CRAWL-DOWN INSTALLATION METHOD FOR A TENSION LEG PLATFORM

BACKGROUND

A Tension-leg Platform (TLP) is an offshore structure comprising a hull with net buoyancy, secured to the seabed by pretensioned vertical tendons. The tendons are secured to the seabed or any other body of water floor with anchors.

The tension in the tendons counteract the hull's net buoyancy, which stabilizes the hull. Traditional TLPs are installed with the following sequence:

- 1. Tendons are pre-installed to anchors in the seabed at the installation site.
- 2. The TLP hull is towed to the installation site.
- 3. Ballast is added to the TLP hull to lower it to a draft sufficiently deep to connect to the pre-installed tendons.
- 4. Jacks may be used to apply additional pre-tension to the tendons.
- 5. The TLP hull is connected to the tendons.
- 6. Ballast is removed to increase the static tension in the tendons.

This standard installation method relies on the TLP hull having sufficient free-floating stability so that it does not capsize while being lowered to its installation draft. In some cases, temporary buoyancy cans are attached to the hull to provide the necessary free-floating stability. These temporary buoyancy cans are removed after the TLP hull is connected to the tendons.

Tendons are used to anchor a variety of tension leg platforms on bodies of water. Examples of platforms include, but are not limited to, platforms including radially extending arms from a center column (for example, platforms 100 and 100(2) FIGS. 12A and 12C), platforms that include diagonally extending arms from a single column that are connected via a triangular or square pontoon that connect the lower sections of the arms (for example, platform 100(1) in FIG. 12B). Other tension leg platforms may include multiple columns, such as four columns, and a square pontoon connecting the four columns at lower sections thereof (for example, platform 100(3) in FIG. 12D). Tension leg platforms have tendon porches where the tendons attach to the platform.

Accordingly, given the plurality of platforms that are anchored via tendons, an improved method for installing or removing tendons from platforms that are anchored on bodies of water is needed.

SUMMARY

In one embodiment, a method for installing or removing tendons from a tension leg platform which comprises three or more tendon porches, the method comprising:

- grasping each of three or more extended tendons by a respective one jacking tool on one tendon porch, wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon.

In one embodiment, a method for installing tendons to a tension leg platform with three or more tendon porches, the method comprising:

- a) connecting one or more tendon extension piece(s) to an end of a tendon forming an extended tendon, and placing the extended tendon on a tendon porch, wherein the jacking tool grasps the tendon extension piece; and
- b) repeating step a) for at least three tendons; and
- c) when each of three or more extended tendons have been placed within a respective jacking tool on a respective tendon porch, three or more of the jacking tools crawl down the one or more tendon extension piece(s) of the extended tendon placed therein to tension the respective extended tendon while lowering the platform to submerge the tendon porches below a water surface.

In one embodiment, the tendon extension piece is a rigid pipe section.

In one embodiment, the method comprises adding ballast to the tension leg platform while the jacking tools are lowering the platform.

In one embodiment, the platform comprises a primary ballast tank and an installation ballast tank, the method further comprising filling the primary ballast tank before the installation ballast tank.

In one embodiment, the method comprises removing ballast from the installation ballast tank after the platform is at the installation depth.

In one embodiment, the method comprises towing the platform to the installation site in a waterplane stabilized condition.

In one embodiment, a sum of lengths of the tendon and the one or more tendon extension piece(s) is equal to or greater than a depth from a tendon anchor to the water surface.

In one embodiment, while the platform is floating on the surface of the water, the tendon is connected to a first pipe section forming an extended tendon, the extended tendon is grasped by the jacking tool, the jacking tool then lowers the extended tendon, and a second pipe section is connected to an upper end of the first pipe section while in the jacking tool, and lowered, and subsequent pipe sections are connected and lowered in series until a length of the extended tendon is equal to or greater than a depth from a tendon anchor to the surface of the water.

In one embodiment, the method comprises attaching a bottom end of the tendon to an anchor and using the jacking tool to apply tension on the extended tendon while the jacking tool crawls down the pipe sections.

In one embodiment, the method comprises using the jacking tool to lower the platform to the installation depth, and removing a pipe section after the jacking tool has crawled below a connection between adjacent pipe sections.

In one embodiment, the method comprises monitoring a tension of the extended tendon during lowering of the platform.

In one embodiment, a method for installing tendons to a tension leg platform with three or more tendon porches, the method comprising:

- a) connecting a tendon extension piece to an end of a tendon to form an extended tendon;
- b) placing the extended tendon on a tendon porch, wherein the jacking tool grasps the tendon extension piece;
- c) the jacking tool crawls up the tendon extension piece, and tendon extension pieces are added to the extended tendon in series until a length of the extended tendon is sufficient to attach the tendon to an anchor;
- d) for each of at least three tendons, steps a) through c) are performed;
- e) after each of the at least three tendons has been attached to a respective anchor, each jacking tool crawls down the series of tendon extension pieces connected thereto to lower the platform; and
- f) after lowering the platform to the installation draft, each of the tendons is locked to the respective one of the tendon porches.

In one embodiment, a method for removing tendons and a tension leg platform with three or more tendon porches, the method comprising:

- a) installing a jacking tool on at least three tendon porches;
- b) connecting one or more tendon extension pieces to an end of a tendon to create an extended tendon;
- c) repeating step b) for at least three tendons;
- d) grasping the tendon extension pieces of each of three or more extended tendons by a respective one jacking tool on one tendon porch,
- e) unlocking each of the tendons from the respective tendon porches;
- f) wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon; and
- g) three or more of the jacking tools crawl up the one or more tendon extension piece(s) of the extended tendon placed therein while the platform rises.

In one embodiment, a method for removing tendons and a tension leg platform with at least three tendon porches, the method comprising:

- a) installing a jacking tool on at least three tendon porches;
- b) connecting one or more tendon extension piece(s) to an end of a tendon to create an extended tendon;
- c) repeating step b) for at least three tendons;
- d) three or more of the jacking tools crawl up the tendon extension piece of each extended tendon while the platform rises, and tendon extension pieces are continually added to each of the extended tendons until a length of extended tendon is sufficient for the platform to reach the surface of the water.

In one embodiment, the method comprises disconnecting an extended tendon from a respective anchor, and the jacking tool crawls down the tendon extension piece thereby raising the disconnected extended tendon.

In one embodiment, the method comprises disconnecting a tendon extension piece of the disconnected extended tendon after the jacking tool passes by a connection between two tendon extension pieces.

In one embodiment, the method further comprises adding ballast to the platform to reduce pre-tension to avoid overloading the jacking tools.

In one embodiment, the method comprises removing ballast from the platform to allow the platform to rise.

In one embodiment, the method comprises monitoring a tension of the tendon during removing the ballast from the platform.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagrammatical illustration of a step in a method of installing a tension leg platform;

FIG. 2 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 3 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 4 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 5 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 6 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 7 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 8 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 9 is a diagrammatical illustration of a of step in a method of installing a tension leg platform;

FIG. 10 is a flow diagram of one embodiment of a method of installing tendons for a tension leg platform;

FIG. 11 is a flow diagram of one embodiment of a method of removing tendons for a tension leg platform;

FIG. 12A is a diagrammatical illustration of a tension leg platform;

FIG. 12B is a diagrammatical illustration of a tension leg platform;

FIG. 12C is a diagrammatical illustration of a tension leg platform; and

FIG. 12D is a diagrammatical illustration of a tension leg platform.

DETAILED DESCRIPTION

In one embodiment, a TLP is designed to support offshore wind turbines. In one embodiment, the TLP comprises a central hull and a plurality of arms extending radially from the central hull. It is to be understood that the particular TLP platform in the figures is for illustrating aspects of the disclosure which are applicable to other types of TLP platforms. For example, FIGS. 12A, 12B, 12C, and 12D illustrate TLP platforms which may be utilized in the present disclosure. Therefore, it is to be further understood that the disclosure can apply to any platform that uses tendons for anchoring the platform in or on a body of water.

FIG. 1 shows a diagrammatical illustration of a TLP 100. A tendon porch 120 is an area where a tendon is attached to the platform. Generally, a tendon porch 120 will be located at the end of an arm 124. However, this disclosure is applicable for installing and removing tendons regardless of the location of the tendon porch on the platform or the configuration of the arms. When a platform is being stabilized by tendons, generally, the platform will include three tendons at a minimum.

In one embodiment of a TLP, the central hull supports a wind turbine and wind turbine tower.

When the TLP 100 is installed at the design draft (depth), the tendon arms 124 are completely submerged and the central column intersects the waterline. By nature of its configuration, the TLP hull is unstable in the free-floating condition, when its arms are submerged. Therefore, during installation and removal, the platform is stabilized when transitioning between free-floating draft and installation draft.

The installation method presented herein describes an installation and removal method that uses jacking tools to stabilize, raise, and lower the platform during installation and removal of tendons. In particular, this disclosure relates to methods for installing or removing tendons from a tension leg platform which comprises three or more tendon porches. The step in the methods comprises grasping each of three or more extended tendons by a respective one jacking tool on one tendon porch, wherein the platform is being stabilized by at least three jacking tools each applying tension on the respective extended tendon.

A tension leg platform 100 can be prepared for installation to anchors on the sea floor in any body of water by placing a jacking tool 102 on each of the tendon porches 120. The jacking tool 102 is installed at any time before the installation of the platform 100. The jacking tool 102 can be installed at the quay. The jacking tool 102 can be installed on the platform 100 when the platform is at the installation site or any time before reaching the installation site.

FIG. 1 is a diagrammatical illustration of a tug of opportunity 114 being used to wet-tow the platform 100 to the installation site. While at the installation site, as seen in FIG. 2, secondary station keeping tugs 118 can connect to the platform 100 using bridles attached to the platform hull. A multi-purpose support vessel (MPSV) 116 equipped with remote-operated vehicles and crane(s) can serve as the installation vessel.

Fiber tendons 104 are yet not attached to the anchors on the seafloor when the platform 100 arrives at the installation site. In one embodiment, the fiber tendons 104 are carried on the MPSV 116. The fiber tendons 104 can be deployed from reels or open top containers, depending on the tendon length and installation vessel capabilities. Fiber tendons are used as an example in this disclosure. However, other materials can be used for the tendons based on the particular application.

Referring to FIG. 2, a series of operations are performed to connect one or more tendon extension pieces 108 to the fiber tendon 104. Individual tendon extension pieces 108 are shorter in length than a fiber tendon 104. Individual tendon extension pieces 108 can be rigid. In the disclosure, rigid pipe sections are described as examples of tendon extension pieces. A tendon extension piece 108 is capable of being grasped by the jacking tool 102 so that the jacking tool 102 can move up and down (“crawl”) on the tendon extension piece 108. The aim of adding pipe sections 108 is to create an “extended tendon” comprising both the fiber tendon 104 and one or more tendon extension pieces 108. The extended tendon has a length allowing the extended tendon (including tendon and pipe sections) to extend from the anchor at the seafloor to the tendon porch 120 at the surface. Pipe sections are used as an example of tendon extension pieces in this disclosure. However, other materials can be used for tendon extension pieces based on the particular application. In this disclosure, an extended tendon refers to the fiber tendon 104 and the one or more of the pipe sections 108.

Generally, the fiber tendon 104 will remain attached to the platform 100 in the final installation, while the pipe sections 108 are temporary and are used in the installation (and removal) process. The pipe sections 108 can be removed after the installation process is completed. It is to be understood that other components can be used to connect the ends of the fiber tendon 104 to the anchor and to the pipe section 108.

In one embodiment, the first pipe section 108 is connected to the end of tendon 104 prior to being deployed by the crane. For example, the first pipe section 108 can be connected onshore or on the MPSV.

After connecting the first pipe section 108, the extended tendon (including the tendon 104 and pipe section 108) is hoisted using the crane as illustrated in FIG. 2. In this step, the crane brings the pipe section 108 with the tendon 104 over to the tendon porch and loads the pipe section into the open jacking tool 102. The jacking tool 102 can be configured to accept the pipe sections 108 from the top or side of the jacking tool 102. Then, the jacking tool 102 is engaged in order to hold the pipe section 108 in place. In one embodiment, the jacking tool 102 on the tendon porch 120 is opened remotely to accept the first pipe section 108. The process can be repeated for each of the jacking tools 102 on each of the tendon porches 120.

As described, the aim of connecting pipe sections to the fiber tendons is to build an extended tendon of sufficient length to connect between an anchor on the seafloor that reaches the jacking tool 102 on the tendon porch while the platform 100 is still on the water surface. After a first pipe section 108 is connected to the fiber tendon 104, additional pipe sections can be connected in series to the first pipe section. A description of the operation of a single jacking tool 102 will be provided with the understanding that each of the jacking tools 102 operates similarly.

FIGS. 3 and 4 are diagrammatical illustrations showing the process of adding pipe sections 108 to build the extended tendon. In one embodiment, the jacking tool 102 lowers the extended tendon (comprising fiber tendon 104 and first pipe section 108) until the top end of the pipe section 108 is engaged by a bottom section of the jacking tool 102. In this disclosure, “crawling” is used to refer to movement of the jacking tool 102 with respect to the pipe sections, and such movement can occur in both directions. It can be seen that when the extended tendon is not attached to an anchor, movement of the jacking tool 102 with respect to the pipe sections causes the extended tendon to move up and down while the platform remains stationary. When the extended tendon is attached to an anchor, movement of the jacking tool 102 with respect to the pipe sections can lower or raise the platform 100.

After the jacking tool 102 crawls to the top of the first pipe section, a second pipe section is brought to the jacking tool 102 by the crane. The jacking tool 102 engages the subsequent pipe section 108, and the subsequent pipe section 108 is disconnected from the crane. The jacking tool 102 is actuated to make the connection between a top of the lower pipe section to the bottom of the subsequent pipe section. Here, various connection means can be employed to make connections between pipe sections. The jacking tool 102 lowers the extended tendon (including the fiber tendon 104 and pipe sections 108) to accept the next pipe section.

The procedure is repeated until the extended tendon is fully assembled to reach the anchor. FIG. 4 shows, for example, five pipe sections as tendon extension pieces 108 connected to the fiber tendon 104 comprising an extended tendon 112. The described process can be repeated for each of the jacking tools 102 on each of the tendon porches 120. The assembly of additional extended tendons 112 can take place simultaneously or consecutively or a combination.

After the final pipe section is connected to the extended tendon 112, the jacking tool 102 lowers the extended tendon 112 (including the fiber tendon 104 and pipe sections 108) to a pre-install position. The platform 100 is still on or near to the surface of the water. A remote-operated vehicle 128 can assist to ensure proper positioning and provide visual feedback.

A series of operations are performed to connect the bottom end of the fiber tendon 104 of each extended tendon 112 to an anchor 110 on the seafloor. Here, various connection means to attach the end of the fiber tendon 104 to the anchor 110 can be employed. In one embodiment, the remote-operated vehicle 128 is used to assist in positioning of the bottom connector. In one embodiment, the jacking tool 102 is used to slowly lower the extended tendon 112 to the anchor 110 by moving along the assembled pipe sections 108.

FIG. 5 is a diagrammatical illustration showing the tendons 104 of each extended tendon 112 being attached to anchors 110 on the seafloor. The pipe sections 108 are still connected to the top ends of the tendons 104. Thereafter, tension can be applied to the extended tendons 112 (including fiber tendon 104 and pipe sections 108) using the jacking tool 102.

In FIG. 6, the jacking tool 102 begins crawling down the series of pipe sections 108, thus applying tension on the anchored extended tendon 112. As the jacking tool 102 crawls down the pipe sections 108, the length of the extended tendon 112 (including fiber tendon 104 and pipe sections 108) between the anchor and the jacking tool 102 is decreased, thereby applying tension.

Where a plurality of extended tendons 112 are attached to the platform 100, each jacking tool 102 is operated to work together. Each jacking tool 102 moves along the respective extended tendon 112 to apply the maximum tension (T_0max). (T_0max) is a calculated value that allows for dynamic loads from wind and waves without exceeding the jacking system, tendon, and anchor capacity at all drafts (depths).

Once (T_0max) is reached on each tendon, the platform 100 is considered to be “jack stabilized.” The platform 100 is still near to or at the water surface. The station keeping vessels and tug can be disconnected from the hull.

Thereafter, an optional process of ballasting the platform 100 can be performed. In one embodiment, the platform 100 includes a primary ballast tank 126 occupying the lower hull 132 and may extend into the inner portion of the arms 124. In one embodiment, ballasting is done by free-flooding the tank, i.e., pumps are not used, for example. The rate of flooding can be monitored and controlled using remotely actuating valves.

In one embodiment, each jacking tool 102 is crawling down the pipe sections while the ballast tank is being flooded, forcing the platform 100 to begin descending below the water surface. In one embodiment, the MPSV can remove the pipe sections once a jacking tool passes by a connection between two pipe sections. FIG. 6 is a diagrammatical illustration of the submerged platform 100 showing the process of the jacking tool 102 crawling down one pipe section 108a, while a second pipe section 108b is removed and lifted to the surface by the MPSV.

During the ballasting and the crawling down process, the tendon tension is monitored to remain between a minimum value required to provide adequate stability and a maximum value to avoid overloading the jacking tools and connected components by controlling the ballasting rate and the crawling down rate.

In one embodiment, with the tendon porches 120 submerged, the pipe sections 108 are removed from the extended tendons in series as the jacking tool 102 passes by a connection between two pipe sections, for example, with assistance by the remote-operated vehicles 128.

Once the primary ballast tank 126 is filled to the pre-determined ballast amount, ballasting of the installation ballast tank 130 can begin if an installation ballast tank is provided in the platform. An installation ballast tank 130 can be provided on the platform in the column above the lower hull 132.

The jacking tool 102 continues to crawl down the pipe sections of the extended tendon in order to keep the tension within allowable amounts. The jacking tool 102 crawling down the extended tendon and ballasting of the installation ballast tank 130 continues until the installation draft (depth) is reached. At this depth, the jacking tool 102 has crawled down to the final pipe extension. Then, the tendon 104 can be connected to the tendon porch 120. The top end connector of the fiber tendon 104 can be engaged and the fiber tendon 104 is locked off. In one embodiment, the final pipe extension (i.e., the first pipe extension connected to the fiber tendon) cannot be removed until the tendon has been locked-off; for example, with a top end connector.

The fiber tendons 104 extend from the anchors 110 to the platform arms at the installation depth without the need for pipe sections. FIG. 7 is a diagrammatical illustration of the submerged platform 100 at the installation depth showing the fiber tendons 104 attached to the tendon porches 120 at the ends of the platform arms. In one embodiment, the jacking tool 102 is used for leveling the platform 100. The fiber tendon 104 length is predetermined for the installation depth so that the top of the fiber tendon 104 rests in the tendon porch 120 once the platform 100 is submerged to the installation draft (depth). The jacking tool 102 can be disengaged from the tendons 104 fully transferring the tension load to the tendon porch 120. The platform 100 is stabilized by the tendons 104 thereafter.

FIG. 8 is a diagrammatical illustration showing the removal of the jacking tools 102. However, the jacking tools 102 can remain on the tendon porches 120 after the installation of the platform 100.

FIG. 9 is a diagrammatical illustration showing the platform 100 at the installation depth with the tendons 104 stabilizing the platform 100, and the jacking tools are removed. The water within the installation ballast tank 130 in the column above the lower hull can be emptied to increase the tension to the design pre-tension.

FIG. 10 is a flow diagram showing the sequence of steps for a method of installing tendons 104 on a tension leg platform 100 in accordance with one embodiment. In step 202, a tendon extension piece 108, for example a pipe section, is connected to an end of the tendon 104, to make an “extended tendon 112” as illustrated in FIG. 2. From step 202, the method enters step 204.

In step 204, the extended tendon 112 is placed within a jacking tool. FIG. 3 illustrates the tendon extension piece 108 being grasped by one of the jacking tools 102. A tendon 104 has been attached to the tendon extension piece 108. From step 204, the method enters step 206.

In step 206, the jacking tool 102 crawls up the tendon extension piece 108. As the jacking tool 102 crawls up the tendon extension piece 108, it is understood that the tendon 104 is in the water and is being lowered as the jacking tool 102 is crawling up the tendon extension piece 108. When the jacking tool 102 reaches the top of the tendon extension piece 108, another extension piece 108 is added to increase the length of the extended tendon as illustrated in FIG. 4. The process of adding tendon extension piece one after the other is continued until the length of the extended tendon is sufficient to attach the tendon 104 to an anchor 110.

Step 208 is used to signify that Steps 202, 204, and 206 are performed for each of the tendons that are used to anchor the platform. A tension leg platform 100 is understood to require at least three tendons 104 to be stabilized when at the installation depth. The construction of each extended tendon 112 may be performed simultaneously, or the construction of each extended tendon can be performed sequentially. Once the extended tendons 112 are assembled and are connected to respective anchors 110, the process of lowering of the platform may begin.

In step 210, each jacking tool 102 now begins to crawl down the tendon extension pieces 108 of the respective extended tendon 112 which begins tensioning the extended tendon. Once the maximum tension is reached, the platform 100 becomes jack-stabilized. Thereafter, the jacking tools 102 continue to crawl down the tendon extension pieces 108 to reach the installation depth. Once the jacking tool 102 crawls below a tendon extension piece 108, the extension piece 108b may be removed. As previously described, the platform may take on ballast during the lowering step.

In step 212, after the platform 100 reaches the installation depth, each of the tendons 104 is locked to the tendon porch 120 to secure the platform 100 via the tendons 104.

Thereafter, in one embodiment, the jacking tools 102 can remain on the tendon porches 120. Alternatively, the jacking tools 102 can be removed after the installation is complete. In either case, a method of removing the tendons 104 from the installed platform 100 generally follows a similar sequence of steps; however, in reverse order.

After the platform is installed in step 212, the tendons 104 may be removed from the platform by the sequence of steps in FIG. 11.

In step 214, the platform 100 is at the installation depth, the tendons 104 are attached to anchors 110, and jacking tools 102 are placed on the tendon porches 120. The removal process includes connecting a tendon extension piece 108 to the tendon 104 to make an extended tendon 112, and the jacking tool 102 can grasp onto the tendon extension piece 108.

Step 216 is for performing step 214 for each of the tendons 104 on the platform 100.

In step 218, each of the jacking tools 102 crawls up the tendon extension piece 108 as the ballast is removed from the platform 100 allowing the platform to rise. As the jacking tools 102 continue to crawl up, tendon extension pieces 108 are continually added to the extended tendons 112 until the platform 100 reaches the surface.

In step 220, the tendons 104 are disconnected from their anchors 110. In this step, since the platform 100 is no longer connected to anchors, the platform requires station keeping by suitable vessels.

In step 222, once the tendons 104 are disconnected from their anchors 110, the jacking tools 102 can be used to raise the extended tendons 112 by reversing direction when the platform 100 is on the surface. The tendon extension pieces 108 can be removed as they are brought up to the jacking tool 102.

One embodiment of the installation method may include combinations of the following steps.

- 1. At the assembly quay, jacking tools 102 can be installed by securing them rigidly to the platform's tendon porches 120. Alternatively, the jacking tools 102 can be installed after the platform leaves the quay and is towed offshore to the installation site, or at any time before reaching the installation site.
- 2. The platform 100 is towed from the quay to the offshore site in a free-floating, waterplane-stabilized condition.
- 3. A tendon 104 with rigid pipe section(s) 108, i.e., the extended tendon 112, is lifted from a support vessel onto the tendon porch 120. The jacking tool 102 is closed around the rigid pipe section 108 and grasped by the jacking tool 102 to hold the extended tendon 112 in place.
- 4. Pipe sections 108 are connected to the top of the pipe section(s) already connected to the fiber tendon 104 until the length of the tendon and pipe sections, i.e., the extended tendon 112, is long enough to reach from the anchor 110 to the jacking tool 102.
- 5. The extended tendon 112 is lowered by the jacking tool 102 to the depth required to connect the extended tendon 112 to a pre-installed anchor 110.
- 6. The fiber tendon 104 is connected to the anchor 110.
- 7. This process is repeated for creating and installing at least three extended tendons 112.
- 8. Once the extended tendons 112 are connected to anchors 110, the jacking tools 102 begin to “crawl down” the extended tendons 112 by applying tension to the extended tendons 112 by pushing down on the platform 100, increasing its draft and upward buoyancy force. This transitions the platform 100 from being waterplane-stabilized to being jack-stabilized (stabilization results from the jacking tools applying tension in the extended tendons 112).
- 9. As the jacking tools 102 are crawling down the pipe sections 108 of the extended tendons 112, seawater ballast may be added to the platform 100 to counter the increased buoyancy force thus reducing the required magnitude of force that the jacking tools 102 have to apply to lower the platform 100.
- 10. Once the platform 100 is lowered to its installation draft, the fiber tendons 104 are locked-off on the platform porches 120. This transitions the platform 100 from being jack-stabilized to being tendon-stabilized.
- 11. The temporary rigid pipe sections 108 are removed.
- 12. The jacking tools 102 are removed.
- 13. If excess seawater ballast was used to manage jacking loads, it may be removed to achieve the final design static tendon tension.

The removal sequence is the reverse of the installation sequence.

The installation method of the tension leg platform 100 includes advantages over previous installation methods. During installation, the platform 100 is stabilized by jacking tools 102 that connect rigidly to the platform 100 and that grasp extended tendons 112 connected to anchors 110. When the extended tendons 112 are connected to anchors 110, the jacking tools 102 apply forces parallel to the extended tendon 112 to lower and raise the platform 100.

When the extended tendon 112 is not connected to its anchor 110, the jacking tool 102 applies forces parallel to the extended tendon 112 to lower and raise the extended tendon 112 by crawling up and down the pipe sections 108.

The method enables the installation of a platform 100 that would otherwise become unstable if lowered in the free-floating condition. The method uses the extended tendons to stabilize a free-floating platform during lowering.

The jacking tools 102 are designed to function while submerged.

The jacking tools 102 grasp temporary rigid pipe sections 108 connected to the end of the fiber tendon 104.

An extended tendon 112, with rigid pipe section(s) 108 is lifted from a support vessel onto the tendon porch 120.

The jacking tool 102 is closed around the rigid pipe section 108 to grasp and hold the extended tendon 112 in place.

Pipe sections 108 are connected to the top of the pipe section(s) already connected to the fiber tendon 104 until the length of the tendon and pipe sections, i.e., the extended tendon 112 is long enough to reach from the anchor 110 to the jacking tool 102.

The extended tendon 112 is lowered and raised by the jacking tool 102 to achieve the depth required to connect the fiber tendon 104 to a pre-installed anchor 110 and to recover the tendon 104 during removal.

The extended tendon 112 is connected to the anchor 110 while suspended from the jacking tools 102.

Once all necessary extended tendons 112 are connected to anchors 110, the jacking tools 102 begin to crawl down the extended tendons 112 by applying tension to the extended tendons 112 by applying a downward force on the platform 100, increasing its draft and upward buoyancy force. This transitions the platform 100 from being waterplane-stabilized to being jack-stabilized (stabilization results from the jacks applying tension in the tendons).

As the jacking tools 102 are crawling down the extended tendons 112, seawater ballast may be added to the platform 100 to reduce the required magnitude of force that the jacking tools 102 have to apply to lower the platform 100. Ballasting is optional and may make the process more cost effective.

Once the platform 100 is lowered to its installation draft, the fiber tendons 104 are locked-off on the platform tendon porches 120. This transitions the platform 100 from being jack-stabilized to being tendon stabilized.

After lowering the platform 100, the temporary rigid pipe sections 108 are removed.

Representative embodiments may include, but are not limited to the following.

In one embodiment, a method for installing or removing tendons 104 from a tension leg platform 100 which comprises tendon porches 120, the method comprising:

- grasping each of three or more extended tendons 112 by a respective one jacking tool 102 on one tendon porch 120, wherein the platform 100 is being stabilized by at least three jacking tools 102 each applying tension on the respective extended tendon 112.

In one embodiment, a method for installing tendons to a tension leg platform 100 with tendon porches 120, the method comprising:

- a) connecting one or more tendon extension piece 108 to an end of a tendon 104 forming an extended tendon 112, and placing the extended tendon 112 on a tendon porch 120, wherein the jacking tool 102 grasps the tendon extension piece 108; and
- b) repeating step a) for at least three tendons 104; and
- c) when each of three or more extended tendons 112 have been placed within a respective jacking tool 102 on a respective tendon porch 120, three or more of the jacking tools 102 crawl down the one more tendon extension piece 108 of the extended tendon 112 placed therein to tension the respective extended tendon 112 while lowering the platform 100 to submerge the tendon porches 120 below a water surface.

The tendon extension piece 108 is a rigid pipe section.

The method comprises adding ballast to the tension leg platform 100 while the jacking tools 102 are lowering the platform 100.

The platform 100 comprises a primary ballast tank 126 and an installation ballast tank 130, the method further comprising filling the primary ballast tank before the installation ballast tank.

The method comprises removing ballast from the installation ballast tank 130 after the platform 100 is at the installation depth.

The method comprises towing the platform 100 to the installation site in a waterplane stabilized condition.

The sum of lengths of the tendon 104 and the one or more tendon extension pieces 108 is equal to or greater than a depth from a tendon anchor 110 to the water surface.

While the platform 100 is floating on the surface of the water, the tendon 104 is connected to a first pipe section 108 forming an extended tendon 112, the jacking tool 102 then lowers the extended tendon 112, and a second pipe section 108 is connected to an upper end of the first pipe section while in the jacking tool 102, and lowered, and subsequent pipe sections 108 are connected and lowered in series until a length of the extended tendon 112 is equal to or greater than a depth from a tendon anchor 110 to the surface of the water.

The method comprises attaching a bottom end of the tendon 104 to an anchor 110 and using the jacking tool 102 to apply tension on the extended tendon 112 while the jacking tool 102 crawls down the pipe sections 108.

The method comprises using the jacking tool 102 to lower the platform 100 to the installation depth, and removing a pipe section 108 after the jacking tool 102 has crawled below a connection between adjacent pipe sections 108.

The method comprises monitoring a tension of the extended tendon 112 during lowering of the platform 100.

In one embodiment, a method for installing tendons 104 to a tension leg platform 100 with tendon porches 120, the method comprising:

- a) connecting a tendon extension piece 108 to an end of a tendon 104 to form an extended tendon 112;
- b) placing the extended tendon 112 on a tendon porch 120, wherein the jacking tool 102 grasps the tendon extension piece 108;
- c) the jacking tool 102 crawls up the tendon extension piece 108, and tendon extension pieces 108 are added to the extended tendon 112 in series until a length of the extended tendon 112 is sufficient to attach the tendon 104 to an anchor 110;
- d) for each of at least three tendons 104, steps a) through c) are performed;
- e) after each of the at least three tendons 104 has been attached to a respective anchor 110, each jacking tool 102 crawls down the series of tendon extension pieces 108 connected thereto to lower the platform 100; and
- f) after lowering the platform 100 to the installation draft, each of the tendons 104 is locked to the respective one of the tendon porches 120.

In one embodiment, a method for removing tendons 104 and a tension leg platform 100 with tendon porches 120, the method comprising:

- a) installing a jacking tool 102 on at least three tendon porches 120;
- b) connecting one or more tendon extension piece 108 to an end of a tendon 104 to create an extended tendon 112;
- c) repeating step b) for at least three tendons 104;
- d) grasping the tendon extension piece 108 of each of three or more extended tendons 112 by a respective one jacking tool 102 on one tendon porch 120,
- e) unlocking each of the tendons 104 from the respective tendon porches 120;
- f) wherein the platform 100 is being stabilized by at least three jacking tools 102 each applying tension on the respective extended tendon 112; and
- g) three or more of the jacking tools 102 crawl up the one more tendon extension piece 108 of the extended tendon 112 placed therein while the platform 100 rises.

In one embodiment, a method for removing tendons 104 and a tension leg platform 100 with at least three tendon porches 120, the method comprising:

- a) installing a jacking tool 102 on at least three tendon porches 120;
- b) connecting one or more tendon extension piece(s) 108 to an end of a tendon 104 to create an extended tendon 112;
- c) repeating step b) for at least three tendons 104;
- d) three or more of the jacking tools 102 crawl up the tendon extension piece 108 of each extended tendon 112 while the platform 100 rises, and tendon extension pieces 108 are continually added to each of the extended tendons 112 until a length of extended tendon 112 is sufficient for the platform 100 to reach the surface of the water.

The method comprises disconnecting an extended tendon 112 from a respective anchor 110, and the jacking tool 102 crawls down the tendon extension piece 108 thereby raising the disconnected extended tendon 112.

The method comprises disconnecting a tendon extension piece 108 of the disconnected extended tendon 112 after the jacking tool 102 passes by a connection between two tendon extension pieces 108.

In one embodiment, the method further comprises adding ballast to the platform to reduce pre-tension to avoid overloading the jacking tools.

The method comprises removing ballast from the platform 100 to increase stabilizing pre-tension to allow the jacking tools 102 to raise the platform 100.

The method comprises monitoring a tension of the tendon 104 during removing the ballast from the platform 100.

While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

CRAWL-DOWN INSTALLATION METHOD FOR A TENSION LEG PLATFORM

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