US3044561A

US3044561A - Support structure

Info

Publication number: US3044561A
Application number: US664574A
Authority: US
Inventors: William F Swiger
Original assignee: Superior Oil Co; Shell Oil Co; Union Oil Company of California; Continental Oil Co
Current assignee: Superior Oil Co; ConocoPhillips Co; Union Oil Company of California; Shell USA Inc
Priority date: 1957-06-10
Filing date: 1957-06-10
Publication date: 1962-07-17
Anticipated expiration: 1979-07-17

Description

w. F. SWIGER 3,044,561

SUPPORT STRUCTURE July 17, 1962 Filed June 10, 1957 3 SheetsSheet 1 F/G./. F/6.2.

INVENTOR. WILL/AM F. SW/GER ATTORNEYS July 17, 1962 w. F. SWIGER 3,044,551

SUPPORT STRUCTURE Filed June 10, 195'? 3 Sheets-Sheet 2 INVENTOR. WILL/4M F. SW/GER 5%J1/Zh5/744 FIG. 5.

United rates This invention relates to structures for supporting a platform above the surface of a body of water.

Co-pending application Serial'No. 553,567, filed December 16, 1955, discloses an elongated tripod support structure with hollow legs adapted to be floated horizontally in a body of water and towed to a desired location. The legs of the structure are adapted to be flooded at one end at a controlled rate so that the flooded ends sink and tilt the structure toward an upright or vertical position. Flooding of the structure is continued until it rests firmly on bottom.

This type of structure is ideally suited to be transported to different locations and erected to support various types of equipment above a body of water. For example, it can be used to support drilling equipment for offshore wells, or it can be used to support electronic equipment such as that used for offshore radar stations. The struc ture has the advantage that it can be dewatered and tilted from a vertical to a horizontal position so that it may be towed easily from one location to another.

When the structure is to be erected in relatively deep water and used to support heavy equipment such as a drilling rig, the structure must be firmly anchored on the formation under the water.

This invention provides an apparatus for improved anchoring of offshore structures having at least one hollow leg.

In terms of method, one aspect of the invention contemplates anchoring a hollow leg structure in a formation under a body of water by positioning the structure in an upright position in the water with the lower end of the legs resting on the formation. At least one hollow leg is filled with a fluid heavier than the water in which the structure is located so thatthe structure is anchored firmly to the formation.

In terms of apparatus the invention includes a hollow leg structure adapted to be floated horizontally in a body least one hollow leg to add to the stability of the struc If the structure is to be anchored permanently. in place, say as a permanent radar installation, the heavy fluid Zis concrete or some similar mate'rial which takesa permanent set and adds to the strength of the structure. Ifthe structure is to be moved from one location tosanother, the fluid is of such a nature that it does not take a permanent set. For example, the fluid could be a concentrated heavy salt solution such as zinc chloride.

If the structure is used in drilling an offshore Well, preferably the heavy fluid is drilling fluid used in drilling the well. Disposed drilling fluid in at least one of the legs of the structure aids in firmly anchoring the structure in place, and stores a large amount of .weight in a position to provide a'low center of'gravity, therebyincreasing the stability of the structure and reducing the Weight which must be supported by a platform on the upper end of the structure. This is an important advantage because at times the weight of the drilling mud can Patented July 17,- 1962 amount to as much as half the load which would have to be supported by the platform if the mud were not stored in at least one of the hollow legs.

Depending on the depthand size of the well being drilled, the amount of drilling fluid required can vary between 500 and 1500 barrels. If a well requires 1,000 barrels of mud weighing 11 pounds per gallon, the total Weight of the mud is about 230' tons. By storing a substantial portion of the mud in at least one of the legs, a considerable load is taken off of the drilling rig platform, and at the same time, the stability of the structure is also increased. Moreover, the drilling mud does not take a permanent set and can easily be flushed from the legs when the structure is to be moved.

In terms of apparatus for drilling an underwater well, the invention contemplates a support structure resting on a formation under a body of water and extending toward the water surface. The structure includes at least one hollow leg in which a drilling fluid is stored, and a drill pipe is supported from the structure to extend down into a well being drilled. Conduit means are provided for connecting the upper end of the drill pipe with the hollow leg, and conduit means are-provided for connecting the hollow leg with the annular space between the drill pipe and the well so that drilling mud can be circulated from the hollow leg through the drill pipe and back to the hollow leg.

In terms of method for drilling an underwater well from a hollow leg structure resting on.a formation under a body of water, the invention includes the steps of forming a hole in the formation with a drill pipe supported by the structure. A drilling fluid is disposed in at least one hollow leg in the structure, and circulated from the leg through the drill pipe and back into the hollow leg. 7

These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 is a side elevation of a hollow leg support structure floating horizontally in a body of water;

FIG. 2 is an end view of the structure shown in FIG. 1;

FIG. 3 is a schematic side elevation, partially broken away, showing the structure of FIG. 1 being tilted toward a vertical position by flooding one end of the legs of the structure; v i I FIG. 3A is a side elevation of the structure of.FIG.v l

flooded to rest in a vertical position on the, bottom of the water body; I

FIG. 4 is a schematic elevation, partially broken away, of the structure of FIG. 1 resting in an upright position on the underwater formation and supporting a'tits upper end a platform and drilling rig being used to drill a well in the formation; i

FIG. 5 is an enlarged view taken online 5-5, of FIG. 4 showing how drilling fluid is circulated from one of the hollow legs into the well andbackfto the hollow g; v FIG. 6 is a schematic sectional elevation of the hollow leg in which drilling fluid is circulated and stored; and

"FIG. 7 is a view taken on line 7-7 of FIG. ';6. Referring to FIGS. v1 and 2, the support comprises a pair or first set of parallel tubularlegs 13, 14 (see FIG, 2) which are designated the lower legs, since these legs are shown floating in a body of waterf15 when the struc I ture is in a horizontal position. A'n upperv or third leg 16 is connected to each of the two lower legs byhollow tubular buoyant bracing members 17 so the'upperleg is parallel to and equidistant from the other two legs. The tubular members are arranged ina K-brace system and the two lower legs are connected to each other by an identical arrangement so that each leg is equidistant from the other two. i

A temporary truss 18 is mounted across the ends of the legs which will be the upper ends when the structure is in an upright position. Unless otherwise indicated, throughout the remainder of the description the terms upper and lower are used to indicate relative positions when the structure is in an upright position.

Referring to FIG. 6, leg 14 is shown in detail, and since all three legs are identical, a description of this leg will suflice :for the other two. Starting at the lower end, the leg has a plurality of longitudinally spaced

transverse diaphragms

19A, 19B, 19C, 19D, etc., dividing the leg into

separate compartments

20A, 20B, 20C, 20D, etc., in ascending order. Compartment 20A is connected to compartment 20B by a conduit 24 extending through the upper (when the leg is in a horizontal position) edge of diaphragm 19A into compartment 2trB. A similarly located conduit 26 connects compartment 20B with compartment 20C, and so on to the uppermost compartment which is sealed at its top by a cap 27.

A valve 28 within the lower end of compartment 20A is adapted to be controlled by a pneumatic line 29 extending to the upper end of the leg to admit water to the compartment 20A. The lower end of leg 14 is closed with'acover plate 32.

Four elongated symmetrically spaced tubular pile guides 42 extend longitudinally throughout the length of the legs, and each guide extends through and is welded to the respective diaphragms to effect fluid-tight seals for the compartments. 7

An air line 46 extends through the cap on the upper end of the structure and is adapted to receive compressed air from a supply (not shown) to pressure the compartments and control flooding or dewatering of the leg.

The upper end of each pile guide terminates just above the cap on the upper end of the leg, and is sealed thereto by welding. These ends of the pile guides are closed by temporary plugs (not shown) when the structure is floated horizontally in the water. The lower ends of the pile guides are welded around openings 50 in the cover plate sliding fit inside the pile guides, are driven into the bottom of the Water body by pile driving means (not shown) on the temporary truss to anchor the structure firmly in place.

If the structure is to be used to support a permanent radar installation, for example, the legs are filled with a concrete slurry (not shown) which is allowed to set to give the structure additional weight to anchor it to the formation and at the same time increase the strength of the legs. The piles and pile guides in the legs serve to reinforce theconcrete and provide additional strength for the structure.

0n the other hand, if the structure is to be used for V drilling, as shown in FIG. 4, a floating barge or platform on the lower end of the leg. The openings are sealed by knock-out plugs 51. The lower end of each of the pile guides (see FIG. 6) has holes 52 to vent the interior of the pile guides to compartment 20A. The knock-out plugs are lightly welded in place so they may be readily knocked off by piles 55 (see FIG. 4) which may be driven down through the pile guides and out the lower end of the legs when the structure is resting on a soft bottom.

To tilt the structure from a horizontal to a vertical position, a controlled amount of water is admitted to the end of each of the lower legs which is to rest on the bottom. Referring to FIG. 3, the structure starts tilting to- 64 adapted to support a drilling rig 65 is then floated into the space between the upper ends of the legs and hoisted above the. water on support rods 66. One of. the pile guides in at least one of the legs, and preferably in each of the legs, is kept open by not driving a pile down it. Water is displaced from each of the legs by pumping a drilling fluid or mud (not shown) down the open pile guide. The mud is heavier than the Water and adds to the stability of the structure. A well 68 is drilled inthe formation with a string of drill pipe 70, and a surface conductor 72 is cemented in the well. Referring to FIG. 5, the surface conduct-or extends from the well up into a bore 74 in the platform and terminates just below a rotary table 76 which is supported by the platform and powered by conventional means (not shown). Drilling fluid flows through a pick up conduit 78 in the upper end of one of the legs of the structure, and is forced by a first pump 80 through a drilling mud hose 82 into a swivel 84 suspended by a hoisting cable 86 which in turn is supported at the upper end of a derrick 88. The mud flows from the swivel down through a kelly joint 89 extending through the rotary table and connected to the upper end of the drill pipe string. The mud flows out the bottom of the drill pipe, picks up cuttings formed in the well and flows back up the annular space between the drill pipe and the surface conductor. A lateral conduit 90 in the upper end of the surface conductor discharges drilling fluid and cuttings on a shaker screen 92 which separates cuttings and drilling fluid so that the drilling fluid flows through the screen into a hopper 94 and into a settling pit 96 in the platform. The cuttings slide oil the screen and are either collected or discharged into the water. A vertical baffle 98 divides the settling pit into two sections, and the mud from the well flows into a remote end of one of the sections. The mud then flows over the baflie into the other section Where it is picked up through a conduit 99 and returned by a second pump 100 down the open pile guides connected by a coupling 101 and line 102 to-the ward an upright position. In the initial stages of flooding the two lower legs to start the structure tilting toward the vertical, the location of conduits 24, 26, etc., in the

diaphragms

19A, 19B, etc., insure that each compartment 6 is completely flooded before flooding of the superadjacent compartment begins. Thus, substantially no air is trapped in the compartments and the flooding of the structure proceeds in an orderly and predictable manner.

If the cross bracing did not exert'a buoyant efiect as the structure tilts, the moment tending to cause the structure to tilt to a vertical position would increase rapidly as the structure tilts, and smash the upperv leg into the water with a force which might cause injury to personnel or damage to the structure. However, the buoyant crossbracing holds the tilting to a safe rate and permits the upper leg to enter the water gently.

The two lower legs are flooded until the structure reaches a vertical position, and then all three legs are gradually flooded to approximately the Water leveljto seat the structure firmly on the bottom. The plugs are re-.

moved from the upper end of each pile guide, if a soft second pump.

The settling pit provides a zone of suflicient quiescence for the drillingmud to permit the settling 0t sand and relatively small cuttings which might not have been separated from the drilling mud by the shaker and screen. The mud jets from the openings 52 in the 'bottom of the l pile guide at a rate sufiicient to keep the mud in the bottom of the leg thoroughly stirred. The mud then flows upwardly through the compartments in the leg where it is finally picked up again by the pick-up conduit'78. By

having the mud flow in an upward direction through the leg, the settling of fine particles in the leg is prevented.

The other two legs may be used for storage or circulation of drilling fluid if required, and provide ideal storage space for standby emergency mud which might be required in the case of a threatened blow-out or lost circulation. By storing the mud in the legs, a considerable bottom is encountered, and piles 55, which make a close 75 weight is relieved from theplatform, and the stability of the structure is increased. Moreover, the mud can easily be removed from the legs to permit the structure to be moved to a new location.

If it is desired to remove the structure, the drilling platform is lowered and towed away, the piles are disengaged at their lower ends below the lower ends of the legs of the structure, either being decoupled, jetted free, or cut by suitable means, such as shaped charges. The lower ends of the pile guides are plugged with a packer 67 (see the right hand pile guide in FIG. 6), the caps 27 are replaced and the legs are dewatered or de-mudded in reverse order from that described above. Recovery of the structure proceeds in the reverse direction to bring the structure back to the horizontal position shown in FIG. 1. If the legs are filled with a drilling mud or other material which is worth saving, the mud may be recovered by pumping water down on top of the mud and forcing the mud up the open pile guide to the upper end of the structure where it may be collected, say on a barge.

I claim:

1. An offshore apparatus for drilling holes in geological formations underlying a body of water, the apparatus comprising a unitary structure floatable horizontally to a drilling site and sinkable in a vertical orientation to the bottom of the body of water at the site, the structure having a set of laterally spaced-apart elongated rigid legs which in vertical orientation extend from the bottom to above the surface of the body of water, rigid braces between the legs, one of the legs having a plurality of compartments along its length, the compartments being in internal fluid communication, a platform supported by the structure above the surface of the water, a drilling rig on the platform comprising a casing extending downwardly to the formation and a drill pipe and a drill in the casing operated from the platform, drilling fluid in the communicating leg compartments, and means including a drilling fluid delivery line extending from the uppermost compartment to the rig and a drilling fluid recovery line extending from the rig to the lowermost compartment for circulating the fluid from the uppermost compartment, into and out of the hole by counterflow circulation through the drill pipe and casing, and into the lowermost compartment.

2. A unitary elongated support structure adapted to float horizontally in a body of water over an underwater formation, the structure comprising a set of elongated and laterally spaced hollow legs, braces connecting the legs together, at least one of the legs having closed internal compartment means extending for a substantial distance longitudinally within the said leg, means for flooding said internal compartment means to tilt the structure from a horizontal to a vertical position so it rests on the underwater formation, a drilling rig mounted on the upper end of the structure above the body of water when in the vertical position, the rig including a hollow depending drill pipe for drilling a hole in the underwater formation, a

casing surrounding the drill pipe from the platform to at least the hole, and means including a drilling fluid delivery line connected between the drill pipe and the com partment means and a recovery line connected between the casing and the compartment means for circulating drilling fluid serially out of the lower end of the drill pipe into the hole, upwardly through the casing, into the compartment means and back, into the upper end of the drill pipe.

3. A unitary elongated marine support structure adapted to float horizontally in a body of water over an underwater formation, the structure comprising a set of elongated and laterally spaced hollow legs, braces connecting the legs together, at least one of the legs having closed internal compartment means extending for a substantial distance longitudinally within the said leg, means for flooding said internal compartment'means to tilt the entire structure from a horizontal to a vertical position so it rests on the underwater formation, drilling fluid disposed in the compartment means, a drilling rig mounted on the upper portion of the structure when in a vertical position, the rig including a hollow depending drill pipe for drilling a hole in the underwater formation, a casing surrounding the drill pipe, and means including drilling fluid delivery conduit means connected between the upper end of the drill pipe and the upper portions of the compartment means and recovery conduit means extending from the upper end of the casing to the lower portions of the compartment means for circulating drilling fluid serially from an upper portion of the compartment means to the upper end of the drill pipe, downwardly through the drill pipe, out the lower end of the drill pipe, up through the hole and the casing, and out of the casing into a lower portion of the compartment means.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.044 561 July l7 1962 William F. Swiger It is hereby certified that error appears in the above numbered patent. requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 65. for "Disposed" read Disposing column 3 line 34, for "pressure" read pressurize Signed and sealed ,this 18th day of December 1962 (SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents