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Title:
A FIXED TO BOTTOM JACKET SYSTEM AND METHOD OF INSTALLATION FOR AN OFFSHORE STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2017/035606
Kind Code:
A1
Abstract:
A jacket system (10) enables construction and installation of multiple jackets Ji utilising a small number of modularised jacket portions. A method is also disclosed for installing a jacket provided with suction piles using a jack up rig where the jacket has a footprint greater than a drillable area of the jack up. A method of delivering the jacket with suction piles to an installation location involves holding a volume of their in the suction piles to provide buoyancy and wet towing the jacket to the installation location.

Inventors:
FIELD DAVID (AU)
Application Number:
PCT/AU2016/050839
Publication Date:
March 09, 2017
Filing Date:
September 05, 2016
Export Citation:
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Assignee:
ICON ENG PTY LTD (AU)
International Classes:
E21B15/02; B63B21/27; B63B35/44; E02B17/02; E04H12/34
Foreign References:
US20020081157A12002-06-27
US6488446B12002-12-03
US3362170A1968-01-09
US3633369A1972-01-11
US3815372A1974-06-11
Attorney, Agent or Firm:
GRIFFITH HACK (AU)
Download PDF:
Claims:
Claims

1 . A method of installing a fixed to bottom jacket system comprising:

lowering a complete jacket provided with one or more suction piles, or a portion of the jacket provided with one or more suction piles, to a seabed using a lifting mechanism of a jack up vessel or derrick barge.

2. The method according to claim 1 wherein the jacket system comprises a

complete jacket including the one or more suction piles.

3. The method according to claim 2 comprising wet towing the complete jacket to the jack up rig and using at least one of the suction piles to hold a volume of air to provide buoyance during wet towing of the jacket.

The method according to claim 3 comprising attaching one or more buoyancy tanks to the jacket spaced from the suction piles to provide buoyancy to the jacket during the wet tow at spaced locations along the length of the jacket.

The method according to claim 2 or 3 comprising using each of at least two of the suction piles to hold a volume of air to provide buoyancy during wet towing of the jacket.

The method according to claim 5 comprising using each of two of the suction piles and three buoyancy tanks to provide buoyance during wet towing of the jacket.

The method according to claim 5 comprising using each of three of the suction piles and two buoyancy tanks to provide buoyance during wet towing of the jacket.

The method according to any one of claims 4 to 7 comprising coupling the jacket to the drilling derrick of the jack up rig and lifting the jacket a height sufficient to enable the suction piles to clear the sea bed. 9. The method according to claim 8 comprising flooding the suction piles previously used to provide buoyancy to orientate the jacket substantially vertically.

The method according to claim 9 comprising before, during or after flooding suction piles, using the drilling derrick of the jack up rig to lift the jacket a heii sufficient to enable the suction piles to clear the sea bed.

The method according to claim 10 comprising progressively flooding the buoyancy tanks while using the jack up rig to progressively lower the jacket that the suction piles land on the sea bed.

12. The method according to claim 1 1 comprising fully flooding the buoyancy tanks.

The method according to any one of claims 9 to 1 1 comprising operating a pump system to pump water from the suction piles when landed on the sea bed to cause the one or more suction piles to be installed into the seabed.

The method according to any one of claims 1 -13 wherein the lifting mechanism is drilling derrick of a jack up drilling rig and the jacket system has a footprint of an area greater than a drillable area of the jack up rig.

A method of installing a fixed to bottom jacket system using a jack up drilling rig having a drilling derrick where the jacket system has a footprint of an area greater than a drillable area of a jack up drilling rig comprising:

forming a complete jacket or a portion of the jacket with one or more suction piles;

lowering the jacket or the portion of the jacket provided with one or more suction piles to a seabed using the drilling derrick of the jack up drill rig; and operating a pump system to pump water from the piles to cause the one or more suction piles to be installed into the seabed.

The method according to claim 15 comprising using the drilling derrick to lift th jacket or a portion of the jacket provided with one or more suction piles from a vessel.

17. The method according to claim 15 or 16 comprising upending the complete jacket or a portion provided with the one or more suction piles floating near the jack up drilling rig using the drilling derrick of the jack up drilling rig prior to or in the course of lowering the jacket or jacket portion to the seabed.

The method according to claim 16 or 17 wherein lowering the complete jacket or jacket portion provided with the one or more suction piles comprises venting air from the suction piles to enable controlled sinking of the jacket or jacket portion through a water plane.

The method according to any one of claims 1 -14 comprising providing the one or more suction piles as a sliding suction pile system having a plurality of sliding suction piles, and a template portion having a respective pile sleeve for each sliding suction pile, the sleeves being connected together; the method further comprising lowering the template portion to the seabed and providing a sliding suction pile in each sleeve wherein a respective sliding suction pile is able to slide through the corresponding sleeves when the pumping system is operated.

The method according to claim 19 comprising lowering the sliding suction piles into respective sleeves after the template portion has landed on the seabed.

21 . The method according to claim 20 comprising releasably locking respective suction piles in corresponding sleeves prior to lowering the template portion to the seabed, wherein the template portion together with the suction piles are lowered together as a unit to the seabed.

22. The method according to claim 20 or 21 comprising removing the template portion from the suction piles after installation of the suction piles.

The method according to claim 20 or 21 comprising fixing the template portion to the suction piles after installation of the suction piles.

The method according to claim 23 comprising fixing at least one other jacket portion to the template portion. 25. The method according to any one of claims 15 to 23 comprising providing the jacket as a plurality of portions constituted by the jacket portion provided with the one or more suction piles and at least one or more other jacket portions.

The method according to claim 25 comprising providing one of the other jacket portions comprise a one piece or a two piece tower portion having a plurality of parallel legs.

The method according to claim 26 comprising providing the two piece tower portion as a bottom piece that when supported by the suction piles in a constructed jacket lies wholly below the water plane, and an upper piece that when supported by the suction piles in a constructed jacket connects to the lower portion and extends above the water plane.

The method according to claim 26 comprising providing the two piece tower portion as a bottom piece that when supported by the suction piles in a constructed jacket extends from below to above the water plane, and an upper piece that connects to the lower portion and lies wholly above the water plane.

The method according to any one of claims 26 to 28 comprising providing a further jacket portion as a battered portion and wherein the battered potion installed prior to installation of the tower portions.

A sliding suction pile system comprising:

a. a plurality of suction piles; and

b. a template portion having a respective pile sleeve for each suction pile, the sleeves being connected together;

c. the suction piles and the sleeves being arranged to enable the suction piles to slide through respective sleeves independently of each other during installation.

The system according to claim 30 wherein the template portion is fixed to the suction piles subsequent to installation of suction piles.

32. The system according to claim 30 wherein the template portion is lifted from the installed suction piles to enable reuse. The system according to any one of claims 30 to 32 wherein each suction pile is provided with an open lower end and a valve mechanism at an opposite end enabling a controllable venting of air from the suction pile.

The system according to any one of claims 30 to 33 comprising a releasable locking device enabling the suction piles to be releasably locked within a respective sleeve.

A method of installing suction piles in a seabed comprising:

i. lowering to a seabed a template portion having a plurality of sleeves which are connected together;

ii. providing a suction pile in each sleeve wherein a respective suction pile is able to slide through the corresponding sleeves; and

iii. pumping water from within the piles.

36. The method according to claim 35 comprising lowering the suction piles into respective sleeves after the template portion has landed on the seabed.

37. The method according to claim 35 comprising releasably locking respective suction piles in corresponding sleeves prior to lowering the template portion to the seabed, wherein the template portion together with the suction piles are lowered together as a unit to the seabed.

38. The method according to any one of claims 35 to 37 wherein the lowering is performed using a drilling derrick of a jack up drilling rig.

39. The method according to any one of claims 35 to 38 comprising removing the template portion from the suction piles after installation of the suction piles.

40. The method according to any one of claims 35 to 39 comprising fixing the template portion to the suction piles after installation of the suction piles. 41 . A method of delivering a fixed to bottom jacket provided with one or more suction piles to an offshore installation location, the method comprising holding a volume of air in one or more of the suction piles to provide buoyancy to the jacket when in a body of water; and wet towing the jacket in the body of water to the offshore installation site using the sealed volume of air to provide buoyancy to the jacket or jacket portion during the wet towing.

The method according to claim 41 comprising attaching one or more buoyancy tanks to the jacket spaced from the suction piles to provide buoyancy to the jacket during the wet tow at one or more locations along the length of the jacket.

The method according to claim 42 comprising using each of at least two of the suction piles to hold a volume of air to provide buoyancy during wet towing of the jacket.

44. The method according to claim 43 comprising using the two suction piles and two or more buoyancy tanks to provide buoyance during wet towing of the jacket.

45. The method according to claim 43 comprising using each of three of the suction piles and two or more buoyancy tanks to provide buoyance during wet towing of the jacket. 46. A method of installing a fixed to bottom jacket having one or more suction piles in a seabed comprising:

delivering the fixed to bottom jacket to an installation location using the method according to any one of claims 41 -45; and

supporting the jacket a height sufficient to enable the suction piles to clear the sea bed.

The method according to claim 46 comprising at least partially flooding th suction piles previously used to provide buoyancy to orientate the jacket substantially vertically.

48. The method according to claim 47 comprising before, during or after flooding suction piles, using a jack up vessel or a derrick barge to lift the jacket a height sufficient to enable the suction piles to clear the sea bed.

49. The method according to claim 47 or 48 comprising progressively flooding the buoyancy tanks while progressively lowering the jacket so that the suction piles land on the sea bed.

50. The method according to claim 49 comprising fully flooding the buoyancy tanks. 51 . The method according to claim 49 or 50 comprising operating a pump system to pump water from the suction piles when landed on the sea bed to cause the one or more suction piles to be installed into the seabed.

Description:
A FIXED TO BOTTOM JACKET SYSTEM AND METHOD OF INSTALLATION FOR AN OFFSHORE STRUCTURE

Technical Field

A fixed to bottom jacket system and method of installation are disclosed. The system and method are particularly suited for, but not limited to, application in the oil and gas industry to facilitate the installation of an offshore production platform. Background Art

Fixed to bottom offshore platforms may be constructed and installed using various techniques depending on factors such as the size of the platform and the lift capacity and reach of a barge and/or rig used for the installation. Irrespective of the installation technique the platform and its jacket must be transported to a designated installation location. If installation is to be via a floating crane barge then the barge will also itself sail or tow the platform and jacket to the installation location. If a jack up drilling rig is used for the installation then the platform and jacket may be transported either by: simple barge, heavy lift vessel; or self-floating.

When installing a platform using a jack up drilling rig, the lift capacity and geometry of the rig will itself determine the weight and geometry of a platform that it can install. Generally only relatively small platforms can be installed using a jack up drilling rig primarily due to the cantilever geometry of the jack up drilling rig, the rated load carrying capacity of the drill rig and it's equipment, the water depth range of the jack up drilling rig and the requirement of an air gap or space between the underside of the jack up drilling rig and the water plane.

In deep water, or with heavy topside weight, the jacket or topside weight can exceed the lift capacity of the jack up drilling rig. Further the geometry of the jacket, which must be fixed to the seabed, necessarily needs to increase in size at greater depth in order to resist the overturning moment caused by wave action. The base can be fixed by driven or drilled piles. However when the base of the jacket becomes overly large installation using a jack up rig becomes problematic. This is because the rig cantilever cannot access directly over the location of the piles to be installed. As a result battered piles are often needed. Battered piles are sometimes difficult to install and carry a greater risk in operational terms to the installation of vertical piles.

A further issue facing the oil and gas industry is the duplication of effort in the design of platform jackets. While there has been an industry want for standardisation of jacket and platform design to date it is believed that this is problematic due to the large number of variables that require consideration in jacket designs such as the number of wells, deck weight, water depth, wave height and soil type. The above references to the background art do not constitute an admission that the art forms part of the common general knowledge of a person of ordinary skill in the art. Further the above references are also not intended to limit the application of the system and method as disclosed herein. Summary of the Disclosure

In one aspect there is disclosed a method of installing a fixed to bottom jacket system comprising:

lowering a complete jacket, or a portion of the jacket, provided with one or more suction piles to a seabed using lifting mechanism of a jack up vessel or derrick barge.

In one embodiment the jacket system comprises a complete jacket including the one or more suction piles. In one embodiment the method comprises wet towing the complete jacket to the jack up rig and using at least one of the suction piles to hold a volume of air to provide buoyance during wet towing of the jacket.

In one embodiment the method comprises attaching one or more buoyancy tanks to the jacket spaced from the suction piles to provide buoyancy to the jacket during the wet tow at spaced locations along the length of the jacket.

In one embodiment the method comprises using each of at least two of the suction piles to hold a volume of air to provide buoyancy during wet towing of the jacket. ln one embodiment the method comprises using each of two of the suction piles and at least two buoyancy tanks to provide buoyancy during wet towing of the jacket.

In one embodiment the method comprises using each of three of the suction piles and two buoyancy tanks to provide buoyance during wet towing of the jacket.

In one embodiment the method comprises coupling the jacket to the drilling derrick of the jack up rig and lifting the jacket a height sufficient to enable the suction piles to clear the sea bed.

In one embodiment the method comprises flooding the suction piles previously used to provide buoyancy to orientate the jacket substantially vertically.

In one embodiment the method comprises before, during or after flooding suction piles, using the drilling derrick of the jack up rig to lift the jacket a height sufficient to enable the suction piles to clear the sea bed.

In one embodiment the method comprises progressively flooding the buoyancy tanks while using the jack up rig to progressively lower the jacket so that the suction piles land on the sea bed.

In one embodiment the method comprises fully flooding the buoyancy tanks.

In one embodiment the method comprises operating a pump system to pump water from the suction piles when landed on the sea bed to cause the one or more suction piles to be installed into the seabed.

In one embodiment the lifting mechanism is a drilling derrick of a jack up drilling rig and the jacket system has a footprint of an area greater than a drillable area of the jack up rig.

In a second aspect there is disclosed a method of installing a fixed to bottom jacket system using a jack up drilling rig having a drilling derrick where the jacket system has a footprint of a size greater than a drilling area of a jack up drilling rig comprising: forming a jacket or a portion of the jacket with one or more suction piles; lowering the jacket or the portion of the jacket provided with one or more suction piles to a seabed using the drilling derrick of the jack up drill rig; and

operating a pump system to pump water from the piles to cause the one or more suction piles to be installed into the seabed.

In an embodiment of either aspect the method may comprise using the drilling derrick to lift the jacket or a portion of the jacket provided with one or more suction piles from a vessel. In an alternate embodiment of either aspect the method may comprise upending the jacket or a portion provided with the one or more suction piles floating near the jack up drilling rig using the drilling derrick of the jack up drilling rig prior to or in the course of lowering the jacket or jacket portion to the seabed. In an embodiment of either aspect lowering the jacket or jacket portion provided with the one or more suction piles comprises venting air from the suction piles to enable controlled sinking of the jacket or jacket portion through a water plane.

In an embodiment of either aspect the method may comprise operating the jack up drilling rig to skid the suction piles on the seabed prior to operating the pump system.

In an embodiment of either aspect the method may comprise providing the jacket or the portion of the jacket provided with one or more suction piles as a sliding suction pile system having a plurality of suction piles and a template portion having a respective pile sleeve for each suction pile wherein the sleeves are connected together; the method further comprising lowering to the template portion to the seabed and providing a suction pile in each sleeve wherein a respective suction pile is able to slide through the corresponding sleeves when the pumping system is operated. In one embodiment the method may comprise lowering the suction piles into respective sleeves after the template portion has landed on the seabed.

In an alternate embodiment the method may comprise releasably locking respective suction piles in corresponding sleeves prior to lowering the template portion to the seabed, wherein the template portion together with the suction piles are lowered together as a unit to the seabed.

In one embodiment the method may comprise removing the template portion from the suction piles after installation of the suction piles.

In an alternate embodiment the method may comprise fixing the template portion to the suction piles after installation of the suction piles.

In one embodiment the method may comprise fixing at least one other jacket portion to the template portion.

In one embodiment the method may comprise providing the jacket as a plurality of portions constituted by the jacket portion provided with the one or more suction piles and at least one or more other jacket portions.

In one embodiment the method may comprise providing one of the other jacket portions comprise a one piece or a two piece tower portion having a plurality of parallel legs. In one embodiment the method may comprise providing the two piece tower portion as a bottom piece that when supported by the suction piles in a constructed jacket lies wholly below the water plane and an upper piece that when supported by the suction piles in a constructed jacket connects to the lower portion and extends above the water plane.

In one embodiment the method may comprise providing the two piece tower portion as a bottom piece that when supported by the suction piles in a constructed jacket extends from below to above the water plane, and an upper piece that connects to the lower portion and lies wholly above the water plane.

In one embodiment the method may comprise providing a further jacket portion as a battered portion and wherein the battered potion is installed prior to installation of the tower portions. In a third aspect there is disclosed a sliding suction pile system comprising: a plurality of suction piles; and

a template having a respective pile sleeve for each suction pile, the sleeves being connected together;

the suction piles and the sleeves being arranged to enable the suction piles to slide through respective sleeves independently of each other during installation. This enables the suction piles to be installed to different depths while maintaining the sleeves and thus the mechanical structure in a common horizontal plane. In some embodiments the template portion can then be fixed to the piles for example by grouting or swaging, and subsequently receive a jacket either of a type disclosed herein or otherwise. However in an alternate embodiment the template may be lifted from the installed suction piles and reused. A jacket either of a type disclosed herein or otherwise can then be lowered onto the installed suction piles and fixed thereto for example by grouting, swaging or ball grip. In one embodiment of the sliding suction pile system each suction pile is provided with open lower end and a valve mechanism at an opposite end enabling a controllable venting of air from the suction pile. This enables control of the rate of decent/sinking of a suction pile as well as control of the buoyancy of the system while being lowered to a seabed.

In one embodiment the sliding suction pile system comprises for each suction pile a releasable locking device which is operable to lock a suction pile within a respective sleeve. This facilitates an installation method where suction piles and the suction piles are lowered as a unit to the seabed. Once the unit has landed the locking device is released enabling each suction pile to be independently installed into the seabed sliding through it respective sleeve to its installation depth. The installation depths for the suction piles may or may not be the same.

In fourth aspect there is disclosed a method of installing suction piles in a seabed comprising:

lowering to a seabed a template having a plurality of sleeves which are connected together;

providing a suction pile in each sleeve wherein a respective suction pile is able to slide through the corresponding sleeves; and

pumping water from within the piles. ln one embodiment the method comprises lowering the suction piles into respective sleeves after the template portion has landed on the seabed. However in an alternate embodiment the method comprises locking respective suction piles in corresponding sleeves prior to lowering the template portion to the seabed, wherein the template portion together with the suction piles are lowered together as a unit to the seabed. In either of the above two alternate embodiments the lowering may be performed using a drilling derrick of a jack up drilling rig. In one embodiment a method further comprises removing the template portion from the suction piles after installation of the suction piles. In an alternate embodiment the method may comprise fixing the template portion to the suction piles after installation of the suction piles. In this embodiment the template portion may be used as a base for fixing a jacket or jacket portion in accordance with the above disclosed fixed to bottom jacket system. In a fifth aspect there is provided an adaptable fixed to bottom jacket system capable of enabling installation in a range of water depths comprising:

a tower portion comprising a plurality of parallel legs and composed of one or more first bays, one second bay and one third bay all of the bays having the same transverse perimeter wherein when the tower is incorporated in a jacket of the fixed to bottom jacket system all of the first bays lie below the water plane, the second bay spans the water plane and the third bay lies wholly above the water plane bay and the bays are arranged end to end to form the legs of the tower portion and wherein the first and third bays each have the same height and the second bay is of height that is less than, or greater than, or equal to the height of the first bays.

In one embodiment the tower portion is constructed in one piece or in two pieces wherein when constructed as two pieces the pieces comprise either (a) a bottom piece that comprises the all first bays and the second bay, and an upper piece which comprises the third bay; or (b) a bottom piece that comprises the all first bays and an upper piece which comprises the second bay and third bay. ln one embodiment the jacket system comprises a battered portion wherein the tower portion is configured to be installed onto of the battered portion and the battered portion is arranged for fixing to the seabed.

In one embodiment the jacket system comprises one or more suction piles enabling fixing the tower portion or the battered portion to the seabed.

In one embodiment the suction piles comprise part of a sliding suction pile system according to the third aspect.

In a sixth aspect there is disclosed a method of delivering a fixed to bottom jacket provided with one or more suction piles to an offshore installation location, the method comprising holding a volume of air in one or more of the suction piles to provide buoyancy to the jacket when in a body of water; and

wet towing the jacket in the body of water to the offshore installation site using the sealed volume of air to provide buoyance to the jacket or jacket portion during the wet towing. In one embodiment the method comprises attaching one or more buoyancy tanks to the jacket spaced from the suction piles to provide buoyancy to the jacket during the wet tow at one or more locations along the length of the jacket.

In one embodiment the method comprises using each of at least two of the suction piles to hold a volume of air to provide buoyancy during wet towing of the jacket.

In one embodiment the method comprises using the two suction piles and two or more buoyancy tanks to provide buoyance during wet towing of the jacket. In one embodiment the method comprises using each of three of the suction piles and two or more buoyancy tanks to provide buoyance during wet towing of the jacket.

In a seventh aspect there is disclosed a method of installing a fixed to bottom jacket having one or more suction piles in a seabed comprising:

delivering the fixed to bottom jacket to an installation location using the method according to the sixth aspect; and supporting the jacket a height sufficient to enable the suction piles to clear the sea bed.

In one embodiment the method comprises at least partially flooding the suction piles previously used to provide buoyancy to orientate the jacket substantially vertically.

In one embodiment the method comprises before, during or after flooding suction piles, using a jack up rig or a derrick barge to lift the jacket a height sufficient to enable the suction piles to clear the sea bed. In one embodiment the method comprises progressively flooding the buoyancy tanks while progressively lowering the jacket so that the suction piles land on the sea bed.

In one embodiment the method comprises fully flooding the buoyancy tanks. In one embodiment the method comprises operating a pump system to pump water from the suction piles when landed on the sea bed to cause the one or more suction piles to be installed into the seabed.

Brief Description of the Drawings

Notwithstanding any other forms which may fall within the scope of the method and system as set forth in Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of an embodiment of the disclosed fixed to bottom jacket system;

Figure 2a is a front elevation of a first jacket which may be incorporated in the disclosed jacket system;

Figure 2b is a cross-section view of the jacket shown in Figure 2a;

Figure 3 is a front elevation of a second jacket that may be incorporated in embodiments of the disclosed jacket system;

Figure 4 is a front elevation of a third jacket that may be incorporated in embodiments of the disclosed jacket system;

Figure 5 is a front elevation of a fourth jacket that may be incorporated in embodiments of the disclosed jacket system; Figure 6 is a front elevation of a fifth jacket that may be incorporated in embodiments of the disclosed jacket system;

Figure 7 is a front elevation of a sixth jacket that may be incorporated in embodiments of the disclosed jacket system;

Figure 8a is a front elevation of a first battered jacket portion that may be incorporated in embodiments of the disclosed jacket system;

Figure 8b is a cross-section view of the first battered jacket portion shown in Figure 8a;

Figure 9 is a front elevation of a seventh jacket that may be incorporated in embodiments of the jacket system;

Figure 10 is a front elevation of an eighth jacket that may be incorporated in embodiments of the jacket systems;

Figure 1 1 is a front elevation of a second form of battered jacket portion that may be incorporated in the disclosed jacket system;

Figure 12 is a front elevation of a third battered jacket portion that may be incorporated in the disclosed system;

Figure 13a is a front elevation of a ninth jacket that may be incorporated in the disclosed jacket system;

Figure 13b is an enlarged view of a template portion of the jacket disclosed in Figure 13a;

Figure 13c is a plan view of the template portion shown in Figure 13b;

Figure 14a is a front elevation of an a tenth jacket incorporated in embodiments of the disclosed jacket system;

Figure 14b is an enlarged front elevation view of a template portion of the jacket portion in Figure 14a;

Figure 14c is a plan view of the template portion shown in Figure 14b;

Figure 15a is a schematic representation of a sliding suction pile system which may be incorporated in the disclosed jacket system and method of installation;

Figure 15b is an isometric view of components of the sliding suction pile system shown in Figure 15a;

Figure 15c is a schematic representation of the sliding suction pile system with a plurality of piles installed into a seabed;

Figure 15d is a schematic representation of an alternate method of installation of piles of the sliding suction pile system;

Figure 16 is a plan view of part of a jack up drilling rig showing footprint of a drilling area of the rig in comparison to and a footprint of suction plies that may be used in the disclosed jacket system or sliding suction pile system;

Figure 17 is a representation of one step in an embodiment of the disclosed method of installing a complete jacket, in which the jacket is on a wharf being connected to a heavy lift vessel for lifting into the water;

Figure 18 shows the jacket of Fig 17 after being lifted into the water and subsequently disconnected from the heave lift vessel.;

Figure 19 shows the jacket connected to a towing tug and an escort vessel;

Figure 20 illustrates the jacket being towed to an installation site;

Figure 21 is a plane elevation showing the jacket at the installation site with the top of the jacket below a cantilevered drilling derrick of a jack up rig;

Figure 22 is a side view of the jacket in the same relationship with the jack up rig in Figure 21 but with a hook line and flooding line form the jack up rig connected to the jacket;

Figure 23 shows the jacket being righted by the jack up rig;

Figure 24 shows the jacket vertical and partially supported by the jack up rig and by buoyancy provided by the suction piles and buoyancy tanks but lifted from the sea bed;

Figure 25 shows the jacket with the suction plies in an intermediate stage of being sucked into the sea bed;

Figure 26 shows the jacket with its suction piles at their final installation depth in the sea bed; and

Figure 27 shows a side view of one stage in an alternate method of installing a complete jacket.

Detailed Description of Specific Embodiments

Figure 1 depicts an embodiment of the disclosed fixed to bottom offshore platform jacket system 10. The system 10 enables for example the construction and installation of multiple jackets J1 - J10 (herein after referred to in general as "jacket Ji" in the singular or "jackets Ji" in the plural). Each of the jackets Ji is shown with a

corresponding topsides T.

In broad terms, the system 10 enables the selection of separate jackets or jacket portions which can be transported in an assembled or disassembled state to an installation site and installed by use of a jack up vessel or derrick barge. The term "jack up vessel" is used in this specification and claims to refer to a jack up vessel having a crane, draw works or other lifting mechanism to facilitate the lifting of a heavy object, and includes for example a jack drill up rig. A jack up rig is a type of jack up vessel which has a drilling derrick vessel usually mounted on an extendable and retractable cantilever. The drilling derrick has a draw works to provide the ability of lift heavy objects such as a completions riser. The individual jackets or jacket portions can be made in a small range of different dimensions and/or designs which when put together in various different combinations enable the construction of jackets which can be used over a wide range of water depths and seabed conditions.

As is evident from Figure 1 there is a high degree of standardisation of design in the jackets Ji. Indeed as will be described in greater detail below many of the jackets Ji are fabricated from different combinations of a small number of generally standardised jacket portions.

In this specific embodiment of the system 10 the jackets Ji are configured for installation at the following water depth:

J1 - 10 metres

J2 - 20 metres

J3 - 30 metres

J3.5 - 35 metres

J4 - 40 metres

J5 - 50 metres

J6 - 60 metres

J7 - 70 metres

J8 - 80 metres

J9 - 90 metres

J10 - - 100 metres

It is however to be stressed these are examples only and the system 10 is not limited to jackets Ji being specifically designed only for the above mentioned water depths or only for 5m or 10m incremental changes in depth. Looking at the jackets Ji in more detail and in particular jackets J1 - J3.5 in Figs 2-5 the following common features and/or similarities in design become apparent. Each of the jackets J1 - J3.5 is formed from a plurality of bays Ba, Bs and Bb (hereinafter referred to in general as "bays B"). Each of the bays except bays Bs has the same height, width and depth. In this particular embodiment the height is 7,500mm with the width and depth each being 5000mm. Thus each of the bays B has the same transverse perimeter.

The bays Bb in an installed jacket Ji are below the water plane 14 (i.e. under water); the bay Ba in an installed jacket is above the water plane 14 (i.e. above water) and would support a topsides T; and the bay Bs spans the water plane 14 connecting the bays Ba to bays Bb. Each jacket Ji has a single bay Ba, a single bay Bs and one or more bays Bb. The bays Bb may also be considered or called first bays, the bay Bs may also be considered or called a second bay, and the bay Ba may also be considered or called a third bay.

In the illustrated embodiment each of the bays B has four faces F1 , F2, F3 and F4 (herein after referred to in general as "face F" in the singular or "faces F" in the plural) arranged to form a square perimeter and four leg portions Lp1 -Lp4. The leg portions Lp of each bay B stack on top of each other to form four corresponding jacket legs L1 , L2, L3 and L4 (herein after referred to in general as "leg L" in the singular or "legs L" in the plural). But in an alternate embodiment the bays B may have three faces arranged to form a triangular perimeter and thus the corresponding jacket Ji would have three legs. Successive bays B are denoted by mutually adjacent leg nodes N. A leg node N is the location where the legs L of a jacket join with one or more braces 16 or 18. The braces 16 extend perpendicular to the legs L while the braces 18 extend diagonally. The braces 16 and 18 together with a corresponding leg L may form well known joint configuration such as for example a K joint, T joint or Y joint. The leg nodes N in a common plane notionally demark one bay B from the next.

The bays Bb in this embodiment have either one diagonal brace 18 per face F (for example the second, third and four from bottom bays in jackets J3 and J3.5 shown in Figures 4 and 5); or two diagonal braces 18 arranged to form a cross brace structure per face F (for example the bottom bays in jacket J1 and J3 and the bottom two bays in jacket J2).

The bays Ba in this embodiment have a single brace 18 per face F for each of the jackets J1 -J10. However in alternate embodiments the bays Ba may have two diagonal braces 18 arranged to form a cross brace structure per face F. In either event the bays Ba also differ from the bays Bb by the inclusion of mounting structures 20 for the topsides T.

The bay Bs is arranged so that when the corresponding jacket Ji is installed on the seabed 24 the bay Bs spans the water plane 14 between the bay Ba and the underwater bays Bb. However one distinction between the bay Bs and the bays Ba and Bb is that the bay Bs may vary in height in accordance with the intended water depth of installation of the corresponding jacket. Nevertheless facilitating the difference in height of the bay Bs is very simple as it requires only the custom cutting of four lengths of pipe 28 that extend between the leg nodes N of the immediately adjacent bays Ba and Bb.

Each of the jackets J1 - J3.5 is manufactured as one piece or two pieces and transported to an installation site. When in two pieces the pieces are either: (a) a bottom piece comprising all the bays Bb as one piece, and an upper piece comprising the bays Bs and Ba as one piece; or (b) a bottom piece comprising all the bays Bb and the bay Bs as one piece, and an upper piece comprising the bay Ba. Indeed all of the jackets or jacket portions described herein with parallel legs (i.e. jackets/jacket portions J1 -J5, Ja and Jb) can be manufactured and transported as one piece or two pieces in the same manner as described in relation to jackets J1 -J3.5.

At the installation site four piles are installed into the seabed at locations to coincide with the legs of the jackets Ji. A length of each of the piles extends upwardly from the seabed. The jackets Ji are lowered so that the extending parts of the piles are received within the legs L1 -L4. Alternatively the jacket Ji (and if in two pieces the bottom piece of the jacket Ji) is installed first and the piles are installed through the jacket legs.

Referring to Figures 6 and 7 the jackets J4 and J5 have a very similar structure to the jackets J1 - J3.5 in that each comprises a plurality of bays Bb, a bay Bs and a bay Ba arranged as a four legged structure. However the jackets J4 and J5 differ from jackets J1 - J3.5 by the addition of foundation bays Bf at the base of the jackets. The bays Bf are of the same construction and design as the bays Bb provided with cross braces on each face. The bays Bf are provided to increase the area of the base of the jacket which is fixed to the seabed 24. The need for this arises as the height of the jackets Ji increases to accommodate for increased overturning moment created by waves and sea currents.

The jackets J1 - J5 are structured and configured so that they may by themselves be fixed to the seabed and support a corresponding topsides T. When the jacket is required for a water depth greater than approximately 50 metres the disclosed system 10 proposes the jackets J6 - J10 made from a combination of jacket portions which are separately fabricated and transported in a fully or partially assembled state to an installation site dependent on the lifting capacity of the jack up drilling rig 12. The jackets J1 -J5 and indeed all jackets J1 -Jx described herein have a tower portion T which consists of, or comprises, a plurality (usually three or four) parallel legs L1 -L3 or L4. The tower portions T are made from a number of the bays B.

When the jacket is transported in a partially assembled state the separate components are individually constructed into a complete jacket at the installation site. Initially a lowermost part of the jacket is lowered to the seabed and fixed to the seabed.

Subsequently the remaining portions of the jacket are inter-fitted for example by use of stabbing rods/pins and fixed together by one of a plurality of means such as grouting, hydraulic swagging or ball grab. With the present configuration of the jackets the jacket portions, when being inter-fitted, are stacked coaxially on top of each other.

In the event that the jacket is transported as a complete (i.e. one piece) assembly, and thus is within the lifting capacity of the jack up vessel it is lifted from a barge, or if floated, it is lifted so as to be upended and lowered to the seabed at the installation location.

Both of the jackets J6 and J7 are provided with the same battered lowermost or foundation portion 30 shown in Figures 8a and 8b. The jacket portion 30 is commonly used for the installation and construction of jackets J6 and J7 of water depth of about 60 metres and 70 metres respectively. The portion 30 has four battered legs 32 which taper inwardly from a jacket base 34 to an upper end 36 of jacket portion 30. (In an alternate embodiment the portion 30 may have three legs.) A plurality of diagonal braces 38 in a diamond configuration extend between and are connected to the legs 32. The upper end 36 of the jacket portion 30 is provided with four (only two shown) upright posts 40. Four piling posts 42 are connected to the outside of the legs 32.

The portion 30 can be fixed to the seabed 24 by installing a plurality of piles into the seabed at locations that correspond to the locations of the piling posts 42. When the jacket portion 30 is lowered to the seabed the piles are stabbed into the piling posts 42. Alternately the portion 30 can be first lowered to the installation location and the piles installed through the pipes 42. In either case the portion 30 can be fixed to the piles by a plurality of means such as but not limited to grouting, hydraulic swaging or ball grab.

The jacket J6 comprises both the portion 30 shown in Figures 8a and 8b, and an upper jacket portion Ja shown in Figure 9. The jacket portion Ja has the same basic design and configuration as the jacket J1 - J5. In particular the jacket Ja comprises three bays Bb which are formed end to end, a water plane bridging bay Bs and a upper bay Ba. The bays Bb and Ba are identical to those of the previously described jackets J1 - J5. The bay Bs is also of the same basic design as the bays Bs of the earlier jackets J1 - J5. As with the previous corresponding bays Bs the pipes 28 of the bays Bs are custom cut to meet the designed water depth to ensure that the topsides T supported on the jacket J6 is at a fixed or designed height above the water plane 14.

When constructing the jacket J6 the jackets portions 30 and Ja are transported to an installation site. The jacket portion Ja may be in one or two pieces as described above in relation to jackets J1 -J5. The jacket portion 30 is installed and fixed to the seabed and subsequently the jacket portion Ja is lowered onto and fitted with the installed portion 30. In this regard the leg portions Lp1 -Lp4 in the lower most bay Bb of the jacket Ja are stabbed onto the posts 40. Subsequently the components can be fixed together by grouting or by a mechanical process such as swaging, or use of a ball grab. Thereafter, a topside T can be lowered onto the upper bay Ba.

In order to construct and install the jacket J7 once again one will use the jacket portion 30 as shown in Figure 8a but this time with a second or alternate jacket portion Jb shown in Figure 10. The jacket portion Jb in Figure 10 is in essence identical to the jacket J3.5 shown in Figure 5 with the exception that the lower most bay Bb of jacket has a single diagonal brace 18 per face F and the bay Bs for the jacket portion Jb is or at least may be of a different height to that of the corresponding bay for the jacket J3.5. As the jacket portion Jb has one extra bay Bb than the jacket portion Ja the resultant constructed jacket J7 is higher or taller by the height of the additional bay Bb. The construction and installation of the jacket J7 is the same as that as described for in relation to the jacket J6. The jackets J8 and J9 are constructed in an essentially identical manner to that described for in relation to jackets J6 and J7. Both the jackets J7 and J8 share a common battered foundation portion 60 depicted in Figure 1 1 . The portion 60 is of the same general configuration of the portion 30 but scaled up in size. For example the total height of the jacket portion 30 may be in the order of about 34.4 metres whereas the jacket portion 60 may have an overall height of 44.4 metres. It should be understood that when the jackets J6 - J9 and indeed J10 are constructed their total overall height is less than the combined overall height of the individual jacket components. This is because of the inter-fitting of the components and in particular the receipt of the posts 40 into the legs L1 -L4 of the jacket portions Ja or Jb as the case may be.

The battered foundation portion 60 comprises legs 32, braces 38, and pipes 40 similar to that of the portion 30 the only exception being the greater length of the legs 32 and the addition of further braces 38. The portion 30 also has a wider base as is required with increased water depth to provide sufficient resistance to the overturning moment generated by wave and current action.

The last jacket J10 in the disclosed system 10 comprises a battered foundation jacket portion 90 shown in Figure 12. The portion 90 is again of the same general configuration of the portions 30 and 60 but of yet again increased overall height and base width. The increased height is provided by using legs 32 of greater length than for the corresponding smaller portions 30 and 60. Commensurate with the increase in height the battered portion 90 has additional braces 38 to provide structural strength. It should be noted that an upper section 100 end of each of the portions 30, 60 and 90 is of identical shape, size and configuration. Therefore irrespective of which battered foundation portion 30, 60 or 90 is used, no modification or change is required to the immediately upper jacket portion to inter-fit with and fix to the battered portion 90.

From the above description of system 10 it should be recognised that with a minimal number of essentially uniform constructed parts, jackets of different lengths to accommodate different water depths can be constructed by simply selecting the separate components required so that the overall jacket or the topsides T is at a desired or required height above the water plane 14. Accordingly inventory can be trimmed and standardisation of design and construction achieved.

The Figures 13a - 13d depict a variation of the system 10. These Figures depict jacket J1 1 which comprises a plurality of jacket parts or portions. The jacket portions comprise a jacket portion Jc, a battered portion 120 and a foundation template portion 130.

The jacket portion Jc is in substance of the same design and configuration as the jackets J1 - J3.5 and jacket portions Ja and Jb. In particular the jacket portion Jc comprises a plurality of end to end arranged bays Bb, Ba. The jacket portion Jc does not in its embodiment have a water plane bridging jacket portion of the same configuration as the bay Bs described hereinbefore. Rather one of the bays Bb constitutes or is disposed so as to constitute the water plane bridging portion. Looked at another way the jacket Jc uses a bay Bs which is modified by the addition of a diagonal brace 18 on each face. This indeed provides a greater standardisation of construction of the portion Jc as each of the bays B now has the same length, the only difference being the number of braces. The uppermost bay Ba has the same construction as in the previously described jackets.

The battered portion 120 is of the same general configuration as the battered portions 30, 60 and 90, and has battered legs 32 and a plurality if braces 38 arranged in a diamond configuration.

The most significant difference between the jacket J1 1 and the jackets J6— J10 is the addition of the template portion 130. The template portion 130 has the general configuration of a squat square frame with upright pipes 132 (which may also be considered to be leg portions) at each of its four sides. Upper and lower beams 134 and 136 extend between and connect the upright pipes 132. Braces 138 interconnect the beams 134, 136 and the upright pipes 132. Attached to and on the outside of each of the pipes 132 is a respective piling post 140. When installing the jacket J1 1 , the separate components 132, 120 and Jc are transported to an installation location. Initially the foundation template 130 is lowered onto the seabed at the desired installation location. If piles have been pre-installed the posts 140 receive the piles. Alternately piles are installed through the piling posts 140 to fix the foundation template to the seabed.

Next, the portion 120 is lowered onto an inter-fitted with the template 130. This is achieved by way of a stabbing connection between the portions 120 and 130.

Specifically, a lower ends of the battered legs 32 of the portion 120 fit into the pipes 132 of the template 130. These can then be fixed together by way of grouting or mechanical means such as swaging, or ball grab. Next, the jacket portion Jc is lowered onto and inter-fitted with the portion 120. This is achieved in the same way as described hereinabove in relation to the jackets J6 - J10.

Each of the jackets or jacket portions J1 -J5, Ja, Jb and Jc may be considered to constitute parallel leg jacket or parallel leg jacket portions as each have parallel legs L1 -L4. This is to be contrast with the battered jacket portions which have non parallel legs. Each of the parallel leg jackets or jacket portions may be provided and transported to an installation site as one piece or two pieces. When in two pieces the pieces are either: (a) a bottom piece comprising all the bays Bb as one piece, and an upper piece comprising the bays Bs and Ba as one piece; or (b) a bottom piece comprising all the bays Bb and the bay Bs as one piece, and an upper piece comprising the bay Ba. Thus when in two pieces, one of the pieces contains the bays Bb, and the other of the pieces contains the bay Ba, with the water plane spanning bay Bs being formed with either one of the two pieces.

Figures 14a - 14d depict yet a further embodiment of a jacket J12 that may comprise part of the system 10 or alternate embodiments of the system 10. The jacket J12 is of similar construction to the jacket J 1 1 and has an identical four legged battered portion 120 and portion Jc. However the jacket J1 1 differs from the jacket J10 by way of the configuration of the template denoted here as 130p. Specifically the template 130p is provided with a plurality of suction piles 150. Generally the number of suction piles matches the number of legs in the immediately adjacent battered portion 120. So in this embodiment the template has four suction piles. But in other embodiments where a three legged battered potion 120 is use then the template may have three suction piles.

A substantial benefit of the use of suction piles 150 whether on the separate template 130p as depicted in Figure 13a - 13d or indeed as an integral part of a battered jacket portion such as the portions 30, 60 and 100 described hereinabove is the ease of installation with a jack up drilling rig even where the area or footprint of the template 130p lies outside of the drilling area of the jack up drilling rig. This is illustrated in Figure 16 which provides a plan view of the rig 12 showing a foot print 154f of its cantilever 154 when fully extended, the drilling area 158 of its derrick and a representation of the relative location of suction piles 150 for a triangular template.

The jacket J1 1 or other corresponding jackets of similar construction and having component parts of different size can be readily installed by a jack up drilling rig in accordance with the following procedure. The jacket J1 1 is transported in a fully or partially assembled state to a jack up rig 12. The choice of fully or partially assembled state is dependent on the load rated capacity and available air gap of the jack up drilling rig. However as explained further below in alternate embodiment the suction pile may be used to provide buoyancy to the jacket thereby effectively enabling jackets of a dry land weigh substantially greater than the load rating of a jack up rig to be installed.

It is important to note that a jack up drilling rig is not specifically designed to install fixed to bottom jackets, they are designed primarily for drilling operations. With reference to Fig 1 , a jack up drilling rig 12 has a drilling derrick 152 which is designed and ordinarily used for lifting and supporting a drill string or a riser. The derrick includes a draw works, travelling block and hook (not shown) to perform lifting and supporting functions. The jack up drilling rig does not have large pedestal or rotating or revolving cranes below their cantilever 154. As a consequence the jack up drilling rig 12 also has limitations in terms of its drilling area. The drilling area is limited by the cantilever 154 which supports the derrick drilling 152. The cantilever is able to slide fore and aft. Thus a combination of lifting/lowering actions using the derrick and fore and aft motion using the cantilever 154 may be required to perform a jacket installation. Often the drilling envelope is not wide enough to be able to install traditional piled foundations. The foundation template 130p can be lifted by drilling derrick of a jack up rig and lowered to the seabed 24. It should be pointed out here that lowering of the jacket portion 130p with the suction piles 150 from the jack drill up rig 12 provides substantial engineering benefits over lowering the corresponding portion 130p from a floating crane barge. The reason for this is that when using a jack up drilling rig to lower the template 130p water entrained in and surrounding the suction piles 150 does not accelerate with rig motions as the rig 12 is fixed to the seabed. The only forces that need to be supported are those from buoyancy, wave and current action on the suction piles 150 and the drag of slowly lowering the structure down through the water. These are lateral loads and are are small compared to the large vertical hydrodynamic forces caused by a moving lift hook mounted on a floating vessel which accelerates the entrained water and water surrounding the structure effectively causing a large added mass to the structure. In layman's terms, moving a structure under water in a sinusoidal motion makes the structure feel significantly heavier. Once the movement stops, it doesn't feel as heavy. This is commonly known as the effect of added mass in underwater lifting operations.

Further the template 130p is able to self-float due to the air pocket within the suction piles 150. Thus the template 130p can be floated into positioned below the rig cantilever, connected to the drilling rig derrick and then flooded in a controlled or regulated manner by venting the air pocket such that the template 130p can be lowered through the water plane in a controlled manner by the jack up drilling rig. This avoids any problems that may otherwise arise with an uncontrolled sinking when the structure moved completely below the water plane 14. During installation of suction piles it is highly desirable to keep landing velocity low so that soil is not damaged by the impact of the piles 150 which would otherwise make forming a suction seal more difficult and may damage the foundation. As the suction piles are being set into the seabed, the jack up drilling rig can hold the template 130p rigging ensuring that the template 130p remains level and allows it to penetrate at a very slow velocity. The jack up drilling rig may correct a tilt of the template 130p by skidding offset from the lift.

When the piles 150 have landed a suction pile pump system may be operated to pump water from the piles so they are forced into the sea bed.

In a further variation the suction pile template 130p may be arranged so that the piles 150 can slide within pipe sleeves within corners of the template. Sliding piles allows the template 130p to be removed after pile installation such that the template itself is used as an installation aid for the suction piles, i.e. it is a non-permanent structure. Sliding piles also allows the suction pile tip to be set at different depths not unlike driven piles where piles are often driven to a certain blow count rather than a certain designed penetration depth. Allowing the suction pile to be installed at different depths mitigates the risk of any hard soil layers being unexpectedly encountered shallower than surveys may otherwise indicate.

Figures 15a - 15d depict a sliding suction pile system 200 which may be incorporated in the present disclosed jacket system 10. Alternately the disclosed sliding suction pile system 200 may be used with alternate jackets or jacket systems. The sliding suction pile system 200 comprises a plurality of suction piles 202. The suction piles 202 are in essence the same as the suction piles 150 shown in Figures 14a - 14d with the exception that the suction piles 202 are not permanently fixed to a mechanical structure prior to installation in the seabed 24. In the sliding suction pile system 200 a template portion 204 has a pile sleeve 206 for each of the suction piles 202, and a mechanical structure 208 that connects the sleeves 206 together. The structure 208 is in the form of a framework which connects the sleeves 206 together in a common plane. A structure 208 also is provided with a plurality of pockets 210 arranged to receive the legs L of a jacket. The suction piles 202 and the sleeves 206 are arranged to enable the suction piles 202 to slide through their respective sleeves 206 independently of each other during installation. As the piles 202 can be installed independently of each other they can be installed to different depths. This is particularly advantageous when the seabed has irregular soil conditions. For example as shown in Figure 15c a rock 212 may be in the path of one of the piles 202 limiting its penetration to a depth D1 . However another one of the piles 202 may be driven to a depth D2 which is greater than D1 . Further, as the piles are able to slide relative to the sleeves 206 the template portion 204 is maintained in a substantially horizontal plane. This ensures that when a jacket is fixed to the template structure 204 the jacket extends substantially vertically from the seabed 24. For example in application of the system 200 with the disclosed system 10 the template portion 204 can be used as a base for securing a jacket or jacket portion such as battered portions of a type described in relation to jackets J6 - J1 1 or indeed parallel leg type jackets J1 - J3.5, when such jacket or jacket portion have three legs L/32. Alternately of course embodiments of the system 200 can be provided with four suction piles 202 and a rectangular (including square) template structure 204 to accommodate a four legged jacket or jacket portion.

The sliding suction template system 200 can be used in several different ways. In one application the template portion 204 can be permanently fixed to the suction piles 202 after installation of the piles 202 in the seabed. This can be achieved for example by way of grouting or mechanical swaging. In this instance the templates portion 204 provides a stabilised base for a jacket which can be installed by subsequently inserting the legs L of a jacket into the pockets 210. However in an alternate application of the system 200 once the piles 202 have been installed the template portion 204 can be lifted from the piles 202 and reused for installation of other suction piles. The suction piles 202 are then left installed in the seabed 24 and subsequently a jacket or jacket portion can be stabbed onto the installed piles 202 and then subsequently fixed thereto for example by way of grouting, swaging, or ball grip.

In the event that the template portion 204 is to be reused in the manner previously described is not necessary for the frame structure to also include the pockets 210. That is, the pockets 210 are optional and are only required when the template portion 204 is itself to be used as a fixed to bottom base for a jacket.

The suction piles 202 can be installed in one of two different ways. Firstly, as shown in Figure 15a the piles 202 can be releasably locked to the respective sleeves 206 of the template portion 204. This forms a template unit which may be lowered to the seabed 24. For example the entire unit can be lowered to the seabed 24 using the drilling derrick 152 of the jack up drilling rig 12. This process may be assisted by the provision of a valve system 214 at an upper end of each of the piles 202. The valve system 214 enables controlled venting or release of air from within the piles 202. This of course enables control of the buoyancy of the unit. Therefore by a combination of the control of the buoyancy via the valve system 214 and control of the drilling derrick 152 it is possible to very finely control the rate of descent/sinking of the unit to the seabed 24. In addition, and as explained in greater detail later, control of the buoyancy of the piles 202 can assist in controlling the load on the drilling derrick 152. Once the unit has landed the releasable locking mechanism can be released enabling the piles 202 to slide relative to their respective or corresponding sleeve 206.

Thereafter a suction pile pumping system can be operated to pump water from the respective piles enabling them to individually or more precisely independently be installed into the seabed 24. It will be noted that during this process irrespective of the rate of penetration of the piles 202 and their respective depth of penetration, the template portion 204 will remain in a substantially horizontal plane assuming that the underlying seabed 24 is substantially horizontal.

Figure 15d depicts an alternate installation method. Here the template portion 204 is first lowered to the seabed 24. Subsequently the respective piles 202 are lowered to the seabed 24 and received in respective sleeves 206. Again the template portion 204 and the suction piles 202 can be sequentially lowered using the drilling derrick 152 of a jack up drilling rig 12. The piles 202 can be installed either immediately upon landing on the seabed 24 and within a respective sleeve 206; or alternately one can first lower all of the piles 202 to the seabed so that they seat in their respective sleeves 206 and then commence the installation of the respective piles 202 by operating a suction pile pumping system.

While the above sliding suction pile system 200 has been described in the context of use with the present jacket system and method of installation, the sliding suction pile system 200 can be used with conventional or other jackets or jacket systems.

Figures 17-26 illustrate a method of installing a jacket Jx with suction piles from initial lifting from a dock into the water to final sinking of the suction piles into the sea bed. Associated with this is a method of delivering the jacket Jx to an installation location. In embodiments of the methods the jacket Jx is similar to the jacket J12 with the main difference being that jacket Jx has a three legged battered portion 120x with three suction piles 150xa, 150xb and 150xc (herein after referred to as "suction piles 150x") and a tower portion Tx with three legs L1 -L3.

In order to facilitate the wet tow of the jacket Jx, plugs 220 are inserted in two of the three suction piles 150xa and 150xb (shown by a cross) to act as air tanks providing buoyancy to the jacket Jx. The third suction pile 150xc is left open. Also three separate buoyancy tanks 222 (shown initially in Fig. 19) are releasably attached to the tower portion Tx. These provide additional buoyancy to an upper portion of the jacket Jx spaced form the suction piles 150x. A manifold 223 is also attached to the top of the jacket Jx to facilitate controlled flooding of the suction piles 150xa and 150 xb; as well as the buoyancy tanks 222. Figure 17 shows a bottom end view of the jacket Jx on a wharf 224 with two of the suction plies 150xa and 150xb plugged and the three additional buoyancy tanks 222 attached. The jacket Jx is then lifted by a heavy lift vessel (HLV) 225 into the water as shown in Fig 18. The open suction tank 150xc fills with water and provides a degree of ballast, orientating the jacket Jx so that the suction piles 150xa and 150xb breach the water plane 14 while the suction pile 150xc lies below the water plane 14 and in a vertical plane between the piles 150xa and 150xb. The tanks 222 keep the jacket Jx in a roughly horizontal plane in the water as shown in Figs 19 and 20.

In order to tow the jacket Jx to its installation site a tug boat 228 is connected by a tow line 230 to the top of the jacket Jx and an escort vessel 232 connected by a tow line

234 to the foundation portion of the jacket Jx near the piles 150x as shown in Figs. 19 and 20. Figs. 21 and 22 show the jacket Jx at the installation site adjacent a jack up vessel which in this embodiment is a jack up rig 12. Top end of the jacket Jx is located under the cantilever 154 which supports the drilling derrick 152 of the jack up rig 12.

A line 236 from the jack up rig 12 is now attached to the top of the jacket Jx. A flooding line 238 is also attached to the manifold 223. The tow line 230 is disconnected from the top of the jacket Jx. The rig 12 lifts the top of the jacket Jx enough to ensure the suction pile 150x will clear the seabed 24 when the jacket Jx is vertical. However the rig/associated drilling derrick does not actually lift the jacket Jx to the vertical at this time. While lifting the jacket Jx the tow line 234 is payed out from escort vessel 232. It should be appreciated that due to the buoyancy provided by the piles 150xa and 150xb as well as the tanks 222, the rig 12 does not need to lift the full weight of the jacket Jx.

The suction piles 150xa and 150xb are now flooded from the rig in the void space behind their respective plugs 220 by opening air vents (not shown) in the top of the suction piles 150ba and 150xb and delivering water into these piles by use of the flooding lines 238 and manifold 223, causing the jacket Jx to vertical. The internal plugs 220 are removed from the suction piles 150xa and 150xb by a ROV which may be associated with any one of the rig 12, the tug 228 and the escort vessel 232. This is shown progressively in Figs. 23 where the jacket Jx is inclined at about 65°, and Fig 24 where the jacket Jx is vertical but lifted from the sea bed 24. The buoyance tanks 222 are partially flooded, with the rig 151 maintaining a share of the load of the jacket Jx while paying out line 236 until the jacket Jx lands on the sea bed 24. Now the tanks 222 are fully flooded and any trapped air in the suction piles is vented and the piles 100% flooded. Submersible pumps 240 mounted on the suction pile 150x are used to pump water out of the piles 150x to create sufficient pressure differential in the suction piles so that the piles are sucked down to the required level below the sea bed 24, with final levelling completed using differential pumping. Figures 25 and 26 show the piles at an intermediate and final installation depth respectively into the sea bed.

The pumps may be pre-installed on the Jacket Jx or fitted using a ROV 239 once the jacket has landed on the sea bed 24. Suction piles inlets (not shown) which were used for by the pumps 240 to remove water from the piles are then locked shut using permanent valves, and the submersible pumps 240 removed. The buoyancy tanks 222 are optionally removed, evacuated and returned for reuse; or may be maintained on the jacket Jx to be used in the removal of jacket Jx at a later time. The topsides can now be lifted into place.

A further aspect of the disclosed method contemplates the removal of jacket Jx for re- deployment at another offshore location. In brief, an embodiment of the method of removal for the installed jacket Jx may comprise the following steps:

• A jack-vessel or derrick barge is set up adjacent the jacket Jx so that it's lifting mechanism (e.g. for a jack up rig, its derrick 152) can substantially aligned with the jacket Jx.

• The jack-vessel or derrick barge is operated to complete all plug and

abandonment activities and sever conductors below mudline.

• The topsides supported on the jacket Jx is removed and lowered to a supply boat.

• A line and associated lift slings from jack-vessel or derrick barge are connected to the top of the jacket Jx.

• Optionally one or more of the buoyancy tanks 222 can are refitted (initially in a flooded condition).

• Flooding lines and compressed air lines are connected to the manifold 223.

• The suction piles inlet valves are opened.

• Compressed air is fed to the piles 150x to displace water and mud from back through the suction pile bottoms. If the buoyancy tanks are re-fitted, or they were never removed after installation of the jacket Jx, they too are dewatered by connection to the compressed air form the manifold 223.

• The weight of the jacket Jx is partially taken by the jack-vessel or derrick barge, and with sufficient buoyancy created, by the suction piles and if used, the buoyancy tanks 222.

• With compressed air contained in the top section of each suction pile and

valves shut, divers water blast out any remaining internal mud and reconnect the caps on the bottom of the suction piles 150xa, 150xb and optionally 150xc, with a one way check valve on each.

• The tow tug 228 will be connected to the jacket base.

• The tug will retrieve the jacket end to surface, while the remaining ballast water is blown out of each suction pile, through the check valves.

• The top valves will be shut and the jacket is now ready to tow to the next

location.

In a variation to the above described method of installing the jacket Jx, shown in Fig. 27, all three suction piles 150Xa, 150xb and 150xc may be initially plugged and filled with air to provide buoyancy in which case only two or maybe one of the buoyancy tanks 222 are required to maintain the jacket in a roughly horizontal plane while being towed to the installation site. With a three legged jacket Jx, now the pile 150xc is above the water plane 14 rather than below it as in the earlier embodiment shown in Fig 20. In all respects the installation of the jacket Jx with the three plugged suction piles 150x is substantially the same as described when only two of the pile are initially plugged; the only difference being the number of suction piles 150x and buoyancy tanks 222 that need to be flooded during the righting of the jacket Jx and load transfer to the rig 12.

Whilst a number of specific embodiments have been described, it should be appreciated that the jacket system and method of installation as well as the sliding suction pile system and its method of installation may be embodied in many other forms. For example the number of legs and/or piles provided in the respective systems is not limited to the specific illustrated embodiments. As mentioned many times throughout this specification the jackets or jacket portions may be provided with a plurality of legs though typically will have three or four legs. Usually a four legged jacket system will also utilise four suction piles. Also, with specific reference to the sliding suction pile system 200 the template portion 204 has been described and illustrated as being suited to the receive a three legged jacket or jacket system.

However the template portion 204 can be easily modified to accommodate any number of legs including a single leg which may extend beyond the water plane 14 and itself support a topside T.

In relation to the methods of delivery, installation and removal of a jacket as described above with reference to Figs 17-27 in one variation instead of plugging the suction piles 150x to provide buoyancy, inflatable bags can be inserted into the suction piles to achieve the same effect. Also the sliding suction pile system 200 with the associated template portion 204 may be incorporated in the jacket Jx in embodiments of the method of installation of the jacket Jx. It should also be appreciated that in terms of the disclosed method of delivering the jacket with suction piles to the installation location, the equipment used to subsequently lift the jacket and lowered the seabed is immaterial to the method of delivery of the jacket Jx. That is, the method of jacket delivery per se is independent of the equipment used (for example a jack-up rig, other type of jack up vessel; or a derrick barge) to lift and subsequently lower the jacket to the seabed. In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence of further features in various embodiments of the apparatus and method as disclosed herein.