Method for subsea connection of anchor lines under tension

Abstract

The present invention is applied in the field of anchor line maintenance and, more particularly, relates to a method for subsea connection of anchor lines under tension, comprising: installing, by means of an ROV (31) of a support AHTS vessel (3), one or more floats (43) on an anchor hook shackle (42) of a fixed-point mooring line (41); providing, by means of a main AHTS vessel (2), a handling line (20) comprising a handling cable (21) attached to the main AHTS vessel (2) and a ballast mooring line (22) connected to the handling cable (21); connecting, by means of the ROV (31), the ballast mooring line (22) to a link of a seabed mooring line (12) of a stationary production unit (UEP) (1) in the vicinity of the anchor hook (13); paying out, by means of the main AHTS vessel (2), the handling line (20) with the ballast mooring line (22) connected to the link of the seabed mooring line (12) in the vicinity of the anchor hook (13); moving the main AHTS vessel (2) toward a fixed anchor point (4), passing over it, until a desired position is reached; connecting, by means of the ROV (31), the anchor hook (13) to the anchor hook shackle (42); and disconnecting, by means of the ROV (31), the ballast mooring line (22) from the link of the seabed mooring line (12). The present invention also relates to other methods for subsea connection of anchor lines under tension.

Description

[0001] METHOD FOR UNDERWATER CONNECTION OF ANCHORING LINES UNDER TRACTION Field of the invention

[0001] The present invention is applied in the area of ​​maintenance of anchoring lines and, more particularly, refers to methods for underwater connection of anchoring lines under tension, without the use of a winch from the stationary production unit (SPU). Background of the invention

[0002] A mooring system comprises various pieces of equipment that hold a stationary unit in place against the forces of waves, wind, and currents. Thus, a mooring system plays a fundamental role in the oil and gas industry, supporting the safe operation of stationary units that produce oil and gas offshore. Stationary units are anchored by mooring systems at a wide range of water depths, from shallow levels as low as 20 meters to depths of 2,000 meters or more.

[0003] There are many different types of anchoring systems, from which the most appropriate system for a given unit is selected to match the environmental conditions.

[0004] For example, in monsoon regions, a turret mounted on the outer bow is often used. In shallow waters, an anchoring system called a tower yoke may be used. In areas where sea conditions are moderate, a catenary anchor leg mooring (CALM) system, which is used for loading and unloading tankers in the Gulf, is used, or a multi-point anchoring system called spread mooring, in which several anchor lines are used to directly secure the unit without a turret system.

[0005] Regardless of the type and configuration of the anchoring system, for the installation of new anchor lines, or even for the reinstallation of sections in broken lines, it is common to use the UEP's own winch to lift and / or support the line sections, or to handle them during the connection operation with other sections and adjust the traction at the end of the process.

[0006] However, situations may arise where it is not possible to use the UEP winch, for example, when the unit is not ready to respond to emergency operations (such as a line break) due to a mechanical problem with the anchoring winches or due to sanitary restrictions, as was the case with the restrictions resulting from the COVID-19 pandemic.

[0007] In these cases, it becomes necessary to develop a method for underwater connection of mooring lines, for the reconstitution of the mooring system, without the use of winches on board the FPSOs. State of the Art

[0008] The state of the art shows some documents that reveal matters within the technological field of the present invention.

[0009] Document EP1318072A2 discloses a floating platform that has a mooring cable that passes through a coupling device tied to the suction anchor. The coupling device allows adjusting the effective length of the mooring cable between the platform and the anchor by means of a vessel independent of the platform. The vessel pulls the mooring cable through the coupling device, reducing the effective length of the mooring cable, until the floating platform is in the desired position. The coupling device includes a locking device to prevent the effective length of the mooring cable from changing when the floating platform is in the desired position.

[0010] In the aforementioned document EP1318072A2, the mechanism used to adjust the tensions in the mooring / anchoring cable is a coupling device, which is connected to a working cable of the vessel and positioned near the anchor. This mechanism is employed by only one vessel, without the use of other vessels to assist in the correct positioning (distance adjustment) and distribution of applied loads, as is the case with the present invention. Furthermore, this document does not reveal or suggest a method for replacing sections of the mooring line that may have broken, including all the steps involved in fishing and the sub-processes of preparing, arranging, and handling the sections between different vessels.

[0011] In turn, document PI0204708-0B1 discloses a quick anchoring apparatus which allows for the underwater connection and disconnection of mooring lines to anchoring devices already fixed to the seabed. The quick anchoring apparatus comprises mooring lines, cables, hooks, and floats specifically arranged and fitted to the submerged end of the mooring line, enabling a single support vessel, together with a remotely operated vehicle, to perform the entire mooring operation of a floating platform's mooring line. The document also refers to a method for installing and uninstalling the quick anchoring apparatus.

[0012] However, in document PI0204708-0B1, the mooring line is reconnected to the floating structure at the end of the process, so that it can be connected to the tensioning devices on the floating structure. That is, the winches on the floating structure are still used to provide the desired tension to the line. PI0204708-0B1 does not reveal or suggest the use of two or more different UEP vessels to handle the line sections, assemble new sections, and the entire positioning and traction scheme between the auxiliary vessels to provide the correct tensioning of the mooring line, as in the present invention.

[0013] Finally, document US20210078676A1 refers to vessels or floating structures that are moored to the seabed by sets of mooring cables that connect the floating vessels to anchors fixed to the seabed. The document discloses a method for tensioning the mooring cable sets to a desired tension without applying tensile forces from the vessel or structure to be moored.

[0014] However, it is not revealed or suggested in document US20210078676A1 how the handling of the mooring lines and the entire scheme of positioning and application of maneuvers and loads by the main and auxiliary vessels to provide the desired traction on the line is carried out, without interacting with the floating platform during the procedure, as is the case with the present invention. Brief description of the invention

[0015] The present invention relates to a method for submerged connection of mooring lines under tension, which includes steps for recovering both ends of a broken mooring line, disconnecting and replacing the damaged components, and submerged reconnection of the line, keeping it close to the designed tension, without the need to operate winches or other equipment on board a UEP (Unit of Production and Exploitation).

[0016] The method of the present invention can be applied in its entirety to anchor line connection operations, and with minor modifications, to flexible duct and umbilical connections.

[0017] Furthermore, by using the method of the present invention, the risks related to the movement of anchor lines on board the UEP are avoided, i.e., the operation becomes safer, since it is not necessary to move the winch or the lines. Moreover, the need for diving to open and close the chain stopper is eliminated – a 100% diverless operation; the risk of collision between auxiliary vessels of the AHTS (Anchor Handling Tug Supply Vessel) type and the UEP is reduced; and the connection operation occurs outside the turning radius and offloading area of ​​the UEP.

[0018] Other advantages related to the implementation of the method of the present invention are associated with an improvement in the productivity / effectiveness of the process, since the total intervention time is reduced by 50%, due to the non-application of anchoring winches, which are slow-operating equipment. Furthermore, as already mentioned, the method of the present invention does not involve steps that require divers to open or close a chain stopper, therefore also contributing to a reduction in operating time, in addition to the aforementioned safety. Additional advantages are: - elimination of the need for a team to board for winch movement; - reduction in the number of BOAT DAYS of the operation; - reduction in pullback time through the UEP towing points; - reduction in the risk of interference between pullback and offloading and pull-in operations.

[0019] Thus, the advantages and objectives of the present invention are achieved by providing a method for underwater connection of mooring lines under tension comprising: installing, by means of an ROV from a supporting AHTS vessel, one or more floats on a mooring hook shackle of a fixed-point mooring; providing, by means of a main AHTS vessel, a handling line comprising a handling cable fixed to the main AHTS vessel and a ballast mooring connected to the handling cable; connecting, by means of the ROV, the ballast mooring to a link of a bottom mooring of a UEP in the vicinity of the mooring hook; launching into the water, by means of the main AHTS vessel, the handling line with the ballast mooring connected to the link of the bottom mooring in the vicinity of the mooring hook; moving the main AHTS vessel towards a fixed-point mooring, passing by it, until reaching a desired position;Connect the anchor hook to the anchor hook shackle using the ROV; and disconnect the ballast mooring from the bottom mooring link using the ROV.

[0020] Furthermore, in one embodiment, the present invention includes a method for underwater connection of mooring lines under tension comprising: connecting, by means of an ROV from a supporting AHTS vessel, a working cable lowered by the supporting AHTS vessel to a link of a fixed-point mooring line from a fixed-point mooring near a mooring hook shackle; providing, by means of a main AHTS vessel, a handling line comprising a handling cable fixed to the main AHTS vessel and a ballast mooring line connected to the handling cable; connecting, by means of the ROV, the ballast mooring line to a link of a bottom mooring line of a UEP near the mooring hook; lowering into the water, by means of the main AHTS vessel, the handling line with the ballast mooring line connected to the link of the bottom mooring line near the mooring hook;Move the main AHTS vessel towards the fixed anchorage point, passing through it, until it reaches a desired position; use a secondary AHTS vessel to attach a handling line containing a handling cable and ballast mooring line; connect, via ROV, the handling line of the secondary AHTS vessel to a link of the fixed anchorage mooring line near the anchor hook shackle; move the secondary AHTS vessel towards the UEP, applying propulsive force equivalent to the horizontal force exerted by the UEP's anchorage line after its connection to the fixed anchorage mooring line, until the anchor hook shackle is close to its working depth; connect, via ROV, the anchor hook to the anchor hook shackle; disconnect, via ROV, the ballast mooring line of the main AHTS vessel from the bottom mooring link and the ballast mooring line of the secondary AHTS vessel from the fixed anchorage link. Brief description of the figures;

[0021] The preferred embodiments of the invention in question will be better understood when read in conjunction with the accompanying drawings. It should be understood, however, that the invention in question is not limited only to the precise arrangements and instruments shown.

[0022] Thus, the present invention will be described below with reference to its typical embodiments and with reference to the attached drawings, in which:

[0023] Figure 1 shows a schematic view of a typical anchor line configuration, according to one embodiment of the present invention.

[0024] Figure 2 shows a schematic view of floats installed on a fixed-point mooring, according to one embodiment of the present invention.

[0025] Figure 3 shows a schematic and representative view of a configuration comprising a UEP, a main AHTS vessel for force application and a support AHTS vessel with ROV to effect the connection of the method, according to a first embodiment of the present invention.

[0026] Figure 4 shows a schematic and representative view of a configuration comprising a UEP, a main AHTS vessel for force application, a secondary AHTS vessel for force application, and a support AHTS vessel with ROV to effect the connection of the method, according to a second embodiment of the present invention. Detailed description of the invention

[0027] The following refers in detail to preferred embodiments of the present invention illustrated in the accompanying drawings. Whenever possible, the same or similar reference numbers will be used throughout the drawings to refer to identical or similar features. It should be noted that the drawings are in simplified form and are not represented to precise scale, so minor variations are expected.

[0028] As used herein, the term "mooring line" refers to a type of chain, formed by links (preferably of steel), used in different sections of an anchor line to anchor stationary units and other maritime structures. Furthermore, the term "line," as used in the descriptions of the present invention, refers to a larger, generic group that can be subdivided into smaller, more specific groups, such as "upper part," "lower part," "bottom mooring line," "fixed point mooring line," "handling cable," etc.

[0029] The present invention relates to methods of underwater connection of mooring lines under tension, without the use of a winch on the stationary production unit (SPU). By way of example, Figure 1 shows a typical configuration of a mooring line, which has an upper mooring line section LA1 (connected to an SPU and descending to a hook GA) and a lower mooring line section LA2 (connected to a fixed point PF and ascending to a shackle MGA, connected to the hook of the upper section LA1). This typical configuration includes mooring sections, cable sections, shackles, a hook, and a fixed anchor point PF (such as a torpedo stake, a suction stake, an anchor, or any other appropriate device for fixing to the seabed). The cables used in different cable sections are preferably polyester cables. It should be noted that the upper section of the mooring line LA1 is generally larger than the lower section LA2.

[0030] Thus, the present invention relates to methods of underwater connection of mooring lines under tension, which differs from those underwater connections of mooring lines without tension on the line, that is, with the mooring line only under its own weight and which will still depend on the action of the UEP winch. Furthermore, the methods of the present invention are aimed at connecting mooring lines that have been broken in some section along their length, or even for connecting new lines.

[0031] In general terms, a method for underwater connection of broken mooring lines according to the present invention comprises: recovery (fishing) of the two ends of the broken mooring line (upper and lower sections); disconnection and replacement of the damaged components; and underwater reconnection of the line in tension close to the design tension, without the use of winches or any other equipment on board the FPSO.

[0032] To describe a first embodiment of the method, an initial configuration will be considered in which an anchor line 10 containing an upper anchor line 11 and a bottom mooring 12 is fixed, at one upper end of the upper anchor line 11, to a UEP 1. The lower end of the upper anchor line 11 is connected to a bottom mooring 12, which has an anchor hook 13 at its lower end (tip). In this initial configuration, the anchor hook 13 hangs down from the bottom mooring 12, below the water surface and at a certain height from the seabed, without being connected.It should be noted that the assembly formed by the upper part of the anchor line 11 and the bottom mooring line 12 may be a new section of the anchor line, in which a first connection to a fixed anchor point 4 has not yet been made; or a section that has been prepared on the deck of a vessel, after a break in some section of the upper part of the anchor line 11, and which includes the bottom mooring line 12. Furthermore, the upper part of the anchor line 11 may be formed exclusively by one or more cables, by a combination of one or more cables connected to one or more mooring lines, or exclusively by one or more mooring lines.

[0033] Furthermore, on the seabed, there is a fixed point 4 embedded in the ground and connected to a fixed-point mooring line 41, which has an anchor hook shackle 42 at its free end (upper end). In this initial configuration, the anchor hook shackle 42 is not connected to any other element and is positioned on the seabed. It is worth noting that a portion of the fixed-point mooring line 41 is also on the seabed, while another portion is under the seabed, being connected to fixed point 4.

[0034] Thus, in a first embodiment of the present invention, the method comprises installing one or more floats 43 on an anchor hook shackle 42 that is positioned on the seabed. This step is shown, by way of example, in Figure 2. To perform this installation, an anchor handling tug supply (AHTS) support vessel is provided, which has a remotely operated vehicle (ROV) attached to it, called the AHTS support vessel 3. By means of the ROV 31, a mapping and preparation of the fixed-point mooring line 41 is carried out, which consists of stretching this mooring line 41 towards the UEP 1. This is done by installing one or more floats 43 on the anchor hook shackle 42 of the fixed-point mooring line 41, so that it is visible and favorable for subsequent connection with the anchor hook 13.In other words, this step is important to ensure that the anchor hook shackle 42 does not become buried, or under a portion of the fixed point mooring line 41 itself, or even covered in soils that create suspension.

[0035] In a first embodiment of the present invention, the method further comprises a step of providing a handling line 20, by means of a main AHTS vessel 2, wherein the handling line 20 comprises a handling cable 21 fixed at its upper end to the main AHTS vessel 2 (on a winch, for example) and a ballast mooring 22, to serve as ballast for the handling line 20 of the main AHTS vessel 2, connected to the lower end of the handling cable 21. In alternative embodiments of the present invention, the weight of the ballast mooring 22 is defined according to the type of anchoring of the UEP 1's anchoring line, and varies between approximately 30% and approximately 60% of the ideal tension of the anchoring line 10, wherein the ideal tension is the intended final tension of the anchoring line 10 connected to a given type of UEP 1's anchoring.For a catenary type of anchoring, the weight of the ballast mooring 22 is preferably closer to 30% of the ideal traction, and for a taut-leg type of anchoring, the weight of the ballast mooring 22 is preferably closer to 60% of the ideal traction. However, it should be noted that the weight of the ballast mooring 22, according to the embodiments of the present invention, is not limited to these values ​​and can be adjusted according to the design of the intended anchoring line. In addition to the ideal traction, the handling line 20 must also be assembled according to the water depth to define loads and positioning distances, as will be seen later.

[0036] The handling cable 21 of the main AHTS vessel 2 must have adequate strength for operation, and may be made of steel, synthetic fiber, a combination thereof, or other suitable materials.

[0037] Additionally, in a first embodiment of the present invention, the method further comprises a step of connecting, by means of the ROV 31 of the supporting AHTS vessel 3, the lower end (or free end) of the ballast mooring 22 to a link of the bottom mooring 12 near the anchor hook 13, so as to leave a small section of bottom mooring 13 free (i.e., a few links of bottom mooring 13) between the connection point of the ballast mooring 22 on the link and the anchor hook 13. It is important to note that the lower end of the ballast mooring 22 is connected to the link of the bottom mooring 12 near the anchor hook 13 by a suitable connecting means coupled to the lower end of the ballast mooring 22, which may be a grappling hook, a sling (preferably steel), a cargo strap (preferably synthetic fiber), among others, provided that the connecting means does not damage the link of the bottom mooring. 12 and withstand the required load.

[0038] Furthermore, in alternative embodiments of the present invention, the method also comprises connecting a guide cable (such as a sling) to the end (tip) of the anchor hook 13 to assist the ROV 31 in handling the anchor hook 13.

[0039] It should be noted that, up to this point, the main AHTS vessel 2 was positioned near the UEP 1 to facilitate the connection of the ballast mooring line 22 to the bottom mooring link 12 via the ROV 31 of the supporting AHTS vessel 3. Once the connection was made, the method comprises a step of lowering the handling line 20 with the ballast mooring line 22 connected to the bottom mooring link 12 near the anchor hook 13, by means of the main AHTS vessel 2, which moves towards the fixed anchor point 4 and passes through it, maintaining direction, until it reaches a desired position where a total length of handling line 20 (containing the ballast mooring line 22 and the handling cable 21) will be approximately 150% of the total length of the anchor line 10 (containing the upper part of the anchor line 11 and the bottom mooring line 12 with the hook). anchorage 13) or anchorage line 10 together with the fixed point mooring 41.Thus, after this step, the main AHTS vessel 2 applies its propulsive force until the anchor hook 13 is close enough to the anchor hook shackle 42, which is suspended at a certain height from the seabed due to one or more floats 43 installed on it. This intermediate configuration of the method scenario, according to a first embodiment of the present invention, is shown in Figure 3. It should be noted that the ballast mooring 22, connected in the vicinity of the anchor hook 13 of the bottom mooring 12, will ensure that the anchor hook 13 remains close to the seabed, so that the water thrust does not cause the anchor hook 13 to rise towards the surface. Optionally, the ROV 31 can perform monitoring to ensure that the anchor hook 13 is close to the anchor hook shackle 42, making small positioning adjustments if necessary.Furthermore, appropriate simulation software capable of representing a type of compound catenary anchorage can be applied to predict the ideal force and position of the main AHTS vessel 2 and adjust the paid length of the handling line 20. Additionally, the ROV 31 of the supporting AHTS vessel 3 can be used to locate the anchor hook 13 and the anchor hook shackle 42 and, if necessary, guide the supporting AHTS vessel 3 in fine-tuning the vessel's position, propulsion, and paid length.

[0040] Furthermore, in a first embodiment of the present invention, the method also comprises the step of connecting, by means of the ROV 31 of the supporting AHTS vessel 3, the anchor hook 13 to the anchor hook shackle 42. It should be noted that to effect the connection between the anchor hook 13 and the anchor hook shackle 42, the ROV 31 passes the guide cable connected to the end of the anchor hook 13 through the inside of the anchor hook shackle 42 until the anchor hook 13 is connected to it.

[0041] In alternative embodiments of the present invention, if the propulsive force of ROV 31 is insufficient to effect the connection between anchor hook 13 and anchor hook shackle 42, the supporting AHTS vessel 3 launches into the water a working cable connected to a thinner steel cable (suitable for the ROV) and a load hook of compatible capacity, and then pays cable until the load hook is close to the seabed. ROV 31 will locate the load hook and connect it to the guide cable at the end of anchor hook 13, after the sling has already been passed through the anchor hook shackle 42. The supporting AHTS vessel 3 will then pull the working cable until ROV 31 has visual confirmation of the connection of anchor hook 13 to anchor hook shackle 42.

[0042] Finally, the method also includes a step of disconnecting, by means of ROV 31 of the supporting AHTS vessel 3, the ballast mooring line 22 from the bottom mooring link 12. In this way, the handling line 20 is disconnected from the mooring line 10 by ROV 31 of the supporting AHTS vessel 3 and retrieved by the main AHTS vessel 2. In alternative embodiments of the present invention, if the working cable of the supporting AHTS vessel 3 has been used, ROV 31 will additionally disconnect the working cable from the guide cable of the mooring hook 13.

[0043] The following describes a method according to a second embodiment of the present invention. For the implementation of this second embodiment, the same initial configuration described above is also considered.

[0044] Thus, the method, according to a second embodiment of the present invention, comprises a step of connecting, by means of an ROV 81 of an AHTS support vessel 8, a working cable 82 lowered by the AHTS support vessel 8 to a link of a fixed-point mooring line 91 which is connected to a fixed point 9 embedded in the seabed. This connection is made in the vicinity of an anchor hook shackle 92 so as to leave a small section of fixed-point mooring line 91 free (i.e., a few links of fixed-point mooring line 91) between the connection point of the working cable 82 on the link and the anchor hook shackle 92.Furthermore, this connection between the working cable 82 and the link of the fixed-point mooring 91 can be made by a suitable connecting means attached to the lower end of the working cable 82, which may be a grappling hook, a sling (preferably steel), a cargo strap (preferably synthetic fiber), among others, provided that the connecting means does not damage the link of the fixed-point mooring 91 and withstands the necessary load. If necessary, the method may include a prior step of connecting one or more floats to the fixed-point mooring 91.

[0045] Furthermore, in a second embodiment of the present invention, the method further comprises a step of providing a handling line 60, by means of a main AHTS vessel 6, wherein the handling line 60 comprises a handling cable 61 fixed at its upper end to the main AHTS vessel 6 (on a winch, for example) and a ballast mooring 62, to serve as ballast for the handling line 60 of the main AHTS vessel 6, connected to the lower end of the handling cable 61. In alternative embodiments of the present invention, the weight of the ballast mooring 62 is defined according to the type of anchorage of the UEP 5 mooring line, and varies between approximately 30% and approximately 60% of the ideal tension of the mooring line 50, wherein the ideal tension is the intended final tension of the mooring line connected to a given type of UEP 5 mooring.For a catenary type of anchoring, the weight of the ballast mooring 62 is preferably closer to 30% of the ideal traction, and for a taut-leg type of anchoring, the weight of the ballast mooring 62 is preferably closer to 60% of the ideal traction. However, it should be noted that the weight of the ballast mooring 62, according to the embodiments of the present invention, is not limited to these values ​​and can be adjusted according to the design of the intended anchoring line. In addition to the ideal traction, the handling line 60 must also be assembled according to the water depth to define loads and positioning distances, as will be seen later.

[0046] Additionally, in a second embodiment of the present invention, the method further comprises a step of connecting, by means of the ROV 81 of the supporting AHTS vessel 8, the lower end (or free end) of the ballast mooring 62 of the main AHTS vessel 6 to a link of the bottom mooring 52 in the vicinity of the anchor hook 53, so as to leave a small stretch of mooring free (i.e., a few links of bottom mooring 52) between the connection point of the ballast mooring 62 on the link and the anchor hook 53.It is important to emphasize that the lower end of the ballast mooring line 62 of the main AHTS vessel 6 connects to the bottom mooring line link 52 near the anchor hook 53 by a suitable connecting means attached to the lower end of the ballast mooring line 62, which may be a grappling hook, a sling (preferably steel), a cargo strap (preferably synthetic fiber), among others, provided that the connecting means does not damage the bottom mooring line link 52 and can withstand the required load.

[0047] Furthermore, in a second embodiment of the present invention, the method also comprises connecting a guide cable (such as a sling) to the end (tip) of the anchor hook 53 for handling the ROV 81.

[0048] Once the connection of the ballast mooring 62 of the main AHTS vessel 6 to the bottom mooring link 52 has been made by means of the ROV 81 of the supporting AHTS vessel 8, the method further comprises sending the handling line 60 with the ballast mooring 62 connected to the bottom mooring link 52 into the water in the vicinity of the mooring hook 53, by means of the main AHTS vessel 6, which moves towards the fixed point of mooring 9 and passes by it, maintaining the direction, until it reaches a desired position where a total length of handling line 60 (containing the ballast mooring 62 and the handling cable 61) will be approximately 150% of the total length of the mooring line 50 (containing the upper part of the mooring line 51 and the bottom mooring 52 with the hook 53) or of the mooring line 50 together with the fixed point mooring 91.

[0049] Additionally, the method further comprises a step of paying, by means of a secondary AHTS vessel 7, a handling line 70, containing handling cable 71 and ballast mooring line 72, and connecting the handling line 70 of the secondary AHTS vessel 7 to a link of the fixed-point mooring line 91 in the vicinity of the anchor hook shackle 92. The fixed-point mooring line link 91 that is connected to the handling line 70 of the secondary AHTS vessel 7 is different from the fixed-point mooring line link 91 that is connected to the working cable 82 of the supporting AHTS vessel 8. Furthermore, it should be noted that the connection can be made by means of the ROV 81 of the supporting AHTS vessel 8. Then, the secondary AHTS vessel 7 applies propulsive force and moves towards the UEP 5 (approximately the same horizontal force to be exerted by the anchor line 50 of the UEP 5 after it is connected to the fixed point tie 91).In this way, the secondary AHTS vessel 7 adjusts the position of the anchor hook shackle 92 so that it is close to its working depth (i.e., the height at which it should be suspended in relation to the seabed considering the final configuration after the anchor line 50 of the UEP 5 is connected to the anchor hook shackle 92).

[0050] Next, the main AHTS vessel 6, which is connected to a link of the bottom mooring line 52 near the mooring hook 53 by means of its handling line 60 (ballast mooring line 62), applies propulsive force in a direction away from the UEP 5, exerting a force approximately equal to the final tension of the UEP 5 mooring line (considering the final configuration after the UEP 5 mooring line 50 is connected to the mooring hook shackle 92 of the fixed-point mooring line 91), leaving the mooring hook 53 close to the mooring hook shackle 92. This intermediate configuration of the method scenario, according to a second embodiment of the present invention, is shown in Figure 4.Appropriate simulation software capable of representing a type of compound catenary anchorage can be applied to predict the ideal force and position of the main AHTS vessel 6 and the secondary AHTS vessel 7, and adjust the paid length of their respective handling lines 60, 70. In this way, the final system configuration is adjusted so that the anchor hook 53 is close enough to the anchor hook shackle 92 (the ballast mooring 62 of the handling line 60 of the main AHTS vessel 6, which has an estimated weight as previously explained, ensures that the hook 53 remains close to the depth of the anchor hook shackle 92).Furthermore, the ROV 81 of the supporting AHTS vessel 8 can be used to locate the mooring hook 53 and the mooring hook shackle 92 during procedures and, if necessary, guide the AHTS vessels 6, 7 in fine-tuning the position, propulsion of the AHTS vessels 6, 7 and paid length of their handling lines 60, 70.

[0051] Furthermore, in a second embodiment of the present invention, the method also comprises the step of connecting, by means of the ROV 81 of the supporting AHTS vessel 8, the anchor hook 53 to the anchor hook shackle 92. It should be noted that to effect the connection between the anchor hook 53 and the anchor hook shackle 92, the ROV 81 passes the guide cable connected to the end of the anchor hook 53 through the inside of the anchor hook shackle 92 until the anchor hook 53 is connected to it.

[0052] In alternative embodiments of the present invention, if the propulsive force of ROV 81 is insufficient to effect the connection between anchor hook 53 and anchor hook shackle 92, the supporting AHTS vessel 8 launches into the water another working cable connected to a thinner steel cable (suitable for the ROV) and a load hook of compatible capacity, and then pays cable until the load hook is close to the seabed. ROV 81 will locate the load hook and connect it to the guide cable at the end of anchor hook 53, after the sling has already been passed through the anchor hook shackle 92. The supporting AHTS vessel 8 will then pull the working cable until ROV 81 has visual confirmation of the connection of anchor hook 53 to anchor hook shackle 92.

[0053] Finally, the method also comprises a step of disconnecting, by means of the ROV 81 of the supporting AHTS vessel 8, the ballast mooring line 62 of the main AHTS vessel 6 from the bottom mooring link 52 and the ballast mooring line 72 of the secondary AHTS vessel 7 from the fixed-point mooring link 91. In this way, the handling lines 60, 70 are disconnected from the mooring line 50 and the fixed-point mooring line 91 by the ROV 81 of the supporting AHTS vessel 8 and retrieved by the main and secondary AHTS vessels 6 and 7. In alternative embodiments of the present invention, if the working cable of the supporting AHTS vessel 8 has been used, the ROV 81 will additionally disconnect the working cable from the guide cable of the mooring hook 53.

[0054] In any embodiment of the present invention, the anchor hook 13; 53 is a KS hook, as described in Brazilian patent PI 9700787-0 B1. However, the present invention is not limited to the use of this hook, so other types of anchor hooks may be used to make the connection between the hook and the shackle.

[0055] Furthermore, in any embodiment of the present invention, the handling cables 21; 61, 71 of the main AHTS vessel 2; 6 and of the secondary AHTS vessel 7 must have adequate strength for operation, and may be made of steel, synthetic fiber, a combination thereof or other suitable materials.

[0056] Thus, in a first embodiment of the present invention, the method of underwater connection of mooring lines under tension comprises: installing, by means of an ROV 31 of a supporting AHTS vessel 3, one or more floats 43 on a mooring hook shackle 42 of a fixed-point mooring line 41; providing, by means of a main AHTS vessel 2, a handling line 20 comprising a handling cable 21 fixed to the main AHTS vessel 2 and a ballast mooring line 22 connected to the handling cable 21; connecting, by means of the ROV 31, the ballast mooring line 22 to a link of a bottom mooring line 12 of a UEP 1 in the vicinity of the mooring hook 13; sending into the water, by means of the main AHTS vessel 2, the handling line 20 with the ballast mooring line 22 connected to the link of the bottom mooring line 12 in the vicinity of the mooring hook 13; move the main AHTS vessel 2 towards a fixed anchorage point 4, passing by it, until it reaches a desired position;Connect, using ROV 31, the anchor hook 13 to the anchor hook shackle 42; and disconnect, using ROV 31, the ballast tether 22 from the bottom tether link 12.

[0057] Similarly, in a second embodiment, the present invention discloses a method for underwater connection of mooring lines under tension comprising: connecting, by means of an ROV 81 of a supporting AHTS vessel 8, a working cable 82 lowered by the supporting AHTS vessel 8 to a link of a fixed-point mooring line 91 from a fixed-point mooring line 9 in the vicinity of a mooring hook shackle 92; providing, by means of a main AHTS vessel 6, a handling line 60 comprising a handling cable 61 fixed to the main AHTS vessel 6 and a ballast mooring line 62 connected to the handling cable 61; connecting, by means of the ROV 81, the ballast mooring line 62 to a link of a bottom mooring line 52 of a UEP 5 in the vicinity of the mooring hook 53; Pay for the water, by means of the main AHTS vessel 6, the handling line 60 with the ballast mooring line 62 connected to the bottom mooring link 12 in the vicinity of the anchor hook 13;Move the main AHTS vessel 6 towards the fixed anchor point 9, passing through it, until it reaches a desired position; pay, by means of a secondary AHTS vessel 7, a handling line 70, containing handling cable 71 and ballast mooring line 72; connect, by means of the ROV 81, the handling line 70 of the secondary AHTS vessel 7 to a link of the fixed point mooring line 91 in the vicinity of the anchor hook shackle 92; move the secondary AHTS vessel 7 towards the UEP 5, applying propulsive force equivalent to the horizontal force to be exerted by the anchor line 50 of the UEP 5 after its connection to the fixed point mooring line 91, until the anchor hook shackle 92 is close to its working depth; connect, by means of the ROV 81, the anchor hook 53 to the anchor hook shackle 92;Disconnect, by means of ROV 81, the ballast mooring 62 of the main AHTS vessel 6 from the bottom mooring link 52 and the ballast mooring 72 of the secondary AHTS vessel 7 from the fixed point mooring link 91.

[0058] Although the present invention has been previously described based on first and second embodiments, additional and alternative embodiments are provided by the present invention, depending on the configuration of the anchor line and the sections that make up its anchor line.

[0059] Those skilled in the art will appreciate the knowledge presented here and will be able to reproduce the invention in the forms presented and in other variations covered by the appended claims.

Claims

CLAIMS 1. Subsea method for connecting mooring lines under tension, characterized in that it comprises: installing, by means of an ROV (31) of a supporting AHTS vessel (3), one or more floats (43) on an anchor hook shackle (42) of a fixed point mooring line (41); providing, by means of a main AHTS vessel (2), a handling line (20) comprising a handling cable (21) fixed to the main AHTS vessel (2) and a ballast mooring line (22) connected to the handling cable (21); connecting, by means of the ROV (31), the ballast mooring line (22) to a link of a bottom mooring line (12) of a UEP (1) in the vicinity of the anchor hook (13); pay for the water, by means of the main AHTS vessel (2), the handling line (20) with the ballast mooring (22) connected to the bottom mooring link (12) in close proximity to the anchor hook (13);1. A method according to claim 1, characterized in that the weight of the ballast mooring line (22) varies between approximately 30% and approximately 60% of the ideal tension of the mooring line (10).

2. A method according to claim 1, characterized in that for a catenary type of mooring; The weight of the ballast mooring (22) is preferably closer to 30% of the ideal tensile strength, and for a taut-leg type of anchoring the weight of the ballast mooring (22) is preferably closer to 60% of the ideal tensile strength.

4. Method, according to any of the preceding claims, characterized in that the handling cable (21) is made of steel, synthetic fiber, or a combination thereof.

5. Method, according to any of the preceding claims, characterized in that the ballast mooring (22) is connected to the bottom mooring link (12) in the vicinity of the anchor hook (13) by a connecting means selected from: a grappling hook, a sling, or a load strap.

6. Method, according to any of the preceding claims, characterized in that it further comprises connecting a guide cable to the end of the anchor hook (13) for handling the ROV (31). 7.A method, according to any of the preceding claims, characterized in that the desired position of the main AHTS vessel (2) is equivalent to a position where a total length of handling line (20) is approximately 150% of the total length of the mooring line (10) or of the mooring line (10) together with the fixed point mooring (41).

8. A method, according to any of the preceding claims, characterized in that it further comprises, after the step of moving the main AHTS vessel (2) to a desired position, applying propulsive force, by means of the main AHTS vessel (2), until the mooring hook. (13) is close enough to the anchor hook shackle (42).

9. Method according to any of the preceding claims, characterized in that the anchor hook (13) is a KS hook.

10. Subsea connection method of mooring lines under tension characterized in that it comprises: connecting, by means of an ROV (81) of a supporting AHTS vessel (8), a working cable (82) lowered by the supporting AHTS vessel (8) to a link of a fixed point mooring (91) from a fixed point mooring (9) in the vicinity of an anchor hook shackle (92); providing, by means of a main AHTS vessel (6), a handling line (60) comprising a handling cable (61) fixed to the main AHTS vessel (6) and a ballast mooring (62) connected to the handling cable (61); connect, by means of the ROV (81), the ballast mooring (62) to a link of a bottom mooring (52) of a UEP (5) in the vicinity of the anchor hook (53);pay into the water, by means of the main AHTS vessel (6), the handling line (60) with the ballast mooring line (62) connected to the bottom mooring link (12) in the vicinity of the anchor hook (13); move the main AHTS vessel (6) towards the fixed anchor point (9), passing by it, until it reaches a desired position; pay into the water, by means of a secondary AHTS vessel (7), a handling line (70), containing handling cable (71) and ballast mooring line (72); Connect, by means of the ROV (81), the handling line (70) of the secondary AHTS vessel (7) to a link of the fixed point mooring line (91) in the vicinity of the anchor hook shackle (92); move the secondary AHTS vessel (7) towards the UEP (5), applying propulsive force equivalent to the horizontal force to be exerted by the anchor line (50) of the UEP (5) after its connection to the fixed point mooring line (91), until the anchor hook shackle (92) is close to its working depth; connect, by means of the ROV (81), the anchor hook (53) to the anchor hook shackle (92); disconnect, by means of the ROV (81), the ballast mooring (62) of the main AHTS vessel (6) from the bottom mooring link (52) and the ballast mooring (72) of the secondary AHTS vessel (7) from the fixed point mooring link (91). 11.Method according to claim 10, characterized in that the connection between the working cable (82) and the link of the fixed point mooring (91) is made by a connection means selected from: a grappling hook, a sling, or a load strap.

12. Method according to claim 10 or 11, characterized in that the weight of the ballast mooring (62) varies between approximately 30% and approximately 60% of the ideal tension of the anchor line (50).

13. Method according to claim 12, characterized in that for a catenary type of anchorage the weight of the ballast mooring (62) is preferably closer to 30% of the ideal tension, and for a type of anchorage. In taut-leg, the weight of the ballast mooring (62) is preferably closer to 60% of the ideal tension.

14. Method, according to any one of claims 10 to 13, characterized in that the ballast mooring (62) is connected to the link of the bottom mooring (52) in the vicinity of the anchor hook (53) by a connecting means selected from: a grappling hook, a sling, or a load strap.

15. Method, according to any one of claims 10 to 14, characterized in that it further comprises connecting a guide cable to the end of the anchor hook (53) for handling the ROV (81).

16. Method, according to any one of claims 10 to 15, characterized in that the desired position of the main AHTS vessel (6) is equivalent to a position where a total length of handling line (60) is approximately 150% of the total length of the mooring line (50) or of the mooring line (50) together with the fixed point mooring (91). 17.Method, according to any one of claims 10 to 16, characterized in that it further comprises, after the step of moving the main AHTS vessel (6) to a desired position, applying propulsive force, by means of the main AHTS vessel (6), exerting force approximately equal to the final traction of the UEP mooring line (5), leaving the mooring hook (53) sufficiently close to the mooring hook shackle (92).

18. Method, according to any one of claims 10 to 17, characterized in that the mooring hook (53) is a KS hook.

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