US3315473A

US3315473A - Offshore platform

Info

Publication number: US3315473A
Application number: US494289A
Authority: US
Inventors: Ferdinand R Hauber; Claude L Clark
Original assignee: Brown and Root Inc
Current assignee: Brown and Root Inc
Priority date: 1965-08-27
Filing date: 1965-08-27
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25

Description

April 25, 1967 F. R. HAUBER ET AL I 3,315,473

OFFSHORE PLATFORM Original Filed Jan. 10, 1962 5 Sheets-Sheet 1 ATTOHA/fy April 25, 1967 F. R. HAUBER ET AL 3,315,473

OFFSHORE PLATFORM Original Filed Jan. 10, 1962 5 Sheets-Sheet 2 INVENTOR.)-

ATTOR/VEV A ril 25, 1967 F. R. HAUBER ETAL 3,315,473

OFFSHORE PLATFORM Original Filed Jan. 10, 1962 5 Sheets-Sheet 5 59/00/70/70 HOz/Zer 4/ (7000 9 Z. C/arA INVENTORSI BY W j f.

A ril 25, 1967 F R, HAUBER ET AL 3,315,473

OFFSHORE PLATFORM Original Filed Jan. 10, 1962 5 Sheets-Sheet 4 Ferd/7000 A. floaer C/ouc/e Z. C/ar/r yf I INVENTORJ M @24 ATTORNEY April 25, 1967 F. R. HAUBER ET AL OFFSHORE PLATFORM 5 Sheets-Sheet 5 Original Filed Jan. 10, 1962 iflt 60 VA \\Y /I INVENTORS ATTO/P/Vf) United States Patent Office 3,315,473 Patented Apr. 25, 1967 3,315,473 OFFSHORE PLATFORM Ferdinand R. Hauber and Claude L. Clark, both of Houston, Tex., assignors to Brown & Root, Inc., Houston, Tex., a corporation of Texas Continuation of application Ser. No; 165,997, Jan. 10, 1962. This application Aug. 27, 1965, Ser. No. 494,289 6 Claims. (Cl. 61-465) This invention, which is a continuation of application Ser No.. 165,997, filed Jan. 10, 1962, relates to offshore platforms and to methods for constructing same and more particularly it relates to such offshore platforms as are used for drilling for and production of petroleum.

In the offshore drilling of oil wells and subsequent production of petroleum from such wells, a major difficulty has been in the provision of suitable structures on which to mount drilling and production equipment. In comparatively shallow water, such as less than about 100 feet, it has been found possible to erect a permanent tower which is affixed to the submarine bottom by means of piling's. Such structures as have been heretofore used, however, are not suitable for operations in extremely deep water such as some 300 to 400 feet deep. It is an object of this invention to provide a structure which can be positioned in deep locations and which will remain as a permanent structure. The tower provided by this invention has considerable stability and is relatively free from any danger of damage by wind and wave action.

Because of the depth of water in which the structure of this invention is used, the structure is necessarily large and quite expensive. Therefore, according to this invention, means are provided for utilizing the structure for the drilling of a large number of wells. For example, from twelve to forty or more wells may be drilled from a single structure of this invention. By use of the structure of this invention it is possible to drill such a large number of wells without shutting down the equipment more than a very short time, since means are provided for easily moving the entire drilling apparatus to drill in a number of locations. In addition, the structure of this invention is readily convertible from a drilling platform to a production platform. The structure has provision for complete crew quarters during the drilling, which may be removed and replaced by a tank to receive petroleum from the wells.

This invention also contemplates the provision of novel piling means for fixedly engaging the lower end of the tower to the ground.

For abetter understanding of the invention, reference is now made to the accompanying drawings wherein FIGURE 1 is an elevational side view showing one embodiment of this invention being transported to the drilling location;

FIGURE 2 is an elevational view of the bottom end of the structure of FIGURE 1, taken at line 2-2 of FIG- URE 1;

FIGURE 3 is a view similar to FIGURE 2, at a later stage of construction;

FIGURE 4 is a view similar to FIGURE 3, at a later stage of construction;

FIGURE 5 is a vertical elevation of one embodiment of the tower of this invention shown in place prior to driving the piles;

FIGURE 6 is a vertical elevation of the embodiment of FIGURE 5 shown in place after the driving of piles and after mounting thereon apparatus for drilling of oil wells;

FIGURE 7 is a fragmentary elevational view of the embodiment of FIGURE 5 shown after drilling has been completed and a production tank has been mounted there- FIGURE 8 is an enlarged view of a portion of the structure shown in FIGURE 6, parts being shown in section for clarity;

FIGURE 8a is a horizontal sectional view of the embodiment of FIGURE 8 taken on line 8a8a of FIG- URE 8;

FIGURE 9 is a horizontal sectional view of the embodiment shown in FIGURE 8 taken at line 9-9 of FIG- URE 8;

FIGURE 10 is a fragmentary vertical elevational view showing an intermediate portion of the structure shown in FIGURE 6;

FIGURE 11 is a horizontal sectional view of the portion of the structure shown in FIGURE 10 taken at line 11-11 of FIGURE 10;

FIGURE 12 is a vertical sectional view of the lower end of one of the legs of the embodiments shown in the previous figures;

FIGURES 13 and 14 are enlarged horizontal sections of the structure shown in FIGURE 12, taken at lines 1313 and 14-14, respectively, of FIGURE 12; and

FIGURE 15 is a fragmentary vertical sectional view showing one embodiment of the pile driving method of this invention.

FIGURE 1 shows the tower 10 of this invention, partially constructed, being transported to a drilling location. The tower comprises a plurality of columnar, cylindrical hollow legs 12, six being used in the embodiment shown, which are assembled to form a hexagon shape, with cross-bracing 24 between the legs to form a rigid structure. Extending longitudinally centrally of the tower is a vertical center leg 18. Intermediate the six legs 12, which are vertical when the tower is in position for drilling, of downwardly and outwardly extending batter columns 14. The batter columns are also hollow cylinders and do not extend all the way to the top of the tower, but extend from the bottom to a distance equal to no more than about two-thirds the depth of the water in which the tower is to be positioned. As is apparent in FIGURES 2, 3, and 4, the cross-bracing 24 serves to connect each batter column to the two adjacent legs 12, but no bracing is provided between the batter columns. Thus, below the juncture of the batter columns with the legs, the form of the tower is that of a six-pointed star, each batter column with its associated bracing forming a wedgeshaped member.

Preferably the tower is constructed ashore, but one of the wedge-shaped members is omitted, for easier transporting of the tower. In shallow water, the tower is transported as shown in FIGURE 1. The ends of the

legs

12 and 18 and columns 14 are covered by plates, and the tower is transported in horizontal position on a plurality of barges 11. Upon arrival at the location at which the tower is to be erected, the barges 11 are partially sunk, as shown in FIGURE 2, by flooding. The tower is thus lowered into the water until it floats by virtue of the buoyancy imparted to it by sealing off the ends of the legs and the batter columns. The barges are then moved out from under the tower, and the tower is rolled over in the water until the unfinished side is at the top. Anchor lines 13 from the tower to barges 11 provide stability during this phase of the operation.

The last wedge-shaped member is then welded on, as shown in FIGURE 4, and the tower is ready to be put into place. Water is let into the batter legs by removing the top closure plate and into the vertical legs by opening valves 56 and 62 (FIGURE 12). These valves are controllable from the top of the tower by means of control leads 58. Upon the opening of these valves, sea Water can flow into the legs through

conduits

60 and 54, re-

as shown in FIGURE 5, are an equal numbermatte contacts the bottom.

, at the lower end by an annular 'top of the pile.

spectively. When the flooding of the legs is suflicient to bring the tower to a vertical position, but before it settles allthe way to the bottom, the tower is towed to the exact position desired, and flooding of the legs is completed to lower the legs to the bottom. Planking comprising a mud matte 22 is provided extending horizontally between adjacent bracing members 24 near the lower end of the legs (see FIGS. 4 and 5). Thus, on a mud or other relatively soft bottom, the legs sink into the bottom until the mud The tower is then in the position shown in FIGURE 5.

The center leg 18 is used for a test pile to determine soil conditions before the other piles are driven. This center pile is driven as far as necessary to determine the depth to which others will be driven. In preparation for driving a pile, the top cover plate of the center leg is removed and the water is pumped out. A pile 48, com- 7 prising a hollow tubular member sized to fit loosely within the leg, is dropped into the leg. The pile is reinforced ring 49 (FIGURE 12), and the end is beveled to provide a cutting edge for easier driving. When the pile is dropped to the bottom of the leg this beveled end will normally pierce the bottom cover plate 50.. A flexible seal 52 is provided in the lower end of the leg 18 to seal between the leg and the pile 48, to prevent the leg from filling with water when the bottom plate is pierced.

A pile follower 64 is then dropped down into the leg on Pile follower 64 is provided with a reduced diameter end 66 which fits within the upper end of the pile 48, and an annular shoulder 68 which abuts theupper end of the pile. repeatedly raising and dropping the pile follower 64 until the pile is driven' to a suflicient depth to firmly anchor the tower to the bottom. Marks on the pile follower adjacent the upper end of the leg determine the penetration of the pile and the location of the top of the pile relative to the leg. Normally the pile length used will be such that the upper end of the pile is about 20 feet above the mud line.

The pile is then grouted into place.

Valves

56 and 62 are opened to allow water to flood the leg and the pile and then a concrete grout is pumped down through line 54 to fill the space between the leg and the pile. A plurality of vertically spaced apart annular rings 70'are welded to the pile and are provided with outwardly extending fingers 72. A plurality of corresponding annular rings 74 are welded around inside the lower end of the leg and these are provided with corresponding fingers 76 which extend inwardly.

Fingers

72 and 76 serve to bind and interlock the leg and the pile. It will be seen, therefore, that the combination of the fingers and V the concrete cooperate to create a unitary structure.

The remainder of the piles in the vertical legs 12 are then driven in the same manner. In driving the piles in the batter columns, an extension pipe of the same diameter as the batter column must first be attached to the top of each batter column, extending upwardly therefrom to above the surface of the water. 7 A threaded connection or other watertight connection is used between the batter column and the extension pipe, so that all the water may be pumped out of the batter column before beginning the pile driving. Pile driving then proceeds in the same manner as with the vertical legs, and, when the piles are grouted in, the extension pipes are removed. When piles have been driven and grouted in all seven vertical legs and all six batter columns, the tower is firmly anchored to the bottom, and the superstructure may be put into place.

The upper portion of the tower comprises a permanent stationary mounting structure on which drilling or v production equipment is mounted. As shown in FIG- URE 8, an annular framework 26 has contained within it i a cylindrical storage tank 28 which during drilling is used as a mud tank and during production is used for storage of products. Immediately above the tank 28 is a cylindri- The pile is then driven by 'after placing them on the tower.

living quarters structure is substantially cylindrical and has a height substantially equal to the depth of the cavity so that the top of the living quarters is about level with the top of the annular framework'26. The living quarters structure is separatelyconstructed and lowered into the cavity. In the center of the living quarters structureis a large diameter vertically extending pivot pin 34 which extends above the top of the annular framework 26. The

in FIGURE 1, which is composed'of skid beams 36. A drilling rig substructure 38 is in position on top of the skid beams and is pivotally mounted on pivot pin 34, a

cylindrical bearing 40 being provided'for this purpose,

In many cases it may be desirable to build the substructure in two or more sections, and fasten them together The drilling rig substructure is pivotable 360 degrees on the skid beams, a skid surface 42 on the bottom of the substructure being provided for skidding contact on the skid beams. Various means well known in the art may be used for reducing the frictional forces resisting pivoting of the substruc ture on the platform.

According to this invention, all equipment utilized in drilling of oil wells is mounted on the substructure 38. This includes such conventional equipment as tanks, generators, pumps, engines, wiring, and piping all completely connected. In the drawing only a portion of the drilling derrick 44 is shown to indicate the presence of such equipment. The drilling derrick is constructed separately and attached to the substructure in a position 0E center of the substructure, so that it may be moved about the axis of the pivot pin simply by pivoting the substructure on the tower. Note that in FIGURE 8a the substructure is preferably substantially square and that the derrick is on one corner. I hen as the substructure is pivoted, the derrick is moved to different positions as required for drilling wells in different locations, so that a plurality of as the operators prepare to drill each well during the V drilling operation. Such conductors are depicted in-FIG URE 8 at 47, and are arranged on a circle having a center coincident with the axis of the pivot pin. The conductors are used to guide the drill string during drilling operations and as a conduit for fluids produced from the well after drilling is completed.

In the embodiment depicted in the drawings 24 conductors are shown, although it will be appreciated that the number may vary according to the number of wells it is desired to drill.

It will be apparent that the features of pivotability of the entire substructure of the drilling rig, including all equipment used in drilling, allows changing from one location to another without shut down or rearrangement of equipment, and with practically no loss of time. Thus a well may be drilled through one conductor, and immediately after completion, another well may be begun through another conductor.

After completion of all the wells desired at this'location, the derrick is removed, and then the substructure, including all equipment mounted thereon, is removed. Following this, the quartersunit may be removed. The tower is then readily adapted for use as a production platform by placing a crude oil tank in the cavity' suited to offshore drilling and production operations. As i is well known, such operations are particularly hazardous because of the necessity for providing a stable platform for the operations, and because of the necessity for a structure which will resist the tremendous lateral forces of wind and water. In addition, the enormous weight of equipment required for such operations complicates the problem. By means of the apparatus of this invention, however, these problems are minimized. A plurality of vertical legs, seven in the embodiment shown, provide support for vertical loading, and a plurality of downwardly and outwardly diverging batter columns absorb lateral or bending loads, in addition to bearing some of the vertical load. Such means for absorbing lateral or bending loads are provided, however, without increasing the cross-sectional area which is exposed to such lateral loads. This is accomplished by extending the batter columns only from the bottom to about twothirds of the way up the tower. It has been determined that substantially all the lateral force due to waves is within the upper one-third of the water so if the batter columns are below this level, they provide substantially no resistance to lateral wave forces, yet provide support against such lateral forces exerted against elements higher up on the tower. By means of the structure of this invention, only the seven vertical legs, their related cross braces, and the conductor pipes provide areas against which wave loads can bear.

The symmetrical shape of the tower gives it the capability of equal resistance to horizontal forces in all direc tions. In addition, such shape has a natural torque resistance to earthquake. Such a shape also greatly simplifies 'construction,-since the tower can be built in panels.

Many modifications ofthis invention will be apparent to those skilled in 'the art, therefore the invention is not limited to the specific embodiments'shown and described, but only as defined by the claims. The claims are written in sub-paragraph form to facilitate examination, but such form is not intended to imply any limitation of the claims which they would not have if in any other form.

We claim: 7

1. A tower resting on the bottom of a body of water in an. offshore location and extending above the surface of said body, said tower comprising: 7

a central, substantially vertically extending leg;

a plurality of mutually spaced and substantially vertically extending intermediate legs, said intermediate legs being disposed laterally outwardly from said central leg;

a plurality of outer legs having upper submerged ends, said outer legs being inclined downwardly and outwardly of said intermediate legs;

said intermediate and said outer legs being generally symmetrically disposed in relation to said central leg,

with said intermediate and said outer legs being generally aligned with planes extending radially of said central leg;

said upper ends of said outer legs being mutually spaced, with each such upper end being disposed generally between adjacent intermediate legs;

each of said central, intermediate, and outer legs having hollow lower ends;

at least one pile projecting downwardly from and out of the hollow lower end of each of said central, intermediate and outer legs and extending into a submerged formation on the bottom of said body of water;

a generally annular body of cementitious material disposed and hardened in situ between an outer peripheral portion of each of said piles and an inner portion of the hollow lower end of the leg from which it projects; 7

a plurality of vertically spaced first securing means carried by the lower end of each of said legs, each comprising a ring secured to a leg interior and having a plurality of circumferentially spaced fingers inclined inwardly and downwardly thereof, and at least partially embedded within said cementitious material;

a plurality of vertically spaced second securing means carried by each of said piles, each comprising a ring secured to a pile exterior and having a plurality of circumferentially spaced fingers inclined outwardly and upwardly, thereof, and at least partially embedded within said cementitious material;

at least some of said first securing means of each leg being each superposed above a second securing means and generally aligned longitudinally therewith in relation to their respectively associated leg and pile;

a plurality of vertically spaced guide stations, each said guide station including a plurality of horizontally displaced but interconnected annular collars, with at least some of the collars of said plurality of guide stations being superposed in axial alignment;

a plurality of conductor conduits, each conductor conduit passing generally axially through a plurality of superposed collars of a plurality of said guide stations; and

frame means interconnecting said central, intermediate, and outer legs, said guide stations and said collars.

2. A tower situated in an otfshore location and resting on the bottom of a body of water, said tower comprising:

a central, substantially vertically extending leg;

a plurality of mutually spaced and substantially vertically extending, intermediate legs, said intermediate legs being disposed laterally outwardly from said central leg;

a plurality of outer legs having upper submerged ends,

said outer legs being inclined downwardly and outwardly of said intermediate legs;

said intermediate and said outer legs being generally symmetrically disposed in relation to said central leg with said intermediate and said outer legs being generally aligned with planes extending .radially of said central leg;

each of said central, intermediate, and outer legs having hollow lower ends;

- a plurailty of vertically spaced guide stations, each said guide station including a pluralityof horizontally displacedannular collars, with at least some of the collars of said plurality of guide stations being superposed in axial alignment;

a plurality of conductor conduits, each conductor conduit passing generally axially through a plurality of superposed collars of a plurality of said ,guide stations; and

'frame means interconnecting said central, intermediate and outer legs, said guide stations, and said'collars. 3. A tower situated in an ofifshore location and resting on the bottom of a body of water, said tower comprising:

a central, substantially vertically extending leg;

a plurality of outer legs having upper submerged ends,

said intermediate and said outer legs being generally symmetrically disposed in relation to said central leg, with said intermediate and said outer legs being generally aligned with planes extending radially of said central leg;

said upper ends of said outer legs being mutually spaced,

I each of said legs 7 at least one pile projecting frame means interconnecting said with each such upper end being disposed generally between adjacent intermediate legs;

each of said central, intermediate, and outer legs having hollow lower ends;

a generally annular body of cementitious material disposed and hardened in situ between an outer peripheral portion of each of said piles and an inner portion of the hollow lower end of the leg from which it projects;

atleast some of said first securing means of each leg being each superposed above a second securing means and generally aligned longitudinally there with in relation to their respectively associated leg and pile; and

frame means interconnecting said and outer legs.

4. A tower. situated in an central, intermediate offshore location and resting on the bottom of a body of water, said tower comprising:

a plurality of legs;

having hollow lower ends;

downwardly from and out of the hollow lower end of each of said legs and extending into a submerged formation on the bottom of said body of water;

'a plurality of vertically spaced second securing means carried by each of said piles, each comprising a ring secured to a pile exterior and having a plurality of circumferentially spaced fingers inclined outwardly and upwardly, thereof, and at least partially embedded within said cementitious material;

at'least some of said first securing means of each leg being each superposed above a second securing means and generally aligned longitudinally therewith in relation to their respectively associated leg and pile;

a plurality of vertically spaced guide stations, each said guide station including a plurality of horizontally displaced annular collars, with at least some of the collars of said plurality of guide stations being superposed in axial alignment;

a plurality of conductor conduits, each conductor conduit passing generally axially through a plurality of superposed collars of a pluralityof said guide stations; and

legs, said guide stations, and said collars.

A l er situated in an ofishore location and resting 8 on the bottom of a body of water, said tower comprising:

a plurality of legs;

each of said legs having hollow lower ends;

at least one pile projecting downwardly from and out of the hollow lower end of each of said legs and extending into a submerged formation on the bottom of said body of water;

a plurality of vertically spaced first securing means carried by the lower end of each of said legs, inclined inwardly and downwardly thereof, and at least partially embedded within said cementitious material;

a plurality of vertically spaced second securing means carried by each of said piles, inclined outwardly and upwardly, thereof, and at least partially embedded within said cementitious material; 7

at least some of said first securing means of each leg being each superposed above a second securing means and generally aligned longitudinally therewith in relation totheir respectively associated leg and pile; and

frame means interconnecting said legs.

6. A tower situated in an offshore location and resting on the bottom of a body of water,'said tower comprising:

a central, substantially vertically extending leg;

a plurality of mutually spaced and substantially vertically extending intermediate legs, said intermediate legs being disposed laterally outwardly from said central leg and extending to a submerged formation on the bottom of said body of water;

said outer legs circumferentially alternating with said intermediate legs with the upper ends of said outer legs being mutually spaced, with each such upper end being disposed generally between adjacent interme-' diate legs;

said central, intermediate,

downwardly projecting extensions extending into said submerged formation on the bottom of said body of water;

a plurality of vertically spaced conductor guide stations; and

means interconnecting said centrallegs, intermediate leg, outer legs, and guide stations.

References Cited by the Examiner OTHER REFERENCES Engineering News-Record (publication) Oct. 20, 1955,

p.'8l. CHARLES E. OCONNELL, Primary Examiner;

JACOB SHAPIRO, JACOB L. NACKENOFF,

' Examiners.

and outer legs each having

Claims

1. A TOWER RESTING ON THE BOTTOM OF A BODY OF WATER IN AN OFFSHORE LOCATION AND EXTENDING ABOVE THE SURFACE OF SAID BODY, SAID TOWER COMPRISING: A CENTRAL, SUBSTANTIALLY VERTICALLY EXTENDING LEG; A PLURALITY OF MUTUALLY SPACED AND SUBSTANTIALLY VERTICALLY EXTENDING INTERMEDIATE LEGS, SAID INTERMEDIATE LEGS BEING DISPOSED LATERALLY OUTWARDLY FROM SAID CENTRAL LEG; A PLURALITY OF OUTER LEGS HAVING UPPER SUBMERGED ENDS, SAID OUTER LEGS BEING INCLINED DOWNWARDLY AND OUTWARDLY OF SAID INTERMEDIATE LEGS; SAID INTERMEDIATE AND SAID OUTER LEGS BEING GENERALLY SYMMETRICALLY DISPOSED IN RELATION TO SAID CENTRAL LEG, WITH SAID INTERMEDIATE AND SAID OUTER LEGS BEING GENERALLY ALIGNED WITH PLANES EXTENDING RADIALLY OF SAID CENTRAL LEG; SAID UPPER ENDS OF SAID OUTER LEGS BEING MUTUALLY SPACED, WITH EACH SUCH UPPER END BEING DISPOSED GENERALLY BETWEEN ADJACENT INTERMEDIATE LEGS; EACH OF SAID CENTRAL, INTERMEDIATE, AND OUTER LEGS HAVING HOLLOW LOWER ENDS; AT LEAST ONE PILE PROJECTING DOWNWARDLY FROM AND OUT OF THE HOLLOW LOWER END OF EACH OF SAID CENTRAL, INTERMEDIATE AND OUTER LEGS AND EXTENDING INTO A SUBMERGED FORMATION ON THE BOTTOM OF SAID BODY OF WATER; A GENERALLY ANNULAR BODY OF CEMENTITIOUS MATERIAL DISPOSED AND HARDENED IN SITU BETWEEN AN OUTER PERIPHERAL PORTION OF EACH OF SAID PILES AND AN INNER PORTION OF THE HOLLOW LOWER END OF THE LEG FROM WHICH IT PROJECTS; A PLURALITY OF VERTICALLY SPACED FIRST SECURING MEANS CARRIED BY THE LOWER END OF EACH OF SAID LEGS, EACH COMPRISING A RING SECURED TO A LEG INTERIOR AND HAVING A PLURALITY OF CIRCUMFERENTIALLY SPACED FINGERS INCLINED INWARDLY AND DOWNWARDLY THEREOF, AND AT LEAST PARTIALLY EMBEDDED WITHIN SAID CEMENTITIOUS MATERIAL; A PLURALITY OF VERTICALLY SPACED SECOND SECURING MEANS CARRIED BY EACH OF SAID PILES, EACH COMPRISING A RING SECURED TO A PILE EXTERIOR AND HAVING A PLURALITY OF CIRCUMFERENTIALLY SPACED FINGERS INCLINED OUTWARDLY AND UPWARDLY, THEREOF, AND AT LEAST PARTIALLY EMBEDDED WITHIN SAID CEMENTITIOUS MATERIAL; AT LEAST SOME OF SAID FIRST SECURING MEANS OF EACH LEG BEING EACH SUPERPOSED ABOVE A SECOND SECURING MEANS AND GENERALLY ALIGNED LONGITUDINALLY THEREWITH IN RELATION TO THEIR RESPECTIVELY ASSOCIATED LEG AND PILE; A PLURALITY OF VERTICALLY SPACED GUIDE STATIONS, EACH SAID GUIDE STATION INCLUDING A PLURALITY OF HORIZONTALLY DISPLACED BUT INTERCONNECTED ANNULAR COLLARS, WITH AT LEAST SOME OF THE COLLARS OF SAID PLURALITY OF GUIDE STATIONS BEING SUPERPOSED IN AXIAL ALIGNMENT; A PLURALITY OF CONDUCTOR CONDUITS, EACH CONDUCTOR CONDUIT PASSING GENERALLY AXIALLY THROUGH A PLURALITY OF SUPERPOSED COLLARS OF A PLURALITY OF SAID GUIDE STATIONS; AND FRAME MEANS INTERCONNECTING SAID CENTRAL, INTERMEDIATE, AND OUTER LEGS, SAID GUIDE STATIONS AND SAID COLLARS.