US2837897A

US2837897A - Automatic underwater bracing system for a mobile drilling rig

Info

Publication number: US2837897A
Application number: US458178A
Authority: US
Inventors: Wendell H Nedderman; Richard T Lietz
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1954-09-24
Filing date: 1954-09-24
Publication date: 1958-06-10
Anticipated expiration: 1975-06-10

Description

J1me 1958 w. H. NEDDERMAN ETAL 2,837,897

AUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG 2 Sheets-Sheet 1 Filed Sept. 24, 1954 FI G. 1.

FIG. 2

P TTORNEY June 10, 1958 w. H. NEDDERMAN EI'AL 2,837,897

AUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG Filed Sept. 24, 1954 2 Sheets-Sheet 2 25 26k 11 i 1L i E 10 u I l 'l [I H II n "25:? ?ii I! 5% I '5' 21 22 ;i 11 1 ii 16{ I 14! 1 l 25" f -26 L 17f L INVENTORS w 5' NE PMYQN RT-LIET i-XTTOPNEY United States Patent AUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG Wendell H. Nedderman, College Station, and Richard T. Lietz, Houston, Tex., assignors, by direct and mesne assignments, to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application September 24, 1954, Serial No. 458,178

3 Claims. (Cl. til-46.5)

This invention relates to an automatic underwater bracing system for a mobile drilling platform which is floated to the site of drilling operations and is there raised and supported on tubular columns or pilings which are lowered to bottom. The mobile structure may includes a submersible barge serving as a foundation unit from which upright columns extend to project above water when the foundation unit rests on bottom and upon which columns the platform is elevated to a position sufiiciently high above water level to be out of the reach of waves.

Such a structure is constantly subjected to lateral forces of varying magnitude and direction which are imposed upon it by wind and water and it must additionally carry heavy loads. Bracing of the relatively thin and long supporting columns is therefore required to impart rigidity to the structure, and especially where the installation is made in relatively deep water, say 70 to 140 feet, the problem arises of erecting underwater braces for the submerged lengths of the supporting columns without restort to the services of a diver or to the use of complicated and expensive clamping means remotely controlled from the platform.

The present invention has as one of its objects to provide an underwater bracing system which is initially collapsed but which is automatically erected between the supporting columns as they are being lowered to bottom.

For the purpose of illustrating the system of bracing without, however, limiting the invention in its application to the particular type of mobile structure illustrated, the accompanying drawings, showing end'elevations in all figures, are as follows:

Figure 1 shows a platform having a foundation barge drawn up to its under side, in which position the structure may be towed to a desired location with the bracing system collapsed and stowed between the platform and the underlying submersible foundation.

Figure 2 shows the mobile unit at a drilling site, the foundation barge being lowered part way to bottom and the bracing system partially erected.

Figure 3 shows the mobile unit with "the foundation barge resting on bottom and with the platform floating,-

in which position the bracing system is fully erected.

Figure 4 shows the structure in final position with the platform elevated above water level.

Referring more particularly to the drawings, a platform which may comprise a buoyant hull is provided with a series of wells 11 through which tubular columns or pilings 12 extend. The lower ends of the columns are permanently built into an underlying foundation barge 13 which can be flooded and sunk to rest on bottom when the platform is in desired location.

Tubular braces

14 and 15 extend horizontally between adjacent columns 12 and at their panel points they carry rings or short tubular sections which encircle the columns and are slidable thereon but without appreciable looseness of fit. These

braces

14 and 15 constitute opposite sides of a truss panel between the adjacent supporting columns. Chain or

wire cables

17 and 18 extend diagonally between the ends of the

horizontal braces

14 and 15, as cross-tie elements, and

similar cables

19 and 20 extend between the brace 15 and the foundation barge 13 to which they are permanently fastened, there being as many of these horizontal braces, and consequently as many truss panels, as may be required, depending upon the length of the supporting columns.

Cables

21 and 22 which are fastened to the opposite ends of the horizontal brace 14 pass upwardly through the wells 11 in the platform, or through separate wells provided therefor, and over

sheaves

23 and 24 mounted on the upper ends of the columns 12.

counterweights

25 and 26 to which the

cables

21 and 22 are attached may suitably ride within the hollow columns, these cables being arranged to be engaged by platform-mounted clamps 27 after the platform has been elevated to the desired height by jacks (not shown) which grip the columns, or by other suitable lifting means such as block and tackle, gearing, etc. Thus, in Figures 1 to 3, the clamps 27 are shown open so that the cables may ride freely therethrough while in Figure'4 they are shown closed on the cables.

As illustrated in Figure, 1, the rig is in towing position. The

cables

21 and 22 are held taut by the

counterweights

25 and 26 which are freely slidable in the columns 12, whereby they assist in drawing the horizontal brace 14 up to the under side of the platform which may be suitably recessed to receive it as well as the similar horizontal brace 15, the

cross bracing cables

17 and 20 being slack. it is within the purview of this invention that the foundation barge, instead, may be recessed in its upper surface for stowing the collapsed bracing system.

When the foundation barge is lowered to bottom, as shown in successive stages in Figures 2 and 3, the lowermost brace 15 drops with the foundation barge, the upper horizontal brace 14 being restrained by the counterweights. Thus, the

crossed cables

17 and 18 are pulled taut and as the foundation barge continues to sink, the

crossed cables

19 and 20 are likewise tightened and the upper horizontal brace 14 is drawn down against the upward pull of the counterweights exerted through the

cables

21 and 22. The counterweights additionally have a cushioning action which avoids sudden shock or impact as slack is taken out of the crossed cables and they reach their full extension.

With the foundation barge resting on bottom, the counterweights hold the underwater bracing system in extended condition under tension. For this purpose, the size of the counterweights is selected according to the weight and number of cross-braced units or truss panels. The submerged weight of the horizontal braces alone will be relatively small since these members are tubular and closed at their ends, and so have considerable buoyancy.

The platform is next elevated above water level on the columns by means of jacks, block and tackle, gearing or other conventional mechanism which is suitable for the purpose. When the platform has reached a desired height, slips (not shown) are set to grip the column and prevent its retrograde movement. Clamps which are mounted on the platform and indicated generally at 27 in the drawings are manipulated to grip the

cables

21 and 22, as shown in Figure 4, whereby the bracing system is maintained under the desired tension for its adequate functioning. Where necessary, the counterweights may be removed from certain of the hollow columns after the platform has been secured in elevated position and the

cables

21 and 22 have been clamped as aforesaid. The necessity for removing the counterweights from the hollow Columns may be expected to arise only where the design of the platform requires that spud piling be driven through certain of the B3 supporting columns, in which case the counterweights would constitute an obstruction.

As an alternative to the use of countcrweights, a winch may be mounted on the platform to haul up and thereby erect the underwater bracing system after the foundation barge has been lowered, and to hold the bracing system at its proper location on the pilings.

The lengths of the crossed cables and the number of horizontal braces between which they extend will depend upon the expected range of operating depths for the platform. Should it be desired to utilize only the upper unit of the bracing system, provision may be made for temporarily securing the horizontal brace to the foundation barge to hold the lower truss panel in collapsed c0ndition. The abbreviated bracing system thus provided may be used where operations are conducted in relatively shallow water.

While the invention contemplates the use of either chain or wire cable for the cross members, heavy anchor chain is desirable for the purpose since it has less tendency to snarl and tangle when stowed. The

lifting cables

21 and 22 are desirably of high tensile strength steel wire.

From the foregoing it will be understood that when the foundation barge is lowered the bracing system is automatically brought into the proper position under the pull exerted by the lower diagonal crossed cables which are fastened to the foundation unit and the opposing pull of the counterweights on the top horizontal brace member. As thus erected, the system affords adequate bracing for the columns without requiring laborious clamping procedures, yet it may be collapsed with facility and conveniently stowed when the platform is to be moved to a different location.

What we claim is:

1. In combination with a platform supported over water on a plurality of columns which are lowered to bottom and partly submerged, an automatically erected underwater bracing system for the supporting columns comprising a number of rigid brace members extending horizontally between the adjacent columns and having rings at their ends encircling the columns and permitting the brace members to move therealong, cross cables connecting adjacent brace members, said cross cables being of such flexibility that the connected brace members may be collapsed together and stowed in stacked relation, further flexible cross cables attached at one end to the lowermost brace member and anchored at their opposite ends in fixed relation to the columns whereby they are placed under tension as the columns are lowered, and means exerting an upward pull on the uppermost horizontal brace member as the lowermost brace member is pulled downwardly in lowering the supporting columns,'whereby the flexible cross cables of the bracing system are placed under tension.

4 l 2. In combination with a platform supported over Water on a plurality of columns which are lowered to bottom and upon which the platform is elevated above water level, an automatically erected underwater bracing system for the supporting columns comprising rigid brace members extending horizontally between the adjacent columns and having rings at their ends encircling the columns, and enabling the brace members to move there along, cross cables extending diagonally between the brace members and because of their flexibility permitting the brace members to be collapsed together and stowed in stacked relation, further cross cables attached at one end to the lowermost brace member and anchored at their opposite ends in fixed relation to the columns, whereby they are placed under tension as the columns are lowered, cables passing upwardly from the uppermost brace member and over sheaves carried by the columns, and counterweights on said last-named cables exerting an upward pull on the extended bracing system sufiicicnt to maintain tension on the diagonally extending cross cables thereof. 3. In combination with a platform supported over water on a plurality of columns projecting from a submersible barge which when sunl: serves as a foundation resting on bottom, an automatically erected bracing system for the supporting columns comprising a plurality of rigid brace members extending between pairs of adjacent columns and having rings at their ends encircling the columns to permit relative vertical movements of the brace members, diagonally crossed cables connecting each brace member with the next in series and, because of their flexibility, permitting the series of brace members to be collapsed together and stowed between the platform and submersible structure drawn up thereto in moving to location, cables passing upwardly from the uppermost brace member and over sheaves mounted on the columns above the platform, counterweights on said cables exerting an upward pull on the bracing system, crossed cables connecting the lowermost brace member to the submersible structure and serving to draw the bracing system of cross cables taut against the upward pull of the counterweights as the fundation structure is sunk, and fastening means on the foundation structure for securing a lower brace member and thereby selectively shortening the span of the extended bracing system.

References Cited in the file of this patent UNITED STATES PATENTS