The anchoring arrangement M comprises a plurality of anchoring lines arranged in the front Mb and in the rear corners Msp (port), Msb (starboard) of the vessel 1, so that the entire anchoring arrangement M is mirrored to the central longitudinal plane CP of the vessel 1. This anchoring arrangement in multiple anchorage M ensures a fixed position and not rotated of the vessel during hydrocarbon production, thus avoiding the need for expensive and complex turret assemblies and/or dynamic positioning (DP) systems. In the particular example shown in Figures 2 and 7, the anchor lines are distributed within three symmetrically arranged recesses 7 carved into the contour blanking element 6.

[0076] Figure 4 shows a cross section of the hull 2 in a plane oriented along the width of the vessel and within the central part of the vessel 1. The particular view visualizes the exemplary tank arrangement, including five cargo tanks 100a side by side, protected by double-sided ballast tanks 101 and a double bottom. A waste tank 100b is illustrated above the intermediate cargo tank 100a. The double bottom can be used to confine the ballast tanks 101 and the empty tanks 104, as illustrated in Figure 4. The required waste capacity is typically 3% of the cargo capacity. Therefore, waste tanks 100b are small compared to cargo tanks 100a. For ventilation, access and operation purposes, it is beneficial to have access to the waste tanks 100b from the main deck D. The waste tanks 100b are therefore typically located towards the deck within the volume of the center cargo tanks 100a.

[0077] Figure 5 shows a view in section through the longitudinally directed central plane CP of vessel 1, illustrating the unloaded zones and the cargo zone, as well as the distribution of the tank, in the longitudinal direction of vessel 1. The figure also clearly shows that the accommodation A is not located above any cargo or waste tank 100a, 100b.

[0078] Figure 6 shows a view in section through the longitudinally directed central plane CP of a second embodiment of the inventive vessel 1. In this embodiment, the accommodation A is located at the stern 4 of the vessel 1, an embodiment that may be preferable in case the predominant wind direction is opposite to the direction of the maximum wave height towards which the bow 3 is facing. From a safety point of view, it is generally a preference to have housing A, downwind of the processing plant and the extended FR region. Figure 6 also shows a design in which the suppression element 6 in the keel is extended compared to the embodiment shown in Figures 1 - 5 to further increase the natural period and dampen the movements. As for Figure 5, the locations of the unloaded zones and the cargo zone are illustrated in the longitudinal direction of vessel 1.

[0079] With the aforementioned project, and within the constraints of an existing facility/standard yard and construction, the inventive FPSO can obtain a storage capacity in excess of 2,000,000 bbls.

[0080] Figures 8 a) and c) show calculated RAOs (Operator Range of Response) for climb/descent and pitch and roll RAOs for the present invention, respectively, while Figure 8b) and d) show the corresponding calculated RAOs for a conventional ship-shaped FPSO design. The axis scale is the same for both concepts to allow direct comparison. As seen in Figures 8 a) and c) the behavior of the movement in the beam and in the head is practically uniform for the present invention, in comparison with the ship-shaped design in Figures 8 b) and d). A comparison between Figure 8 a) and Figure 8 b) also shows that the natural rise/descent period is significantly longer for the present invention (about 16.6 s) than for the conventional ship (about 11 s). Furthermore, it is evident from these figures that there will be almost no response for wave periods of less than 10 seconds for the inventive vessel, whereas the conventional ship-shaped design will experience up/down motion in waves from 5 seconds onwards.

[0081] As is clearly seen when comparing Figure 8 c) with Figure 8 d), the difference is even greater when it comes to rocking and pitching movements. In a wave example period of 12 seconds, the conventional ship-shaped vessel will experience roll angles in the upper seas that are more than 3 times those seen for the inventive vessel and roll angles in the beam seas more than 10 times that of the inventive vessel.

[0082] The calculations presented are for a Suezmax tanker with a storage capacity of about 1,000,000 bbl, where 1 bbl is equal to about 159 liters. The following input values were used in the calculations:

[0083] Calculations of the RAO curves are made for motion responses in regular waves using potential theory, including corrections for viscous forces using Morison elements. The computer program used for the analyzes is WADAM from DNV-GL. Calculations for vessels of larger and smaller sizes show the same pattern of behavior.

[0084] For the inventive vessel 1, the pitching and rocking movements (Figure 8 (c)) are very small compared to the up/down movements (Figure 8 (a)). Therefore, vertical movement at any point will be governed by up/down movements. This provides a vessel 1 with nearly uniform vertical motion and acceleration over the entire length and width, regardless of wave direction, which in turn offers flexibility in the location and/or orientation of equipment on the topside and allows for suspension of the riser in any position of the vessel 1. That is, suspension of the riser at the front, side, aft or along the center line of the vessel 1. elevation of the main deck D. Figure 3 shows an example of the location of the riser guide tubes 8 arranged aft and on the port side or aft on the starboard side. The number of riser guide tubes 8 shown in the figures is illustrative only. The present invention can allow the use of up to 60 risers, if necessary.

[0085] In the foregoing description, various aspects of the vessel according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations have been established in order to provide a complete understanding of the vessel and its operation. However, this description should not be interpreted in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the vessel, which are apparent to those skilled in the art to which the disclosed subject matter relates, are considered to be within the scope of the present invention.

[0086] List of reference numbers/letters 1 vessel 2 hull 2a port side portion 2b starboard side portion 3 bow 4 stern 5 deck/deck structure 6 suppression elements/bilge box 7 recess 8 riser guide tubes 9 mooring winch 10 hull bottom 100a cargo tanks 100b waste tanks 101 tank s of ballast 102 fuel tank/MDO tank 103 pump room 104 empty tank A accommodations Lwl maximum hull length at waterline Bwl maximum hull width at waterline CP Center plan D main deck F forward deck FR flared region from waterline to process deck BA bow angle M mooring arrangement P process deck S safety division w(l) vessel water level at maximum draft

Claims (23)

1. Vessel (1) moored at multiple moorings for the production and storage of hydrocarbons, the vessel (1) comprising - a main deck (D) extending laterally, - a mooring arrangement (M) for anchoring the vessel (1) to a seabed when the vessel is afloat on a body of water (W) and - a longitudinal hull (2), wherein the ratio of a maximum length (Lwl) to a maximum width (Bwl) of the longitudinal hull (2 ), at the maximum draft of the vessel (1), is between 1.1 and 1.5 and in which the longitudinal length of the vessel (1) is separated into a cargo zone (CZ) comprising at least one cargo tank (100a) and at least one unloaded zone (NCS), characterized by the fact that the longitudinal hull (2) comprises - a motion suppression element (6) projecting outwards from the longitudinal hull (2), below the maximum draft of the vessel (1), for suppression of rise/fall cid, pitch and roll, - a bow (3) with a lateral cross-section in the form of a rounded triangle, - a central body (2a, 2b) and - a stern (4), in which the lateral cross-section of the central body (2a, 2b) and the stern (4) at the maximum draft of the ship has a rectangular shape. 2. Vessel (1), according to claim 1, characterized by the fact that the ratio between the maximum length (Lwl) and the maximum width (Bwl) of the longitudinal hull (2), at the maximum draft of the vessel (1) is between 1.2 and 1.4. 3. Vessel (1), according to claim 1 or 2, characterized by the fact that the movement suppression element (6) projects outwards from the bow (3), central body (2a, 2b) and stern (4), below the maximum draft of the vessel (1). 4. Vessel (1), according to any one of claims 1 to 3, characterized in that the movement suppression element (6) projects laterally from the hull (2) along at least 70% of the circumference of lateral extension of the hull (2). 5. Vessel (1), according to any one of claims 1 to 4, characterized by the fact that the movement suppression element (6) projects laterally from the lowest part of the hull (2). 6. Vessel (1), according to any one of claims 1 to 5, characterized in that the lateral protrusion length of the motion suppression element (6) is between 5% and 30% of the maximum width (Bwl) of the hull (2) at the maximum draft of the vessel (1). 7. Vessel (1), according to any one of claims 1 to 6, characterized in that the central body (2a, 2b) comprises a portion of the port side (2a) and a portion of the starboard side (2b), in which at least 30% of the longitudinal length of the central body (2a, 2b) is flat and oriented parallel to the central plane (CP) of the hull (2), the central plane (CP) being the plane that intercepts the hull (2) in the half between the port and starboard side portions (2a, 2b) and aligned perpendicularly to the main deck (D) which extends laterally. 8. Vessel (1), according to any one of claims 1 to 7, characterized by the fact that the transition region between the bow (3) and the central body (2a, 2b) forms a sudden angle change (BA) at the maximum draft of the vessel, relative to the central plane (CP), the central plane (CP) being the plane that intercepts the hull (2) in the middle between the port and starboard side portions (2a, 2b) and aligned perpendicularly to the main deck (D) extending laterally. 9. Vessel (1), according to claim 8, characterized by the fact that the angle (BA) is at least 20 degrees. 10. Vessel (1), according to any one of claims 1 to 9, characterized in that the longitudinal length of the bow (3) at the maximum draft of the vessel is at least 25% of the maximum length (Lwl) of the hull (2). 11. Vessel (1), according to any one of claims 1 to 10, characterized in that the anchoring arrangement (M) comprises a plurality of anchoring lines (M), in which at least one anchoring line (Mb) is anchorable from a location near or in the center of the bow (3) in relation to the width of the hull (2), at least one anchoring line (Msp) is anchorable from a location adjacent to the stern (4) on the port side of the hull and at least one mooring line (Msb) is anchorable from a location adjacent to the stern (4) on the starboard side of the hull. 12. Vessel (1), according to claim 11, characterized by the fact that the movement suppression element (6) exhibits recesses (7) in the lateral locations of the plurality of anchoring lines (M) when the vessel (1) is anchored to the seabed. 13. Vessel (1), according to any one of claims 1 to 12, characterized in that the longitudinal hull (2) also has at least one waste tank (100b) located adjacent to at least one cargo tank (100a). 14. Vessel (1), according to claim 13, characterized in that at least one waste tank (100b) is arranged in or adjacent to the central plane (CP) of the hull (2), the central plane (CP) being the plane that intersects the hull (2) in the middle between a portion of the port side (2a) and a portion of the starboard side (2b) constituting the central body (2a, 2b) and aligned perpendicularly to the main deck ( D) extending laterally. 15. Vessel (1), according to any one of claims 1 to 14, characterized by the fact that at least one of the at least one no-load zone (NCZ) is located inside the bow (3). 16. Vessel (1), according to any one of claims 1 to 15, characterized in that the longitudinal hull (2) comprises at least two walls with a space between them, in which at least one ballast tank (101) is located. 17. Vessel (1), according to any one of claims 1 to 16, characterized in that the vessel (1) is configured to allow the suspension of an arrangement of multiple risers in at least one of the central body (2a, 2b), the bow (3) and the stern (4). 18. Vessel (1), according to any one of claims 1 to 17, characterized in that a plurality of riser guide tubes (8) are arranged along at least part of the lateral circumference of the longitudinal hull (2), wherein each of the plurality of riser guide tubes (8) is configured to allow at least one riser to be guided through it. 19. Vessel (1), according to any one of claims 1 to 18, characterized by the fact that the projected lateral surface area of the hull (2) in the vertical position of the main deck (D) is greater than the projected lateral surface area of the hull (2) in the vertical position of the maximum draft of the vessel. 20. Vessel (1), according to any one of claims 1 to 19, characterized in that the projected lateral surface area of the hull (2) in the vertical position of the main deck (D) is at least 10% greater than the projected lateral surface area of the hull (2) in the vertical position of the maximum draft of the vessel. 21. Vessel (1), according to claim 19 or 20, characterized by the fact that the beginning of the increase in the projected lateral surface area of the hull (2) from the vertical position of the maximum draft of the vessel to the vertical position of the main deck (D) begins equal to or above the maximum draft of the vessel (1). 22. Vessel (1), according to claim 20 or 21, characterized by the fact that the increase in the projected lateral surface area of the hull (2) from the vertical position of the maximum draft of the vessel to the vertical position of the main deck (D) is constant. 23. Vessel (1), according to any one of claims 1 to 22, characterized by the fact that the ratio between the maximum length (Lwl) of the longitudinal hull (2) and a maximum depth (Dwl) of the longitudinal hull (2) defined as a distance from the vertical position of the main deck (D) to the lowest part of the hull (2) is between 2 and 6.