US2979910A - Offshore platform structure and method of erecting same - Google Patents

Description

W. S. CRAKE April 18, 1961 OFFSHORE PLATFORM STRUCTURE AND METHOD OF ERECTING SAME 5 Sheets-Sheet 1 Filed June 6, 1955 FIG.2

R O T N E V N w.s. CRAKE 6 guwufl HIS AGENT FIG.3

W. S. CRAKE April 18, 1961 OFFSHORE PLATFORM STRUCTURE AND METHOD OF ERECTING SAME 5 Sheets-Sheet 2 Filed June 6, 1955 SOIL LINE ORIGINAL BARGE POSITION I\\\\\\\BI I (FLOATING) FIG. 5

FIG. 9

R O T N E V N W.S.CRAKE BY: H.741 00x17 FIG.8

FIG.7

HIS AGENT April 18, 1961 w. s. CRAKE 2,979,910

OFFSHORE PLATFORM STRUCTURE AND METHOD OF ERECTING SAME Filed June 6. 1955 5 sheets sheet s FIG.||

INVENTOR:

w.s. ORAKE HIS AGENT April 18, 1961 w. s. CRAKE 2,979,910

OFFSHORE PLATFORM STRUCTURE AND METHOD OF ERECTING SAME Filed June 6, 1955 5 Sheets-Sheet 4 FIG. l3

INVENTOR= W.S. CRAKE HIS AGENT W. S. CRAKE April 18, 1961 OFFSHORE PLATFORM STRUCTURE AND METHOD OF ERECTING SAME Filed June 6, 1955 5 Sheets-Sheet 5 FIG. l5

INVENTOR W.S. CRAKE HIS AGENT OFFSHORE PLATFORM STRUCTURE METHOD OF ERECTING SAME Wilfred S. Crake, Houston, Tex., assignor to Shell Oil Company, a corporation of Delaware Filed June 6, 1955, Ser. No. 513,213

2 Claims. (Cl. 61-46) This invention relates to marine foundation structures and pertains more particularly to oifshore platforms for drilling oil wells and to methods of constructing said platforms.

At present, there are several proven methods of drilling for oil in submerged lands. When drilling in quiet waters at shallowdepths; it is possible to employ a drilling rig mounted on a barge of sufiicient height for the deck of the barge to remain out of water when the barge is submerged and rests on the ocean floorf For drilling in deeper waters, a drilling barge having a drilling rig mounted thereon may be provided with tall legs which are extended or lowered to the ocean floor while the operating platform and drilling rig remain above the water surface. Another method of drilling in deep waters is to drive a number of piles and construct a complete platform on top of the piles above the level of the wave action. Further, it is well known to use a small drilling platform mounted on piling and to use a ship or tender anchored adjacent the structure, while drilling, for carrying supplies, crews quarters, etc 7 Other methods of constructing offshore drilling plate w Patent forms have been proposed which combine some of the above-mentioned methods, but the proposed methods are usually severely limited as to the depth of water in which they can be used throughout the year under the various wave and wind conditions that exist at offshore drilling locations. An ideal ofishore drilling foundation or n'g should be usable in waters of depths of from 5 feet up to 100 feet or more so that, after drilling, the supporting drilling platform can be removed and re-used elsewhere, leaving only a light substructure for well maintenance and operation use at the wellhead. In addition, an offshore drilling platform should bereasonably light in weight so that its transportation to and from a drilling location, and its installation there should not require extra heavy or expensive construction equipment.

To date, the best proven and least expensive drilling method is the use of a shallow water drilling barge which can drill in open waters in almost complete safety in, say, 10 feet of water. An attempt has been made to use barges of this type in deep water drilling, but in order to do so it has been necessary to provide the barge with long legs that can reach to the bottom or ocean floor. Legs of a length and weight sufficient to support a drilling barge for deep water drilling cannot be carried vertically on a light-weight drilling barge without making the barge topheavy. Constructing a barge big enough and, heavy enough to carry vertical legs increases the weight and con- ,A further objectof this invention is to provide an offshore drilling site or foundation having a drilling platform which can be subsequently removed for transportation to another drilling location with a minimum of difliculty and expense. I

Another'obiect of this invention is to provide a method of constructing a'deep water offshore drilling foundation and platform in which a shallow water drilling barge is utilized as the drilling platform.

A still further object of this invention is to provide an offshoredrilling structure having an operating floor, and drilling rig mounted thereon, at a substantial height above the water level and adapted to be rapidly lowered to the water level and disconnected from the rest of the structure for transportation to another location.

These andothe'r objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

Figures 1, 2 and 3 are side and end views showing the sub-structure of the present offshore drilling foundation as it is being floated to a drilling location by barges secured thereto. r

Figure 4 is a view, partially in cross section, of an enlarged detail of the lower end of a column of the substructure of Figures 1, 2 and 3.

Figure 5 is a view in cross section illustrating the opera- 7 tion of washing silt out of the bottom of .a tubular piling.

Figure 6 is across sectional view of a sub-structure column and section of piling positioned therein at the time a seal at the bottom of the piling is being tested to withstand high hydraulic pressures.

Figures 7, 8 and 9 are views in partial cross section showing details of a piston or hydraulic lift as it is positioned in a column of the sub-structure.

Figure 10 is a view partly in cross section illustrating the anchoring means for holdingthe columns of the hydraulic lift at a desired level. t

Figure 11 is a view of a drilling barge taken in cross section to show the inner bracing members of said barge.

Figures 12 and 13 are views of the present drilling foundation showing end and side views of a drilling barge which has been floated into position over the sub-structure shown in Figure 1. I Figures 14 and 15 are schematic views of the barge and substructure shown in Figure 12 after the barge has been raised above the water level.

Referring to Figures 1, 2 and 3 of they drawing, the substructure 11 of the present offshore installation is constructed in the form of a large template, preferably composed of a single section comprising a group of spaced hollow steel columns 12. rigidly held together by structural bracing 13. The columns 12 are normally made of a predetermined length of pipe or casing so as to extend from the ocean floor at theotfshore drilling location to above the average wave level.

The sub-structure or template 11 is transported to the offshore drilling location in any suitable manner, as by a pair of pontoons 14 and 15 (Figure 2) secured to either side .of the substructure, or by a single pontoon 16 (Figure 3) secured within the sub-structure 11 near the upper end thereof. As shown in Figures 1 and 2, the sub-structure 11 is secured to the pontoons 14 and 15 by suitable cables 17 and winches 18 to permit the raising and lowering of the, sub-structure relative to the pontoons 14 and 15. While floating to the drillinglocation the sub-structure 11 is preferably suppored by the pontoons 14 and 15 so that at least one-half of the total height of the sub-structure is above the surface of the water.

In many instances, piles 21 or a part thereof which are to be used to anchor the sub-structure 11 to the ocean floor, may be carried within the steel columns 12 as the means may be provided for securing the piles 21 to the columns 12 so that they do not slip through the lower end thereof. Preferably, the bottom of each vertical col umn 12 is closed and sealed in a fluidtight manner by a thin knockout plate 22 (Figure 4) which is lightly welded 21 are to be carried within the steel columns 12 duringtransportation to the drilling site, the knockout plates 22 serve as support means for the piles 21.

On arrival at a drilling location, cable 17 is unwound from the winches 18 until the sub-structure 11 is resting on the bottom. The pontoons 14 and 15 are then disconnected from the sub-structure 11 and removed. Alternatively, the pontoons may be flooded to sink the substructure, after which operation the pontoons may be detached and raised by pumping in air. With the sub-structure 11 resting on the ocean floor, the piles 21 (Figure 2) are driven down through the tubular columns 12 into the ocean floor as shown in Figure 5. Prior to driving the piles 21 into the ocean floor and subsequent to rupturing the knockout plates 22 (Figure 4) water or air may be jetted down the piles 21 or the steel columns 12 if necessary to jet earth away from some of the columns in a manner well known to the art so that the sub-structure 11 is in a level position on the ocean floor.

When open-ended tubular piles 21 are driven into the ocean floor, the soil 23 enters the piles 21 to a level close to, and somewhat below, the soil level outside the pile (Figure After driving the piles 21 into the ocean floor, the inside soil therein should normally be removed either by boiling or by circulating fluid down a tubular pipe string 25 (Fig. 5) so as to wash some of the soil up the annular space 26 between the inner wall of the pile 21 and the outer wall of the pipe string 25.

Since the piles 21 are to serve as the housings for bydraulic lifts or elevator means, the piles 21 are driven sufiiciently deep into the ocean floor to be fluidtight at their lower ends thus preventing loss of hydraulic fluid to the formation. In the event that the soil at the bottom of the piles 21 does not close the piles in a fluidtight manner, a chemical or some other material having wall building qualities such as bentonite, or even a light cement slurry, may be added to form a bottom seal 27 (Fig. 6). Alternatively, a commercial Well packer could be set in the bottom of the pile to form a seal.

The length of the chamber formed within the pile above the seal 27 positioned therein must be equal to the length of the piston 28 of the hydraulic lift that is to be positioned in each column 12. Thus, for example, if a substructure 11 has steel columns 12 which are 20 feet high with the tops thereof substantially at water level, and it is desired to provide hydraulic lifts in the columns which could raise an operating platform 30 feet above the surface of the water, a hydraulic lift piston of about 35 feet would have to be used so as to leave about a 5 foot overlap of piston in the top of the pile 21 when the piston 28 is raised to its most elevated position. When using a 20 foot steel column 12 and a 35 foot piston 28, the seal 27 in the pile 21 must be located at least 35 feet down from the top of the pile which would mean that any soil inside the pile would have to be circulated out or otherwise removed from the pile for another 5 feet down to provide room for inserting the sealing material 27.

After placing the seal 27 at the predetermined position within the piling 21, the seal 27 is tested against water loss by temporarily cappingthe top of the pile 21 in the top of the steel column 12 by a slip-type testing unit of the cement head type commonly used in Well cementing operations which provides closure means 30 and 31 (Fig. 6) for closing the column 12 and pile 21 together with conduit means 32 for introducing a pressure fluid into the piling 21. A hydraulic pressure fluid is applied through conduit 32 so that the seal in the pile is tested normally to at least twice the pressure expected to be required to lift the drilling equipment.

With the sub-structure 11 firmly anchored by piles 21 to the ocean floor, the tops of the piles 21 are cut 011 substantially flush with the tops of the steel columns 12 and a tubular holding device such as a slip assembly 35 (Fig. 7) is mounted on the top of each steel column 12. Thereafter, a tubular piston rod 36 is inserted into the pile 21 through the slip assembly 35. A shallow water drilling barge 37 (Fig. 9) is then floated between the steel columns 12 of the sub-structure 11 and secured to the tops of the piston rods 36 of the hydraulic lift system.

It is to be understood that in fabricating the sub-structure 11, the cross bracing members 13 are installed at suitable levels to permit the drilling barge 37 to be readily floated between the steel columns 12 and over the members 13.

The shallow water drilling barge 37 is of any suitable type, complete with a drill rig 38 and other auxiliary drilling equipment necessary to carry on offshore drilling operations. As schematically illustrated in Figure 12, the barge 37 is preferably provided with an overhanging deck 39 together with the necessary internal bracing members 40 (Fig. 11) and, if desired, additional external bracing members 41 so that the barge may be readily hoisted out of the water by hydraulic lift system which contacts the overhanging deck 39.

As shown in Figure 7, the lower end of the piston rods 36 are enlarged and provided with suitable packing 42 to form a piston in any suitable manner known to the art. If desired, the lower end of the piston rod 36 (Figure 8) below the packing unit 42 may be provided with a small diameter tubular section extending below the packing 42, to form a shock absorber. As the loaded piston rod is lowered in the piling 21, the small diameter tube 43 below the piston 42 contacts the seal 27 and traps air in the annular space 44 between the pile 21 in the tube 43. An effective shock absorber is thus provided when the air between the seal 27 and the packing 42 is compressed.

The upper end of each piston rod 36 is closed in a suitable manner and secured to the overhanging deck 39 of the barge 37 as shown in Figure 9. For example, a tapered plug 47 having a fluid conduit 48 therethrough is welded in the upper end of the piston rod 36 to close the end of the rod while the conduit 48 permits the injection of a hydraulic pressure fluid into the piston rod for lifting the piston 42. The conical shoulder 49 formed on the plug 47 is adapted to fit in a conical recess in the overhanging deck 39 of the barge. The top of the piston rod 36 protrudes through the overhanging deck 39 and is held from falling downward by a clamp ring 50 which fits around a further reduced ring groove 51 in the top portion of the plug 47.

The slip assembly unit 35 for holding a piston rod 36 from downward movement is shown in greater detail in Figure 10. Steel straps 55 are welded to the outer surface of the pile 21, so that a slip housing assembly 56, having an inner tapered bowl 57, may be rigidly secured to the top of the pile 21 by bolts 58. A plurality of toothed slips 59 are mounted in the bowl 57 and adapted to slide thereon to contact the outer surface of the piston rod 36 and prevent the downward movement thereof. Thus, with the slips 59 in contact with the piston rod 36, upward movement of the piston rod 36 is possible while downward movement is prevented. Thus, in the event of failure of the hydraulic pressure in the piston rod 36, the rods 36, and the barge 37 carried thereon, are held in position until hydraulic power is restored. The slips 59 are held in place by a weight ring 60 or by springs (not shown) and may be lifted clear of the slip bowl 57 by a pull line 61 after hydraulic pressure has lifted all weight off of the slips. The slips 59 are connected to the housing 56 by suitable linkage means 62 and 63. When lowering the barge back into the water and the .piston rods 36 back into the piles 21, the slips 59 are held clear out of engaging position until the barge is in the water.

With a barge 37 positioned as shown in Figure 12 so that its deck 39 is connected to the tops of the piston rods 36 of the hydraulic lift system, a hydraulic pressure fluid from any suitable source (not shown) is pumped down through the conduit 48 (Figure 9) and down through the piston rod 36 and the lower open end thereof into the chamber 44 (Fig. 8) inside the pile 21 and above the seal thereof. Pressure simultaneously applied to all of the pistons 42 of the hoist system raises the barge 37, 20 feet or 30 feet or any desired height above the water level so that only the lattice work of the tubular sub-structure 11 is exposed to the wave action, as shown in Figure 14. In this manner the barge is transferred from buoyant support in the water to direct support on the lift means and substructure. In the event that the barge 67 (Figure 15) is not provided with an overhanging deck, as shown in Figure 14, suitable barge support means may be provided, such as length of construction steel 68 bent to conform with the contours of the bottom of the barge 67. One of these preformed support members 68 is secured between each pair of hydraulic pistons 36 to form a saddle on which the barge rests so that it can be elevated above the surface of the water. To stabilize further the barge, suitable means can be provided for clamping the barge to the saddle members 68.

I claim as my invention:

1. The method of erecting an offshore platform structure for drilling oil and gas wells on the ocean floor at oi'rshore locations, said method comprising transporting to an offshore location a complete platform substructure having a plurality of vertical tubular members connected together by cross-bracing members secured to and buoyantly supported by detachable barge means, lowering said substructure from said barge means to the ocean floor, anchoring the sub-structure to the ocean floor by driving open-ended tubular piles coaxially through the tubular members of said substructure, sealing the piles in a fiuidtight manner intermediate the ends thereof to form a piston chamber near the top thereof to contain a piston of a hydraulic lift means, installing hydraulic lift means in said chamber of said piles, floating a complete shallow water drilling barge through the open portion of the top of said substructure to a position wherein a portion of said barge projects above said lift means, transferring the barge from buoyant support in said Water to direct support on said lift means and substructure, and raising the barge above the wave action at said offshore location.

2. The method of erecting an ofishore platform structure for drilling oil and gas wells on the ocean floor at offshore locations, said method comprising transporting to an offshore location a complete platform substructure having a plurality of vertical tubular members connected together by cross-bracing members secured to and buoyantly supported by detachable barge means, lowering said substructure from said barge means to the ocean floor, anchoring the substructure to the ocean floor by driving open-ended tubular piles coaxially through the tubular members of said substructure, sealing the piles in a fluidtight manner intermediate the ends thereof to form a piston chamber near the top thereof to contain a piston of a hydraulic lift means, testing the sealed ends of said piles under a hydraulic pressure greater than that of a load to be mounted on said piles, installing hydraulic lift means in said chamber of said piles, floating a complete shallow water drilling barge through the open portion of the top of said substructure to a position wherein a portion of said barge projects above said lift means, transferring the barge from buoyant support in said water to direct support on said lift means and substructure securing said barge to said lift means, and raising the barge above the wave action at said ofishore location.

References Cited in the file of this patent UNITED STATES PATENTS 1,531,371 Belknap Mar. 31, 1925 1,558,127 Upson Oct. 20, 1925 2,151,394 Rogers Mar. 21, 1939 2,318,685 Gross May 11, 1943 2,531,983 McCoy Nov. 28, 1950 2,539,695 Moon Jan. 30, -1 2,591,225 Wilson May 27, 1952 2,602,636 Travers July 8, 1952 2,607,198 Parks Aug. 19, 1952 2,612,025 Hunsucker Sept. 30, 1952 2,652,693 Goldman et al Sept. 22, 1953 2,667,038 Bayley Jan. 26, 1954 2,689,460 Wilson Sept. 21, 1954 2,736,172 McChesney Feb. 28, 1956 2,771,747 Rechtin Nov. 27, 1956 2,775,869 Pointer Ian. 1, 1957 2,846,851 Pelham Aug. 12, 1958 2,873,580 Suderow Feb. 17, 1959

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