The invention relates to an apparatus for transferring hydrocarbons from a subsea source to a vessel, wherein a number of risers are suspended from a rotating body and communicate with a swivel unit comprising a number of swivel rings having outlets which are coupled to a pipe system on the vessel, the apparatus comprising a block arranged between the risers and the swivel unit and provided with interior ducts for connection of the risers with respective swivel rings, means for selective closing of the ducts being arranged between the risers and the swivel unit.
In offshore production of hydrocarbons (oil or gas) there are today often used floating production vessels. The vessel is kept in position above an oil or gas field by means of a suitable anchoring, and the oil and/or gas (the production) is conducted into the vessel by means of risers extending from the seabed up to a rotating body (turret) on the vessel.
The production is often transferred to the vessel in several independent risers. On the turret the production is conducted through a swivel and into the processing plant on the vessel. On suitable occasions, for example once per week, produced oil is transferred to a shuttle tanker.
It is very important that the production can take place continuously in order to avoid great economic losses, and it is therefore important to be able to protect oneself against faults which may cause shutdown of the production in one or more of the risers.
It is possible that faults may occur in the sealing system on one of the swivel rings after the outlet from the associated riser. In order to stop leakage of oil or gas, the fluid flow through this riser has to be stopped in that valves on the connections into and out of the swivel are closed. This may imply that the production going from the riser which is connected to said swivel ring, is stopped, with a great economic loss as a result.
On this background it is an object of the invention to provide an apparatus having a compact construction which eliminates pipes and reduces the number of flange connections, so that the number of possible leakage points is reduced, at the same time as the construction enables disconnection between the vessel and the riser system in a relatively short time.
Another object of the invention is to provide an apparatus enabling reconnection of the production from one or more risers from one swivel ring to another in a practical, simple, safe and quick manner, so that loss of production can be avoided or limited.
For the achievement of the above-mentioned objects there is provided an apparatus of the introductorily stated type which, according to the invention, is characterised in that the means for selective closing are integrated in the block.
The apparatus according to the invention is particularly advantageous and cost-effective for smaller fields where there is a need for a limited number of risers. By means of the apparatus there is obtained a compact construction involving a reduced number of flange connections and therewith a reduced number of leakage points, something which will be an advantage with respect to security.
In an advantageous embodiment of the apparatus, wherein said rotating body consists of a buoy which can be connected to the vessel, the block consists of two block units of which an upper block unit is permanently secured to the swivel unit and a lower block unit is permanently secured to the buoy, the two block units being arranged for releasable interconnection with each other.
By means of this embodiment there is obtained a common connection point which may either be bolted or comprise a remotely operated connection means. This will imply a reduced number of working operations and a reduced time consumption in case of a possible disconnection.
There may be arranged common fluid courses through the swivel unit and the upper block unit, wherein these courses are split up in the lower block unit. This implies that one gets a cost-optimal solution wherein the number of seals and valves are reduced to a minimum. This may be an attractive solution for a gas lift swivel.
A further advantageous embodiment of the apparatus according to the invention is characterised in that the block is also provided with means for selective interconnection of two or more of the ducts in the block.
By means of this embodiment there is provided an apparatus which in advance is prepared for the relevant reconnections, so that these can be carried out in a safe and quick manner.
The invention will be further described below in connection with exemplary embodiments with reference to the drawings, wherein
In the various Figures, corresponding parts are designated by the same reference numerals.
The risers 2 are suspended from a rotating body in the form of a so-called turret 8 which is mounted in the vessel 1 by means of suitable bearing means 9, 10, 11. The turret 8 is anchored to the seabed by means of anchor chains (not shown), so that it is stationary relative to the seabed whereas the vessel can turn freely about the turret under the influence of wind and weather.
Between the risers 2 and the swivel unit 3 there is arranged a block 12 which is provided with channels or ducts 13 connecting the risers to respective swivel rings 5 through appurtenant axial courses 14 in the swivel core 4. Valve means in the form of closing or shut-off valves 15 are arranged at the top of the risers 2, and similar shut-off valves 16 are arranged between the outlets 6 of the swivel rings and the pipes 7.
The block 12 is fastened to a supporting pedestal 17 which in turn is fastened to the turret 8. Further, the swivel rings are fastened to the vessel 1 by means of moment arms 18.
With normal production, oil and/or gas flows up from the topical well through the risers 2, through the shut-off valves 15, the ducts 13 and the courses 14, and via the swivel rings 5 into the pipes 7 in the pipe system. When the vessel turns about the turret 8, the swivel rings are kept stationary relative to the vessel by means of the moment arms 18, and the swivel core 4 rotates within the rings 5. Between the swivel rings and the core there are arranged seals 19 seeing that liquid and gas do not leak out during the rotation. Normally, one riser is connected to one ring, so that each riser has a swivel ring of its own, even if it occurs that several risers are connected to one ring, or that one riser is connected to several rings.
As mentioned in the introduction, faults may arise in the sealing system on one of the swivel rings. In order to stop a leakage of oil or gas, the fluid flow through the ring in question has to be stopped in that the appurtenant valves into and out of the swivel are shut off. In the conventional installation shown in
The above-mentioned drawback is avoided with the apparatus according to the invention, of which a first embodiment is shown in FIG. 3.
As appears from
In each of the bores 26 there is placed a sealing plug 29 which can be moved between the shown position and a position in which the duct 28 in question is closed. For movement of the plugs, in the illustrated embodiment there is provided a threaded rod 30 which is in threaded engagement with a lid or cover 31 covering and sealing the bore 26 in question. The two additional bores 27 are in turn covered by a sealing lid 32. The lids 31 and 32 suitably may be fastened in a sealing manner to the block 25 by means of screw bolts (not shown).
The two additional bores 27 may be interconnected by means of a branch pipe 33, as shown in
When using the illustrated apparatus, the sealing plugs 29 are operated for example as shown in
In practice there will be arranged branch pipes with different lengths, so that different branch pipes fit between different connecting points on the block 25. With reference to
The connection points for the branch pipes in the illustrated embodiment are arranged at the underside of the block 25. However, they may also be arranged at the top or at the side of the block, dependent on where it is most practical to place such connection points in each individual case.
Also in this embodiment a reconnection is carried out after one has registered a leakage in the seals of a swivel ring. In this connection reference is made to
As appears from
The reconnection arrangement in the apparatus according to the invention may of course also be used if the relevant fluid runs in the opposite direction.
A further embodiment of an apparatus according to the invention is shown in a side view in FIG. 8.
This embodiment is constructed for use in cases where the rotating body to which the relevant risers are connected, consists of an underwater buoy which is arranged for releasable fastening in a receiving space in the vessel in question. In the Figure, an upper portion of such a buoy is suggested at 50.
As shown in the Figure, the apparatus comprises a block 51 which is arranged between the buoy 50 and a swivel unit 3 mounted on the block. The swivel unit may be constituted by a swivel stack of standard design. The block 51 here consists of an upper block unit 52 on which the swivel stack 3 is mounted, and a lower block unit 53 which is permanently secured to the buoy 50. The block units 52, 53 are adapted to be interconnected to each other by means of a suitable interconnection means, for example a hydraulic structure coupler. In the illustrated example each of the block units is provided with an encircling flange ring 54 and 55, respectively, and the flange rings are releasably interconnected by means of a number of hydraulic connecters 56 which can be operated for example by means of a remotely operated control means.
The block 51 is divided into an upper block unit 52 and a lower block unit 53 in order to reduce spill of hydrocarbons to a minimum when the block units are separated from each other when disconnecting the buoy.
In each of the block units there is built in a number of valves for selective closing of the interior ducts arranged in the block units and connecting the risers (not shown in
As further appears from
An example of integration or building-in of shut-off valves in the block units 52 and 53 is shown in FIG. 9. As appears, a valve 62 in the form of a ball valve is connected in a duct 63 through the upper block unit 52. The valve is shown to comprise a rotatable valve ball 64 and a valve seat 65. The valve is coupled to an ESD valve 60 having an actuator 66 comprising e.g. a built-in spring package for closing and a hydraulic cylinder for opening. In a similar manner a valve 67 in the form of a ball valve is connected in a duct 68 through the lower block unit 53. The valve is coupled to a manual isolation valve 61 which is operated by a wheel 69 via a gearbox 70.
The ducts 63 and 68 are interconnected in a sealing manner by means of a sleeve-shaped sealing element 71 which is loosely preassembled in the upper block unit 52. Further, there is shown a sealing sleeve 72 for forming a tight connection between the duct 63 and the adjacent course in the swivel unit 3.
A flange connection 73 for a riser is suggested at the upper end of the relevant buoy 50.
Number | Date | Country | Kind |
---|---|---|---|
2001 0850 | Feb 2001 | NO | national |
2002 0091 | Jan 2002 | NO | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NO02/00068 | 2/19/2002 | WO | 00 | 8/14/2003 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO02/07241 | 9/19/2002 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
1971381 | Penick et al. | Aug 1934 | A |
4448568 | Gentry et al. | May 1984 | A |
5697732 | Sigmundstad | Dec 1997 | A |
5895077 | Sigmundstad | Apr 1999 | A |
6021848 | Breivik et al. | Feb 2000 | A |
6050747 | Midttveit | Apr 2000 | A |
Number | Date | Country | |
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20040042856 A1 | Mar 2004 | US |