AU619002B2 - Platform - Google Patents

Description

slgniture of Applicant (E) or oal of Company and BfInature of Its Officers a prescribed by Its Articles of AuocItioon.

ESSO AUSTRALIA LTD ARRYL B. MISCHLEWSKI REGISTERED PATENT ATTORNEY f 1- FORM COMMONWEALTH OF AUS AL Patents Act 19002 COMPLETE SPECIFICATION (Original) Class Application Number: PI7827 PJ2564 Lodged: 20th April 1988 6th January 1989 Complete Specification Lodged: Accepted: Published: Int. Class c o PI o a

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Priority: Related Art: Name of Applicant: ESSO AUSTRALIA LTD Address of Applicant: 127 Kent Street, Sydney, N.S.W. 2000 Actual Inventors: GERRARD RAYMOND BORGHESI, DR. SYDNEY FRENCH, RUSSELL FORRESTER STALEY and ANTHONY MARK HYDEN Address for Service: EDWD. WATERS SONS, QUEEN STREET, MELBOURNE, AUSTRALIA, 3000 Complete Specification for the invention entitled:

PLATFORM

The following statement is a full description of this invention, including the best method of performing it known to us.

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PLATFORM

The invention relates to a marine drilling and/or production platform for offshore hydrocarbon recovery. More particularly, the marine platform is of the tripod type and relocatable.

Conventionally, marine platforms comprise three or more upright legs which are anchored to the seabed and extend to a well head deck above the sea level. Cross members are obliquely positioned between these legs to strengthen the structure to resist the action of wave and wind forces on the legs. These platforms are large and are not designed to be readily relocated to other sites.

Consequently, these platforms are too costly to use for the recovery of hydrocarbon in fields with an expected life of 1.5 five to ten years. These fields are becoming increasingly important as the sources of hydrocarbon dissipate. Simpler, relocatable platforms have resulted.

One type of simplified platform is disclosed in U.S. Patent No. 4,687,380 in the name of Meek et. al.

(Assignee Heerema Engineering) based upon a tripod arrangement. The tripod consists of an upright conduit which is supported against lateral movement about its lower end by three legs having first ends attached to the conduit and each diverging away from and downwardly of the conduit.

The legs connect to a horizontally orientated triangle of base arms. These base arms are in turn connected to the upright conduit by horizontal struts which extend from the three apices of the triangle of base arms to the upright conduit. The tripod is anchored to the seabed by providing each apex of the base arms with vertical conduits through which piling can pass into the seabed.

Whilst this arrangement has served to simplify the platform structure useable in short life oil fields, it is nevertheless cumbersome. To transfer the platform from one 35 location to another it is necessary for the legs to be 3blasted free, making the relocation procedure costly, if blasted free, making the relocation procedure costly, if cc~c cOCC i 4b, -3there is any damage to the platform, inconvenient and because of the nature of the procedure, dangerous.

Further, the upright conduit must extend high above the sea level so it may support the production deck, which considerably complicates well work-over procedures that rely on long tool wire line operations. Further it can be seen from this particular art tower structure, in the event of one of the legs being damaged the tripod may also be rendered unsafe.

Thus it is an object of the present invertion to provide a platform which is primarily relocatable but does address the disadvantages of the prior art.

In one aspect of the invention the invention provides a platform for offshore hydrocarbon recovery 1 comprising: a deck super structure; a central conduit; at least one well-head connected to said C central conduit; C Cz S20 at least three support legs; and C 20 feet at the lower extremity of said legs wherein said feet have a plate-like surface C C adapted to be in contact with the seabed when c the platform is insitu.

2 Preferably said legs are downwardly diverging and Smore preferably connected to said central conduit.

Preferably the feet are ballast receiving containers, wherein the ballast may be located in these containers before or after the platform is positioned on the seabed. Similarly, the ballast may be permanently or removably located in these containers, but preferably removable. In some instances, it may be desirable to positively anchor the platform to the seabed. To achieve this the container may be provided with a sleeve through which a pile can be driven in to the seabed.

1 1.~ 4 Preferably, the plate-like surface of each of the feet is provided with a space and a further means foi grout to be carried into said space after installation of the platform, so that water is displaced and in the event of a particularly uneven seabed, to ensure an even bearing of the footing loads onto the soil.

More preferably the space is segmented wherein each segment of the space may be provided with a grout inlet means and a grout outlet means. Further the space is preferably annular.

Preferably, base legs are provided which inter-connect each of the feet and struts may be connected to each of the feet and one upwardly inclined and connected to the central conduit. These struts constitute a lower tr. angled reinforcement to the conduit then the diverging legs.

c 15 c Preferably, said central conduit extends the necessary distance about the sea level to allow access to the at least one well-head during normal operating V conditions, but also to allow the at least one well-head to cc 2 be submerged during severe storms.

o 20 Preferably said central conduit has a ledge whereon a flexible ring is seated and wherein a connection sleeve of the deck super structure, at the connecting end thereof, has t a shape compatible with the ledge of said central conduit.

More preferably said flexible ring is made of rubber.

ccc8 In another aspect of the invention, the invention provides a platform for offshore hydrocarbon recovery r comprising: Ct '3a deck super structure at least one well-head S3connected to said central conduit; connected t adcnrlcnut a central conduit; and at least three support legs; wherein said central conduit extends the necessary distance above the sea level to allow access to said at least one well-head during normal operating conditions, but also to allow said at least one well-head to be submerged during severe storms.

:Ii i: Preferably said legs are downwardly diverging and more preferably connected to said central conduit.

Previously, the well head was positioned at cellar deck level then wire-line operations are conducted from the main deck, there being no limitation on height. This positioning is costly and results in a very large platform.

In providing the well head at such lower position relative to sea level, a production deck may be superimposed above the well head and long-tool wire-line operations carried out from the production deck in an easier manner.

This enables the size and cost of the platform to be minimised. More than one well may be located within tht: upright conduit and would be specially designed. Further, one or more wells may be located externally of the upright conduit.

'r C In a further aspect of the invention, it is Cr r desirable to fabricate the entire super structure as a single unit and connect it to the conduit either on land or rc in situ. In either case the super structure will preferably C comprise a number of supports having ends connected to a short connection sleeve to receive the upper end of the upright conduit and having the other ends of the supports diverging to present a support array for a production deck.

*T1 The lightweight super structure reduces dynamic loads on the ystem. The well head is therefore kept devoid of interference by the super structure to permit easy maintenan=e and operation. Typically, the connection sleeve of the super structure is grouted or welded to the conduit.

A further aspect of Lie invention is a unique 0 bearing/seal detail for the connection of the connection sleeve of the superstructure to the conduit. Normally, in typical grouted connections, fluid inflated rubber packer elements are used to seal the bottom of the annulus to be grouted. In this present aspect of the invention the S conduit has a ledge preferably conical whereon a flexible ring is seated. The connection sleeve of the superstructure i L 6 at the connecting end thereof has a shape compatible with the ledge. The flexible ring is preferably made of rubber.

A preferred embodiment of the invention will now be further illustrated with reference to the accompanying drawings in which Figure 1 is a perspective view of a platform according to the invention.

Figure 2 is a side view of the platform of Figure 1.

10 Figure 3 is a cross sectional plan view of the i0 platform of Figure 1.

Figure 4A shows another embodiment of the invention; feet with grout inlets and piping there attached.

Figure 4B shows an exploded cross-section B-B of the feet shown in Figure 4C.

15 Figure 4C shows a plan view of one of the feet.

Figure 5A shows an exploded view of the connection end of the connection sleeve superstructure.

a. *S Figure 5B shows an exploded view of the connection end of the conduit with seal thereon.

20 In the drawings, a platform 1 comprises a super structure 2 and a sub structure 3.

The superstructure 2 includes a production deck 4 a" which is supported on supports 5 emanating from connection sleeve 6 and diverging up to production deck 4.

25 25,: The super structure 2 surrounds well head 7 and as production deck 4 is spaced above well head 7, it is conducive to easy maintenance on well head 7.

The connection sleeve 6 connects super structure 2 cr to sub structure 3 adjacent sea level 8. Thus, the well (rr§ 30 head 7 is just above sea level 8. In use this means that long-tool wire-line operations can be carried out between the well-head 7 and the helicopter deck 19.

One or more wells 18 may be located externally of the upright conduit 9.

i: J 1 .li. I 7 Sub sea structure 3 comprises upright conduit 9 which extends almost to the seabed 17. Three diverging legs are connected to upright conduit 9 and diverge outwardly and downwardly of conduit 9. A horizontal triangular base is comprised of base legs 11 and diverging legs 10 connect at the apices of this triangle. Also at the apices of the triangle are feet 13. Struts 12 are also provided inclined from the feet 13 towards and connecting to conduit 9. In operation, should one of the diverging legs 10 be accidently 0 damaged and rendered ineffective, the corresponding lower strut 12 will take on the full supportive load of the original leg 10. The angled struts 12 are in essence a secondary safety system which in their own operation simultaneously secure the upright conduit 9 at its lower region. The angled struts 12 also allow installation of the monotower over an existing well-head.

c, The feet 13 comprise a ballast receiving container 14 with partitions 15. Ballast is positioned in the container 14 to provide a secure weighted connection between 20 the platform 1 and seabed 17. In some conditions, it is still desirable to provide a means for remedial piling.

Sleeve 16 enables such remedial piling to pass through multipurpose footing 13 into seabed 17.

If piling is not required the bottom of sleeve 16 would be closed and the sleeve 16 would also contain Vitt ballast.

Preferably sleeve 16 penetrates into the sea bed about the same distance as the outer skirt of the container 14.

crr Figures 4A, B and C illustrate a further embodiment _0 of the feet. In this case, each of the containers, 14a have a base plate 20 at the bottom face. As can be seen from the Figures, a segmented annular space 21 is provided under the base plate 20 inside the outer skirt of the container 14a.

Thus grout can be pumped into the space (see grout lines 22) displacing the water therein and after installatio displacing the water therein and hL Ai I 1 6 8 ensuring an even bearing of the footing loads onto the soil.

Each segment of the annular space is provided with a grout inlet pipe 23 and a large capacity grout outlet tube 24 (see Figure 4B). The grout outlet means may also serve as a water outlet during installation when the footing is forced into contact with the soil.

Also as can be seen from the Figures, the grout is preferably carried to the annular spaces 21 through pipes.

Preferably, main carrier pipes run down a preinstalled well conductor (not shown) inside conduit 9 and are designed to be removable after grouting.

The removal of the grout lines is made possible by a length of hose 25 which will break when the grout pipes 22 are withdrawn.

Figures 5A and B illustrate a preferred embodiment i 1 of a unique bearing/seal design.

The embodiment shows a rubber ring 26 mounted on a conical steel ledge 27 welded to the central conduit 9.

When the superstructure 2 is lowered over the conduit 9, a similar cone 28 attached to the bottom of the superstructure connection sleeve 6 comes into bearing contact with the rubber ring 26. The self-weight of the superstructure 2 compresses the rubber ring 26 to form a seal, thus avoiding the need for packer inflation lines. A secondary benefit is that the bearing allows the connection sleeve 6 to be jacked ,44 sideways to level the superstructure 2.

The platform of the present invention provides a simplified arrangement which reduces development costs and l allows easy relocation of the platform to other sites.

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Claims (5)

1. A platform for offshore hydrocarbon recovery comprising: a deck super structure; a central conduit; at least one well-head connected to said central conduit; at least three support legs; feet at the lower extremity of said legs wherein said feet have a plate-like surface adapted to be in contact with the seabed when the platform is insitu.

2. ballast The platform of claim 1 wherein said feet are receiving containers. cr s o o sa a o i* i D r D o r s D r r rr r ~er a r o P

3. The platform of claim 1 wherein said plate-like surface of each of said feet is provided with a space and a further means for grout to be carried into said space after installation of the platform.

4. A platform for offshore hydrocarbon recovery comprising: a deck super structure; a central conduit; at least one well-head connected to said central conduit; and at least three support legs connected to said central conduit; wherein said cental conduit extends a.necessary distance above the sea level to allow access to at least one well-head during normal operating conditions, but also to allow at least one well-head to be submerged during severe storms. y 10 The platform of anyone of claims 1-4 wherein said central conduit has a ledge whereon a flexible ring is seated and wherein a connection sleeve of the deck super structure, at the connecting end thereof, has a shape compatible with the ledge of said central conduit.

6. A method of making the platform as defined in any one of claims 1 to 5 comprising: fabricating the deck structure as a single unit; connecting said super structure to the central conduit on land or in-situ. DATED this 18th day of October 1991 ESSO AUSTRALIA LTD. WATERMARK PATENT TRADEMARK ATTORNEYS C THE ATRIUM 290 BURWOOD ROAD HAWTHORN, VICTORIA 3122 e AUSTRALIA DBM:LPS:KG 3(10) cc c C C C C *C C C 'C t Cs