FIELD

The present embodiments generally relate to a method for operating a floating platform, storage and offloading (FPSO) vessel.

BACKGROUND

This present invention pertains to a method for operating floating production, storage and offloading (FPSO) vessels and more particularly to hull designs and offloading systems for a floating drilling, production, storage and offloading (FDPSO) vessel.

The present embodiments meet these needs.

SUMMARY

Various embodiments provide a method for offshore floating petroleum production, storage and offloading comprising the steps of: (a) receiving hydrocarbons from at least one of: an FPSO, production risers, or wellhead on the seabed by a floating hull; (b) processing received hydrocarbons forming hydrocarbon product in the floating hull; (c) storing the hydrocarbon product, in the floating hull, the floating hull comprising: a hull plan view that is circular and wherein the floating hull comprises: (i) a bottom surface; (ii) a top deck surface; (iii) at least three connected sections, joined in series and symmetrically configured about a vertical axis with the connected sections extending downwardly from the top deck surface toward the bottom surface; the at least three connected sections comprising of: upper cylindrical portion; a lower conical section, a cylindrical neck section; and (iv) a set of fins secured to the hull configured to provide hydrodynamic performance through linear and quadratic damping; and (d) offloading the stored hydrocarbon product to at least one of: a tanker, or a pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction with the accompanying drawings as follows:

Fig. 1 is a top plan view of an FPSO vessel, according to the present invention, and a tanker moored to the FPSO vessel.

Fig. 2 is a side elevation of the FPSO vessel of Fig. 1

Fig. 3 is an enlarged and more detailed version of the side elevation of the FPSO vessel shown in Fig. 2.

Fig. 4 is an enlarged and more detailed version of the top plan view of the FPSO vessel shown in Fig. 1

Fig. 5 is a side elevation of an alternative embodiment of the hull for an FPSO vessel, according to the present invention.

Fig. 6 is a side elevation of an alternative embodiment of the hull for an FPSO vessel, according to the present invention.

Fig. 7 is a side elevation of an alternative embodiment of an FPSO vessel, according to the present invention, showing a center column received in a bore through the hull of the FPSO vessel.

Fig. 8 is a cross section of the center column of Fig. 7, as seen along the line 8-8.

Fig. 9 is a side elevation of the FPSO vessel of Fig. 7 showing an alternative embodiment of the center column, according to the present invention.

Fig. 10 is a cross section of the center column of Fig. 9, as seen along the line 11-11. Fig. 11 is an alternative embodiment of a center column and a mass trap as would be seen along the line 11-11 in Fig. 9, according to the present invention.

Fig. 12 is a top plan view of a moveable hawser connection, according to the present invention.

Fig. 13 is a side elevation of the moveable hawser connection of Fig. 12 in partial cross-section as seen along the line 13-13.

Fig. 14 is a side elevation of the moveable hawser connection of Fig. 13 in partial cross-section as seen along the line 14-14.

Fig. 15 is a side elevation of a vessel, according to the present invention.

Fig. 16 is a cross section of the vessel of Fig. 15 as seen along the line 16-16 shown in cross-section.

Fig. 17 is a cross section of the vessel of Fig 15 as seen along the line 17 - 17 as shown in cross section.

Fig. 18 is a cross section of the vessel of Fig 15 as seen along the line 18-18 as shown in cross section.

The present embodiments are detailed below with reference to the listed Figures.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Before explaining the present apparatus in detail, it is to be understood that the apparatus is not limited to the particular embodiments and that it can be practiced or carried out in various ways.

The present invention provides a floating platform, storage and offloading (FPSO) vessel with several alternative hull designs, several alternative center column designs and a moveable hawser system for offloading, which allows a tanker to weathervane over a wide arc with respect to the FPSO vessel.

The invention more specifically relates to a method for offshore floating petroleum production, storage and offloading.

The first step of the method involves receiving hydrocarbons from at least one of: an FPSO, production risers, or wellhead on the seabed by a floating hull.

The next step involves processing received hydrocarbons forming hydrocarbon product in the floating hull.

Then, the method continues by storing the hydrocarbon product, in the floating hull, wherein the floating hull uniquely has: a hull plan view that is circular and wherein the floating hull comprises: a bottom surface; a top deck surface; at least three connected sections, joined in series and symmetrically configured about a vertical axis with the connected sections extending downwardly from the top deck surface toward the bottom surface; the at least three connected sections comprising of: upper cylindrical portion; a lower conical section, a cylindrical neck section; and a set of fins secured to the hull configured to provide hydrodynamic performance through linear and quadratic damping.; and offloading the stored hydrocarbon product.

Turning now to the Figures, the unique hull can be viewed.

An FPSO vessel 10 is shown in a plan view in Fig. 1 and in a side elevation in Fig. 2, according to the present invention.

FPSO vessel 10 has a hull 12, and a center column 14 can be attached to hull 12 and extend downwardly.

FPSO vessel 10 floats in water W and can be used in the production, storage and/or offloading of resources extracted from the earth, such as hydrocarbons including crude oil and natural gas and minerals such as can be extracted by solution mining.

FPSO vessel 10 can be assembled onshore using known methods, which are similar to shipbuilding, and towed to an offshore location, typically above an oil and/or gas field in the earth below the offshore location.

Anchor lines l6a, l6b, l6c and l6d, which would be fastened to anchors in the seabed that are not shown, moor FPSO vessel 10 in a desired location. The anchor lines are referred to generally as anchor lines 16, and elements described herein that are similarly related to one another will share a common numerical identification and be distinguished from one another by a suffix letter.

In a typical application for FPSO vessel 10, crude oil is produced from the earth below the seabed below vessel 10, transferred into and stored temporarily in hull 12, and offloaded to a tanker T for transport to onshore facilities. Tanker T is moored temporarily to FPSO vessel 10 during the offloading operation by a hawser 18. A hose 20 is extended between hull 12 and tanker T for transfer of crude oil and/or another fluid from FPSO vessel 10 to tanker T.

Fig. 3 is a side elevation of FPSO vessel 10, Fig. 4 is a top plan view of FPSO vessel 10, and each view is larger and shows more detail than the corresponding Figs. 2 and 1, respectively. Hull 12 of FPSO vessel 10 has a circular top deck surface l2a, an upper cylindrical portion l2b extending downwardly from deck surface l2a, an upper conical section l2c extending downwardly from upper cylindrical portion l2b and tapering inwardly, a cylindrical neck section l2d extending downwardly from upper conical section l2c, a lower conical section l2e extending downwardly from neck section l2d and flaring outwardly, and a lower cylindrical section l2f extending downwardly from lower conical section l2e. Lower conical section l2e is described herein as having the shape of an inverted cone or as having an inverted conical shape as opposed to upper conical section l2c, which is described herein as having a regular conical shape. FPSO vessel 10 preferably floats such that the surface of the water intersects regular, upper conical section l2c, which is referred to herein as the waterline being on the regular cone shape.

FPSO vessel 10 is preferably loaded and/or ballasted to maintain the waterline on a bottom portion of regular, upper conical section l2c. When FPSO vessel 10 is installed and floating properly, a cross-section of hull 12 through any horizontal plane has preferably a circular shape.

Hull 12 can be designed and sized to meet the requirements of a particular application, and services can be requested from Maritime Research Institute (Marin) of The Netherlands to provide optimized design parameters to satisfy the design requirements for a particular application.

In this embodiment, upper cylindrical section l2b has approximately the same height as neck section l2d, while the height of lower cylindrical section l2f is about 3 or 4 times greater than the height of upper cylindrical section l2b. Lower cylindrical section l2f has a greater diameter than upper cylindrical section l2b. Upper conical section l2c has a greater height than lower conical section l2e.

Figs. 5 and 6 are side elevations showing alternative designs for the hull.

Fig. 5 shows a hull l2h that has a circular top deck surface l2i, which would be essentially identical to top deck surface l2a, on a top portion of an upper conical section l2j that tapers inwardly as it extends downwardly.

A cylindrical neck section l2k is attached to a lower end of upper conical section l2j and extends downwardly from upper conical section l2j. A lower conical section l2m is attached to a lower end of neck section l2k and extends downwardly from neck section l2k while flaring outwardly. A lower cylindrical section 12h is attached to a lower end of lower conical section l2m and extends downwardly from lower conical section l2m. A significant difference between hull l2h and hull 12 is that hull l2h does not have an upper cylindrical portion corresponding to upper cylindrical portion l2b in hull 12. Otherwise, upper conical section l2j corresponds to upper conical section l2c; neck section l2k corresponds to neck section l2d; lower conical sectionl2m corresponds to lower conical section l2e; and lower cylindrical section 12h corresponds to lower cylindrical section l2f.

Each of lower cylindrical section 12h and lower cylindrical section l2f has a circular bottom deck that is not shown, but which is similar to circular top deck surface l2a, except center section 14 extends downwardly from the circular bottom deck.

Fig. 6 is a side elevation of a hull 12r, which has a top deck l2q that looks like top deck surface l2a. An upper cylindrical section l2r extends downwardly from top deck l2q and corresponds to upper cylindrical section l2b.

An upper conical section l2s is attached to a lower end of upper cylindrical section l2r and extends downwardly while tapering inwardly. Upper conical section l2s corresponds to upper conical section l2c in Fig.l.Hull 12r in Fig. 6 does not have a cylindrical neck section that corresponds to cylindrical neck section l2d in Fig. 3.

Instead, an upper end of a lower conical section l2t is connected to a lower end of upper conical section l2s, and lower conical section l2t extends downwardly while flaring outwardly. Lower conical section l2t in Fig. 6 corresponds to lower conical section l2e in Fig. 3.

A lower cylindrical section l2u is attached at an upper end, such as by welding, to a lower end of lower conical section l2t and extends downwardly, essentially corresponding in size and configuration to lower cylindrical section l2f in Fig. 3. A bottom plate 12n (not shown) encloses a lower end of lower cylindrical section l2u, and the lower end of hull 12 in Fig. 3 and hull l2h in Fig. 5 are similarly enclosed by a bottom plate, and each of the bottom plates can be adapted to accommodate a respective center column corresponding to center column 14 in Fig. 3.

Turning now to Figs. 7-11, alternative embodiments for a center column are illustrated. Fig. 7 is a side elevation of an FPSO vessel 10 partially cut away to show a center column 22, according to the present invention. FPSO vessel 10 has a top deck surface 20a that has an opening 20b through which center column 22 can pass. In this embodiment, center column 22 can be retracted, and an upper end 22a of center column 22 can be raised above top deck surface 20a. If center column 22 is fully retracted, FPSO vessel 10 can be moved through shallower water than if center column 22 is fully extended. U.S. Patent No. 6,761,508, issued to Haun, provides further details relevant to this and other aspects of the present invention and is incorporated by reference in its entirety.

Fig. 7 shows center column 22 partially retracted, and center column 22 can be extended to a depth where upper end 22a is located within a lowermost cylindrical portion 20c of FPSO vessel 10. Fig. 8 is a cross- section of center column 22 as seen along the line 8-8 in Fig 7, and Fig. 8 shows a plan view of a mass trap 24 located on a bottom end 22b of center column 22. Mass trap 24, which is shown in this embodiment as having a hexagonal shape in its plan view, is weighted with water for stabilizing FPSO 10 as it floats in water and is subject to wind, wave, current and other forces. Center column 22 is shown in Fig. 8 as having a hexagonal cross-section, but this is a design choice.

Fig. 9 is a side elevation of the FPSO vessel 10 of Fig. 7 partially cut away to show a center column 26, according to the present invention. Center column 26 is shorter than center column 22 in Fig. 7. An upper end 26a of center column 26 can be moved up or down within opening 20b in FPSO vessel 10, and with center column 26, FPSO vessel 10 can be operated with only a couple or a few meters of center column 26 protruding below the bottom of FPSO vessel 20.

A mass trap 28, which may be filled with water to stabilize FPSO vessel 10, is secured to a lower end 26b of center column 26.

Fig. 10 is a cross-section of center column 26 as seen along the line 10-10 in Fig. 9.

In this embodiment of a center column, center column 26 has a square cross- section, and mass trap 28 has an octagonal shape in the plan view of Fig. 10.

In an alternative embodiment of the center column in Fig. 9 as seen along the line 10-10, a center column CC and a mass trap MT are shown in Fig. 11 in a top plan view. In this embodiment, center column CC has a triangular shape in a transverse cross-section, and mass trap MT has a circular shape in a top plan view.

Returning to Fig. 3, FPSO vessel hull 12 has a cavity or recess 12c shown in phantom lines, which is a centralized opening into a bottom portion of lower cylindrical section l2f of FPSO vessel hull 12. An upper end l4a of central column 14 protrudes into essentially the full depth of recess 12c.

In the embodiment illustrated in Fig. 3, center column 14 is effectively cantilevered from the bottom of lower cylindrical section l2f, much like a post anchored in a hole, but with the center column 14 extending downwardly into the water upon which FPSO vessel hull 12 floats. A mass trap 17 for containing water weight to stabilize hull 12 is attached to a lower end l4b of center column 14.

Various embodiments of a center column have been described; however, the center column is optional and can be eliminated entirely or replaced with a different structure that protrudes from the bottom of the FPSO vessel and helps to stabilize the vessel. One application for FPSO vessel 10 illustrated in Fig. 3 is in production and storage of hydrocarbons such as crude oil and natural gas and associated fluids and minerals and other resources that can be extracted or harvested from the earth and/or water. As shown in Fig. 3, production risers PI, P2 and P3 are pipes or tubes through which, for example, crude oil may flow from deep within the earth to FPSO vessel 10, which has significant storage capacity within tanks within hull 12.

In Fig. 3, production risers Pl, P2 and P3 are illustrated as being located on an outside surface of hull 12, and production would flow into hull 12 through openings in top deck surface l2a. An alternative arrangement is available in FPSO vessel 10 shown in Figs. 7 and 9, where it is possible to locate production risers within opening 20b that provides an open throughway from the bottom of FPSO vessel 10 to the top of FPSO vessel 10. Production risers are not shown in Figs. 7 and 9, but can be located on an outside surface of the hull or within opening 20b. An upper end of a production riser can terminate at a desired location with respect to the hull so that production flows directly into a desired storage tank within the hull.

FPSO vessel 10 of Figs. 7 and 9 can also be used to drill into the earth to discover or to extract resources, particularly hydrocarbons such as crude oil and natural gas, making the vessel a floating drilling, production, storage and offloading (FDPSO) vessel.

For this application, mass tank MT, 24 or 28 would have a central opening from a top surface to a bottom surface through which drill string can pass, which is a structural design that can also be used for accommodating production risers within opening 20b in FDPSO vessel 10. A derrick (not shown) would be provided on a top deck surface 20d of FPSO vessel 10 for handling, lowering, rotating and raising drill pipe and an assembled drill string, which would extend downwardly from the derrick through opening 20b in FPSO vessel 10, through an interior portion of center column 22 or 26, through a central opening (not shown) in mass tank 24 or 28, through the water and into the seabed below.

After drilling is successfully completed, production risers can be installed, and the resource, such as crude oil and/or natural gas, can be received and stored in tankage located within the FPSO vessel. U.S. Patent Application Publication No. 2009/0126616, which lists Srinivasan as a sole inventor, describes an arrangement of tankage in the hull of an FPSO vessel for oil and water ballast storage and is incorporated by reference. In one embodiment of the present invention, a heavy ballast, such as a slurry of hematite and water, can be used, preferably in outer ballast tanks. A slurry is preferred, preferably one part hematite and three parts water, but a permanent ballast, such as a concrete could be used. A concrete with a heavy aggregate, such as hematite, barite, limonite, magnetite, steel punching and shot, can be used, but preferably a high-density material is used in a slurry form. Drilling, production and storage aspects of the floating drilling, production, storage and offloading vessel of the present invention have thus been described, which leaves the offloading function of an FDPSO vessel.

Turning to the offloading function of the FDPSO vessel of the present invention, Figs. 1 and 2 illustrate transport tanker T moored to FPSO vessel 10 by hawser 18, which is a rope or a cable, and hose 20 has been extended from FPSO vessel 10 to tanker T. FPSO vessel 10 is anchored to the seabed through anchor lines l6a, l6b, l6c and l6d, while tanker T's location and orientation is effected by wind direction and force, wave action and force and direction of current.

Consequently, tanker T weathervanes with respect to FPSO vessel 10 because its bow is moored to FPSO vessel 10 while its stem moves into an alignment determined by a balance of forces. As forces due to wind, wave and current change, tanker T may move to the position indicated by phantom line A or to the position indicated by phantom line B. Tugboats or a temporary anchoring system, neither of which is shown, can be used to keep tanker T a minimum, safe distance form FPSO vessel 10 in case of a change in net forces that causes tanker T to move toward FPSO vessel 10 rather than away from FPSO vessel 10 so that hawser 18 remains taut.

If wind, wave, current (and any other) forces remained calm and constant, tanker T would weathervane into a position in which all forces acting on the tanker were in balance, and tanker T would remain in that position. However, that is generally not the case in a natural environment. Particularly, wind direction and speed or force changes from time to time, and any change in the forces acting on tanker T cause tanker T to move into a different position in which the various forces are again in balance. Consequently, tanker T moves with respect to FPSO vessel 10 as various forces acting upon tanker T change, such as the forces due to wind wave and current action.

Figs. 12-14, in conjunction with Figs. 1 and 2, illustrate a moveable hawser connection 40 on the FPSO vessel, according to the present invention, which helps to accommodate movement of the transport tanker with respect to the FPSO vessel.

Fig. 12 is a plan view of moveable hawser connection 40 in partial cross- section. Moveable hawser connection 40 comprises in one embodiment a nearly fully enclosed tubular channel 42 that has a rectangular cross-section and a longitudinal slot 42a on a side wall 42b; a set of stand- offs 44, including stand-offs 44a and 44b, that connect tubular channel 42 horizontally to an outside, upper wall l2w of hull 12 in Figs. 1-4; a trolley 46 captured and moveable within tubular channel 42; a trolley shackle 48 attached to trolley 46 and providing a connection point; and a plate 50 pivotably attached to trolley shackle 48 through a plate shackle 52.

Plate 50 has a generally triangular shape with the apex of the triangle attached to plate shackle 52 through a pin 54 passing through a hole in plate shackle 50. Plate 50 has a hole 50a adjacent another point of the triangle and a plate hole 50b adjacent the final point of the triangle. Hawser 18 terminates with dual connection points l8a and l8b, which are connected to plate 50 by passing through holes 50a and 50b, respectively. Alternatively, dual ends l8a and l8b, plate 50 and/or shackle 52 can be eliminated, and hawser 18 can be connected directly to shackle 48, and other variations in how the hawser 18 is connected to trolley 46 are available.

Fig. 13 is a side elevation of moveable hawser connection 40 in partial cross- section as seen along the line 13-13 in Fig. 12. A side elevation of tubular channel 42 is shown in cross-section. Wall 42b, which has slot 42a, is a relatively tall, vertical outer wall, and an outside surface of an opposing inner wall 42c is equal in height.

Stand-offs 44 are attached, such as by welding, to the outside surface of inner wall 42c. A pair of opposing, relatively short, horizontal walls 42d and 42e extend between vertical walls 42b and 42c to complete the enclosure of tubular channel 42, except vertical wall 42b has the horizontal, longitudinal slot 42a that extends nearly the full length of tubular channel 42.

Fig. 14 is a side elevation with tubular channel 42 in partial cross-section in order to show a side elevation of trolley 46. Trolley 46 includes a base plate 46a, which has four rectangular openings 46b, 46c, 46d and 46e, for receiving four wheels 46f, 46g, 46h and 46i, respectively, which are mounted on four axles 46j, 46k, 46m and 46n, respectively, that are attached through stand-offs to base plate 46a.

Tanker T is moored to FPSO vessel 10 in Figs. 1-4 through hawser 18, which is attached to moveable trolley 46 through plate 50 and shackles 48 and 52. As wind, wave, current and/or other forces act on tanker T, tanker T can move in an arc about FPSO vessel 1 O at a radius determined by the length of hawser 18 because trolley 46 is free to roll back and forth in a horizontal plane within tubular channel 42. As best seen in Fig. 4, tubular channel 42 extends in about a 90-degree arc about hull 12 of FPSO vessel 10. Tubular channel 42 has opposing ends 42f and 42g, each of which is enclosed for providing a stop for trolley 46. Tubular channel 42 has a radius of curvature that matches the radius of curvature of outside wall l2w of hull 12 because standoffs 44a, 44b, 44c and 44d are equal in length. Trolley 46 is free to roll back and forth within enclosed tubular channel 42 between ends 42f and 42g of tubular channel 42. Standoffs 44a, 44b, 44c and 44d space tubular channel away from outside wall l2w of hull 12, and hose 20 and anchor line l6c pass through a space defined between outer wall l2w and inside wall 42c of tubular channel 42.

Typically, wind, wave and current forces will position tanker T in a position, with respect to FPSO vessel 10, referred to herein as downwind of the FPSO vessel 10. Hawser 18 is taut and in tension as wind, wave and current action applies a force on tanker T that attempts to move tanker T away from and downwind of stationary FPSO vessel 10. Trolley 46 comes to rest within tubular channel 42 due to a balance of forces that neutralizes a tendency for trolley 46 to move.

Upon a change in wind direction, tanker T can move with respect to FPSO vessel 10, and as tanker T moves, trolley 46 will roll within tubular channel 42 with the wheels 46f, 46g, 46h and 46i pressed against an inside surface of wall 42b of tubular channel 42. As the wind continues in its new, fixed direction, trolley 46 will settle within tubular channel 42 where forces causing trolley 46 to roll are neutralized.

One or more tugboats can be used to limit the motion of tanker T to prevent tanker T from moving too close to FPSO vessel 10 or from wrapping around FPSO vessel 10, such as due to a substantial change in wind direction.

For flexibility in accommodating wind direction, FPSO vessel 10 preferably has a second moveable hawser connection 60 positioned opposite of moveable hawser connection 40. Tanker T can be moored to either moveable hawser connection 40 or to moveable hawser connection 60, depending on which better accommodates tanker T downwind of FPSO vessel 10.

Moveable hawser connection 60 is essentially identical in design and construction to moveable hawser 40 with its own slotted tubular channel and trapped, free -rolling trolley car having a shackle protruding through the slot in the tubular channel. Each moveable hawser connection 40 and 60 is believed to be capable of accommodating movement of tanker T within about a 270-degree arc, so a great deal of flexibility is provided both during a single offloading operation (by movement of the trolley within one of the moveable hawser connections) and from one offloading operation to another (by being able to choose between opposing moveable hawser connections).

Wind, wave and current action can apply a great deal of force on tanker T, particularly during a storm or squall, which in turn applies a great deal of force on trolley 46, which in turn applies a great deal of force on slotted wall 42b (Fig. 13) of tubular channel 42. Slot 42a weakens wall 42b, and if enough force is applied, wall 42b can bend, possibly opening slot 42a wide enough for trolley 46 to be ripped out of tubular channel 42. Tubular channel 42 will need to be designed and built to withstand anticipated forces. Inside comers within tubular channel 42 may be built up for reinforcement, and it may be possible to use wheels that have a spherical shape. The tubular channel is just one means for providing a moveable hawser connection. An I-beam, which has opposing flanges attached to a central web, could be used as a rail instead of the tubular channel, with a trolley car or other rolling or sliding device trapped to, and moveable on, the outside flange. The moveable hawser connection is similar to a gantry crane, except a gantry crane is adapted to accommodate vertical forces, while the moveable hawser connection needs to be adapted to accommodate a horizontal force exerted through the hawser 18. Any type of rail, channel or track can be used in the moveable hawser connection, provided a trolley or any kind of rolling, moveable or sliding device can move longitudinally on, but is otherwise trapped on, the rail, channel or track. The following patents are incorporated by reference for all that they teach and particularly for what they teach about how to design and build a moveable connection. U.S. Patent Nos. 5,595,121, entitled "Amusement Ride and Self-propelled Vehicle Therefor" and issued to Elliott et al.; 6,857,373, entitled "Variably Curved Track-Mounted Amusement Ride" and issued to Checketts et ak; 3,941,060, entitled "Monorail System" and issued to Morsbach; 4,984,523, entitled "Self- propelled Trolley and Supporting Track Structure" and issued to Dehne et a ; and 7,004,076, entitled "Material Handling System Enclosed Track Arrangement" and issued to Traubenkraut et ak, are all incorporated by reference in their entirety for all purposes. As described herein and in the patents incorporated by reference, a variety of means can be used to resist a horizontal force, such as applied on FPSO vessel 10 through hawser 18 from tanker T, while providing lateral movement, such as by trolley 46 rolling back and forth horizontally while trapped within tubular channel 42.

Wind, waves and current apply a number of forces on the FDPSO or FPSO vessel of the present invention, which causes a vertical up and down motion or heave, in addition to other motions. A production riser is a pipe or tube that extends from a wellhead on the seabed to the FDPSO or the FPSO, which is referred to herein generally as an FPSO. The production riser can be fixed at the seabed and fixed to the FPSO. Heave on the FPSO vessel can place alternating tension and compression forces on the production riser, which can cause fatigue and failure in the production riser. One aspect of the present invention is to minimize the heave of the FPSO vessel.

Fig. 15 is a side elevation of an FDPSO or FPSO vessel 80, according to the present invention. Vessel 80 has a hull 82 and a circular top deck surface 82a, and a cross-section of hull 82 through any horizontal plane, while hull 82 is floating and a rest, has preferably a circular shape. An upper cylindrical section 82b extends downwardly from the circular top deck surface 82a, and an upper conical section 82c extends downwardly from upper cylindrical portion 82b and tapers inwardly. Vessel 80 could have a cylindrical neck section 82d extending downwardly from upper conical section 82c, which would make it more similar to vessel 10 in Fig. 3, but it does not. Instead, a lower conical section 82e extends downwardly from upper conical section 82c and flares outwardly. A lower cylindrical section 82f extends downwardly from lower conical section 82e. Hull 82 has a bottom surface 82g. Lower conical section 82e is described herein as having the shape of an inverted cone or as having an inverted conical shape as opposed to upper conical section 82c, which is described herein as having a regular conical shape.

FPSO vessel 80 is shown as floating such that the surface of the water intersects the upper cylindrical portion 82b when loaded and/or ballasted. In this embodiment, upper conical section 82c has a substantially greater vertical height than lower conical section 82e, and upper cylindrical section 82b has a slightly greater vertical height than lower cylindrical section 82f.

For reducing heave and otherwise steadying vessel 80, a set of fins 84 is attached to a lower and outer portion of lower cylindrical section 82f, as shown in Fig. 15. Fig. 16 is a cross-section of vessel 80 as would be seen along the line 16-16 in Fig. 15. As can be seen in Fig. 16, fins 84 comprise four fin sections 84a, 84b, 84c and 84d, which are separated from each other by gaps 86a, 86b, 86c and 86d (collectively referred to as gaps 86). Gaps 86 are spaces between fin sections 84a, 84b, 84c and 84d, which provide a place that accommodates production risers and anchor lines on the exterior of hull 82, without contact with fins 84. Anchor lines 88a, 88b, 88c and 88d in Figs. 15 and 16 are received in gaps 86c, 86a, 86b and 86d, respectively, and secure FDPSO and/or FPSO vessel 80 to the seabed. Production risers 90a, 90b, 90c, 90d, 90e, 90f, 90g, 90e, 90g, 90h, 90i, 90j, 90k and 90m are received in the gaps 86 and deliver a resource, such as crude oil, natural gas and/or a leached mineral, from the earth below the seabed to tankage within vessel 80. A center section 92 extends from bottom 82g of hull 82. Fig. 17 is the elevation of Fig. 15 in a vertical cross-section showing a simplified view of the tankage within hull 82 in cross-section. The produced resource flowing through production risers 90 is stored in an inner, annular tank 82h. A central vertical tank 82i can be used as a separator vessel, such as for separating oil, water and/or gas, and/or for storage. An outer, annular tank 82j having an outside wall conforming to the shape of upper conical section 82c and lower conical section 82e can be used to hold ballast water and/or to store the produced resource. In this embodiment, an outer, ring- shaped tank 82k is a void that has a cross-section of an irregular trapezoid defined on its top by lower conical section 82e and lower cylindrical section 82f with a vertical inner side wall and a horizontal lower bottom wall, although tank 82k could be used for ballast and/or storage. A torus-shaped tank 82m, which is shaped like a washer or doughnut having a square or rectangular cross-section, is located in a lowermost and outermost portion of hull 82. Tank 82m can be used for storage of a produced resource and/or ballast water. In one embodiment, tank 82m holds a slurry of hematite and water, and in a further embodiment, tank 82m contains about one part hematite and about three parts water.

Fins 84 for reducing heave are shown in cross-section in Fig. 17. Each section of fins 84 has the shape of a right triangle in a vertical cross-section, where the 90° angle is located adjacent a lowermost outer side wall of lower cylindrical section 82f of hull 82, such that a bottom edge 84e of the triangle shape is co-planar with the bottom surface 82g of hull 82, and a hypotenuse 84f of the triangle shape extends from a distal end 84g of the bottom edge 84e of the triangle shape upwards and inwards to attach to the outer side wall of lower cylindrical section 82f at a point only slightly higher than the lowermost edge of the outer side wall of lower cylindrical section 82 [, as can be seen in Fig. 17. Some experimentation may be required to size fins 84 for optimum effectiveness. A starting point is bottom edge 84e extends radially outwardly a distance that is about half the vertical height of lower cylindrical section 82f, and hypotenuse 84f attaches to lower cylindrical section 82f about one quarter up the vertical height of lower cylindrical section 82f from the bottom 82g of hull 82. Another starting point is that if the radius of lower cylindrical section 82f is R, then bottom edge 84e of fin 84 extends radially outwardly an additional 0.05 to 0.20 R, preferably about 0.10 to 0.15 R, and more preferably about 0.125 R.

Fig. 18 is a cross-section of hull 82 of FDPSO and/or FPSO vessel 80 as seen along the line 18-18 in Fig. 17. Radial support members 94a, 94b, 94c and 94d provide structural support for inner, annular tank 82h, which is shown as having four compartments separated by the radial support members 94. Radial support members 96a, 96b, 96c, 96d, 96e, 96f, 96g, 96h, 96i, 96j, 96k and 96m provide structural support for outer, annular tank 82j and tanks 82k and 82m. Outer, annular tank 82j and tanks 82k and 82m are compartmentalized by the radial support members 96.

An FPSO vessel according to the present invention, such as FPSO vessels 10, 20 and 80, can be made onshore, preferably at a shipyard using conventional ship- building materials and techniques. The FPSO vessel preferably has a circular shape in a plan view, but construction cost may favor a polygonal shape so that flat, planar metal plates can be used rather than bending plates into a desired curvature. An FPSO vessel hull having a polygonal shape with facets in a plan view, such as described in U.S. Patent No. 6,761,508, issued to Haun and incorporated by reference, is included in the present invention. If a polygonal shape is chosen and if a moveable hawser connection is desired, then a tubular channel or rail can be designed with an appropriate radius of curvature and mounted with appropriate standoffs so as to provide the moveable hawser connection. If an FPSO vessel is built according to the description of FPSO vessel 10 in Figs. 1-4, then it may be preferred to move the FPSO vessel, without a center column, to its final destination, anchor the FPSO vessel at its desired location, and install the center column offshore after the FPSO vessel has been moved and anchored in position. For the embodiment illustrated in Figs. 7 and 9, it would likely be preferred to install the center column while the FPSO vessel is onshore, retract the center column to an uppermost position, and tow the FPSO vessel to its final destination with the center column installed by fully retracted. After the FPSO vessel is positioned at its desired location, the center column can be extended to a desired depth, and the mass trap on the bottom of the center column can be filled to help stabilize the hull against wind, wave and current action.

After the FPSO vessel is anchored and its installation is otherwise complete, it can be used for drilling exploratory or production wells, provided a derrick is installed, and it can be used for production and storage of resources or products. To offload a fluid cargo that has been stored on the FPSO vessel, a transport tanker is brought near the FPSO vessel.

With reference to Figs. 1-4, a messenger line can be stored on reels 70a and/or 70b. An end of the messenger line can be shot with a pyrotechnic gun from FPSO vessel 10 to tanker T and grabbed by personnel on tanker T. The other end of the messenger line can be attached to a tanker end l8c (Fig. 2) of hawser 18, and the personnel on the tanker can pull hawser end l8c of hawser 18 to the tanker T, where it can be attached to an appropriate structure on tanker T. The personnel on tanker T can then shoot one end of the messenger line to personnel on the FPSO vessel, who hook that end of the messenger line to a tanker end 20a (Fig. 2) of hose 20. Personnel on the tanker can then pull tanker end 20a of hose 20 to the tanker and fasten it to an appropriate connection on the tanker for fluid communication between the FPSO vessel and the tanker. Typically, cargo will be offloaded from storage on the FPSO vessel to the tanker, but the opposite can also be done, where cargo from the tanker is offloaded to the FPSO vessel for storage.

Although the hose may be large, such as 20 inches in diameter, the hose hook-up and the offloading operation can take a long time, typically many hours but less than a day. During this time, the tanker T will typically weathervane downwind of the FPSO vessel and move about some as wind direction changes, which is accommodated on the FPSO vessel through the moveable hawser connection, allowing considerable movement of the tanker with respect to the FPSO, possibly through a 270-degree arc, without interrupting the offloading operation. In the event of a major storm or squall, the offloading operation can be stopped, and if desired, the tanker can be disconnected from the FPSO vessel by releasing hawser 18. After completion of a typical and uneventful offloading operation, the hose end 20a can be disconnected from the tanker, and a hose reel 20b can be used to reel hose 20 back into stowage on hose reel 20b on the FPSO vessel. A second hose and hose reel 72 is provided on the FPSO vessel for use in conjunction with the second moveable hawser connection 60 on the opposite side of FPSO vessel 10. Tanker end l8c of hawser 18 can then be disconnected, allowing tanker T to move away and transport the cargo it received to port facilities onshore. The messenger line can be used to pull tanker end l8c of hawser 18 back to the FPSO vessel, and the hawser can either float on the water adjacent the FPSO vessel, or the tanker end l8c of hawser 18 can be attached to a reel (not shown) on the deck l2a of FPSO vessel 10, and the hawser 18 can be reeled onto the reel for stowage on the FPSO, while dual ends l8a and l8b (Fig. 12) of hawser 18 remain connected to moveable hawser connection 40.

The invention relates to a method for offshore floating petroleum production, storage and offloading that first involves receiving hydrocarbons from at least one of: an FPSO, production risers, or wellhead on the seabed by a uniquely shaped floating hull.

The next step involves processing the received hydrocarbons forming hydrocarbon product in the floating hull.

The method continues by storing the hydrocarbon product, in the uniquely shaped floating hull, with the floating hull having a hull plan view that is circular and wherein the floating hull has a bottom surface; a top deck surface; at least three connected sections, joined in series and symmetrically configured about a vertical axis with the connected sections extending downwardly from the top deck surface toward the bottom surface; the at least three connected sections comprising of: upper cylindrical portion; a lower conical section, a cylindrical neck section; and a set of fins secured to the hull configured to provide hydrodynamic performance through linear and quadratic damping.

Both the linear damping and quadratic damping are empirical approaches for quantifying the hydrodynamic behaviour of a floating body in an incompressible homogenous Newtonian fluid. In the context of various embodiments, the fin and the hull of the floating driller are each designed and configured in a manner to provide hydrodynamic performance through linear and quadratic damping, which involve numerical assessments and experiments by applying numerical methods (linear or non-linear methods) for determining an accurate estimate of viscous damping.

Compared to conventional circular floaters, which do not include a fin feature, the hull as described herein including the set of fins may contribute towards better performance hydrodynamically (related to damping) of the FPSO. The shapes and/or sizes of fins may also positively affect, thereby contributing towards better performance hydrodynamically (related to damping). However, different shapes and/or sizes of fins may respond differently in a water embodiment where current may have an effect on the flow and pressure which may be vastly different depending on the shape and/or size of the fin.

The method continues by offloading the stored hydrocarbon product to at least one of: a tanker, or a pipeline.

In embodiments, the method contemplates that the floating hull is moored to a seafloor.

In embodiments of the method the floating hull has an upper frustoconical side section engaging the cylindrical neck section, and the upper cylindrical side section extending downwardly from the main deck and the upper frustoconical side section located below the upper cylindrical side section and maintained to be above a water line for a transport depth and partially below a water line for an operational depth of the petroleum drilling, production, storage and offloading vessel; and wherein the upper frustoconical side section has a gradually reducing diameter from a diameter of the upper cylindrical side section.

In embodiments the method includes the step of installing a side extending at the hull bottom surface.

In embodiments the method includes using a plurality of fin sections, which are separated from each other by gaps which provide a place that accommodates production risers and anchor lines on the exterior of hull, without contact with fins.

In embodiments the method includes using a fin of the set of fins for reducing heave has the shape of a right triangle in a vertical cross-section.

In embodiments the method includes using a fin with a bottom edge wherein the triangle shape is co-planar with the bottom surface of hull.

In embodiments the method includes a fin wherein a hypotenuse of the triangle shape of the fin extends from a distal end of the bottom edge of the triangle shape upwards and inwards to attach to the outer side wall of lower cylindrical section at a point only slightly higher than the lowermost edge of the outer side wall of the hull.

In embodiments the method includes using a uniquely shaped a hull with a center column, center column with a square cross-section, and a mass trap with an octagonal shape.

In embodiments the method includes using at least three connected sections that can be joined in series and symmetrically configured about a vertical axis with the connected sections extending downwardly from the top deck surface toward the bottom surface.

Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis of the claims and as a representative basis for teaching persons having ordinary skill in the art to variously employ the present invention.

While these embodiments have been described with emphasis on the embodiments, it should be understood that within the scope of the appended claims, the embodiments might be practiced other than as specifically described herein.