Hybrid Mooring System

Abstract

The present invention relates to a hybrid mooring system between a stationary production unit (SPU) and a fixed mooring point, wherein the SPU balcony comprises: at least one hydraulic power unit (HPU); at least one rotary winch; and one or more chain-stoppers equipped with an eyebolt. Furthermore, the hybrid mooring system has a mooring line comprising: a fixed mooring point, at least two bottom chain sections, one of which comprises a waiting shackle; a KS hook; an in-line tensioner, a sacrificial line; at least one main polyester cable; at least two mooring pigtails; a top chain line; and an end assembly connection.

Claims

1. A hybrid mooring system between a stationary production unit (SPU) and a fixed mooring point wherein: the SPU balcony comprises: at least one hydraulic power unit (HPU); at least one rotary winch; and one or more chain-stoppers equipped with a gantry with an eyelet; the hybrid mooring system additionally features an mooring line comprising: at least two bottom chain sections connected to the fixed mooring point, wherein one of the bottom chain sections comprises a waiting shackle; a KS hook; an in-line tensioner; an active chain followed by a sacrificial line; a main polyester cable; at least two chain tails; a top chain; and an end assembly connection.

2. The system, according to claim 1, wherein the gantry with the chain-stopper eyelet, when in operation, is used to couple a pulley to assist in moving the chain.

3. The system, according to claim 1, wherein the fixed mooring point is one of: torpedo piles, suction piles, or vertical load anchors (VLA).

4. The system, according to claim 1, wherein the KS hook is coupled underwater to the waiting shackle of the fixed mooring point.

5. The system, according to claim 1, wherein the in-line tensioner is positioned in the deepest section of the mooring line, below the polyester cables, to minimize the negative effect on the top angle of the mooring line.

6. The system, according to claim 1, wherein the sacrificial cable is used to allow the mooring line to be opened during maintenance or demobilization of the SPU.

7. The system, according to claim 1, wherein the top chain is divided into two sections, allowing the AHTS to leave the first section mounted on the top polyester cable and deliver the second section to the SPU.

8. The system, according to claim 1, wherein the end assembly connection between the two sections of the top chain is made on board the AHTS, before releasing the mooring line into the water.

9. The system, according to claim 1, wherein the operation of the balcony requires only the repositioning of the pulley and the winch cable to serve the next mooring line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0020] The present invention will be described below with reference to its typical embodiments and with reference to the accompanying drawings.

[0021] FIGS. 1A and 1B are representations of the SPU balcony of the system of the present invention.

[0022] FIG. 2 is a representation of the mooring line of the system of the present invention.

[0023] FIGS. 3A to 3F illustrate the hook-up procedure using the system of the present invention.

[0024] FIG. 4 illustrates the AHTS actuating the in-line tensioner, applying tension to the active mooring line, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The hybrid mooring system of the present invention comprises three main structures: the SPU balcony, the mooring line, and a fixed mooring point. As shown in FIGS. 1A and 1B, the balcony is small in size and is equipped with chain-stoppers (10), with their respective fairleads below the balcony. Above the balcony, there should be a standard rotary winch (12), with a drum and steel cable, and a pulling capacity in the last layer adequate to handle a portion of approximately 70 m of the top chain (approximately 30 t), in addition to a HPU (16).

[0026] Above each chain-stopper (10) there must be a gantry (14) with an eyelet, to which a pulley (18) is connected when operating the chain-stopper (10). The apparatus above the balcony (HPU (16), rotary winch (12), gantry (14), and pulley (18)) serves only to bring the chain (20) from the AHTS to the messenger cable support (22) of the chain-stopper (10), without any traction other than the own weight of the chain. Traction must be provided by an in-line tensioner located on the mooring line and closest to the bottom. The chain-stopper (10) also has a load cell (24) to measure the force exerted on this structure.

[0027] To complete the assembly of the hybrid system of the present invention, the fixed point of the mooring line must be provided with a chain section with a waiting shackle for a KS hook at the end. The KS hook is of the type described in U.S. Pat. No. 6,915,754, reference numeral 34. Possible fixed points for the mooring line include: torpedo piles, suction piles, or VLA anchors (vertical load anchors).

[0028] As can be seen in FIG. 2, which depicts the mooring line (2), a KS hook (34) is connected underwater to the waiting shackle (32). A section of bottom chain (30) is incorporated into the eyelet of the KS hook (34), which is, in its turn, connected to the eyelet of an in-line tensioner (36).

[0029] The chain that passes through the in-line tensioner (36) (also known as the active chain (52)), which is pulled by the AHTS to provide traction), must be connected to a short polyester rope (38), between 10 m and 15 m, an intermediate chain section (42), and the main polyester rope (40), followed by the assembly of the line with an arbitrary number of polyester ropes and intermediate chain sections, up to the top section.

[0030] It should be noted that the short polyester rope is a sacrificial rope (38), and its purpose is to provide a means of opening the mooring line by cutting it. Since the means to open the mooring line, in the event of maintenance or demobilization of the unit, is guaranteed by the sacrificial rope, the risks associated with the loss of operability of the in-line tensioner during the useful life of the Stationary Production Unit (SPU) cease to exist.

[0031] The top chain (44) is divided into two sections, so that the AHTS can leave the first section mounted on the upper polyester rope and the second section can be delivered to the SPU, closing the mooring line between these two chain sections.

[0032] The weight of the tensioner (36) and the chain downstream of the tensioner (52) (the chain that has already passed through the tensioner) has a negative influence on the top angle of the mooring line, and consequently, on the ability of the mooring line to maintain the position of the SPU. For this reason, the tensioner (36) should be positioned in the deepest section of the mooring line, below the polyester ropes, as shown in FIG. 2. In this position, the negative effect is minimized.

[0033] Furthermore, since the tensioner (36) does not have the function of opening the mooring line, the active chain downstream of the tensioner can be cut by an ROV, relieving weight on the mooring line and further reducing the negative influence on the top angle. In this case, the shackle at the end of the active chain, suitable for KS hook connection, would be lost, leaving only a common link at the end, unsuitable for subsea connections with KS hooks.

[0034] More specifically, the invention relates to a hybrid mooring system between a stationary production unit (SPU) and a fixed mooring point (50), wherein the balcony of the SPU (1) comprises: at least one hydraulic power unit (HPU) (16); at least one rotary winch (12); and one or more chain-stoppers (10) equipped with a gantry (14) with an eyelet.

[0035] Furthermore, the hybrid mooring system features an mooring line (2) comprising: at least two bottom chain sections (30) connected to the fixed mooring point (50), wherein one of the bottom chain sections comprises a waiting shackle (32); a KS hook (34); an inline tensioner (36); an active chain (52) followed by a sacrificial line (38); a main polyester line (40); at least two chain tails (42); a top chain line (44); and an end assembly connection (46).

[0036] As depicted in FIGS. 3A to 3F, the hook-up operation occurs much like the traditional operation-on the balcony, the steel cable of the winch is passed through the pulley and connected to the messenger line. The AHTS approaches carrying the bottom section of the mooring line and receives the other end of the messenger line; the AHTS retracts the messenger line, bringing the 30 t winch cable of the SPU to its deck. The AHTS connects the 30 t cable to the top chain and begins lowering it into the water, while the 30 t winch pulls the top chain to the balcony. It is worth noting that the rotary winch is about 10 times faster than the chain-jack.

[0037] FIG. 3A depicts the procedure for passing the messenger line, also called the retained (represented by the blue and orange sections). Next, FIG. 3B shows the transfer of the synthetic fiber messenger line (represented in green). FIG. 3C depicts the AHTS retracting the synthetic fiber messenger line, bringing the steel messenger line. As shown in FIG. 3D, the AHTS retracts the steel messenger line connected to the winch cable of the SPU until the rotary winch cable (represented in orange) reaches the AHTS.

[0038] FIG. 3E shows the procedure for connecting the top chain to the platform cable (PSC). The AHTS pays the chain and the PSC retracts the rope, bringing the chain to the balcony until the chain-stopper can be closed.

[0039] In FIG. 3F, the AHTS brings the bottom section aboard, connects the first section of the top chain (connected to the polyester rope) to the second section (seated on the chain-stopper), and releases the mooring line into the water.

[0040] FIG. 4 shows the AHTS (100) actuating the in-line tensioner, applying tension to the active chain of the mooring line (2) through its working rope (106), connected to the active chain through a second KS hook (102) associated with a second shackle (104).

[0041] Since the rotary winch employed has a complexity similar to that of a single subsystem of a chain-jack, fewer incidents are expected during operation.

[0042] Furthermore, this type of winch is off-the-shelf, mass-produced equipment, and therefore typically has superior reliability than complex, custom-designed equipment such as a chain-jack.

[0043] The speed of the rotary winch is much higher than that of a chain-jack, and the AHTS winch that drives the in-line tensioner is also significantly faster and more reliable. Thus, both hook-up and tensioning operations are faster than existing alternatives.

[0044] An important detail is that in hybrid balcony operation, to service the next mooring line, simply reposition the winch pulley and cable, whereas with the traditional system, it is necessary to move the entire chain-jack structure from one chain-stopper to the other.

[0045] With the hybrid system, the operation of the mooring balcony becomes as simple as the operation of the pull-back winches, which are used during hook-up to connect the positioning AHTSs. Thus, the mooring operation can be performed 12/12 by the same team that operates the pull-back winches. In other words, the hybrid system eliminates the need for additional personnel onboard, as does the system with a pure inline tensioner.

[0046] The combination of all these factors makes the hybrid mooring system of the present invention extremely desirable for operations in rough waters and challenging marine scenarios, facilitating everything from the hook-up process to decommissioning at the end of the service life of the unit.