WO2007115387A1

WO2007115387A1 - Anchor for floating structures, method of installation and removal thereof

Info

Publication number: WO2007115387A1
Application number: PCT/BR2007/000091
Authority: WO
Inventors: Jorge Carlos Ferreira Jorge; Antônio Manoel Ferreira dos Filho SANTOS
Original assignee: Fluke Engenharia Ltda.
Priority date: 2006-04-10
Filing date: 2007-04-10
Publication date: 2007-10-18
Also published as: BRPI0601146A

Abstract

When it collides with the marine soil, the anchor rips and penetrates it, leaving an aperture behind itself. The support boat then pulls the anchorage line to the top, making the anchor to rotate inside the soil and keeping it in a position of approximately 90° in relation to the anchorage line. The uninstallation of the anchor can be made by overloading in the soil or by the use of devices that enables a second rotation to align the anchor inside the soil, allowing it to ascend by the aperture formed in the moment of the installation or to open a way through it.

Description

"ANCHOR FOR FLOATING STRUCTURES, METHOD OF INSTALLATION AND REMOVAL THEREOF".

FIELD OF THE INVENTION

The present invention relates to an anchor for floating structures positioned in a definitive or provisional way in non-profound, profound or ultra-profound seas .

The invention has particular application in the anchorage of floating structures related to the exploitation and production of offshore petroleum resources . FUNDAMENTALS OF THE INVENTION

Nowadays the anchorage of floating structures, such as ships, semi-submersibles, floats or rafts used in support, drilling or production services of offshore petroleum is made through conventional anchors (with catenary anchorage line) or vertical anchors (with rigid anchorage line) , both fixed in the bottom of the sea by drilling, or even through fixed, drilled and cemented stakes, or suction stakes. One of the known disadvantages in the use of either anchors or stakes is that their installation processes need the use of special equipments, such as tugboats, crane barge, submersed hammers, drilling equipments and/or special pumps, etc. In addition to the aforementioned disadvantage, dragging anchors, for example, needs to pass through a long distance to be fixed for its installation, because in most cases they are sent to the bottom of the sea linked to fastening cable (s) and are pulled by a tugboat in order to be slanted in relation to the marine soil and to be buried therein. In an attempt to solve these difficulties, a new stack, named torpedo stack due to the shape similar to a torpedo, was developed (Brazilian Patent No. PI 9603599-4, granted in December 26, 2000) . This stack comprises a tubular elongated body with a sharpened tip in its inferior edge and a closing disc in its superior edge and further vertical fins at the top of the tubular body. In the interior of its tubular part there is a ballast formed by high specific weight material distributed in a pattern that the center of gravity of the stack is below its floating center. The torpedo stack is installed by free fall with the assistance of simple and lower cost devices. Nevertheless, the torpedo stack presents as a disadvantage the impossibility of easily removal during the movements of the floating structures .

In view of the disadvantages found nowadays for the installation and uninstallation of anchors and stacks, the purpose of the present invention is to make available an anchor of very easy installation and removal, with the application in a vast area of sea depth that does not need to reach large penetration due to its dimensions and areas. The anchor of the present invention, in comparison with the dragging anchors, enables the same advantages in the concern of having a great capacity of horizontal load, but without the requirement of a preload, that is, it reaches the bottom of the sea only using its own weight and without the need of a long trail for installation.

In comparison with the torpedo stack, the anchor of the present invention is equivalent regarding the simple process of installation but independent of the capacity of the required load, also shows facility to uninstall because it demands low loads and simple equipments, and mainly has lower cost and weight since the anchor now claimed is much more light than the equivalent torpedo in terms of the same load capacity. DESCRIPTION OF THE STATE OF THE ART

New anchorage techniques have been developed in order to facilitate the process of installation and uninstallation of the anchors or stacks and also to allow the anchorage of a great load capacity leading to cost reductions .

Examples of developed techniques are showed by the Brazilian patent No. PI 8704412-9 (granted in June 30, 1992) which refers to the stack of closed edge; by the Brazilian patent No. PI 9002463-0 (granted in February 25, 1997) which refers to the gravity stacks that absorb part of the load with its heavy weight; by the Brazilian patent No. PI 9303646-9 (granted in July 27, 1999) which deals with a foundation system for vertical anchorage with a connector assembled in the interior of the stack; by the Brazilian patent No. PI 9603599-4 (granted in December 26, 2000) , already mentioned above, related to torpedo stack; by the Brazilian patent application PI 9603600-1 (filed in August 30, 1996) which refers to a plate anchor that uses a stack to its release to the bottom of the sea and by the Brazilian patent application PI 9906153-8 (filed in November 08, 1999) which refers to a stack that is fixed in the bottom of the sea by free fall.

As a manner of improving the state of the art, the present invention uses the concept of torpedo stacks extending it to conventional anchors, allying in a novel way the advantages of having a great load capacity, easiness in handling and low installation and recuperation costs.

Thus, the anchor of the present invention, incorporating the advantages of the torpedo stack with the conventional anchor, is a plate anchor, that is released to the bottom of the sea by vertical free fall, and whose balance among its weight, releasing height and area of attack assures the penetration required by the anchorage design of the floating structure. DETAILED DESCRIPTION OF THE I3WENTI0N

The present invention refers to a plain anchor composed by. a) an attack board (1) located in the inferior edge of the anchor that composes the heaviest part of it and has a pointed format in order to facilitate its penetration in the bottom of the sea; b) a predominantly plain surface (2) that composes the main plane of the anchor and is lighter than the attack tack

(D ; c) at least one sustentation structure of the anchor located in the plain surface (2) , particularly, two external structural ribs (3) located in the frontal part of the plain surface (2) for the case of using a halter, and that optionally can be internal to the plain surface (2) . In the case of using an eye instead of the referred halter, the referred ribs are not required; d) a plain and slant surface (6) in relation to the main plane of the anchor (2) located in its superior edge, opposed to the attack board, being this plain and slant surface (6) smaller than the plain surface (2) ; e) one or more longitudinal bars (7) located along the plain surfaces (2) and (6) in the posterior part of the anchor and; f) four fixing points installed in the structural ribs (3) in which the four cables of the halter (4) are fixed. The disposal of the fixing points of the halter in the structural ribs (3) and the length of the halter's cables (4) are defined in such a way that the anchor keeps its frontal area ((1) + (2)) approximately of 90° with the anchorage line when the same is under tension. Optionally, the fixing points can be substituted and, consequently, the halter (4) by an eye (5) assembled in a superstructure in the main plain surface (2) of the anchor.

The cited elements that compose the anchor of the present invention give it such a shape and different weight distribution that enable its installation being simply made by vertical free fall, that is, the anchor falls until it reaches the bottom of the sea using, thus, the potential energy of gravity to become fixed in the marine soil. In this way, the main parameters used to the installation of the anchor are its own weight and the height from which it falls . Such parameters are defined in accordance with the type of marine soil and with the required penetration to reach the load capacity of the design of the anchorage system.

In order to install the anchor of the present invention, the anchor is fastened to the anchorage line by the halter (4) or by the eye (5) and is sustained by only one boat and is released from a certain height defined by the anchorage's design. The attack board (1) and the plain surface (2) guide the anchor to always stand vertical during its fall. During the fall, the anchor increases its vertical speed till the moment in which it collides against the marine soil. In this moment, the inferior part of the anchor (1) , which concentrates the greatest part of its weight and inertia, rips and penetrates the soil while it speeds down until the anchor stops inside the soil, leaving behind a vertical passage in the format of an aperture.

Afterwards, the anchor is pulled out by the anchorage line. When the boat pulls the anchor upside, the anchor starts rising and rotating inside the soil, becoming traversed in relation to the aperture where it entered.

The plain and slant surface (6) is responsible for guiding the anchor' s rotation after the penetration in the soil and during the time it is pulled upwards. This surface (6) has a dimension which does not interfere in the fixation of the anchor, and which, on the other hand, is able to rotate the same. The surface (6) has a chamfered finishing in its final edge to assist with the cut of the soil during the rotation of the anchor. The frontal area ((1) + (2)) formed after the anchor's rotation inside the soil must be vast enough to attend the required capacity of supporting the tension of the anchorage line in which it will work.

The structural ribs (3) assist the frontal area ((1) + (2)) to support the strength applied by the anchorage line. The structural ribs (3) presents fixing points that assist in an important way the installation of the anchor, in the final rotating step during the ascension, penetrating and beginning the soil split, removing the anchor from the inside of the aperture formed in the initial penetration. After the end of the rotation, the anchor is positioned with its plain surface (2) making approximately 90° with the tensioned anchorage line.

In this position, the strength required to pull the anchor away from the inside of the soil increases more than five times in comparison with the strength required to pull it away when pulling it back aligned with the same aperture where it entered.

The halter (4) determines the plain angle of the anchor with the anchorage line. If the anchorage line is pulled making any angle with the vertical, the anchor will get positioned until it stays again approximately 90° in relation to the anchorage line. During all the time established for the lifetime of the project, it is in this position of approximately 90° in relation to the anchorage line that the anchor will work, supporting the tension of the anchorage line.

By this way, the installation method dispenses alignments of the anchor in relation to the final direction of tension of the anchorage line.

When the uninstallation of the anchor is required, a conventional device for the opening of hook escape lines, pelican hook lines or a similar one is activated to release the frontal part of the halter lines. Once the halter is disassembled, the anchor is pulled only by the lines fixed from the behind, so as the anchor rotates again in the direction to be aligned with the traction of the anchorage line and easily leaves the soil. Alternatively, can also occur the uninstallation by the possible opening of the rear cables of the halter. Another option of uninstallation is to simply pull the anchorage line into the vertical position until it overcomes the resistance limit of the soil, when the anchor will get out from the same. If the anchor has the eye (5) instead of the halter (4) , the uninstallation must only be by overloading with shearing of the soil.

Due to its simplicity, the anchor of the present invention can be manufactured from welded steel sheets by melting, forging or boiling. This invention can be applied to any anchorage system, permanent or provisional, from flat seas to ultra profound seas (more than 3.000 m of water depth) .

Moreover, the loading test for the anchor of the present invention is practically vertical in a simple tension-rotation operation.

The dimensional and parametric details of the anchor were not shown because the same is dimensioned in accordance with each project of anchorage system that takes into consideration the required load, the soil and the installation resource.

The details of the connection accessories of the halter's cables were also not shown because they are not objects of this invention. DETAILED DESCRIPTION OF THE FIGURES

A description of 11 figures is presented below, where can be observed that the anchor concept is completely associated to the peculiar features of the same. FIGURE 1 - Frontal perspective view. Shows the general and conceptual aspects of the anchor, beneath the pointed and very heavy attack board (1) to rip the soil during the penetration; above the surface predominantly plane (2) with the fixed halter (4) and with structural ribs (3) to resist the efforts of the anchorage line and of the soil; at the top, the plain and slant surface (6) in relation to the main plane (2) with longitudinal bars (7) so as to force the anchor's departure from the inside of the aperture formed in its descent, that is, to force the rotation of the same inside the soil during the tensioning of the anchorage line. FIGURE 2 - Rear perspective view. Shows the details of the longitudinal bars (7) that rip the aperture's wall and assist in the beginning of the rotation.

FIGURE 3 - Frontal perspective view with the option of the eye (5) substituting the halter (4) . FIGURE 4 - Shows the anchor, before its free fall releasing. It stays fastened in the anchorage line, in vertical position, sustained by a single boat, with the attack board completely positioned to the bottom of the sea. FIGURE 5 - Shows the anchor's outline, immediately after the fall and the penetration in the soil.

FIGURE 6 - Shows the anchor after its anchorage line being tensioned in the end of its rotation inside the soil, with its main plane (2) approximately 90° in relation to the anchorage line.

FIGURE 7 - Shows the alternative of removing the anchor from the inside of the soil, by the opening of the frontal cables of the halter (4) , showing only one disconnection point, because they can be in such many places and using so many different devices that is not possible to put the description of all of them. FIGURE 8 - Shows the end of the anchor's removal from the inside of the soil, by the opening of the frontal cables of the halter (4) , showing that the anchor shape and the fixing position of the rear cables is that impose the rotation of the same from the inside of the soil to its outlet .

FIGURE 9 - Shows the alternative of removing the anchor from the inside of the soil by overloading, with soil shearing . FIGURE 10 - Shows the anchor in use, in this case, holding an oil platform, showing its capacity of auto-alignment with the connected anchorage line.

FIGURE 11 - Shows three frontal view alternatives of the attack board of the anchor (1) -. FIGURE 11a - the first alternative with the plain surface practically straight;

FIGURE lib - the second alternative with the plain surface forming a dihedral, similar to that formed by airplane wings. This resource is recommended basically for heterogeneous soils where the dihedral helps the halter to stabilize the anchor in approximately 90° in relation to the tensioned anchorage line;

FIGURE lie - the last represents an alternative to the halter, where the same is substituted by an eye assembled in a superstructure. The eye height substitutes the halter, and to assist in the

^■ stabilization of the anchor 90° in relation to the tensioned anchorage line the plane must have the resource in the form of a dihedral .

Claims

1. Anchor for floating structures characterized in that it is comprised by: a) an attack board (1) located in the anchor's inferior edge; b) a predominantly plain surface (2) which constitutes the anchor's main plane; c) at least one sustentation structure for the anchor located in the plain surface (2) ; d) a plain and slant surface (6) in relation to the anchor's main plane (2) located in its superior edge, opposed to the attack board, being this plain and slant surface (6) smaller than the plain surface (2) ; and e) at least one longitudinal bar (7) located along at least one of the plain surfaces (2) and (6) in the posterior part of the anchor.

2. Anchor for floating structures, according to claim 1, characterized in that the referred sustentation structure is composed by two structural ribs (3) .

3. Anchor for floating structures, according to claim 2, characterized in that the referred structural ribs (3) are external or internal in relation to the plain surface (2) .

4. Anchor for floating structures, according to claim 1, characterized in that the referred sustentation structure is an eye, assembled in a superstructure (5) in the main plain surface (2) of the anchor to fix the anchorage line.

5. Method for the installation of an anchor for floating structures, wherein the anchor is fixed in the marine soil by vertical free fall from a height which is defined in function of the soil type, anchor's weight and required penetration to reach the loading capacity of the project of the anchorage system, characterized in that the attack board (1) of the anchor, when hits the marine soil, penetrates forming an aperture behind it and said anchor is pulled by the boat, making said anchor to initiate the ascension through the aperture and to rotate, positioning itself in a perpendicular way in relation to the anchorage line that tensions it.

6. Method for the installation of an anchor for floating structures, in accordance with claim 5, characterized in that said anchor rotates around its rotation axis after the pulling movement is initiated.

7. Method for the installation of an anchor for floating structures, in accordance with claim 5, characterized in that the plain surface (2) , after the anchor is rotated inside the soil, forms an angle of approximately 90° in relation to the tensioned anchorage line. ...

8. Method for the installation of an anchor for floating structures, in accordance with claim 4, characterized in that it dispenses alignments of the anchor in relation to the final tensioning direction of the anchorage line, wherein said anchor auto-aligns in relation to the anchorage line that tensions it .

9. Anchor for floating structures, in accordance with any preceding claims, characterized in that the loading test is conducted practically in vertical position, without the need to control the anchor alignment inside the soil with the tensioning direction of the anchorage line during the projected lifetime.

10. Method for the removal of an installed anchor for floating structures, in accordance with claims 3 to 5, characterized in that the frontal part of the halter's lines is released using conventional devices and the anchor is pulled by the support boat, making said anchor to rotate, becoming aligned with the traction of the anchorage line and being dug up from the marine soil.

11. Method for the removal of an anchor for floating structures, in accordance with claim 7, characterized in that it releases the rear part of the halter lines, using conventional devices and the anchor is pulled by the support boat, making said anchor to rotate, becoming aligned with the traction of the anchorage line and being dug up from the marine soil .

12. Method for the removal of an installed anchor for floating structures, in accordance with claims 3 to 5, characterized in that the anchorage line is pulled by a single support boat until it overcomes the resistance limit of the marine soil, making the anchor being pulled back by shearing of the same.