US3517516A - Folding support structure for offshore drilling platforms - Google Patents

Description

June 30, 1970 E O. 3,517,516

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 51, 1968 s Sheets-Sheet 1 FIG. 2

INVENTOR'.

ROBERT G. BEA

R. G. BEA

June 30, 1970 FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS 5 Sheets-Sheet 2 Filed July 51, 1968 INVENTORI ROBERT G. BEA

June 30, 1970 R. G. BEA 3,517,516

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 31, 1968 5 Sheets-Sheet 5 ROBERT e. BEA

FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Filed July 51, 1968 R. G. BEA

June 30, 1970 5 Sheets-Sheet 4 FIG.

FIG.

INVENTORI ROBERT G. BEA I June 30, 1970 R. 5. BEA

FOLDING SUPPORT STRUCTURE Filed July 31, .1968

FOR OFFSHORE DRILLING PLATFORMS 5 sheets-sheet 5 I NVENTOR'.

ROBERT G. BEA

United States Patent i 3,517,516 FOLDING SUPPORT STRUCTURE FOR OFFSHORE DRILLING PLATFORMS Robert G. Bea, Houston, Tex., assignor to Shell Oil gonlipany, New York, N.Y., a corporation of New Filed July 31, 1968, Ser. No. 749,182 Int. Cl. E02b 17/02 US. Cl. til-46.5 8 Claims ABSTRACT OF THE DISCLOSURE An offshore drilling structure having a buoyant, selectively floodable base unit and a plurality of buoyant, selectively floodable leg units pivotally attached to said base unit whereby the structure can be set-up by towing the entire assembly on the surface of a body of water to a predetermined offshore location, lowering the assembly to the water floor by flooding the base unit and legs, and pivoting the leg units upwardly to form a composite offshore drilling structure.

This invention relates to portable support structures for deep water offshore drilling platforms.

It is well known in the prior art to prefabricate support or tower structures for drilling platforms at inland or coastal locations and float the completed structure down a river or through a channel out to the sea or gulf to the desired location where it is sunk in an upright position. When in place, the drilling platform, derrick structure, draw works and other necessary equipment are positioned atop the tower structure.

The main load-bearing columns of these structures are usually tubular steel pipes of a relatively large diameter. The ends of these tubular columns are capped so that each column constitutes a buoyant, watertight vessel. This is for the purpose of providing inherent flotation to the structure so it may be towed over the surface of the water to the location of use.

As the quest for oil has progressively pushed the drilling locations into the deeper water covering the outer limits of the Continental Shelf, it has been necessary to build these tower structures larger and higher to accommodate the depth of the water and the wind and wave forces imposed in the open sea. This necessary increase in size of the structures has had the consequent effect of increasing the draft of the structures as they are laid over on their sides to be floated from the construction point to the drilling location. Many of these construction sites are located far inland on rivers such as the Mississippi. These rivers are relatively shallow and cannot accommodate a deep draft vessel, hence presenting one problem sought to be solved by this invention.

It is therefore an object of this invention to provide a deep water drilling support structure that may be constructed at a shipyard and carried through shallow waterways to the sea.

It is another object of this invention to provide a floatable tower structure having a very shallow draft.

It is still another object of this invention to provide a prefabricated floatable tower structure in which each structural element buoyantly supports little more than its own weight.

It is a further object of this invention to provide a partially disassembled, prefabricated tower structure that may 3,517,516 Patented June 30, I970 be floated to location where assembly may be quickly and easily completed. I

It is an additional object of this invention to provide a prefabricated floatable tower structure which may be recovered and moved to another location when it is utility at a first location is complete.

Another object of this invention is to provide a foldable tower structure in which the folding legs thereof are quickly and easily assembled together as a unitary structure.

Still another object of this invention is to provide means for securing the folding legs of a transportable, deep water tower structure together at great depths with means that is manipulated into position at or near he surface.

These and other objects will be readily seen from the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatical side elevational view of the articulately assembled floating tower structure as it is being towed over a body of water to location;

FIG. 2 is a diagrammatic view of the tower structure in the initial erection stage;

FIG. 3 is a diagrammatic view of the tower structure in a more advanced erection stage;

FIG. 4 is a diagrammatic plan view of the tower structure as erection approaches completion;

FIG. 5 is a diagrammatic view of the completed tower structure equipped for drilling;

FIG. 6 is a sectional view of the tower structure shown in FIG. 5 taken along line 66;

FIG. 7 is a sectional view of the tower structure shown in FIG. 5 taken along line 77;

FIG. 8 is a sectional view of the tower structure shown in FIG. 5 taken along the line 8-8;

FIG. 9 is a sectional view of the hinge structure which joins the leg unit with the base;

FIG. 10 is a sectional view of the hinge structure shown in FIG. 9 taken along line 10-10;

FIG. 11 is an alternative embodiment for the structure shown in FIG. 7;

FIG. 12 is a sectionalized detail of connecting carrier lower end secured in place within its respective guide track; and

FIG. 13 is a partial cross section of the guide trace showing means for sealing the'longitudinal slot therein.

Broadly, the tower structure of this invention is preferably divided into at least three segments, a base 10 and two leg units 20 and 20a. One end of each leg unit is secured to respectively opposite ends of the base unit by an articulating connection such as a hinge. Although only two leg units are shown and preferred, it is, of course, possible to provide four leg units, each one articulately connected to a respective side of a rectangular base structure.

Another possible base configuration for this invention is that of a triangular base. In the case of a triangular base, there would be three leg units, each hingedly connected along the edge of a base triangle lying in the plane of the water surface.

With reference to FIGS. 5, 6 and 8, each leg unit 20 and 20:: comprises two primary columns 21 and 22 which are of suflicient length to extend from the marine floor 72 to a height of, for example, approximately feet about the surface 76 of a body of water 70. The water depth at a location of drilling activity may be 400 feet, for example.

o The primary columns are secured directly together by a plurality of cross spanners 23 disposed at several vertically spaced locations of, for example, 100 feet, to form a lattice structure. Additionally, at the ends of the primary columns intended to extend above the water surface, a platform beam 51 is rigidly secured between said primary columns 21 and 22 respective to each leg unit. The primary columns 21 and 22 may, for example, be constructed of 12-foot diameter steel tubing. The cross spanners 23 may, for example, be of 4-foot diameter steel tubing.

From the lattice structure comprising the primary columns and cross spanners, there is provided gabled spanners such as 24'and 25. The gable spanners 24 and 25 intersect to form, with the cross spanner 23, a triangular cross section for the leg unit 20 (see FIG. 6). Each apex formed by the intersection of gable spanners 24 and 25 is supported and reinforced by cross bracing 29 (FIG.

Supported by the apex of the gable spanners 24, 24a, 25

and 25a, as shown in FIGS. 5-7, are guide tracks 30 and 30a which should extend from at least the surface level of the structure down past the lowermost gabled spanner 24. Each of the guide tracks 30 and 30a shown in FIGS. 5-7 are tubular structural members having a slot 31 in the Wall thereof extending substantially the entire length. The lower ends of the guide tracks 30 and 30a may be provided with abutment means such as a crossbar 32 shown in FIG. 12.

Secured between the gabled spanners 24 and 25 along the length of each leg unit is a cluster of conductor pipes 34 and 34a. Each of these conductor pipes constitutes drill string guides and is sized according to the programmed equipment necessary to the drilling and completion of individual wells which are to be drilled therethrough and angled directionally therefrom.

Alternatively, the guide tracks respective to each leg unit may take the form of channel members 45 having guide ways 46 extending partially across the channel opening from each channel leg leaving a longitudinal space 47 therebetween as shown in FIG. 11.

In connection with the guide tracks 30 and 30a. but fabricated as a separate structure is a connecting carriage 54 comprising, in the embodiment of FIGS. 5-7, two tubular carriers 55 and 55a. The carriers 55 and 55a are interconnected along their length, which is at least as long as the guide tracks 30 and 300, with run members 56. If the intended use of the completed tower structure calls for permanent positionment, the carriers 55 and 55a may have their ends plugged with a pipe cap 57 and perforated along the length of the carrier with apertures 58 as shown in FIG. 12. Also, when the contemplated placement of the tower structure is to be permanent, the slot 31 along the length of the guide tracks 30 and 30a is loosely sealed with overlapping welting 59.

To provide sufficient spacing between the platform beams 51 for the stable positionment of the operating platform 50 thereacross and to rigidly secure the two leg units together in the upright position during the initial assembly stage, spacer means 37, shown in FIG. 5, for example, have been provided at the ends of the leg units and 20a. The portion of the spacer means secured to each leg unit constitutes half of a diagonally reinforced box truss. The two halves are secured together with mating flanges 38.

The base unit 10, shown in FIG. 8, is preferably in the form of a square having two sides, the primary beams 11 and 12, constructed of, for example, 8-foot diameter steel tubing, and the other two sides, the secondary beams 13 and 14, constructed of 38-inch diameter tubing, for example. The base square 10 is reinforced by a truss structure 15 constructed of, for example, 4-foot diameter steel tubing. The truss structure 15 supports at the center a template plate 16 having apertures 17 of a size at least equal to the inside diameter of the conductor tubes 34. The apertures 17 are positioned on the template plate 16 in alignment with the bores of conductor tubes 34 with the legs 20 and 20a are in the raised, operative position,

The leg units 20 and 2011 are secured to the base unit 10 by articulating joints shown at FIGS. 9 and 10. Each articulating joint has a journal pin 42 mounted on a hydraulic ram 43 for reciprocal movement within the secondary beams 13 and 14 and at each end of the primary beam members 11 and 12 of the base unit 10. The journal pin 42 mates with a journal sleeve 41 mounted in the bottom end of the primary columns 21 and 22. The fluid power for the hydraulic rams 43 is received from an auxiliary barge unit 60 or a portable power unit (not shown) mounted at a convenient location on the base unit 10.

All construction tubing excepting the guide tracks 30' and 30a is preferably sealed watertight, either by construction design or by means of end caps 44, for example, on the primary column 21 shown in FIG. 8. It should be noted, however, that although it is intended that each of the basic units of the structure should be buoyantly selfsupporting in the water, this does not preclude the possibility of using auxiliary flotation means to which the units may be attached for whole or partial support. By attaching pontoons or other auxiliary flotation means, the structure may be made to gain a still more shallow draftthan would otherwise be possible. Buoyancy of the structure may also be changed by altering the outside diameterthickness ratio of the individual structural tubing elements. In other words, for structural elements having the same load-bearing properties, the unit specific gravity would be greater for a tubular element having a smaller outside diameter but greater wall thickness. For this reason, unusual circumstances of draft and buoyancy may be met by constructing the primary columns from very large diameter but thin-walled tubing having load-bearing capacities greatly in excess of what is necessary.

Extending throughout the internal length of primary columns 21 and 22 are provided piling sleeves 39. The piling sleeves 39 extend through the end caps 44 and a short distance therebeyond. The piercing point of the piling sleeves 39 through the ends caps 44 is also made watertight. The opposite ends of the piling sleeves 39 may also be temporarily capped and made watertight until at such later time as they are ready to receive the pilings 40.

The basic units of the tower structure comprising the base 10 and the two leg units 20 and 2011 may be conveniently assembled at an inland shipbuilding or drydock facility. Since each unit is preferably constructed as 'a buoyant vessel, the three units may thereafter be launched in the carrier waterway where they are assembled in the manner shown by FIG. 1. This assembly operation is made relatively simple by the hydraulic-ram powered tapered journal pins 42. Since the pins 42 are provided with a reduced diameter tapered end, it is only necessary to bring each leg unit within such reasonable proximity of the pin 42 as to allow the pin 42 to enter the confines of the sleeve 41. When the pin and sleeve are sufiiciently aligned, the ram 43 is energized so as to force the pin 42 home within the sleeve 41.

When assembled, the three units present a low profile to the forces of wind and wave action and also have a shallow draft, thereby making it navigable in shallow rivers and canals. In this manner, the floating structure is towed, as by a tug 75, to the desired drilling location on the outer limits of the continental shelf where the water depth may be 400 feet or more.

It is also possible, of course, to tow each unit separately to the drilling location where it will be assembled in the manner described above by aligning the journal sleeves 41 with the pins '42 and ramming the latter into position with the hydraulic motors 43. This latter method of individual transport of each unit to the location and assembly thereat may be desirable when short-radius turns are anticipated on the way to location. However, sea conditions will present a greater hindrance to the alignment of the pin 42 in the sleeve 41 than would be encountered by such assembly in a river or canal.

When the articulated structure has arrived over the desired location, an auxiliary barge 60 is moved into position adjacent the base unit (FIG. 2). Control cables 62 are secured to the opposite ends of the base unit 10 and to winches secured to the auxiliary barge 60. Also from the auxiliary barge 60 are connected ballast control lines 66, 66a and 67 which are at their other ends connected to water pumps in the barge 60.

At the outer end of each leg unit 20 and 20a tugs 75 and 75a secure tow cables 76 and 76a. The barge 60 is held in lateral position with anchor lines 61 and 61a.

At the desired moment, the ballast tanks internally of. the base structure 10 are filled with water pumped through the base ballast control line 67. Simultaneously, the internal voids of the leg structures 20 and 20a are flooded with water through the leg ballast control lines 66 and 66a. The result of such flooding is to cause the platform and the hinged ends of the leg units 20 and 20a to sink toward the marine floor 72. In order to control the attitude of sinking, both control cables 62 are let out from the barge 60 at the same rate. The objective of control lines 62 is to keep the platform 10 in a horizontal attitude as it approaches the marine floor. Also effective to control the rate of sinking and the attitude of the plat form 10 is the tensile eifect of the tugs 75. The tugs 75 pull in opposition to one another to lighten the corrective loads imposed on the control lines 62 as the entire base structure approaches the bottom and the legs 20 and 20a pivot to an upright position.

When the base unit 10 is firmly positioned on the marine floor 72 (FIG. 3) erection cables 63 are threaded through the sheaves 64 and 64a located on the respective surface ends of leg units 20 and 20a. A tension line 65 extends from the erection cables to a power winch located on the barge 60. As the tension cable 65 is drawn up, the leg units 20 and 20a are pulled together into the upright position as shown in FIG. 3. In the upright position the flanges 38, located on the ends of the spacers 37, are secured together, thereby providing the structure with a modicum of rigidity in the proper alignment position.

At this juncture of the assembly, the connecting carriage 54 is inserted and slid down through the guide tracks 30 and 30a until the lower end thereof rests against the abutment member 32. In the case of very high tower structures where the guide tracks are proportionally long, the connecting carriage 54 may be fabricated on location by joining as by Welding a plurality of short lengths of connecting carriage that are more conveniently handled and hoisted into place. When the alternative guide track embodiment of FIG. 11 is used, the connecting carriage may take the form of a structural I or H beams 48.

If, as suggested above with respect to FIG. 12, the tower structure is to be permanently located, the carriers 54 and 54a may be permanently secured in place by pumping cement 33 down the bore of the carrier tubes to be extruded through the perforations 58 into the annulus between the outer and inner walls of the carriers and guide tracks, respectively. The welting '59 provides sufficient sealing means along the slot 31 which is necessary to longitudinally, slidably accommodate the rungs 56 as the connecting carriage is being slid into position.

Next in the order of assembly, an operating platform 50 may be constructed across the platform beams 51 upon which a doghouse 52 and derrick structure 53 may be erected. It is to be understood that other arrangements of control lines and erection cable may be employed in erecting the structure of the present invention.

In order to firmly secure the tower structure to the ocean floor, pilings 40 are extended through the piling sleeves 39 and driven deeply into the marine floor and cemented in position.

The structure disclosed above may be used to drill many wells from a single location. For this purpose, the multiplicity of conductor pipes 34 is provided as drill string guides from the operating platform down through the truss network of the tower structure. A separate well is drilled through each conductor by directionally drilling each according to a predetermined radial pattern.

When the tower structure has exhausted its utility as a drilling platform, it will usually be left permanently in place where it is used to mount such equipment as is necessary for the continuous production and control of the oil and other minerals produced from all the wells terminating thereat. However, should it be desired to do otherwise, it is possible to recover the entire tower structure for movement to another location. This is accomplished by merely dismantling and removing the platform 50 and superstructure, removing the connecting carriage 54, separating the flanges 38, severing each piling with an internal pipe cutter and pumping the ballast water from the internal spaces of the base and leg units. The tower structure will then be free to rise to the surface where it can be towed by tugboat to the new location.

I claim as my invention:

1. An offshore drilling structure comprising:

a floatable base unit having variable ballast means;

a plurality of floatable leg units having variable ballast means and including column means having spanner means projecting laterally from said column means;

hinge means operatively associated with said units and having horizontal pivot axes securing one end of said leg units to an edge of said base unit;

longitudinal guide means comprising track members fixedly secured to said laterally projecting spanner means along a substantial portion of the length of said leg units in such a position that when said leg units are pivoted to the upright operative position guide means for each respective leg unit extend substantially parallel with, laterally spaced from, and in close proximity of guide means for another leg unit; and

carriage means simultaneously slidably received by guide means respective to at least two of said leg units whereby said leg units are eitectively secured together along substantially the full length of the carriage means.

2. Apparatus as described by claim 1 wherein each of said guide means has slot means along the length thereof on the side adjacent said cooperative guide means, said slot means adapted to slidably receive interconnecting structural means of said carriage means to secure the respective leg units together.

3. Apparatus as described by claim 2 wherein said carriage means is a structural I-beam member and the interconnecting structural means is the web of said I- beam.

4. Apparatus as described by claim 2 wherein said guide means are tubular track members and said carriage means comprises tubular members having outside diameters less than the inside diameters of the respective guide means tubular track members, each carriage means tubular member being concentrically received by respective guide means tubular track members, said interconnecting structural means comprising a plurality of structural bracing members secured at opposite ends to at least two cooperative carriage means tubular members concentrically disposed in the guide means tubular track members of at least two respective leg units.

5. Apparatus as described by claim 4 wherein each of said carriage means tubular members are perforated along the length thereof and capped at the bottom end, said carriage means being secured in place in said guide means by cement.

-6. Apparatus as described by claim 1 wherein each of said hinge means comprises a journal pin mounted on one of said units, said journal pin being axially reciprocal by power means and a journal sleeve mounted on the other of said units, receiving said journal pin when same is axially extended.

7. Apparatus as described by claim 1 additionally comprising anchor means extending telescopically through said one end of said leg units whereby said structure is secured to the earth.

8. Apparatus as described by claim 1 wherein said leg units each comprise a truss structure of diminishing triangular cross-sectional area along the length thereof from said one end to the other end, two longitudinal edges of said truss structure being primary tubular support columns and interconnecting respective base angles of longitudinally displaced triangular cross sections, said guide means passing longitudinally through the respective apex angles of said cross sections whereby the base plane common to said primary support columns stands at batter and substantially includes an edge of said base unit when said leg unit is in an upright, load-supporting 641,838 1/1900 Cavanagh 2872 0.92 3,253,417 5/1966 Manning 61-465 3,348,459 10/1967 Harvey 52-58 96 JACOB SHAPIRO, Primary Examiner U .8. C1. X.R.

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