Folding torpedo anchor for marine moorings

Abstract

The present invention comprises a deepwater anchor that combines the high holding capacity of a plate anchor with the simple installation procedures associated with torpedo anchors. The complex embedding procedure typical for plate anchors is avoided. Instead, the anchor is installed by allowing it to free-fall through the water and then impact into the seabed. After penetrating the seabed, a pull on the anchor line causes the deployment of initially folded flukes. In their deployed positions, one or more flukes or plate-like structures extend perpendicularly toward the anchor shank, and function similar to conventional plate anchors. As a result of the fluke deployment, the holding capacity of the anchor against uplift loads is significantly greater than with a conventional torpedo anchor. Another aspect of the invention relates to the modular construction of a torpedo anchor, wherein the properties of an anchor can be adapted to the specific conditions determined at the deployment site. Still another aspect of the invention relates to fast, inexpensive procedures for installing a torpedo anchor in a desired operational environment.

Description

FIELD OF THE INVENTION

The present invention relates generally to torpedo type anchors, and in a particular, though non-limiting embodiment, to a folding torpedo anchor useful for attaching objects to a seabed and methods of deployment therefor.

BACKGROUND

Successful operation of a sea vessel in deep water often requires the vessel to be temporarily or permanently moored to an associated seabed. This is most commonly achieved by attaching mooring lines to the vessel, and then fixing the remote ends of the mooring lines to the seafloor using anchors. While sea anchors have been in use for more than 2000 years, the development of deepwater anchors was brought about by the oil & gas industry's more recent venturing into deep waters. Typical for anchors deployed in deep water is the steep angle between the anchor line and the seabed, which leads to a high uplift load being imparted to the anchor. In order to sustain these high vertical loads, deepwater anchors must be entrenched deeply into the seabed. As a consequence, installation procedures for such anchors are usually complex and require the involvement of one or more installation vessels for a considerable time period.

Driven mainly by the high cost of marine operations, the total cost associated with a mooring system installation in deep water constitutes a significant financial investment for any offshore facility requiring such operations. With the maturing of giant hydrocarbon reservoirs in shallow water, the oil & gas industry has been forced to turn toward smaller fields and toward fields located in deeper waters. The increasingly marginal economics of such deepwater fields make field development costs a particular concern, and elevates the need for anchors that can be installed quickly and inexpensively.

Rapid anchor deployment is also of importance for temporary offshore installations where a vessel remains on site for only a short time. This is especially true for regions prone to violent storms like the Gulf of Mexico, because vessels operating in such regions must regularly cope with hurricanes and other sudden, violent weather phenomena. In particular, lead times frequently prove too short to move the vessel out of the path of an approaching hurricane. In such instances the vessel is often abandoned and left to weather nature's destructive forces. History has shown that currently used temporary mooring systems are insufficient to sustain a hurricane environment. For example, in the year 2005 two hurricanes occurring in the Gulf of Mexico in rapid succession lead to numerous offshore drilling rigs to break loose from their moorings. In order to prevent such accidents, rapid-deployment anchors could be used to reinforce the mooring systems of vessels operating in hurricane regions.

DESCRIPTION OF THE PRIOR ART

The two main types of anchors currently used for deepwater applications are plate anchors and vertical piles. Different subgroups of these two main types can be distinguished primarily by their methods of installation. For example, plate anchors may be embedded by dragging them into the seafloor and are then called drag embedded plate anchors, or DEPLAs. Alternatively, the anchor can be implanted in the seafloor by a suction pile; these anchors are called suction pile embedded plate anchors or SEPLAs.

Vertical piles, on the other hand, are conventionally driven into the seafloor through hammering, while suction pile anchors use a hydrostatic pressure differential to force them into the soil. Some efforts have also been made to drive piles and anchors into the seafloor by means of explosive charges or pressurized gas but none of these technologies are currently in commercial use in the offshore industry. For example, U.S. Pat. No. 4,682,559, No. 3,032,000, No. 3,036,542, No. 3,054,123, and No. 3,291,092 provide descriptions of these efforts.

More recently, piles have been installed by being dropped into the sea and allowed to freefall, thereby impacting into the seabed. These latter types of piles are also known as torpedo anchors or deep penetrating anchors (or DPAs). An example of this approach can be found in U.S. Pat. No. 6,106,199, which discloses a pile for anchoring floating structures in deep water that features an elongated tubular body partly filled with ballast and radial fins attached to its aft. During installation, the pile is lowered into the sea to a predetermined depth and then released, thereby allowing it to descend in free fall and ultimately penetrate the sea floor. Another free-fall type anchor is described in U.S. Pat. No. 6,257,166 B1. In the '166 patent, the anchor has large flukes extending radially from the shank. In order to generate sufficient soil friction after installation, the flukes have a surface area constituting a substantial portion of the anchor's total surface area. U.S. Pat. No. 6,941,885 B2 describes another free-falling anchor with radial fins attached not only to the tail section, but also to the nose section of the anchor. It is generally understood by those of skill in the art that fins disposed on the nose section will facilitate relatively deeper entrenchment of the anchor into the seabed.

There has been, therefore, a longstanding need for an anchor that combines the simple and fast installation of torpedo anchors with the high vertical holding capacity of plate anchors. There has also been a need for a means of insuring a stable and controlled descent during free fall, even when an anchor is launched from the water surface. There has also been a need for modular anchor construction methods that allow adjustment of the anchor's ballistic properties for a specific combination of water depth and seafloor condition. There has also been a need for a design that allows fast anchor recovery and redeployment. And finally, there has long been a need for an anchor well suited for temporary moorings as well as for permanently moored facilities used in the development of marginal oil fields.

SUMMARY OF THE INVENTION

A substantially solid torpedo pile is provided, including at least a substantially solid, longitudinally elongated anchoring member, wherein the anchoring member further includes a tapered tip, a shaft, and a connecting member.

Also provided is a substantially solid torpedo pile wherein the anchoring member further includes a plurality of inter-connectible modules.

Also provided is folding torpedo pile including at least a substantially solid, longitudinally elongated anchoring member, wherein the anchoring member further comprises a tapered tip, a shaft, and a connecting member; and at least one fluke member, wherein the fluke member further includes an end portion pivotally disposed in communication with the anchoring member, so that the fluke member pivots from a first position substantially parallel to the longitudinal axis of the anchoring member to a second position substantially perpendicular to the longitudinal axis of the anchoring member.

Also provided is a folding torpedo pile wherein the anchoring member further includes a plurality of inter-connectible modules.

A method of deploying a torpedo pile in a body of water is also provided, wherein the method includes connecting the pile to a connecting member; connecting a first portion of the connecting member to a first deployment position, and connecting a second portion of the connecting member to a second deployment position, wherein the first deployment position and the second deployment position are separated by a spatial distance; releasing the first portion of the connecting member from the first deployment position while the second portion of the connecting member remains connected to the second deployment position; and allowing the pile and the first portion of the connecting member to free fall through the body of water and thereafter penetrate into a ground surface disposed beneath the body of water, while the second portion of the connecting member remains connected to the second deployment position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a folding torpedo anchor in a deployed configuration.

FIG. 2 shows a perspective view of a folding torpedo anchor in a launch configuration.

FIG. 3 shows a perspective view of a folding torpedo anchor in a recovery configuration.

FIG. 4 shows an anchor assembly including a folding torpedo anchor and a hawser chain, with trailing bodies incorporated into the hawser chain.

FIGS. 5 and 6 show a trailing body featuring a buoyancy chamber.

FIGS. 7 and 8 show a trailing body featuring a drag plate.

FIGS. 9 and 10 show a trailing body featuring radial fins.

FIG. 11 shows an assembled modular torpedo anchor.

FIG. 12 shows a disassembled modular torpedo anchor.

FIG. 13 shows another embodiment of a modular torpedo anchor.

FIG. 14 shows the folding torpedo anchor of FIG. 1 equipped an alternative penetration head.

FIG. 15 illustrates an installation method for torpedo anchors.

FIG. 16 illustrates an alternative installation method for torpedo anchors.

FIG. 17 illustrates another alternative installation method for torpedo anchors for launch from the water surface.

DETAILED DESCRIPTION OF THE INVENTION

The main embodiment of the present invention effectively combines features of a torpedo anchor with features of a plate anchor, the combination of which is unknown in the prior art. The anchor is installed by means of free fall and subsequent penetration into the seafloor following impact. Once embedded in the seafloor, a pulling force exerted on the anchor line will deploy the anchor flukes from their longitudinal launch position into an extended holding position. With the flukes deployed in a holding position, the anchor is able to generate a high resistance against uplift forces. During anchor recovery the connection of the flukes to the anchor shaft is released, which allows the flukes to rotate back into their recovery position. At that point the anchor force is greatly reduced, and the anchor can be pulled out and recovered for redeployment. The holding position, launch position, and recovery position of the anchor are depicted in FIGS. 1, 2 and 3, respectively, and are further described in detail below.

FIG. 1 is a perspective view of the claimed anchor as disposed in a holding position. The anchor comprises an anchor body 101 and a forward section member or pointed penetration head 106, while the tail section features a longitudinally extending anchor shaft 102. Pivotally attached to the anchor body are one or more flukes 104. In some embodiments, each of said flukes 104 pivots about a pivoting pin 111.

In a deployed configuration the flukes extend from the anchor body at an angle of about 90 degrees measured relative to an anchor shaft 102. At the top of the anchor a shackle 105 provides a connection means for the hawser. When a tensile mooring force is applied to the anchor at the shackle 105, the load is transferred to the shaft 102, where a sleeve 107 distributes the load to the individual flukes through one or more struts 108.

Sleeve 107 is disposed in such a manner that it can slide upwardly along the shaft 102. Downward travel, however, is limited by a load shoulder disposed along a portion of the shaft 102. Struts 108 are depicted as chains in FIG. 1, but those of skill in the art will appreciate that the struts can be replaced using a functionally equivalent design, e.g., using wire ropes or solid connecting rods with pinned ends or the like. In the depicted embodiment, connection between the struts 108 and the sleeve 107 is designed using pins 110 in a manner such that the pulling of the pins breaks the connection. At the tail section of shaft 102, the anchor further comprises one or more radially extending fins 103. The purpose of the fin(s) is to provide directional stability to the anchor during the free-fall.

FIG. 2 shows a perspective view of the anchor disposed in a launch position. As seen, the flukes 204 are folded so that they are disposed approximately parallel to the anchor's longitudinal axis. In this particular embodiment, sleeve 207 is moved into an upward position, and the tips 213 of the flukes are flared out so that when a pulling force is applied to the shackle 205 of the anchor after installation in the seabed, the flukes will deploy through the resistance in the soil. The deployment process is sometimes referred to as “keying the anchor.” In order to keep the flukes from deploying into their holding position during anchor handling and launch, they are secured by a tape 212, or a thin wire or the like. Whatever means of securing the flukes is used, it must be fragile enough to break away when the anchor is keyed.

FIG. 3 shows a perspective view of the anchor in its recovery position. During anchor recovery, the connection between the struts 308 and the sleeve 307 is broken. The connection can be broken various means, for example, by pulling the pins 310 out of sleeve 307 using a recovery cable 311. When the pins 310 are removed and a pulling force is applied to shackle 305, the flukes 304 rotate into their recovery position, and the anchor can be pulled, thereby allowing the anchor to be removed from the seabed. During anchor installation and operation, the recovery cable would generally be routed to the water surface along a length of the mooring line.

1. Anchor Stability

In order to function properly, the weight of a torpedo anchor has to be significantly larger than its buoyancy. Once an anchor is dropped into the water, it will accelerate due to its weight until the drag imparted by the water is approximately equal to its submerged weight. At that point, the anchor is considered to have reached its terminal (or equilibrium) velocity. Those of skill in the art will appreciate that while it would take an infinite amount of time for an anchor to reach its absolute equilibrium velocity, a typical torpedo anchor will reach around 99% of its terminal velocity in just a few seconds.

In order to achieve the correct penetration depth, the anchor must have proper velocity, kinetic energy, and alignment with respect to its vertical direction prior to impacting the seabed. While velocity and kinetic energy are determined by the anchor's submerged weight, hydrodynamic drag, and the desired launch elevation, the angular alignment is strongly influenced by the anchor's directional stability. Since the magnitude of the drag is also strongly dependent on the anchor's angular position during free fall, it is evident that directional stability of a torpedo anchor is of crucial importance for proper and predictable anchor installation.

Contrary to typical ship designs, the location of the center of buoyancy does not significantly affect stability. Instead, directional stability is primarily determined by the position of the center of hydrodynamic pressure relative to the center of gravity. In general, an arbitrarily shaped solid anchor in free fall is not stable in its angular position. However, another aspect of the invention contemplates that stability can be lent to the anchor while traveling through the water by using a plurality of attached fins 103 or the like disposed in mechanical communication with the anchor's tail section, as indicated in FIG. 1.

Another possibility for stabilizing the anchor is to attach one or more trailing bodies 422 and 423 using a stabilizer connecting means, for example, a cable or chain, as depicted in FIG. 4. Since the anchor will normally have a hawser chain, one possible configuration comprises the integration of trailing bodies 422 and 423 into the hawser 421, which is in turn attached to a tail section of the anchor 420. Such trailing bodies act as stabilizers when their terminal velocity is lower than the terminal velocity of the leading anchor. In this manner, the entire assembly will remain straight and under slight tension. The lower terminal velocity of a trailing body can be achieved by either a low submerged weight or by a high hydrodynamic drag. In alternative embodiments, additional radial fins are attached to the trailing bodies to improve their effectiveness in stabilizing the system.

FIG. 5 depicts a section of an exemplary trailing body having a buoyancy chamber 525. In the depicted embodiment, the body comprises a central load member 526 having pad eyes 527 and 528 disposed near both its top and bottom portions, respectively. These pad eyes are used to attach the trailing body to the hawser, so that the load member 526 acts like a chain link of the hawser chain. In this particular embodiment, the opening 529 in the bottom portion equalizes pressure inside and outside the buoyancy chamber so that it will not be crushed under hydrostatic pressure in deep water.

FIG. 6 shows a perspective view of the trailing body in FIG. 5. Another embodiment of a trailing body is shown in FIG. 7, comprising a drag plate 730, which creates a high hydrodynamic resistance for the assembly. Again, a central load member 731 featuring pad eyes 732 and 733 are used for hawser attachment. In this example of the invention, the drag plate 730 is stiffened using stiffener plates 734 that impart structural rigidity to the system. FIG. 8 shows a perspective view of the trailing body of FIG. 7.

A further embodiment of a trailing body is shown in an elevated view in FIG. 9, and in a perspective view in FIG. 10. Here, radially extending fins 935 are attached to the load member 936. Again, pad eyes 937 and 938 are used to attach the body to the anchor and the hawser. Several trailing bodies of different designs can also be used in a single anchor assembly as shown in FIG. 4. An additional advantage to incorporating a trailing body is that it serves as a means for controlling the terminal velocity of the anchor. That consideration is of greater importance when the anchor is launched from a point at or near the water surface. Another purpose of a trailing body is to limit the penetration depth of the anchor. That, again, is likely to be of greater importance when the anchor is launched from the water surface, because under such circumstances the drop height is fixed and cannot be adjusted to achieve the desired impact conditions.

2. Modular Anchor Design

In addition to the directional stability, a torpedo anchor has to achieve sufficient impact velocity and impact energy in order to be able to penetrate the seafloor to the required depth. When it is desired to use a particular anchor for different soil conditions or for different mooring loads, may be advantageous to control the impact velocity of the anchor more precisely. For a given anchor diameter and drop height, the velocity and kinetic energy of the anchor is primarily influenced by its weight. For example, changing the length of the anchor will also generally change its weight, and thereby increase the system's terminal velocity when deployed. Another parameter influencing the penetration depth is the shape of the penetration head.

Accordingly, it is contemplated in further aspects of the invention that it is advantageous to facilitate reconfiguration of a torpedo anchor so that its weight, shape, and center of gravity can be adjusted to fit the particular conditions in which it is deployed. Flexible reconfiguration can be achieved when the torpedo anchor is formed from several modular sections, as shown on FIGS. 11, 12 and 13.

In FIG. 11, a simple torpedo anchor is depicted in an assembled state, comprising nose section 1139, a mid section 1140, and a tail section 1141. FIG. 12 shows the same anchor with the modular sections disassembled. In some embodiments, the modules are mutually connected by means of an external thread 1242 disposed on one module, and a reciprocally mated internal thread 1243 disposed on a matching portion of a second module. Another embodiment of the modular design is shown in FIG. 13. Here, a tail section 1341 and a nose section 1339 are depicted as being screwed on to a stud bolt 1344, which extends through a hole formed in the mid section. In this particular embodiment, the mid section is formed by additional modules 1345 and 1346. In still another example of the modular design (see FIG. 14), it is seen that the anchor of FIG. 1 can be equipped with a modular alternative penetration head 1439.

3. Anchor Installation

Possible installation methods for the torpedo anchors claimed herein are illustrated in FIGS. 15, 16 and 17. The methods differ primarily with respect to initial launch configurations and the number of installation vessels involved. For example, FIG. 15 illustrates an installation procedure accomplished using a single vessel 1547. After casting the anchor 1548 overboard, it is lowered using an installation line 1549 to a predetermined launch position at distance 1550 from the seafloor 1552. In this position the installation line is fixed to the vessel 1547 on a first shark jaw. Then a loop 1551 is formed with the remaining length of the installation line in a manner such that said length is sufficient to allow unrestricted anchor penetration of the seafloor. After the end of the loop is connected to a second shark jaw the anchor is released by opening the first shark jaw. In order to accomplish deployment in an even more controlled manner, control buoys or the like can be attached along a length of the installation line to better control its descent. It may also be desirable to use installation lines composed of sections different weights and thicknesses, for example, a lighter line disposed above the point where a control buoy is attached, with a thicker, heavier line being disposed below the control buoy attachment point so that the descent of the anchor is not affected by the line. Those of ordinary skill in the art will appreciate that any number of lines, each having greater or lesser weights and thicknesses, can be combined to achieve the optimal controlled descent characteristics.

Another exemplary installation method in which two installation vessels are employed is illustrated in FIG. 16. Here, the installation line 1649 is attached to a hawser chain 1653 by means of a transition joint 1654, and then lowered from vessel 1647 to a predetermined drop height 1650 above the seafloor 1652. The mooring line 1655 is attached with one end to vessel 1656, with the other end being attached to the transition joint 1654 with sufficient slack in the line to facilitate deployment. The installation line 1649 is then released from the transition joint 1654. Alternatively, installation line 1649 can remain attached to the transition joint during launch, and then released from a fixed point on vessel 1647. In that case, the line 1649 would require an installation loop similar to 1551 in FIG. 15. Again, one of ordinary skill in the art will appreciate that any number of lines, each having greater or lesser weights and thicknesses, can be combined to achieve the optimal controlled descent characteristics.

Yet another example method for installing a torpedo anchor from the water surface with the entire mooring line attached is shown in FIG. 17. The advantage of this method is that it is faster than the previously described methods and involves only a single vessel. A combination of anchor and trailing bodies and/or line portions of greater or lesser weight and size are selected to achieve a desired impact velocity with the mooring line still attached to the anchor. During installation, the anchor 1745a is cast overboard and then hung from the installation vessel 1747 by its hawser chain 1753. A portion of mooring line 1755a is then paid out to form a loop 1761 long enough to allow unrestricted anchor penetration. One end 1757 of the mooring line 1755a is held above the water surface at a desired distance 1758 from the anchor's support point 1760. In this configuration, the anchor is ultimately released from the anchor support point 1760 established on the vessel 1747. A view seconds after release, the anchor reaches position 1745b with the mooring line forming an essentially upwardly bent, catenary shape 1755b. In order to facilitate the forming of the upward bend, the mooring line is supported at an intermediate point 1759, from which it is released at the same time as the anchor. A few seconds later the anchor reaches position 1745c with the associated mooring line shape 1755c, and finally impacts the seafloor 1752. If necessary, the anchor is then keyed and the mooring line secured.

The foregoing is provided for illustrative purposes only, and is not intended to describe all possible aspects of the present invention. Those of ordinary skill in the pertinent arts will appreciate that minor changes to the description, and various other modifications, omissions and additions can be made without departing from either the spirit or scope of the invention as claimed.

Claims

1. A substantially solid torpedo pile, said pile comprising:

a substantially solid, longitudinally elongated anchoring member, wherein said anchoring member further comprises a tapered tip, a shaft, and a connecting member,

wherein said tapered tip, shaft, and connecting member further comprise a plurality of inter-connectible modules.

2. (canceled)

3. The pile of claim 1, wherein said pile further comprises a trailing body stabilizing member.

4. The pile of claim 3, wherein said stabilizing member further comprises a buoy.

5. The pile of claim 3, wherein said stabilizing member further comprises a fin.

6. The pile of claim 3, wherein said stabilizing member further comprises a drag plate.

7. The pile of claim 2, wherein said pile further comprises a stabilizing member.

8. The pile of claim 7, wherein said stabilizing member further comprises a buoy.

9. The pile of claim 7, wherein said stabilizing member further comprises a fin.

10. The pile of claim 7, wherein said stabilizing member further comprises a drag plate.

11. A folding torpedo pile, said pile comprising:

a longitudinally elongated anchoring member, wherein said anchoring member further comprises a tapered tip, a shaft, and a connecting member; and

at least one fluke member, wherein said fluke member further comprises an end portion pivotally disposed in communication with said anchoring member, so that said fluke member pivots from a first position substantially parallel to the longitudinal axis of said anchoring member to a second position substantially perpendicular to the longitudinal axis of said anchoring member.

12. The pile of claim 11, wherein said anchoring member further comprises a plurality of inter-connectible modules.

13. The pile of claim 11, wherein said pile further comprises a trailing body stabilizing member.

14. The pile of claim 13, wherein said stabilizing member further comprises a buoy.

15. The pile of claim 13, wherein said stabilizing member further comprises a fin.

16. The pile of claim 13, wherein said stabilizing member further comprises a drag plate.

17. The pile of claim 12, wherein said pile further comprises a stabilizing member.

18. The pile of claim 17, wherein said stabilizing member further comprises a buoy.

19. The pile of claim 17, wherein said stabilizing member further comprises a fin.

20. The pile of claim 17, wherein said stabilizing member further comprises a drag plate.

21. A method of deploying a torpedo pile in a body of water, said method comprising:

connecting said pile to a connecting member;

connecting a first portion of said connecting member to a first deployment position, and connecting a second portion of said connecting member to a second deployment position, wherein said first deployment position and said second deployment position are separated by a spatial distance;

releasing said first portion of said connecting member from said first deployment position while said second portion of said connecting member remains connected to said second deployment position; and

allowing said pile and said first portion of said connecting member to free fall through said body of water and thereafter penetrate into a ground surface disposed beneath said body of water, while said second portion of said connecting member remains connected to said second deployment position.

22. The method of claim 21, wherein said spatial distance between said first deployment position and said second deployment position comprises approximately 4 percent of the water depth through which said pile is allowed to free fall prior to penetrating into said ground surface.