The present invention relates to a loading system for transferring at least one medium between a first installation and a floating vessel, a retrieval system for use with such a loading system and a method for connecting the loading system to a vessel.
A number of systems exist for transferring a medium between two units offshore, where one of the units is often a subsea installation, a floating storage unit or a platform and a transport vessel.
Several of these systems have devices whereby, when the vessel is not in use, a transfer hose between the installation and the vessel is positioned partly located on the seabed. Having the hose located in such a position causes severe wear on some parts of the hose, resulting in the need to monitor the wear and carry out regular replacements of parts of the hose. These known loading systems are also often arranged so as to enable the loading vessel to rotate freely according to the weather when it is connected. In some systems this is accomplished by having a swivel system close to the point of attachment between the hose and the vessel, such as a swivel system round the attachment of the hose to the vessel or as a submerged buoy housed in a receiving station in the vessel where the actual buoy or the end of the hose that is attached to the vessel comprises swivel devices, described, for example, in U.S. Pat. No. 6,688,348. In this case either the vessel must have a swivel system or alternatively a relatively heavy buoy/hose end will be required which has to be pulled up into the vessel by a swivel. The flexible hose, however, offers rather more limited flexibility. Another known system is the arrangement of a swivel system at the anchor point of the hose to the seabed. This provides greater flexibility since the axis of rotation is located at the seabed, but with such a solution all the dynamic elements are on the seabed with the problems this entails with regard to maintenance and repair. There are also systems which have anchored towers with swivel devices located above the surface of the water. However, these are exposed to wind and weather and represent an obstruction to traffic on the water.
An object of the present invention is to provide a system which reduces the problems associated with previously known loading systems. It is a further object to provide a loading system which impedes shipping to the least possible extent, can be employed in a relatively large weather window, is easy to use and where the dynamic parts can easily be repaired and maintained. A further object is to provide a system where an assistance vessel is not required for connecting and disconnecting the loading vessel. It is also an object to provide a system which can be used for relatively great depths as well as in areas subject to drift ice and icebergs.
These objects are achieved by a system as defined in the following independent claims where further features of the invention will be apparent from the dependent claims and the following description.
The present invention relates to a loading system for transferring at least one medium between a first installation and a floating vessel. The first installation may need to transfer one or more media, such as a fluid, gas and/or liquid, signals, electricity, etc. The first installation may be a storage station in the form of a platform, either floating or fixed to the bottom, a vessel, a subsea storage station for a well, a well, a manifold for several wells or other types of installation located in connection with a body of water. The floating vessel will normally be a loading ship, but may also be other types of floating vessels such as a production ship, interim storage vessel or the like.
The loading system according to the invention comprises an anchoring device which can be fixed relative to a seabed, at least one elongated first transfer element, normally vertically oriented in an installed state and connected to the anchoring device, comprising devices for connection to the first installation, a buoyancy system for ensuring that the first transfer element is under tension in an installed state, at least one flexible second transfer element arranged in the extension of the first transfer element, with a swivel arrangement mounted between the first and second transfer element, which swivel arrangement is rotatable at least about a longitudinal axis of the first transfer element, where a free end of the second transfer element comprises devices for connection to the floating vessel and in an installed state when the system is not being used are located freely suspended in the body of water.
A loading system of this kind for transfer of medium is particularly suitable for use at depths typically from 100 meters and greater. It is also suitable for greater depths from 1000 meters and greater.
The anchoring system may be any type of anchoring device which, when installed, is in a fixed position relative to the seabed. In this application, the term “seabed” should be understood to include the bed of a lake or fjord. In an embodiment the first transfer element may comprise internal devices for transfer of more than one type of medium, for example by having coaxial internal annuli or spaces or pipes extending substantially parallel in the longitudinal direction of the transfer element. It may also be composed of an assembly of a plurality of hoses or pipes. In an embodiment the first transfer element may also be a substantially rigid pipe, such as, for example, a normal riser. This rigid pipe may be composed of several parts, which, for example, are welded or screwed together. It is also conceivable for the first transfer element to be a flexible element such as a hose.
This first transfer element is connected to the anchoring device in such a manner that a point of the first transfer element is kept stable relative to the seabed. This point of the first transfer element which is kept stable may be close to the seabed or at a distance from the seabed. In an embodiment the first transfer element may be extended some distance past this point which is connected to the anchoring device, thus enabling it to be easily connected to devices mounted on the seabed and/or wells, thereby providing transfer of the desired medium. In a second embodiment the connection point between the anchoring device and the first transfer element is provided at a good distance from the seabed, with the result that the first transfer element is terminated at a distance from the seabed and connected to the first installation at this point. In this case the first installation may be a floating unit which is connected to the loading system according to the invention via a transfer line located floating in the body of water between the first installation and the loading system. A combination of these alternatives may also be envisaged.
A second end of the first transfer element facing away from the anchoring device and located in an installed state in the body of water above the anchoring device is normally located at a depth substantially outside the wave zone, normally 30-50 meters below the surface. At such a depth the relatively upper end of the first transfer element will not represent an obstruction to shipping and the influence of the waves on the end will also be minimal.
The system comprises a buoyancy system which in an installed state keeps the first transfer element under tension. This buoyancy system may comprise one or more buoyancy elements at an end of the first transfer element away from the anchoring device and/or buoyancy devices along the first transfer element. If the buoyancy element has been mounted at an end of the first transfer pipe, this may be at the top of the pipe, between the pipe and the swivel arrangement and/or secured to the pipe but mounted with the swivel arrangement between the top of the pipe and the buoyancy element. The buoyancy system may have adjustable buoyancy or include buoyancy elements with fixed, non-adjustable buoyancy, or a combination thereof.
The second transfer element is a flexible element, which should be understood to mean that a longitudinal axis for the second transfer element can be bent, for example, into an S or a J-shape. This can be achieved in various ways, either by means of an inherently flexible element such as a hose or an element composed of a number of rigid elements which together form a flexible element. In an installed state when the system is not in use, the flexible transfer element has an orientation substantially parallel to the first transfer element, and the free end is located at a distance from the seabed. The free end of the flexible second transfer element will also be located at a distance from a connection of the loading system to the first installation. This should be understood to mean that a connecting point for the first installation to the loading system will normally be located vertically below the free end of the flexible second transfer element when it is installed and not in use. The free end of the flexible second transfer element comprises a coupling for joining with a receiving device on board a vessel, where this coupling may be a standard hose coupling. In a normal service position the flexible transfer element will have a so-called gooseneck at the attachment to the swivel arrangement and the first transfer element. The flexible element, moreover, may normally have a vertical lower point during use when it is connected to a vessel, which lower point is located vertically below a horizontal plane of rotation for the swivel arrangement between the first and the second transfer element. This provides the system with greater flexibility, since the vessel has greater freedom before it has to release the end of the second transfer element, in addition to which with such an arrangement, the second transfer element and the system as such experience a minimum amount of strain.
When the system is installed, the swivel arrangement mounted between the first and the second transfer element is therefore located at a depth of around 30-50 meters. The swivel arrangement comprises a first swivel unit with an axis of rotation substantially parallel to a longitudinal axis of the elongated first transfer element. The inlet of this first swivel unit is usually parallel to the longitudinal axis of the first transfer element. Where there is only one swivel unit in the swivel arrangement, the outlet of the swivel unit has an orientation which is not parallel to the longitudinal axis and forms an angle thereto. The swivel arrangement may also comprise a second swivel unit with a second axis of rotation oriented with a different axis of rotation to the first swivel unit, in an embodiment substantially perpendicular relative to the first axis of rotation. The result of having these two swivel units is to relieve the stress and strain on the transfer between the first and the second transfer element, as well as providing a loading system capable of withstanding greater moments since the strain on the second transfer element is relieved at the attachment point with the second swivel unit. A swivel arrangement of this kind makes it possible for the flexible transfer element to be rotated relative to the first transfer element. The vessel which is secured to the second transfer element thereby acquires a very large operating surface in a connected state. The S-shape of the second transfer element with the vertical lower point arranged below the swivel arrangement also permits the vessel to move for some distance directly towards a vertical axis of rotation for the swivel arrangement. With a direction slightly to the side of the vertical axis of rotation this swivel will be rotated. The aforementioned vertical axis of rotation is an axis of rotation substantially parallel to the first transfer element, as indicated above, but this axis may have an angular deviation of at any rate 15 degrees with a vertical axis. One or both of the swivel units in the swivel arrangement may also include locking devices in order to be able to lock or restrict the rotating motion at one point.
Thus in an embodiment at least a part of the buoyancy system, usually a buoyancy element, forms a base for the swivel arrangement. The swivel arrangement may be connected to this buoyancy element by releasable couplings which make it easy to detach the swivel arrangement from the first transfer element when it has to be taken to the surface for repair and maintenance. Otherwise this swivel arrangement is mounted at a depth which enables repairs to be carried out on site, for example by divers or ROV. If the swivel arrangement has to be released and raised to the surface, it will be possible to lock the swivels by means of the locking devices, thereby making it easier to lift them straight up from the loading system after being released. Devices will normally also be provided for facilitating the release or replacement of the flexible second transfer element from the swivel arrangement. Valves and the like will be provided in the system to ensure that no environmentally harmful media are released to the environment. This will be understood by a person skilled in the art.
According to the invention the first transfer element may also comprise shock-protection devices in the area where a free end of the flexible second transfer element will be located in an installed state when not in use. These shock-protection devices may be of different types such as mats placed round the first transfer element or more projecting framework to prevent the end of the second transfer element from knocking against the first transfer element. The end of the second transfer element may also include devices for eliminating/minimising any damage should the second transfer element come into contact with the first transfer element.
In an embodiment the first transfer element may further comprise a flexible coupling near the securing point to the anchoring device, which coupling permits angular deviation between a longitudinal axis of the first transfer element and a vertical axis when the system is in an installed state. There is a greater need for a flexible coupling of this kind when the system is employed for lesser depths than when it is employed for greater depths, since the length of the first transfer element offers a certain amount of flexibility depending on the length of the first transfer element. In a variant of the invention a portion of the first transfer element may also be mounted at the anchoring device, which portion is provided as a flexible portion of the first transfer element.
The loading system also comprises a retrieval arrangement, thereby enabling a vessel to retrieve the free end of the second transfer element and connect the free end to the receiving system on board the vessel. This retrieval arrangement may constitute a standard retrieval arrangement, with a bottom-moored marker buoy, where the buoy and the anchor have to be brought up on to the vessel before work can begin on pulling in the free end. This process has to be reversed when the vessel is to be released. Recovery and deployment of the anchor system takes time and is not advantageous.
As an alternative, a modified retrieval arrangement may be envisaged where instead of a bottom-moored marker buoy, a buoy connected to a retrieval line is used which has increased deadweight in at least one portion compared with the rest of the retrieval line, with the result that the weight of the line causes it to stay on the seabed. Since this weight is attached to and/or integrated in the lines, the lines can be pulled up by normal winches without having to stop the process in order to connect/disconnect the anchor arrangement as has to be done in previously known solutions.
According to the invention other new retrieval arrangements have also been developed which are also easier to use than previous solutions.
The retrieval arrangement according to the invention for a flexible transfer element in a transfer system between a first installation and a vessel, which transfer element in an installed state is arranged freely suspended in the body of water with a substantially vertical orientation and with the free end comprising connecting devices for connection to a vessel at a distance from the seabed, comprises a guide element which is mounted slidably along the transfer element, a recovery line connected to the guide element and the transfer element at one end, and a marker buoy connected to the recovery line at a second end thereof.
In a variant, the guide element comprises buoyancy devices, and the arrangement further comprises a guide line, where the recovery lines are secured to the free end of the transfer element, the guide line is secured to the transfer element near the free end and to the recovery line at a distance from an attachment point between the recovery line and the free end of the transfer element and where the guide element is further mounted slidably along the guide line between its two attachment points.
In a second variant, the guide element comprises weight elements and the recovery line is secured to the guide element, where the arrangement further comprises a releasable holding device for securing the guide element, mounted at a distance from the free end of the transfer element.
In a free state the guide element is freely slidable along the transfer element. Where the transfer element comprises portions with a smaller diameter, the guide element is provided with a length which permits it to come into abutment with the transfer element on both sides of the portion with a smaller diameter, thus preventing it from becoming jammed in the portion with a smaller diameter.
According to the invention a vessel will arrive at the loading system location as described above and pick up the marker buoy, whereupon the vessel reverses away from the loading system and begins to pull in, for example winch in, the recovery line attached to the marker buoy, whereupon the free end of the flexible transfer element is pulled towards the vessel and connected thereto.
A loading system, recovery system and method according to the invention provide a system which can be employed in a larger weather window, the system has great flexibility with regard to the motion of a connected vessel both on the horizontal and vertical plane, by means of the provision of both the swivel arrangement and the flexible transfer element. This provides a system which has increased operational reliability. Furthermore, a retrieval system according to the invention provides a simplified connection and disconnection system. Mounting the dynamic parts on the top of the first transfer element also provides the advantage of simplifying repair and maintenance. The fact that the flexible second transfer element is arranged freely suspended down in the water when the system is not in operation will contribute to less wear on the second transfer element, while a shorter hose is required with such a system, resulting in a saving in costs and a reduction in the dynamic forces influencing the system when it is in operation.
The invention will now be explained in greater detail with reference to the attached figures, in which:
In
In
In
Where it is only a case of repairing the second flexible transfer element 7, the first and second swivel units 16, 17 can be locked by means of locking devices 18, thus preventing them from rotating freely, as indicated in
An alternative retrieval arrangement is illustrated in
In this case the recovery line 21 is secured directly to the free end of the flexible transfer element 7. Furthermore, a guide line 23 is secured to the end of the flexible transfer element 7 and a point on the recovery line 21 at a distance therefrom. The guide element 20 is connected slidably to the guide line 23. When a vessel has picked up the marker buoy 22 and begins to winch in the recovery line while reversing away from the loading system, the guide line 23 and the guide element 20 with their built-in buoyancy will guide the lifting point between the recovery line 21 and the flexible transfer element 7 to the end of the flexible transfer element 7, as illustrated in the sequences 1 to 5.
The retrieval arrangement according to the invention with a guide element running along the flexible transfer element will also have the effect of cleaning fouling off the flexible transfer element.
An alternative retrieval arrangement is illustrated in
The invention has now been explained with reference to special embodiments illustrated in the attached figures. A person skilled in the art will appreciate that changes and modifications may be made to these embodiments which fall within the scope of the invention as defined in the attached claims. The loading system will also be equipped with the necessary shut-off valves, corrosion protection, etc. which will be understood by a skilled person.
Number | Date | Country | Kind |
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20064550 | Oct 2006 | NO | national |
This application is a Divisional of U.S. Ser. No. 12/443,803, filed 8 Mar. 2010, now U.S. Pat. No. 8,152,580 issued 10 Apr. 2012, which is a National Stage Application of PCT/NO2007/000347, filed 4 Oct. 2007, which claims benefit of Ser. No. 20064550, filed 6 Oct. 2006 in Norway and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.
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Number | Date | Country | |
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20120225597 A1 | Sep 2012 | US |
Number | Date | Country | |
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Parent | 12443803 | US | |
Child | 13415202 | US |