US3922868A

US3922868A - Deep water platform construction

Info

Publication number: US3922868A
Application number: US500913A
Authority: US
Inventors: Reagan W Mcdonald; Walter B Joseph
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-08-27
Filing date: 1974-08-27
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02

Abstract

A self-erecting offshore platform for deep water installations comprised of three or more (optimum four) leg modules, and one platform module, all of which are buoyant and towable to an offshore site. At a site location the leg modules are pivotally interconnected to the platform and rigged with cables for limiting their relative lateral motion while being pivoted into contact with the ocean floor. The pivoting action is obtained by decreasing the buoyancy of the outer (lower) ends of the leg modules. Upon initial positioning of the leg modules in contact with the ocean floor, they are then lightened by expelling water from their upper buoyancy chambers. The lower ends of the leg modules are drawn toward one another as increased buoyancy in their upper ends raises the platform out of the water. When predetermined elevation of platform has been reached, the supporting foot pads (mats) are pivotally moved downward to flat contact with the ocean bottom by flooding their upper buoyancy tanks.

Description

United States Patent 11 1 McDonald et al.

[ Dec. 2, 1975 DEEP WATER PLATFORM CONSTRUCTION [75] Inventors: Reagan W. McDonald; Walter B.

Joseph, both of Houston, Tex.

[73] Assignee: Reagan W. McDonald, Houston,

Tex.

[22] Filed: Aug. 27, 1974 [21] Appl. No.: 500,913

[52] U.S. Cl 6l/46.5; 114/.5 [51] Int. Cl. E02D 21/00 [58] Field of Search 61/465, 47, 50, 46; 114/05, 26, 31, 50; 175/7, 8, 9; 166/.5, .6

[56] References Cited UNITED STATES PATENTS 2,600,76l 6/1952 Halliburton 6l/46.5

Primary Examiner-Dennis L. Taylor [57] ABSTRACT A self-erecting offshore platform for deep water installations comprised of three or more (optimum four) leg modules, and one platform module, all of which are buoyant and towable to an offshore site. At a site location the leg modules are pivotally interconnected to the platform and rigged with cables for limiting their relative lateral motion while being pivoted into contact with the ocean floor. The pivoting action is obtained by decreasing the buoyancy of the outer (lower) ends of the leg modules. Upon initial positioning of the leg modules in contact. with the ocean floor, they are then lightened by expelling water from their upper buoyancy chambers. The lower ends of the leg modules are drawn toward one another as increased buoyancy in their upper ends raises the platform out of the water. When pre-determined elevation of plat- 2,772,539 12/1956 Sandberg.... 61/465 form has been reached, the Supporting foot pads g (mats) are pivotally moved downward to flat contact 3 327 668 6/1967 Vil s c bin; 'g' 5 with the ocean bottom by flooding their upper buoy- 3.673973 7/1972 Glosten 114/.5 D ancy tanks- 3,739,737 6/1973 Baler 114/.5 D 13 Claims, 7 Drawing Figures 1 1 t Q *4 71w? Z -Kv US. Patent Dec. 2, 1975 Sheet 1 of 3 3,922,868

US. Patent Dec. 2, 1975 Sheet 2 of3 3,922,868

U.S. Patent Dec. 2, 1975 Sheet 3 of3 3,922,868

oo o o ofio I lad 1f DEEP WATER PLATFORM CONSTRUCTION FIELD OF THE INVENTION This invention relates to offshore platforms and more particularly to systems for erecting offshore platforms in water depths in excess of 450 feet.

BACKGROUND OF THE INVENTION Offshore platform construction in deep water is a complex problem of technology. Time and equipment involved become very critical due to the great expense incurred in offshore operations. In deep water, divers have limited capabilities and submersible diving equipment is expensive and slow going in actual use. In U.S. Pat. No. 2,857,744 a system is proposed where an entire structure is towed to a location and tilted from a horizontal to a vertical position. This system has limitations as to the effective depth that can be reached by this system and the complexity of handling an extremely large piece of equipment. Design factors also limit the depth at which a structure of this type can be used. In U.S. Pat. No. 3,253,417, a system is proposed wherein the entire platform is hinge connected together and the base is submerged first. This system lacks control of the components and requires a certain amount of precision which is difficult to obtain in large structures.

The foregoing systems lack structure configurations which are stable both in the transportation to the site and upon erection at the site. In the present invention, a modular multiple articulated system provides for easy transportation, and a stable structural configuration during all phases of construction and operation.

SUMMARY OF THE INVENTION The present invention is embodied in a system wherein an optimum of four leg modules and a platform module for an offshore platform are made selectively buoyant, and are independently towable to an offshore location site. At the location site, the leg modules and platform module are pivotally interconnected. Support mats or pad members, while still in protected waters, are attached to their respective leg modules by massive pins which are capable of transmitting large values of thrust and transverse moment. Each leg module is constructed from three equidistantly spaced tubular members which are laced together by tubular webs or spacing members. An alternative design included in this concept would be to use a single large tube for each leg module rather than three smaller tubes laced together. Each support mat may be rectangularly shaped in plan view. Cables are provided to extend along the length of each leg module, from winches mounted at the top, and are anchored at remote locations on the ocean floor in order to furnish lateral control while lowering the leg modules.

At the site location, the platform module is anchored by four large anchor cables or chains extending diagonally away from the corners of the platform. Each cable can be connected to its own winch for control. The leg modules, which are pivotally connected to the platform module, contain buoyancy compartments which are selectively flooded to accomplish smooth, slow submergence. After all of the support mats engage the ocean floor, the buoyancy of the leg modules is selectively increased beginning at the top, to bring the leg modules toward one another and to lift the platform above the 2 water level. At the precalculated elevation and altitude of the legs, the support mats are flooded to rotate them into final position flat on the ocean floor. All four mats are interlocked by tie cables or chains, and the structure is in its final position. No diiving operations are necessary for this erection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a leg member and support mat in towing position;

FIG. 2 is a view taken along line 22 of FIG. 1;

FIG. 3 is a plan view of the structure as it is assembled prior to submergence of the leg modules;

FIG. 4 is a side view showing a leg module in an ocean floor touching position;

FIG. 5 is a side view showing a leg member in a position just prior to the rotating of a support mat member;

FIG. 6 is a side view illustrating the assembly in an erected position; and

FIG. 7 is a view taken along line 77 of FIG. 6.

BACKGROUND OF THE INVENTION Referring first to FIG. 3, an offshore platform 10 is schematically illustrated in a plan view where the members are floating in the water prior to submergence of the leg modules. In FIG. 6, a side view illustrates the platform 10 as located in position on an offshore site.

In FIG. 3, the platform body module 11 is illustrated with a generally square shaped configuration defined by

sides

11a, 11b, 11c, and 11d, although it will be appreciated that the configuration can assume other shapes. At

pivot points

12a, 12b, 12c and 12d midway of the length of each side, a load supporting

leg module

13a, 13b, 13c and 13d is pivotally connected to the platform body 11 by a massive pin. As illustrated in FIG. 6, in the final assembly position, the leg modules 13 a-d are disposed at an acute angle with respect to a vertical. Pivotally connected to the lowermost ends of the leg modules l3( a-d) are support mats 14 a-d which are illustrated with a generally rectanguar configuration. Depending spuds 15 a-d from the mats 14 a-d are embeddable into the underwater ocean floor l6 and prevent shifting of the support mats relative to the ocean floor. The leg modules 13 a-d have a length adequate to suspend or support the platform body 11 above the surface 17 of the water. Each of the support mats l4 a-d is connected to both adjacent support mats by a chain or cable 18 a-d (see FIG. 7).

The completely assembled platform assembly is basically comprised of the platform module 1 1 and the four supporting leg modules 13 a-d. Each of the leg modules is constructed to have buoyancy chambers, such as the chambers lle, 13c and 15e illustrated in FIG. 2. The buoyancy of the leg modules permit the leg modules to be towed in a floating or semi-submerged condition to the selected offshore location. At the selected location, the individual leg modules 13 a-d are pivotally interconnected at pivot connections 12 a-d, while floating, to the sides 11 aa' of the platform body module 1 1. The legs 13 a-d and mats 14 a-d are then selectively (or simultaneously) controlflooded in such manner that their outer ends submerge and slowly sink to engage the ocean floor, while upper ends, which are pinned to platform module 1 1, remain buoyant. The support mats are pivotally connected to the support leg modules at 20 a-d. When water is expelled from upper ends of the legs, their increasing buoyancy lifts them and the platform'module 11 such that it rises out of the water to a predetermined elevation. Then the support mats 14 u-d are pivoted into anchoring position on the ocean floor 16 by flooding their chambers.

Referring now in FIG. 1, one typical load-supporting leg module 13a is illustrated in a floating position in the water. The leg module will be several hundred feet in length, as necessary for the desired height of the platform above the water level. Each leg module is separately fabricated and separately launched so that it can be independently towed to the platform site location in the body of water. If desired, a pad le can be outfitted with marine propulsion equipment (not shown). As illustrated in FIGS. 1 and 2, the support leg module 1330 consists of three generally cylindrically shaped and elongated tubular elements 22 ac which are equidistantly spaced from one another by transverse truss web members 23 ac. These web members 23 ac may also be tubular. The truss web members 23 ac are angularly disposed with respect to the lengthwise axis of Iongitudinal members 22 ac and suitably interconnected thereto. At the upper end of the supporting leg module 13a is a connecting frame means 24 which is adapted for pivotal connection at a location 12a to the platform body module. As illustrated in FIGS. 1 and 2, the connecting frame means 24 included an upper plate member 25 which is attached to and made a part of two supporting

tubular elements

22a and 22b so as to intersect and lie in a plane coextensive with the longitudinal axis of the two supporting

elements

22a and 22b. The plate member 25 has a pivotal means 12a with a pivot axis disposed in a plane transverse to the lengthwise axes of the supporting members 22a and 2219. A depending support means 26 extends from the transverse pivotal means 12ato the remaining supporting element 22c. At the other end of the supporting element 13a is a pivot means 20a for providing a pivotal connection to the mat member a. The mat member 15a may be rectangular in section and has a hollow interior which is divided into forward and rearward compartments 27 and 28. The forward compartment being to one side of the axis of the pivot connection and the rearward compartment being to the other side of the pivot connection. In the pivot position illustrated, the upper face 30 of a mat member and the lower surface 31 are generally parallel to the plane through the supporting

elements

22a and 22b. On the upper face of the supporting mat are transverse anchor spuds 15a which can be embedded in the subsea formation strata. The spuds 15a, as shown in FIG. 1, are retracted in that they face outwardly from the upper face 30 for towing purposes. At.a site location, the spuds are extended through the lower surface 31 and locked into position by suitable means (not shown).

Along the length of each of the supporting elements 22 ac and for approximately the mid-third portion thereof, the main tubular supporting element 22 a-c may be surrounded or encased by an outer concentri- Cally-arranged tubular member 32 a-c to form an annular floatation chamber 33 0-6. While reference is made here to a single chamber, it will be appreciated here and elsewhere that multiple chamber compartments and common control valves can be used. By appropriate flooding of the chamber 330 in the leg element and one of the chambers 27 in the foot mat member, a leg element 13a can, if desired, be partially submerged for towability and yet be sufficiently buoyant to permit an easy tow. As illustrated in FIG. 1, the leg member is inclined with pivot end 12a submerged and the mat member 15 at an incline. Thus, the member can be moved to the right with any suitable towing or motor means.

All leg modules 13a-d and the platform module 11 are independently towed to the selected platform site. The platform module 11 may be made buoyant by construction or by float means as desired. At the selected site, the leg modules 13 ad are aligned with the platform body 11 so that the pivotal interconnections 12 a d between the leg modules 1 1 a-a' and platform 11 can be made. The platform module 11 is anchored in place by corner cables 38 awhich extend from corresponding winches on the platform at 45 angles to the platform sides to retrievable underwater anchors (not shown). The cables 38 a-d, by control of the winches, maintain the position of the platform module 11. On each leg module a dual cable system 39 ad and 40 ad extends from

separate winches

41 and 42 on the platform 11 along guides (not shown) disposed along the length of the leg module to pulleys at the end of the leg element. From the end of each leg module, the cables 39 a-d are extended transversely to a leg module and lie in a vertical plane. The ends of the respective cables are anchored to the ocean floor at suitable distances from the ends of the leg members by suitable retrievable anchors. Upon actuation of the

winches

41 and 42 and control of the forces on the cables, the outer ends of all leg members can be maintained in proper alignment and orientation with respect to the platform body 11 while they are flooded and slowly lowered to the bottom. The cables also provide a control so that excess force is not applied to the pivot connections 12 a-d. When the pins are in place, the entire system gives the appearance of gigantic pinwheel lying flat on the surface of the water.

While not shown, the chambers 33 ac can be compartmentalized along the length of the leg modules so as to selectively flood the compartments of a leg module beginning at the end of the leg module nearest the mat member 15a. This will insure an even disposition of the forces and can be controlled by any suitable control system. Any water in chamber 27 of the anchor mat 15a is pumped into the chamber 28 to provide a clockwise force about the pivot 20a and to maintain the pad in the aligned position. The lowering of the end of a leg module continues until the ends 42 of the mat members engage the floor 16 of the ocean as illustrated in FIG. 4. Because of the flooding of the lower tank chamber 28 of the mat members, the mat members are kept in an aligned position with respect to the leg modules. During this phase, the platform module 1 1 continues floating and buoyant.

In the position shown in FIG. 4, the water ballast contained in upper chambers 33 ac in the leg modules is expelled to provide buoyant lifting forces, the center of which is designed to remain always above the center of gravity to prevent any possibility of capsizing. As water continues to be expelled from the upper chambers of the leg modules, the entire interconnected system of platform body 11 and legs 13 ad continue to rise, causing the lower ends of the leg modules 13 ad with their pivoted mats 14 ad to move toward each other along bottom of the ocean. As the platform module rises, the

lower ends of the mats will be dragged by gravity toward each other along the bottom of the ocean.

As an alternative, a winch 44 and cable 45 (shown in FIG. 5) can be used to assist in drawing the leg modules toward one another. A cable 45 can be passed over a pulley 46 to extend horizontally to an opposite leg module. As shown in FIG. 5, the cable 45 would extend to the leg member 13c while a cable 48 from leg member 130 extends to leg member 13a and is attached thereto by a sling connector 49. By simultaneously applying tension to cables connected to all of the mid-sections of the leg members, the lifting of the platform 1 1 relative to the level 17 of the water can be accomplished.

In the position shown in FIG. 5 the compartments 27 in the anchor mat 14a are filled with water to decrease the buoyancy. An anchor mat pivots about the pivotal connection a into a position where the spuds 15a are embedded into the ocean floor under the mat. Each of the leg members and mat members is provided with a suitable mechanical or hydraulic interlock 50 which is actuated from the platform 11 above water and rigidly connects the leg member and mat member.

The stabilizer chains 18 ad, when required for a particular type of bottom soil condition, are transported to the drill site in separate segments lying in guideways (not shown) prepared along each leg 13 a-d. After rotation of anchor mats 14 a-d into final flat position on the ocean floor and before flooding the upper leg buoyancy compartments which lifted the platform out of the water, the upper ends of these chains 18 a-d between each pair of adjacent legs, such as 13a and 13b, are joined at a location 52 above water (See FIG. 6) with assistance of the deck cranes (not shown). Then by means of winches connected to the other ends of the cables and pulleys (not shown) at the lower ends of leg modules 13 a-d, the chains 18 ad are drawn down and locked into final position as shown in FIG. 7.

Summarizing the method of the present invention, it involves construction of a marine platform at an offshore location site in very deep water, wherein the platform consists of an above-water platform module plus at least three supporting leg modules. Each of the leg modules is comprised of a leg, proper, and a pivotally interconnected foot pad or mat. The method consists of the following major steps:

1. Separate fabrication of the several modules and sub-modules (even at different fabrication plants, if necessary or desirable),

2. Separate launching of the several modules and sub-modules,

3. Separate towing the each completed molule by one or more tugs across the open ocean to the selected location site for rendezvous with all companion modules. A minimum of four modules is necessary for a non-drilling three leg platform, whereas six or more modules are required for a drilling platform,

4. Mating and pivotally interconnecting of each leg sub-module 13a to its own mat sub-module 14a while in protected water facilitated by partial flooding of selective buoyancy compartments 27 at inner end of the mat and 336 at the far (upper) end of the leg,

5. Temporary anchorage of the platform module 11 with the anchor cables 38 a-d in such manner as to maintain precise location during the erection sequence without interfering with said sequence,

6. Careful maneuvering by tugs of each leg module 13 a-d into correct position with respect to the platform module 11, then temporary lateral anchoring of the outer mat ends of all leg modules with the cables 39 a-d and 40 a-d so as to limit and restrain the relative lateral movements of the leg modules, I

7. Connecting the inner ends of all leg modules 13 a-d by cables to winches mounted on the deck of the platform module, then winchin g all the legs into their respective guideways prepared in the platform module, and securing them all together by inserting and locking the pins in place. When this step is completed, the entire system will form a gigantic pinwheel lying flat on the surface of the ocean, and articulated with respect to the water plane at all connection points between modules and sub-modules,

8. Sinking the outertips of the leg modules 13 a-d (outer edges of mat sub-modules) until they touch the bottom of the ocean, by carefully controlled selective flooding of the tanks, with progressively greater flooding taking place toward outer tips. During this phase, the platform module 11 continues floating and is totally buoyant, providing the required stability to prevent any and all modules from capsizing,

9. The platform module is lifted out of the water (actually lifting the entire platform assembly, including the legs and the mats), by means of progressively increasing buoyancy of the upper ends of the legs, through carefully controlled selective expulsion of water from the buoyancy compartments. Precalculations for each platform design will insure that for each said design, the center of buoyancy will always remain above the center of gravity, permitting no tendency to capsize. As the platform assembly rises, the lower tips of the mat sub-modules will be dragged by gravity toward each other along the bottom of the ocean. The lifting phase will be terminated at a predetermined elevation of the platform module 11 above the water, with the bottom (outer) edges 42 of all mat submodules in contact with the ocean floor, and with all forces (buoyancy and gravity still in a stable state of equilibrium, 7

10. The mat sub-modules 14 a-d are pivoted about their bottom (outer) edges 42 which are in contact with the ocean floor, so as to bring the bottoms of the mats down flat on the ocean floor. If the spuds 15 ad are required for a given location, they will be forced to penetrate into the ocean floor under the mat bottoms. While all the mats are pivoting about their outer edges, another simultaneous pivoting motion will be occuring at all of the mat pin connections between the legs and the mats, changing the angle between the axis of each leg with respect to the axis of its corresponding mat from nearly parallel, to about 65. At the same time, a third set of simultaneous pivoting motions will be taking place at all main pins which connect the legs to the platform module. When all of these carefully controlled pivoting actions have been completed,

the entire platform assembly will be seated in final I position on the ocean floor,

l l. The mat tie chains 18 a-d which were transpofted the bottom. When all chains have been lowered to the bottom and snugged-up with the deck winches, they are then locked in position so that they will permanently prevent horizontal movement of the mats relative to each other,

12. Fill-in and support members 54 are added between the platform and upper ends of legs for strength,

13. Locking mechanisms 50 on the mats are actuated to prevent any further change in the angles between the legs and the mats. These locking mechanisms, where deemed necessary for a particular design (they may not be required at some locations), can be hydraulic and reversible. Their use will ap preciably increase rigidity of the structure, and reduce flutter of the slim legs due to wave action,

14. The legs can then be reflooded in order to firmly seat the mats into the mud on bottom of the ocean, and provide sufficient gravitational anchorage to prevent dislocation of the platform by storm forces. When this is completed, then all compartments is all legs and mats will become available for underwater storage of oil, utilizing the same piping and valving which was used for control flooding and dewatering during the erection sequence, with all valves located above water.

In the present system, the drilling conductors can also be floated to an offshore location site in very deep water. The conductors are bundled together into an integral structural package of sufficient strength to span or extend vertically from ocean bottom to the platform above. The fabrication of the conductor bundle is accomplished at a location where it can be launched like a ship or barge. It consists of several parallel rows of conductors, for example, 30 inch diameter pipes trussed together in both directions with smaller pipes at appropriate angles and spacing throughout their full lengths. The length of the pipes is about 50 feet greater than the water depth at the drilling location. All of the conductors have water-proof closures at both ends, the lower ends probably being closed with rubber diaphrams which are commercially available. The conductor bundle is suitably valved at each end in such mannner that flooding can be precisely controlled from above water. A typical conductor bundle can be constructed in a similar manner to a leg module such as illustrated in the drawings without the pad or mat and without the hinge connection.

A conductor bundle is lauched and towed to the drilling location by one or more tugs. At the location, controlled flooding of one end of the conductor bundle is performed while the opposite end is held in approximate location by moderately tensioned cables to the platform. This step is completed when the bundle is floating in vertical attitude with its lower end a few feet above bottom of the ocean. Further flooding of the bundle after precise location is accomplished in order to sink the lower end into the mud and fix it in location so that no more horizontal movement can occur. At this time, another section can be added on at top of the bundle. The prefabricated add-on will be shorter, perhaps only 50 or 100 feet, and may be transported on a barge, instead of floating, but will otherwise be like the main bundle. This add-on will take considerable time to complete all of the welding. Temporary closures at the top of the main bundle will also be removed at this time. Further flooding of the bundle will force its lower end further into the bottom of the ocean. Since total flooding will not produce sufficient penetrationfor safe anchorage and safe support of wells and wellheads, sea water is pumped into the tanks on the top of the bundle to cause more penetration, as required for load support. When final penetration is obtained, the upper end of the conductor bundle will be laterally secured to the platform in such manner that differential vertical settlement can be accommodated without causing structural distress. The conductor bundle will then be vertically and horizontally supported at mud line, and horizontally supported at the platform level, and its own flexural strength will permit it to span as a vertical beam between top and bottom, resisting wave forces.

The advantages of the present system are that all fabrication, erection and operational work are accomplished above water, under atmospheric conditions and no diving or submarine work is required. No pile-driving of the type normally required for template type steel platforms will be required. No derrick barge or derrick ship will be ordinarily required for initial installation. However, a derrick barge may be needed if some equipment modules later need to be changed out during switchover from a predominantly drilling operation to a predominantly production operation. Also, still later, when compression becomes necessary, a derrick barge will again be needed to change out equipment modules. The several anchors and cables (also Winches) used during the erection can be salvaged almost immediately if desired and reused on other projects. The entire platform assembly including legs and mats can be totally salvaged and re-erected at a different location if necessary. A large volume of oil can be temporarily stored under water, within the legs and mats of this platform, during the production phase of its useful life.

While particular embodiments of the present inven tion have been shown and described, it is apparent that changes and modifications may be made without departing from this invention is its broader aspects; and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for erecting a marine platform at a deep water offshore location site where the platform consists of a surface platform module and at least three supporting leg modules, the method comprising the steps of floating each of platform and supporting leg modules independently to an offshore site,

at a given offshore site, pivotally interconnecting the leg modules at one of their ends to the platform module,

increasing the density of said leg modules at their other ends so as to pivot said leg modules about the pivotal interconnection until said other ends of said leg modules are in engagement with the ocean floor,

after said other ends of said leg modules are in engagement with the ocean floor, decreasing the density of the upper ends of said leg modules and pivoting said leg modules further about the pivotal interconnection to raise said platform member above the surface of the water.

2. The method as defined in claim 1 and further including the step of anchoring said other ends of said leg modules in the ocean floor after said platform module is raisedabove the surface of the water.

3. The method as defined in claim 1 wherein said leg modules are floated to the offshore site with their lengthwise dimension in a nearly horizontal position.

4. The method as defined in claim 3 wherein the density of the leg modules is increased by filling hollow interiors of the leg modules with water, and further including the step of maintaining counterbalancing forces on each leg module while it is being pivoted into position.

5. A method of erecting a marine platform at an offshore location site where the platform consists of a surface platform module and three or more supporting leg modules, and where each of said modules have buoyancy chambers along their length, and each of said leg modules have pivotally connected anchor mats at an outer end thereof, the method comprising pivotally connecting each of said supporting leg modules in horizontal positions, respectively, to one of the sides of said surface platform module,

filling said buoyancy chambers of said leg modules with water beginning at the outermost ends of said leg modules for tilting said leg modules toward near vertical positions until the outermost ends of said anchor mats engage the bottom of the ocean floor,

increasing the buoyancy of said leg modules while moving said leg modules to a desired near vertical attitude for raising said platform module above the level of the water, and

pivoting said anchor mats to an anchoring position with respect to the ocean floor.

6. The method as defined in claim 5 and further including the step of maintaining an anchoring surface of said anchor mats in alignment with the lengthwise dimension of a leg module until said platform module is elevated above the surface of the water, and thereafter pivoting said anchor mats relative to a leg module by placing the anchoring surface into engagement with the ocean floor.

7. The method as defined in claim 6 wherein said pivoting of said anchor mats is followed by the step of locking said leg module and an anchor mat in position relative to one another.

8. The method as defined in claim 6 and further including the step of maintaining counterbalancing lateral forces in a direction transverse to a leg module while it is being pivoted into an anchoring position.

9. A method for erecting an offshore platform in deep water comprising the steps of floating separate modules of said platform to an offshore site where said modules include a surface platform and legs, said leg modules including buoyancy chambers for controlled flooding and expelling of water,

at the offshore site, anchoring said platform at a site position, connecting all of the legs pivotally to said platform while said legs are in a nearly horizontal position, extending transverse cables in opposite directions from the outermost ends of said legs and connecting said cables through the length of said legs to winches on the platform,

flooding the outermost ends of said legs with water and controlling the lateral forces on the legs with said transverse cables to pivot said legs into a nearly vertical position, until the outermost ends of said legs engage the bottom of the ocean floor, and expelling water from said legs to increase their buoyancy for lifting said platform out of said water while pivoting said legs to an anchoring position and 10 maintaining the center of buoyancy above the center of gravity for the assembly. 10. The method as defined in claim 9 and further including the step of floating a conductor bundle to the site location in a horizontal condition where said bundle has buoyancy chambers for control flooding of water,

at the site location, after the platform is raised, flooding the outermost end of said conductor bundle while fixing the location of the other end relative to the platform until the conductor bundle is in a vertical position,

maintaining said bundle in a vertical position off of the ocean floor and moving said bundle into location relative to said platform module, and

filling said bundle with water to set it in location for well operations. 11. A method for erecting an offshore platform in deep water comprising the steps of floating separate modules of said platform to an offshore site where said modules include a surface platform and leg modules, said leg modules including buoyancy chambers for controlled flooding and expelling of water, said leg modules further including mat modules pivotally interconnected to the outermost ends of said leg modules, said mat modules having buoyancy chambers for controlled flooding, flooding said mat modules so as to maintain said mat modules in general horizontal alignment with the length of said leg modules, at the offshore site, anchoring said platform at a site position, connecting all of the leg modules pivotally to said platform while said leg modules are in a nearly horizontal position, extending transverse cables in opposite directions from the outermost ends of said leg modules and connecting said cables through the length of said leg modules to winches on the platform, flooding the outermost ends of said leg modules with water and controlling the lateral forces on the leg modules with said transverse cables to pivot said leg modules into a nearly vertical position and maintaining said mat modules in general horizontal alignment with the leg modules while said leg modules are pivoted so that said mat modules are brought into engagement with the ocean floor, and

following the expelling of water from said leg modules, the step of flooding said mat modules with water to pivot said mat modules into anchoring position with the ocean floor.

12. The method as defined in claim 11 and further including the step of interconnecting one end of chains extending from each of said legs at the platform where the chains extend along the length of a leg and pass over a pulley at the outermost end of a leg and return to the other end of the leg, and

after interconnecting the one end of said chains, taking up the slack in the other ends of said chains to position said chains as an interconnection between the outermost ends of said legs.

13. A marine platform for deep water installation comprising a surface platform module,

at least four supporting leg modules disposed at locations lying on perpendicular, intersecting, horizontal axes, means pivotally connecting one end of said leg modules to said surface platform module, said pivot means respectively having pivot axis at said locations in a position normal to an axis, each 11 12 of said leg modules including tubular members arpartments, and ranged in an equidistant triangular relationship means for selectively flooding said buoyancy comwith interconnecting support members, each of partments with sea water. said tubular members including buoyancy com 5

Claims

1. A method for erecting a marine platform at a deep water offshore location site where the platform consists of a surface platform module and at least three supporting leg modules, the method comprising the steps of floating each of platform and supporting leg modules independently to an offshore site, at a given offshore site, pivotally interconnecting the leg modules at one of their ends to the platform module, increasing the density of said leg modules at their other ends so as to pivot said leg modules about the pivotal interconnection until said other ends of said leg modules are in engagement with the ocean floor, after said other ends of said leg modules are in engagement with the ocean floor, decreasing the density of the upper ends of said leg modules and pivoting said leg modules further about the pivotal interconnection to raise said platform member above the surface of the water.

2. The method as defined in claim 1 and further including the step of anchoring said other ends of said leg modules in the ocean floor after said platform module is raised above the surface of the water.

5. A method of erecting a marine platform at an offshore location site where the platform consists of a surface platform module and three or more supporting leg modules, and where each of said modules have buoyancy chambers along their length, and each of said leg modules have pivotally connected anchor mats at an outer end thereof, the method comprising pivotally connecting each of said supporting leg modules in horizontal positions, respectively, to one of the sides of said surface platform module, filling said buoyancy chambers of said leg modules with water beginning at the outermost ends of said leg modules for tilting said leg modules toward near vertical positions until the outermost ends of said anchor mats engage the bottom of the ocean floor, increasing the buoyancy of said leg modules while moving said leg modules to a desired near vertical attitude for raising said platform module above the level of the water, and pivoting said anchor mats to an anchoring position with respect to the ocean floor.

9. A method for erecting an offshore platform in deep water comprising the steps of floating separate modules of said platform to an offshore site where said modules include a surface platform and legs, said leg modules including buoyancy chambers for controlled flooding and expelling of water, at the offshore site, anchoring said platform at a site position, connecting all of the legs pivotally to said platform while said legs are in a nearly horizontal position, extending transverse cables in opposite directions from the outermost ends of said legs and connecting said cables through the length of said legs to winches on the platform, flooding the outermost ends of said legs with water and controlling the lateral forces on the legs with said transverse cables to pivot said legs into a nearly vertical position, until the outermost ends of said legs engage the bottom of the ocean floor, and expelling water from said legs to increase their buoyancy for lifting said platform out of said water while pivoting said legs to an anchoring position and maintaining the center of buoyancy above the center of gravity for the assembly.

10. The method as defined in claim 9 and further including the step of floating a conductor bundle to the site location in a horizontal condition where said bundle has buoyancy chambers for control flooding of water, at the site location, after the platform is raised, flooding the outermost end of said conductor bundle while fixing the location of the other end relative to the platform until the conductor bundle is in a vertical position, maintaining said bundle in a vertical position off of the ocean floor and moving said bundle into location relative to said platform module, and filling said bundle with water to set it in location for well operations.

11. A method for erecting an offshore platform in deep water comprising the steps of floating separate modules of said platform to an offshore site where said modules include a surface platform and leg modules, said leg modules including buoyancy chambers for controlled flooding and expelling of water, said leg modules further including mat modules pivotally interconnected to the outermost ends of said leg modules, said mat modules having buoyancy chambers for controlled flooding, flooding said mat modules so as to maintain said mat modules in general horizontal alignment with the length of said leg modules, at the offshore site, anchoring said platform at a site position, connecting all of the leg modules pivotally to said platform while said leg modules are in a nearly horizontal position, extending transverse cables in opposite directions from the outermost ends of said leg modules and connecting said cables through the length of said leg modules to winches on the platform, flooding the outermost ends of said leg modules with water and controlling the lateral forces on the leg modules with said transverse cables to pivot said leg modules into a nearly vertical position and maintaining said mat modules in general horizontal alignment with the leg modules while said leg modules are pivoted so that said mat modules are brought into engagement with the ocean floor, and following the expelling of water from said leg modules, the step of flooding said mat modules with water to pivot said mat modules into anchoring position with the ocean floor.

12. The method as defined in claim 11 and further including the step of interconnecting one end of chains extending from each of said legs at the platform where the chains extend along the length of a leg and pass over a pulley at the outermost end of a leg and return to the oTher end of the leg, and after interconnecting the one end of said chains, taking up the slack in the other ends of said chains to position said chains as an interconnection between the outermost ends of said legs.

13. A marine platform for deep water installation comprising a surface platform module, at least four supporting leg modules disposed at locations lying on perpendicular, intersecting, horizontal axes, means pivotally connecting one end of said leg modules to said surface platform module, said pivot means respectively having pivot axis at said locations in a position normal to an axis, each of said leg modules including tubular members arranged in an equidistant triangular relationship with interconnecting support members, each of said tubular members including buoyancy compartments, and means for selectively flooding said buoyancy compartments with sea water.