EP-4737305-A1 - ARRANGEMENT AND METHOD FOR RETRIEVING BROKEN MOORINGS

EP4737305A1EP 4737305 A1EP4737305 A1EP 4737305A1EP-4737305-A1

Abstract

The present invention relates to an arrangement for retrieving broken moorings comprising: at least three shackles; at least two slings; at least one mooring; at least one hook; at least one ROV needle rope; and a treble hook. The upper end of the mooring is connected to a working rope with a swivel link, and the lower end of the mooring is connected to the treble hook. In addition, the invention also describes a method for retrieving broken moorings, using said arrangement for retrieving moorings, comprising the following steps: positioning a treble hook close to a mooring to be retrieved; passing a sling around the mooring; connecting a sling to the hook; applying traction; and accommodating the mooring. In this way, the invention combines the flexibility and adaptability necessary to operate in different suspension conditions on the seabed, ensuring the efficient retrieval of the broken moorings, both in environments with high-suspension seabeds and in low-suspension seabeds.

Inventors

ALVES PONS, Rodrigo
NUNES PEREIRA DA SILVA, Leiz
MEIRA DE OLIVEIRA, Eleandro

Assignees

Petroleo Brasileiro S.A. - PETROBRAS

Dates

Publication Date: 20260506
Application Date: 20250905

Claims (12)

An arrangement for retrieving broken moorings, characterized in that it comprises: at least three shackles (30A, 30B, 30C); at least two slings (32A, 32B); at least one mooring (34); at least one hook (36); at least one ROV needle rope (38); and a treble hook (40).
The arrangement according to claim 1, characterized in that the upper end of the mooring (34) is connected to a working rope with a swivel link and the lower end of the mooring is connected to the treble hook (40).
The arrangement according to claim 1, characterized in that the third eye of the treble hook (40) receives the sling (32A), in which the two legs of the sling (32A) are joined by means of the shackle (30C).
The arrangement according to claim 1, characterized in that the ROV needle rope (38) is joined to the end of the sling (32B) by the eye splice technique, and the end of the sling (32B) is joined to the sling (32A) by the shackle (30C).
The arrangement according to claim 1, characterized in that the hook (36) must be connected to the mooring (34) using at least one shackle (30A) in an intermediate link of the mooring.
The arrangement according to claim 5, characterized in that the hook (36) must be connected to the intermediate link of the mooring in a position such that the distance between the hook (36) and the treble hook (40) is greater than the combined length of the slings (32A, 32B).
A method for retrieving broken moorings using the arrangement for retrieving moorings as defined in any one of claims 1 to 6, characterized in that it comprises: i. positioning a treble hook close to a mooring to be retrieved; ii. passing a sling around the mooring; iii. connecting a sling to the hook; iv. applying traction; and v. accommodating the mooring.
The method according to claim 7, characterized in that positioning a treble hook comprises: laying it on the seabed if the seabed has little suspension; and positioning it close to the bottom, but without touching the ground, if there is a lot of suspension.
The method according to claim 7, characterized in that passing a sling comprises: passing the needle rope, with the aid of an ROV, underneath the broken mooring and pulling the sling from the other side.
The method according to claim 7, characterized in that the connection of a sling to the hook comprises: displacing the sling, with the aid of the ROV, to the hook; and attaching the sling to the hook.
The method according to claim 7, characterized in that the application of traction comprises: monitoring the ROV; and pulling, by means of the AHTS, the working rope until the broken mooring accommodates itself in the treble hook's pocket.
The method according to claim 7, characterized in that , after the accommodation of the mooring, it comprises: slackening the sling; and releasing the connection with the hook.

Description

FIELD OF THE INVENTION The present invention is applied in the field of subsea inspection and maintenance and, more particularly, relates to a method and arrangement for retrieving broken anchor moorings, for fishing sections of anchor lines that break and are disposed on the seabed. The present invention can be applied in congested seabeds (with many nearby subsea structures) or non-congested seabeds (with few or no nearby subsea structures). The invention can also be applied in hard soils, which generate little suspension of soil particles in the water, or in soft soils, which generate a lot of suspension of soil particles in the water, hindering the visibility. BACKGROUNDS OF THE INVENTION In maritime operations, the retrieval of broken anchor lines is essential for the maintenance of Maritime Units. The traditional method of retrieval involves the use of an AHTS (Anchor Handling Tug Supply) - an ocean-going tugboat - to drag a treble hook across the seabed in an attempt to hook the broken line. However, this method is often unfeasible due to the congested layout of the seabed and the proximity of other anchor lines or other subsea structures. The treble hook is a traditional piece of equipment in the industry that is roughly shaped like a four-point hook, in which each point (also called a "throat") is a metal piece with a shape suitable for engaging and locking the mooring. As a result, the retrieval of the moorings in congested locations has been carried out mainly by means of steel cable arrangements connected to the AHTS working rope. These arrangements need to be light and flexible in order to be installed with the aid of an ROV (Remotely Operated Vehicle) and, for this reason, they often break, resulting in the anchor line falling back to the seabed. In view of these challenges, a fishing method and arrangement were developed that eliminate the need for steel cables, providing a more reliable retrieval, avoiding accidents and reducing operating costs. STATE OF THE ART Document PI 0204708-0 B1 presents a fast anchoring apparatus, which allows the subsea connection and disconnection of anchor lines to anchor devices already attached to the seabed. The fast anchoring apparatus comprises moorings, cables, hooks and floats particularly ordered and arranged, which, attached to the submerged end of the anchor line, allow a single support vessel, together with a remotely operated vehicle, to perform the entire anchor line anchoring operation on a floating platform. This document also refers to a method for installing and uninstalling the fast anchoring apparatus. However, the system proposed in document PI 0204708-0 B1 requires pre-installation and, further, must be perfectly stretched under the seabed, making it unfeasible for removing broken moorings on congested seabeds. Document CN102219047A presents a device and a method for retrieving a subsea mooring system that sinks in muddy seabeds. The device comprises a small vessel, a winch, a steel cable, and a rescue hook, in which the winch is mounted on the aft deck of the vessel. One end of the steel cable is connected to the rescue hook and the other end is wound onto the winch; the steel cable connected to the rescue hook is released by the winch, and the rescue hook is pulled by the vessel to pass transversely through an anchor chain of the mooring system on the seabed. The anchor chain is hooked and secured by the rescue hook, and the steel cable is pulled by the winch to straighten the anchor chain. However, the method proposed in document CN102219047A cannot handle congested subsea environments, resembling conventional methods of retrieving broken moorings, in which it is necessary to displace the vessel horizontally to couple the broken mooring to the treble hook. Document US3927636A, belonging to the General State of the Art, discloses a method for retrieving an anchor buried in the seabed and attached by a long mooring line to an anchored floating structure. A submerged remote release hook, having a yieldable catch, is towed with a service line in a direction intersecting the mooring line at a point between the floating structure and the anchor until the hook catches the mooring line. This method is not applicable to broken moorings. Document CN102632976B discloses a retrieval device for a maritime mooring system comprising: a retrieval rope with one end provided with an anchor and the other end connected to a vessel and a plurality of rescue hooks that are hung from the rope and are located between the anchor and the vessel, wherein the rescue hooks comprise a main shank. The document also provides a method for retrieving maritime mooring systems. CN102632976B is mentioned because it deals with a system and a method for retrieving anchor lines on the seabed. However, the techniques used by the same resemble traditional mooring retrieval methods, in which mechanisms are provided for hooking into the submerged sections from displacements of the v