US3163147A

US3163147A - Floating drilling platform

Info

Publication number: US3163147A
Application number: US111847A
Authority: US
Inventors: Bruce G Collipp
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1961-05-22
Filing date: 1961-05-22
Publication date: 1964-12-29
Anticipated expiration: 1981-12-29
Also published as: DK112573B; GB963082A

Description

Dec. 29, 1964 B. G. COLLIPP 3, 7

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 1 INVENTORL B. G. COLLIPP HIS AGENT Dec. 29, 1964 B. G. COLLIPP 3,163,147

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 2 INVENTORI B. e. COLLIPP HIS AGENT Dec. 29, 1964 B. G. COLLIPP 3,163,147

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 5 INVENTORI B. G. COLLlPP IS AGEJNT Dec. 29, 1964 B. G. COLLIPP FLOATING DRILLING PLATFORM 6 Sheets-Sheet 4 Filed May 22, 1961 FIG. 4A

INVENTORI B. G. COLLIPP BYI H M IS AGENT Dec. 29, 1964 B. e. COLLIPP 3,

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 5 INVENTORI B. G. COLLIPP BYI .1m

HIS AGENT Dec. 29, 1964 B. G. COLLlPP 3,163,147

FLOATING DRILLING PLATFQRM Filed May 22. 1961 6 SheetsSheet 6 INVENTORI B. G. COLLIPP BY: +7. 9 (l -22g HIS AGENT United States Patent 3,163,147 FLOATTNG DRILLHNG PLATFGRM Bruce G. Coliipp, Metairie, La, assignor to Shell Gil Company, New York, Nfil, a corporation of Delaware Filed May 22, 1961, Ser. No. 111,347 Claims. ((11. 114.5)

This invention relates to apparatus for use in drilling offshore wells and pertains more particularly to a floating drilling platform which may be anchored in deep water and from which an underwater well may be drilled.

In an attempt to locate new oil fields, an increasing amount of well drilling has been conducted at offshore locations, such for example, as off the coasts of Louisiana, Texas and California. Well drilling operations are being carried out further and further from shore and in increasingly deeper water. At present, however, substantially all offshore well drilling is being conducted from a platform having legs affixed to the ocean floor, as by piling, or from mobile drilling platforms or barges having legs which may be extended downwardly through the water and in contact with the ocean floor in order to fixedly support the barge thereon. To date, using either of the two above-described platforms, well drilling operations have been limited to water depths of about 125 feet. The only known deep Water drilling that has been conducted to date has taken place from a converted boat in which a drilling well has been provided. Since boats are prone to roll fairly easily, deep water drilling operations carried out from boats can only take place when wind and wave forces are fairly small.

It is therefore an object of the present invention to provide a moored floating drilling platform for use in carrying out drilling operations in waters that are too deep to have bottom supporting legs extending down through the water to the ocean floor and to drill during sea conditions not possible with converted boats or too severe for converted boats.

Another object of the present invention is to provide a floating drilling platform having sufficient stability to remain upright in hurricane weather without the assistance of any mooring line forces.

A further object of the present invention is to provide a floating drilling platform of the semi-submersible type (one relying on freeboard for stability, but having much ofits mass underwater) from which drilling operations may be carried out economically and safely in deep waters.

Another object of the present invention is to provide a floating drilling platform which is designed with a natural period of movement different from the wave periods so that resonance is avoided.

Still another object of the present invention is to provide a floating drilling platform designed to have a natural period of roll larger than that of the wave periods to be encountered.

A further object of the present invention is to provide a floating drilling platform having stabilizing columns of a design whereby the wave force of the larger waves with heights in excess of a predetermined height, say feet, are decreased.

A- further object of the present invention is to provide a floating drilling platform having a discontinuous natural period of roll, so that when the vessel rolls more than, say 5 degrees, which occurs only in extremely high waves, means are provided for changing the natural period of roll from, say, 17 to 32 seconds, thus destroying any resonance effect between the waves and the platform.

It is also an object of the present invention to provide a hull of unique desgn for the floating drilling vessel so forces.

"ice

Still another object of the present invention is to provide a floating drilling platform having little natural roll thereby precluding subjecting drill pipe or casing to stresses as it hangs from the drilling platform.

It is also an object of the present invention to provide time the hull has sufficient area in the water plane zone watertight bulkheads as shown'in FIGURE}.

to resist large changes in draft of the platform with changes in deck loads.

Still another object of the present invention is to provide a floating drilling platform with a hull of a design which is virtually independent of direction of wave approach whereby motions at 90 for head or beam seas would be the same.

It is also an object of this invention to provide afloat-r 'near the water surface are ballasted so that damages to them will have little or no effect on the seaworthinessof the platform.

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

FIGURE 1 is a view showing the outboard profile of the floating platform of the present invention;

FIGURE 2 is a plan view of the floating platform of FIGURE 1;

FIGURE 3 is a diagrammatic plan view of the lower portion of the hull of the floating platform of FIG- URE l; v

FEGURE 4 is a schematic view illustrating the ballast system piping in one of the stabilizing legs of the hull;

FIGURE 4A is a plan view of the piping system for flooding and evacuating the buoyancy chambers of the floating platform of the present invention;

FIGURE 5 is a diagrammatic view showing the float ing platform being towed to a drilling location;

FIGURE 6 is a diagrammatic view showing the floating barge of FIGURE 5 after it has been anchored at the drilling location;

FIGURE 7 is a diagrammatic view illustrating the present floating platform in its semi-submerged position employed during'drilling operations;

FIGURE 8 is a diagrammatic View illustrating a tug positioning a barge with drilling equipment thereon underneath the operating deck of the floating platform, and

FIGURE 9 is an isometric view of the platform of the present invention when employed as a fluid handling station connected to several wells.

Referring to FlGURE 1 of the drawing, the hull of the floating drilling platform comprises three vertically-ex tending support or stabilizing

columns

111, 12 and 13 which are interconnected in a closed triangular configuration by

cross-bracing hull members

14, 15 and 16 which extend laterally between the stabilizing columns near the lower ends thereof. The

cross-bracing hull members

14, 15 and 16 are preferably hollow, fluidtight members divided into a plurality of buoyancy tanks by means of Thus,

hull members 14 may be provided with flu'l'dtight bulkheads 17 and 18, while member 15 is provided with

fluidtight bulkheads

21 and 22, and member 16 is provided with fluidtight bulkheads 2 3 and 24. This divides hull member 14 into buoyancy tanks 25, 26 and 27, hull member 15 into

buoyancy tanks

28, 29 and 3t and hull memit ber '16 into

buoyancy tanks

31, 32 and 33. The

hull members

14, and 16 may be interconnected by smaller and preferably hollow and fluidtight hull members 36, 37 and 33 which may also be sub-divided by suitable bulkheads for containing water and fuel oil to be used during drilling operations.

The three corner support or stabilizing columns ll, 12 and 13 are preferably in the form of cylindrical tanks, as illustrated, which may be selectively flooded in order to lower the entire drilling platform in the water, thus stabilizing it by lowering its center of gravity. The stabilizing columns ll, 12. and 13 may be of the same diameter throughout their height, say for example feet in diameter. However, the upper ends il, 4-2 and 43 of the stabilizing columns ll, 12 and 13 are preferably reduced in diameter a substantial amount, say to 24 feet, a short distance above the water line when the floating platform is in its semi-submerged position as illustrated in FIGURE l. The diameter of the lower part of the stabilizing columns ll, 12. and 13 is large in order to reduce the amount of immersion which takes place when abnormally high hook loads are imposed on the floating platform through the fall lines and derrick. The upper ends ll, 42 and 53 of the stabilizing columns ll,

-12 and 13 are reduced in size to decrease the wave force of the larger Waves with heights in excess of a predetermined size, say 10 feet.

The reduction in diameter of the upper ends ll, 42 and 43 of the support columns ll, 12 and 13 also provides the floating platform with a discontinuous ma ural period of roll. When the floating platform rolls more than a predetermined amount, say past 5, which occurs only in extremely high waves, the corner stabilizing column diameter suddenly changes from 46 feet to 24 feet and the natural period of roll increases from 17 to 32. seconds. Therefore, if the floating platform were subjected to hurricane waves of a period of 17 seconds so that a resonance build-up occurs, the sudden increase in the natural period of roll from 17 to 32 seconds for roll angles above 5 would destroy any further resonant affects. Since the natural period of roll of the floating platform'is a function of the water plane area of the stabilizing columns, a radical change in the natural period of roll of the platform takes place when a wave comes along to dip one supporting column below the surface of the water into the range of reduced diameter on the column. Since the period of the vessel and that of the waves are then different, resonance is destroyed and the amount of roll of the vmsel immediitely decreases.

The stabilizing columns ll, 12 and 13 serve as the primary ballast tanks with the tanks being filled substantially to the water level 44- When the vessel is positioned as shown in FIGURE 1. Each stabilizing column is provided with a series of circular steel fenders 45 to protect these members from damage by boats. Since the water level inside the stabilizing columns is nearly the same as that outside, a leak caused by a boat rupturing the wall of the column would not be serious. Since the buoyancy tanks l4, l5 and 16 are deeply submerged and support the weight of the platform there is little likelihood of their being damaged. Damage to the sta bilizing columns would not atiect the intact buoyancy tanks so the. platform would neither sink nor heel. This feature provides a safer floating platform than can be achieved by converting ships. The smaller diameter

upper sections

41, 42 and 43 of the stabilizing columns ll, 12 and 13 are separated by a watertight bulkhead (not shown) which would prohibit further flooding of the stabilizing column in case they'Were damaged.

' The ballast system piping for supplying water to and evacuating the stabilizing columns ll, 12 and 13 is shown in FIGURES 3 and 4A. Ballast piping to the interconnec'ting hull members M, 15 and T16 is preferably used only in the event it is desired to submerge the platform to a deeper draft than that used for floating drilling 0perations. This can occur when it is desired to set the platform on the sea floor in shallow water to efiect repairs. A pump motor d? is provided at the top of each column with a drive shaft 23 extending downwardly through the column to a pump 43 positioned in the lower end of the large diameter ballast tank. To the intake of the pump l) are connected conduits all, 52, 53 and 54 for evacuating fluid from the respective buoyancy chamber and discharging it up conduit 55 and out conduit 56. Floodtbrough lines 52, 53 and 54 is only used when it is desired to set the platform on the sea floor in shallow water as described above. Flooding of the tanks is accomplished by gravity of iiow of fluid through intake port 57, check valve "5% and thence through conduit till into the lower end of the e last tank of. support column ll. All three support columns ll, 12 and 13 are provided with pumps 4%, 4 9a and 4% together with the associated valves and conduits for flooding and evacuating all buoyancy chambers in the hull, as shown in FIGURE 4A.

When the Floating drilling platform of the present invention is in its semi-submerged state, as illustrated in FIG- URE l, the section of the large diameter portion of the stabilizing columns ll, 12 and 13 above the water line provide reserve buoyancy to absorb heavy shock loads, increase the stability of the vessel, and afford a sharp change in the natural period of roll pitch as previously discussed. These tanks are further designed to have the correct size for the ballast water required to bring the platform down to the predetermined drilling draft, ize being such that the ballast water inside the tanks will be at or near the water level outside the tank.

Extending upwardly from the horizontal buoyancy tanks l-l, l5 16, as shown in FIGURE 1, are a plurality of vertical support legs d2, 63, d4 for supporting with or w bout the aid of the stabilizing columns, an suitable type or" operational platform thereon. The buoyant force in

tanks

1d, 15 and 16 is designed to equal the weight of the equipment and structure of the support legs d2, 63, 6d and 65 and the operational platform. When floating horizontally no vertical force is transmitted between stabilizing columns 12. and buoyancy tanks 14 and. 16 for example. Thus stabilizing column 12 only exerts a vertical force when the platform rolls or lists. In this way a safer platform is achieved. The particular platform illustrated is a multi-deck platform having an operating deck 6'7, a living deck 68 and a storage deck 6.9, as well as a partial or spider deck 7% suspended between the legs 63 and 6 's and which is preferably movable horizontally toward and away from the center hole of the well 59 extending down through the decks and bull. A derrick 72 is positioned over the center of the hull structure on the operating deck 67. Suitable hoist means '73 and cable reeling means 74 may be provided. A crane 75 is also provided for hoisting drill pipe and other supplies onto the drilling vessel. If desired the operational platform may be entirely supported on the stabilizing columns.

As shown in PEGURE 2 the vessel is provided with a pair of mooring lines F6 and 77 running from the top of each of the stabilizing columns ll, 12 and 13. Anchor winches 78 and 79 are provided for handling the anchor lines 76 and '77 which preferably extend outwardly in line with the sides of the hull. As shown in FIGURE 2 a pipe rack 81 is supported by one support column 13 and the operating platform. A casing rack 82 is mounted on the platform diametrically opposite the pipe rack 81 on the opposite side of a rotary table 8-3. A pipe skidway 84 is also provided.

eferring to FIGURES 5 through 8, in FIGURE 5 a pair of tugs 85 and 36 are shown towing the floating drilling vessel of the present invention to a drilling location where six anchor buoys have been previously set. During this stage all of the ballast tanks in the floating rilling vessel are evacuated. In FIGURE 6 the floating drilling vessel has been centered over the location and anchor cables have been run to the anchor buoys 90. In FIGURE 7 the sea suction valves of the stabilizing tanks have been opened and the float chambers flooded to lower the vessel in the water after which the mooring line cables are tightened to a predetermined tension and the ballast in the tanks is adjusted until the vessel is level. FIGURE 8 illustrates a tug 86 moving a barge 87 into place between the supporting legs of the platform and beneath the deck thereof. An underwater wellhead structure 88 is mounted on the barge 87 and has been centered below the spider deck 70 after which it will be removed from the barge by a hoist and later lowered to the ocean floor during drilling operations.

The triangular-shaped semi-submersible vessel of the present invention provides a drilling platform that does not have preferred rolling and pitching directions as waves can be taken from any direction and the vessel reacts about the same. Further, the inertia and drag forces on the present structure are less than those on other rectangular structures 'assumingthat the same weight is to be supported. Further, the triangular-shaped hull is inherently stronger than a square or other rectangular shaped hull. A further advantage of the present triangular shaped vessel is that waves passing over the

hull members

14, 15 and 16 only hit one at a time and strike them at varying angles. Additionally, the tendency for the structure to roll is less with only three legs supporting it than if a greater number were employed.

In FIGURE 9, a floating platform in accordance with the present invention is illustrated as a production platform being connected to a plurality of oil or gas Wells for handling the production fluid from the wells and pumping it to shore or to storage facilities. In this structure the interconnecting hull members 1%1, 102 and 103 are preferably arranged in a manner to provide an opening 104 of a size and shape to permit the lowering of a manifold float 105 therethrough of the type described in copending patent application, Serial No. 75,709, filed December 14, 1960, now Patent No. 3,111,692.

The barge of FIGURE 9 is provided with a Gena-a1 platform 196 supported on legs 167, 108, 109 and 110. Hoists 111 and/or other equipment for operating the barge and handling Well production fluid may be mounted on platform 1%, or on the other platforms 112-117 on the tops of the stabilizing columns. Preferably, the platforms support oil separating, treating and metering apparatus through which well roduction fluid is run before being pumped to shore. The oil and gas may be received through flexible flowlines 118 and pumped to shore through flowlines 119. Alternatively, the oil from the production fluid may be pumped into some of the tanks in the columns or cross membersof the hull for storage purposes, displacing some of the water therefrom.

I claim as my invention:

1. A semi-submersible floating platform for carrying out well operations at offshore locations when in a floating position, said platform comprising a hull having a plurality of vertically-extending stabilizing columns, rigid cross-bracing hull members laterally extending between said stabilizing iCOIlIII'iHS and interconnecting said hull members in a triangular configuration, operational platform means supported by said stabilizing columns, each of said hull stabilizing columns at the angles of said triangular configuration containing floodable buoyancy tank means at least in the lower part thereof, pump means and valve means and conduit means carried by said drilling platform and being in communication between the buoyancy tank means of said stabilizing columns and the water outside the hull for selectively flooding said buoyancy tank means and pumping water therefrom, said tanks being flooded an amount suflicient to lower the hull in a body of water to the semi-submerged position taken during drilling operations, each of said buoyancy tank means in the lower part of said stabilizing columns being 6 filled substantially to the level of said body of water when the hull is in the semi-submerged floating position.

2. A semi-submersible floating drilling platform for drilling wells at offshore locations when in a floating position, said platform comprising a hull having a plurality of vertically-extending stabilizing columns, rigid cross-bracing hull members laterally extending between said stabilizing columns and interconnecting said hull members at least near the lower ends thereof in a closed triangular configuration, operational platform means supported by said stabilizing columns, each of said hull stabilizing [columns at the angles of said triangular configuration containing floodable buoyancy tank means at least in the lower part thereof, pump means and valve means and conduit means carried by said hull and being in communication between the buoyancy tank means of said stabilizing columns and the water outside the hull for selectively flooding said buoyancy tank means and pumping water therefrom, said tanks being flooded an amount suflicient to lower the hull in a body of water to the semisubmerged position taken during drilling operations, the lower portion of each stabilizing column at the angles of said triangular configuration having a cross-section area substantially greater than that of the upper portion, the change in cross-sectional area taking place at a point near to but above the water level outside the stabilizing column in its semi-submerged floating position.

3. A semi-submersible floating drilling platform for drilling wells at offshore locations when in a floating position, said platform comprising a hull having a plurality of vertically-extending stabilizing columns, rigid cross-bracing hull members laterally extending between said stabilizing columns and interconnecting said hull members at least near the lower ends thereof in a closed triangular configuration, a plurality of vertical legs extending upwardly from said lateral hull members, operational platform means supported at least partially by said vertical legs on the tops thereof, each of said hull stabilizing columns at the angles of said triangular configuration containing floodable buoyancy tank means at leastin the lower part thereof, pump means and valve means and conduit means carried by said hull and being in communication between the buoyancy tank means of said stabilizing columns and the water outside the hull for selectively flooding said buoyancy tank means and pumping water therefrom, said tanks being flooded an amount sufiicient to lower the hull in abody of water to the semisubmerged position taken during drilling operations, the lower portion of each stabilizing column at the angles of said triangular configuration having a cross-sectional area substantially greater than that of the upper portion, the change in cross-sectional area taking place at a point near to but above the Water level outisde the stabilizing column in its semi-submerged floating position.

4. A semi-submersible floating drilling platform for drilling wells at ofishore locations when in a floating position, said platform comprising a hull having a plurality of vertically-extending stabilizing columns, rigid cross-bracing hull members laterally extending between said stabilizing columns and interconnecting said hull members at least near the lower ends thereof in a closed triangular configuration, a plurality of vertical legs extending upwardly from said lateral hull members, operational platform means supported at least partially by said vertical legs on the top thereof, each of said hull stabilizing columns at the angles of said triangular configuration containing floodable buoyancy tank means 'at least in the lower part thereof, said cross-bracing hull members being hollow fluid tight membevs at least a portion of which form buoyancy tank means which are selectively floodable, pump means and valve means and conduit means carried by said hull and being in communication between the buoyancy tank means of said stabilizing columns and said cross-bracing hull members and the water outside the hull for selectively flooding said buoyancy tank means and pumping Water therefrom, said tanks being flooded an amount suflicient to lower the hull in a body of water to the semi-submerged position taken during drilling operations, the lower portion of each stabilizing column at the angles of said tniangular configuration having a crosssectional area substantially greater than that of the upper portion, the change in cross-sectional area taking place at a point near to but above the water level outside the stabilizing Column in its semi-submerged floating position.

5. The semi-subrnersible floating drilling platform of claim 1 including a drill derrick supported on the top of said platform means and substantially centrally positinned with respect to said triangular hull, said platform means and said hull being provided with a hole therethrough of a size to accommodate the well pipe used during drilling operations.

References fit ed by the Examiner UNITED ST TES PATENTS FOREIGN PATENTS G erm any.

FERGUS S. MIDDL TON, Primary Examiner.

15 EACOB L. NACKENOFF, MILTON EUCHLER,

Exam iners.

Claims

1. A SEMI-SUBMERSIBLE FLOATING PLATFORM FOR CARRYING OUT WELL OPERATIONS AT OFFSHORE LOCATIONS WHEN IN A FLOATING POSITION, SAID PLATFORM COMPRISING A HULL HAVING A PLURALITY OF VERTICALLY-EXTENDING STABILIZING COLUMNS, RIGID CROSS-BRACING HULL MEMBERS LATERALLY EXTENDING BETWEEN SAID STABILIZING COLUMNS AND INTERCONNECTING SAID HULL MEMBERS IN A TRIANGULAR CONFIGURATION, OPERATIONAL PLATFORM MEANS SUPPORTED BY SAID STABILIZING COLUMNS, EACH OF SAID HULL STABILIZING COLUMNS AT THE ANGLES OF SAID TRIANGULAR CONFIGURATION CONTAINING FLOODABLE BUOYANCY TANK MEANS AT LEAST IN THE LOWER PART THEREOF, PUMP MEANS AND VALVE MEANS AND CONDUIT MEANS CARRIED BY SAID DRILLING PLATFORM AND BEING IN COMMUNICATION BETWEEN THE BOUYANCY TANK MEANS OF SAID STABILIZING COLUMNS AND THE WATER OUTSIDE THE HULL FOR SELECTIVELY FLOODING SAID BUOYANCY TANK MEANS AND PUMPING WATER THEREFROM, SAID TANKS BEING FLOODED AN AMOUNT SUFFICIENT TO LOWER THE HULL IN A BODY OF WATER TO THE SEMI-SUBMERGED POSITION TAKEN DURING DRILLING OPERATIONS, EACH OF SAID BUOYANCY TANK MEANS IN THE LOWER PART OF SAID STABILIZING COLUMNS BEING FILLED SUBSTANTIALLY TO THE LEVEL OF SAID BODY OF WATER WHEN THE HULL IS IN THE SEMI-SUBMERGED FLOATING POSITION.