Patent Application
20190144083
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 connection of a plurality of submarine risers, such as a Floating Production, Storage and Offloading vessel (FPSO).
A Floating Production, Storage and Offloading (FPSO) system is a floating facility above or close to an offshore oil and/or gas field to receive, process, store and export hydrocarbons.
The system consists of a floater, which may either be a purpose built vessel or a converted tanker that is moored at a selected site. The cargo capacity of the vessel is used as buffer storage for the oil produced. The process facilities (topsides) and accommodations are installed on the floater. The mooring configuration may be of a spread mooring type or a single point mooring system, generally a turret.
The high pressure mixture of produced fluids from the well is delivered to the process facilities on the deck of the vessel, where the oil, gas and water are separated. The water is reinjected in the reservoir or discharged overboard after treatment eliminating hydrocarbons. The stabilized crude oil is stored in the cargo tanks of the vessel and subsequently transferred into shuttle vessels, either direct, via a buoy, or by laying side by side/in tandem to the FPSO vessel.
The gas may be used for enhancing the liquid production through gas lift and/or for energy production onboard the vessel. The remainder of the gas may be compressed and transported by pipeline or reinjected into the reservoir.
There are three main types of mooring systems for FPSO vessels:
WO 2015/038003 A1 discloses a platform arranged to float in water. The platform comprises a hull with a main portion which is substantially symmetrical about a center axis. The upper end of the platform is supporting a deck and the lower end of the platform, situated below a nominal water line, is provided with a stabilizing element which protrudes from the main portion.
WO 2012/104308 A1 discloses a platform for production and storage of hydrocarbons. The substantially circular hull of the vessel is configured to allow suspension of risers on at least one frame arranged in a moonpool in the center of the hull. The frame is placed so that connection of risers may be performed above the water when the platform has its minimum draft. The moonpool may comprise a conical form at its lower end allowing static and dynamic angular deflections of the risers. The moonpool extends above the main deck wherein the extended vertical moonpool is narrowed down for increasing the space availability on the deck. The hull may further be equipped with a protrusion to reduce stamping and rolling movements.
WO 98/30439 A1 discloses a drilling and production vessel comprising one or more wells extending through the hull for inward and outward flow of water from below. The vessel comprises a number of lips as water flow delaying elements.
The above mentioned prior art does not provide an optimized longitudinal vessel comprising a protective moonpool/well. Further, prior art does not provide an optimized area configuration for the risers, access to the risers, suspension for the risers, or connection or disconnection of the risers.
Consequently, the object of the present invention is to provide a longitudinal vessel for production and/or storing of hydrocarbons arranged to float in a body of water, where the vessel provides an optimal protective well, as well as an optimized solution for a multiple riser arrangement.
A second object of the present invention is to provide a vessel with optimized solutions for a vessel's motion characteristics, for example a longitudinal vessel having reduced motions in heave, roll and pitch. Such motion reduction will reduce mooring system requirements and/or renders possible use of free-hanging rigid risers at deep depths instead of traditional flexible risers. Deep depths may be depths exceeding 1000 meters, for example deeper than 2000 meters
A third object of the present invention is to provide a longitudinal vessel providing optimized usage of a vessel's deck area, for example for installation of equipment/tools used during production of oil and gas.
A fourth object of the present invention is to provide a longitudinal vessel with a large storage capacity for produced oil and/or gas compared to the vessels total size, in view of the prior art.
A fifth object of the present invention is to provide a longitudinal vessel that provides an increased safety in view of the prior art in case of incidences such as gas leakage.
A sixth object of the present invention is to provide a longitudinal vessel able to withstand severe forces from waves without leading to significant hull deflection/deformation.
A seventh object of the present invention is to provide a longitudinal vessel having the possibility of combining drilling and production of oil and gas.
These objects are obtained according to the present invention represented by the features disclosed in the following independent claim, with additional features of the invention set forth in the dependent claims and the description below.
The above mentioned objects are obtained by the invention as set forth and characterized in the main claims, while the dependent claims describe further embodiments of the invention.
In particular, the present invention relates to a longitudinal vessel for production and/or storing of hydrocarbons arranged to float in a body of water. The vessel may also be combined with drilling and/or utilized for cooling and storage of gas.
The longitudinal vessel comprises a hull that extends between a bow and a stern of the vessel along a longitudinal axis of the vessel, where the hull is provided with at least one longitudinal well for a riser arrangement comprising an upper section and a lower section, the at least one longitudinal well being arranged on or adjacent to a centerline along the longitudinal axis of the vessel and extending vertically through the hull. Thus the bottom of the well is open to the sea.
The hull of the present invention is hereinafter defined as the area of the longitudinal vessel situated below the deck area of the vessel.
When fully assembled and in use, the longitudinal well(s) of the inventive vessel may accommodates a riser arrangement comprising a plurality of risers arranged successively along the longitudinal axis of the well(s).
The longitudinal well(s) may be arranged on or close to the centerline, following the centerline along the longitudinal axis of the vessel. In case of a plurality of longitudinal wells, the wells may be arranged successively on the center line. Alternatively, or in addition, the longitudinal well(s) may be arranged adjacent to the centerline, following the center line along the longitudinal axis of the vessel. For example, two longitudinal wells may be arranged adjacent to each other with the center line as a mirror line.
The longitudinal well(s) may advantageously extend over at least 20% of a length of the hull and advantageously up to 10% of a maximum width of the hull. In case of a plurality of wells, the wells may advantageously have the same length and/or width. However, it should be understood that the longitudinal wells may also be provided with different lengths and/or widths.
The longitudinal vessel may advantageously have a length/width ratio of less than 2, more preferably a length/width ratio of less than 1.75, more preferably equal or less than 1.5. Compared to longer vessels, a length/width ratio of less than 2 reduces the effect that the waves have on the movements on the vessel.
In order to prevent undesired motions of the vessel, the vessel may in one embodiment comprise at least one suppressing element protruding outwards from an area of the hull located below the vessel's maximum draught, typically several meters outwards from the vessel. Furthermore, the at least one suppressing element may be provided fully around a circumference of the hull, or may alternatively extend partially around the circumference of the hull. As a person skilled in the art will recognize, the at least one suppressing element may be provided with or without local recesses. The suppressing element reduces the movement of the vessel due to waves, reducing especially the heaving, stamping, and rolling of the vessel.
Due to less movement of the vessel the mooring arrangement, which typically comprises a plurality of mooring lines/wires, can be operated satisfactory with a reduced number of mooring lines compared to the prior art, thus reducing the cost of the mooring arrangement.
In one embodiment of the present invention, the hull comprises double sides and possibly a double bottom. Such hull configurations may be used as ballast tanks for protection of the loading tanks and/or storage tanks situated inside the hull.
A first track arrangement for at least one winch may advantageously be arranged in the upper section of the longitudinal well(s). The first track arrangement may be arranged over at least a part of the length of the longitudinal well, preferably over at least 20% of the length of the longitudinal well(s), more preferably over at least 50% of the length of the longitudinal well(s), most preferably over the entire length of the longitudinal well(s). During assembly and use, the multiple risers are placed underneath the first track arrangement.
In one advantageous embodiment of the invention, the longitudinal well(s) may comprise a plurality of hang-off structures or support structures for connection and/or disconnection of risers. Through this arrangement the at least one winch can be moved along the longitudinal well(s) in order to handle the risers when the risers are to be connected and/or disconnected from the hang-off structures. The support structure(s) may be located at the upper section of the well, underneath the winch(es) and first track arrangement, providing a configuration most suitable for flexible risers.
In another advantageous embodiment of the invention the upper section may be isolated from the adjacent storage and/or loading tanks by cofferdams.
In yet another advantageous embodiment of the invention the support structure is located at the upper section of the well(s), and the lower section of the well(s) comprises a plurality of guide pipes. These guide pipes are configured to guide risers vertically through the well(s) and may comprise riser bending restrictors, or connections for riser bending restrictors, at their lower ends.
In yet another advantageous embodiment of the invention, the support structure(s) is/are located at the lower section of the well, thereby providing a configuration most suitable for rigid risers such as steel catenary risers (SCR). However, the configuration may accommodate flexible risers as well.
In yet another advantageous embodiment of the invention, at least one ventilation duct is connected to an area of the longitudinal well(s), preferably in the upper section of the longitudinal well(s) for ventilating the well(s). The at least one ventilation duct may further comprise at least one valve for controlling the ventilation of the well(s).
In yet another advantageous embodiment of the invention, the lower part of the lower section of the well(s) is provided with at least one support structure securely suspending the risers during use. The support structure may comprise a locking device enabling locking of the risers.
In yet another advantageous embodiment of the invention, the longitudinal well(s) may be provided with an enlarged area underneath the support structure(s). The enlarged area can be gradually extending in its width towards the bottom of the well(s). Such a configuration is especially advantageous during use of rigid risers, such as the above mentioned SCR-risers or any other risers having stiffness in a similar range. The reason is that the risk of riser fracture/damage caused by movement of the vessel is decreased since the enlarged area provides space for the risers to swing/deflect away from the vertical axis. It should be understood by a person skilled in the art that any configurations suitable for rigid risers will also be applicable for flexible risers. However, the opposite case may not necessarily be the case.
In yet another advantageous embodiment of the invention, the lower part of the lower section of the well(s) is provided with a support structure. A platform may be used to guide the riser into the locking device of the support structure. The guiding process involves guiding the riser past the support structure and into the locking device in the support structure. The platform may in this embodiment comprise a guiding arrangement to move the riser sideways within the longitudinal well(s). Furthermore, the platform may be arranged on a second track arrangement extending over at least a part of the length of the respective longitudinal well, preferably over at least 20% of the length of the respective longitudinal well, more preferably over the entire length of the respective longitudinal well. The platform, the guiding arrangement and the second track arrangement is positioned above the support structure.
The well(s) and the risers should be positioned in areas where the movements of the vessel are smallest. The well zone(s)/area(s) in which the risers are connected or disconnected is/are preferably protected from external weather conditions. Hence, the equipment required for pulling, connecting and disconnecting the risers is situated in the protected zone(s), thus requiring less maintenance and providing higher security. The riser arrangement of the present invention further allows connection and disconnection of the risers to be performed in a water-free and dry environment.
Due to ventilation ducts, the present invention enables ventilation of possible gas leakages or the like to be evacuated from the main deck and/or the processing area(s). By installing valves on the ventilation ducts control of potential gas leakages is ensured, thereby reducing significantly the risk of fire and explosions.
Furthermore, a robust construction of the part of the hull surrounding the well contributes to a hull damage control in the unlikely event of gas explosion and/or fire.
The combination of reduced movement, large deck area, large load capacity and a large storage volume are all important characteristics for FPSOs, storage vessels and units for floating production, cooling and storage of natural gas (FLNG). The combination of a longitudinal vessel with length/width ratio of less than two and the riser arrangement within longitudinal well(s) situated on or adjacent to a center line along the longitudinal axes of the hull contributes to these characteristics.
The particular design of the hull of the vessel enables the use of SCR risers. This is a great advantage over use of traditional flexible risers since the latter solution is in general more expensive, gives a more complex installation and requires more maintenance compared to a solution with rigid risers. Furthermore, flexible risers are more sensitive to irregularities during operation and have a shorter lifetime than rigid risers. Since repair of a flexible riser has proved difficult, they are often exchanged with new ones, thereby increasing cost further.
By connecting the risers inside wells, protected from external weather conditions, an efficient arrangement for connection and operation is established, enabling connection/disconnection of the risers in a dry environment.
In the following description, numerous specific details are introduced to provide a thorough understanding of embodiments of the claimed longitudinal vessel. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.
The invention will now be described with reference to the attached drawings, wherein:
The suppressing element 6 inter alia reduces the stamping, rolling and heaving of the vessel 1 caused by external forces such as waves. The suppressing element 6 is thus designed to influence the amplitude and frequency of the vessel's movements such that it does not coincide with the amplitude and frequency of the external forces. The coupling effect between the inertia forces, dampening forces and buoyancy force influence the movements of the vessel as well. The combination of change in amplitude and frequency of the movements and the effects from the inertia, dampening and buoyancy forces results in a significant reduction in vessel movements.
A total of twelve risers 9 are shown supported from within the vessel 1. In
The vessel 1 is further provided with a longitudinal well 7 for a multiple riser arrangement. The longitudinal well 7 is in
The upper section 7A is connected to two ventilation ducts 13. Possible gas leakage or the like in the upper section 7A may thus be effectively removed, avoiding any exposures to the main deck D and/or the processing deck P. These ventilation ducts 13 may be arranged horizontally and/or vertically, preferably at each end of the upper section 7A. The ventilation ducts 13 may further comprise valves (not shown), enabling controlled opening/closing and thereby full gas control of the whole well 7.
The well 7 and the ventilation ducts 13 may comprise gas detectors (not shown) which enables fast detection of any gas leakage, and therefore also fast closing and sealing of the upper section 7A. By a rapid closing of the valves within the ducts 13, any potential explosion caused by gas leakage may be completely isolated inside a well 7 having surrounding walls configured/manufactured to sustain such explosions without severe damage. One or more winches 11 are moving horizontally along the upper section 7A on an upper track arrangement 12. The winches 11 are used for handling of the risers 9, i.e. to lift or lower a single riser 9 during connection or disconnection to/from the support structure 8.
A plurality of guide pipes 10A, one for each riser 9, is arranged at a distance from each other along the longitudinal well 7. One end of each guide pipe 10A is provided with a connection 10B for riser bending restrictors 10C. The water level w(l) is shown for a loaded vessel 1 at it's maximum draft. Hence, the support structure 8 in
As in
The area adjacent to the guide pipes 10A is in the embodiment shown in
However, in contrast to the first embodiment illustrated in
A winch wire 11′ suspended from the winch 11 is guided through a guiding arrangement 16 situated on a platform 14, the latter being arranged on a lower track arrangement 18, thus enabling horizontal movement along the lower section 7B of the longitudinal well 7.
In
The configuration of the locking device 15 of the support structure 8 and the enlarged area 17 of the well 7 renders the risers 9 to have a pendulum movement without breaking.
Since the well 7 is open to the sea at the bottom 20 the lower section 7B can be partly or fully filled with water depending on the vessel's loading condition.
In the preceding 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 were set forth in order to provide a thorough understanding of the vessel and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the vessel, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/059367 | 4/27/2016 | WO | 00 |
