US3186180A - Offshore well drilling and oil storage platform - Google Patents

Description

June 1, 1965 c. A. SWANLUND, JR, ETAL 3,185,130

OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORM Filed April 25, 1963 3 Sheets-Sheet l I-: -Z--' |3 I4----- INVENTORS! fimfifi c. A. SWANLUND, JR.

I6 32 I? c. H. SIEBENHAUSEN, JR.

FIG, BYI 5.. H514 Gad;

THEIR AGENT 3,186,180 OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORM Filed April 25, 1963 June 1, 1965 c. A. SWANLUND, JR., ETAL 3 Sheets-Sheet 2 FIG. 9

INVENTORSZ C. A. SWANLUND, JR.

c. H. SIEBENHAUSEN, JR. BY: H M

v THEIR AGENT June 1965 c. A. SWANLUND, JR., ETAL 3,186,180

OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORM 3 Sheets-Sheet 3 Filed April 25, 1965 FIG. I3

FIG. l4

INVENTORSZ C. A. SWANLUND, JR. C. H. SIEBENHAU FIG. 5

United States Patent 0 3,186,189 UFFfiHGRE WELL DRILLKNG AND GIL STORAGE PLATFORM Clifford A. Elwanlund, Ira, Metairie, Lea, and Christian H. Siebenhansen, .lra, Midland, Tex, assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware FiledApr. 25, 1963, Ser. No. 275,607 4 Claims. (Cl. 61-465) This invention relates to marine foundation structures and pertains more particularly to offshore platforms for ,drilling oil and gas wells while providing storage facilities for the oil produced from offshore wells. At present, one type of a stationary platform structure commonly used for offshore drilling or producing of wells makes use of a substructure which is constructed in the form of a large template, preferably composed of a single section cornprising a group of spaced hollow steel column rigidly held together by structural cross bracing, Piles are then driven through the hollow template legs or columns to the depth required for foundation support purposes. The piles are then fixedly secured to the template, preferably by welding and/or cement grouting and then cut off at predetermined levels. The columns of the template are normally made of a predetermined length of pipe or casing so as to extend from the ocean floor at an offshore drilling location to a point above the average wave level of the water. However in some instances, in order to minimze wave forces on the structure, the template columns and piling are terminated below the normal level of the water. Mounted upon the substructure formed by the template and piles is a deck section from which drilling or producing operations are conducted. The deck section is generally constructed of a plurality of parallel structural trusses extending longitudinally and transversely of the area of the platform and intersecting each other at a plurality of points to form a generally rectangular box-like open work structure having a surface area of required dimensions for its intended use as a working platform. This structural framework of the deck section then covered by a suitable flooring material upon which a conventional drilling derrick and suitable drilling or producing equipment may be mounted. It is common for the deck section to have a plurality of legs extending downwardly therefrom which are so constructed that they are in alignment with and seat within the tops of a plurality of legs of columns of the template or in the piles installed therein.

Offshore platform structures .of the above-described type utilizing a unitary template through which piles are driven and on which a deck section is mounted have been used for several years in drilling and producing locations on the Continental Shelf along the coasts of Louisiana and Texas.

The well locations are generally several miles from shore.

These templates are of enormous weight and as the selected drilling locations have been in deeper and deeper water it has been found to be impossible at some water depths to transport and install an ofifshore platform structure .of the template type because of the great size and weight of the template. Merely dividing the template into a number of sections that are installed separately and connected above sea level at the drilling location is expensive and also in deep water exact alignment of the various segments of the structure is difficult. Also, there is no underwater continuity of a sectionalized structure of this type thus reducing its ability to withstand forces due to wind and wave action and reducing the load-carrying capacity.

For installing an offshore platform structure in a deep water location, say 300 feet, it has been suggested that the platform be sectionalized with each section being provided with buoyancy tanks so that the sections may be floated separately to the assembly location. It is then proposed to drive four legs into the ocean floor in spaced apart relationship, lift each fioatable platform section out of the water and lower it over the legs and subsequently flood the buoyancy tanks to cause the platform section to sink to the bottom while sliding along the four legs as guide members. It may be seen that this arrangement has considerable drawbacks as it is almost impossible to accurately space the lower ends of the 300 foot piles in the ocean floor without the use of some sort of template.

Another suggested scheme for buoyant deepwater offshore structures involves the use of large diameter vertical legs two of which support the structure while being transported to the site. In this scheme oil and gas wells may be drilled through the vertical legs. An objection to this scheme is the fact that the columns and consequently the piling are not battered; and therefore, the large lateral wind and wave forces cannot be resisted as well as they would be resisted by battered piles and columns.

It is therefore a primary object of this invention to provide an offshore drilling platform capable of being fabricated on land and transported to a deep water location where it is subsequently erected and positioned on the ocean floor as a unit.

A further object of the present invention is to provide an offshore platform structure provided with sufiicient buoyancy so that the structure may be floated to a water location.

Another object of the present invention is to provide a buoyant platform structure having superior lateral stability characteristics in that the template columns and piles are inclined on a batter.

A further object of the present invention is to provide a buoyant platform structure adapted to be erected at a deepwater location from which drilling operations can be carried out with the oil produced from any underwater wells being stored by the platform structure.

Still another object of the present invention is to provide a buoyant offshore platform structure adapted to be erected in deepwater locations by presently available equipment.

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 longitudinal view showing the platform structure of the present invention positioned at an offshore location with the deck section of the platform being provided with well production handling facilities;

FIGURE 2 is a longitudinal view of the upper portion of a platform of FIGURE 1 wherein the deck section is provided with storage shed or living quarters;

FIGURE 3 is a longitudinal view of the upper section of the platform structure of FIGURE 1 wherein the deck section is equipped with a derrick while drilling operations are being carried out;

FIGURE 4 is a cross-sectional view along the line 4-4 of FIGURE 2;

FIGURE 5 is an isometric view diagrammatically showing one arrangement of a production facility for handling production fluid from wells and transferring it into and out of the central storage tank of the platform structure of FIGURE 1;

FIGURE 6 is a cross-sectional view taken in longitudinal projection of the lower end of a template column with a removable cover plate;

FIGURES 7 through 14 are schematic views illustrating the sequential steps of one manner of towing the platform structure of the present invention to a selected offshore location, unloading the platform structure from a barge, floating the platform structure horizontally in the water with hoses connected for flooding the buoyancy tanks of the structure, upending the platform structure and setting it in place on the ocean floor, installing the deck portion of the platform structure after driving piles through the legs of the structure, drilling wells from the platform structure into the ocean floor while employing a second structure adjacent the first platform for storing equipment and serving as living quarters, drilling wells into the ocean floor from the second platform structure, and finally producing the wells of both structures with one of the structures being provided with production facilities in order to carry out operations such as separating the oil, gas and water phases of the production fluid and metering and storing the oil.

Referring to FIGURE 1 of the drawing, an offshore platform structure in accordance with the present invention is shown as comprising a plurality of long substantially vertical legs 11 and 12 in spaced relationship with each other and interconnected by cross bracing members 13, 14 and 15 arranged in any suitable configuration, preferably in a manner to provide the greatest rigidity to the structure. It is preferred that the tubular legs 11 and 12 slant downwardly and outwardly from a center line through the platform structure so that the base of the structure encloses an area greater than the top of the platform structure thereby giving the platform structure greater stability. Although only two legs 11 and 12 appear in FIGURE 1, it is to be understood that the platform structures comprise at least three and preferably four legs of a length greater than the water depth at which they are located and cross-braced together in a configuration with a closed periphery. The legs 11 and 12 are preferably open throughout their entire length so that piles 16 and 17 can be driven through them into the ocean floor 18. Prior to driving the piles 16 and 17 through the legs 11 and 12, at least one of the legs and preferably all of the legs are closed in a fluid-tight manner at both ends by suitable removable closure means well known to the art, for example as by welding a knock-out plate 19 (FIGURE 6) over the end of the leg. The plate 19 would be driven out when a pile was driven through the leg. The closed legs form auxiliary buoyancy tanks which aid in floating the platform structure. For a platform 300 feet high, the legs may be from 3 to feet in diameter.

Positioned within the center of the platform structure a large diameter tank, for example 20 to feet in diameter, which extends longitudinally within the structure substantially the length of the legs 11 and 12 and being cross-braced thereto so that it is rigidly supported. The top of the tank 21 is positioned a distance below the surface of the ocean 22 a distance sufficient to be below the most violent wave action, thus reducing the wave forces imposed upon the platform structure.

Extendinglongitudinally through the tank 21 are a plurality of relatively large diameter conduits 23, 24 and 25 or well casing which extend through the ends of the tank in a fiuidtight manner. The well conduits 23, 24

and 25 may be closed at both ends in a manner similar to the legs and described with regard to FIGURE 6 so as to serve as auxiliary buoyancy tanks for the platform structure. The main buoyancy tank in the structure is the central tank 21 which is provided with port means 26 and 27 at the upper and lower ends thereof one of which is adapted to be connected to a hose for pumping water in the tank when the structure is sunk into place on the ocean floor while allowing air to leave through the other port 26 at the top of the tank while water is being pumped into the bottom of the tank through a hose 28 (FIGURE 9) connected to the port 27. As an alternative flooding method sea water is allowed to flow into the cylinder and controlled by exhausting air at the top through a valve. If desired, the tank 21 (FIGURE 1) may be provided with a transverse plate member 29 which divides the tank 21 but not the well conduits 23, 24 and 25 into upper and lower fluidtight sections. In the event that the tank 21 is divided into upper and lower fiuidtight sections, the upper section would be provided with ports 26 and 2701 while the lower section was provided with ports 26a and 4 27 whereby both tanks could be selectively flooded and/ or evacuated if necessary. Additionally, if necessary, instead of employing a horizontal transverse plate 29 the plate member could extend vertically through the tank to divide the tank into at least two longitudinal fluidtight sections which could be independently flooded.

The well conduits 23, 24 and 25 are of a diameter suflicient so that drilling operations can be carried out through them with well casings 31, 32 and 33 being subsequently extended through the well conduits 23, 24 and 25 and extending up to the lower deck 34 where they would be closable in a normal manner as by valve assemblies in the form of Christmas trees 35, 36 and 37.

Mounted on the upper ends of legs 11 and 12 of the platform structure It) is a deck unit 38 comprising a plurality of vertical legs 41 and 42 interconnected as necessary by cross bracing members 43 and 43a and spaced apart sufficiently to mate with the top of the legs 11 and 12 of the platform structure. The legs 41 and 42 sup port one or more decks 34 and 44 which in turn support the necessary equipment normally associated with a production facility at an offshore location, such for example as separators 45 and 56, pump 47 and storage shed and living quarters 43. It is to be understood as described hereinbelow with regard to FIGURE 5, the production handling equipment such as the separators 45 and 46 are interconnected by means of conduits with the central tank 21 of the platform structure, or with the several independent sections of the tank if it is divided into more than one section. In FIGURE 2, the identical platform structure described with regard to FIGURE 1 is shown except that the deck unit 38 is provided with a living quarters building 49. The upper ends of the well conduits 23, 24 and 25 (FIGURE 1) may be provided with funnel-shaped openings 50, 51 and 52 at their upper ends (FIGURE 2) to aid in inserting pipe therethrough.

In FIGURE 3 the identical platform structure of FIG- URE 1 is illustrated with the top thereof being provided with a derrick 53 having a fall line system 54 and a traveling block 55. These elements together with a hoist 56 and associated auxiliary drilling equipment suspend a drill string 57 which extends down through a rotary table 58 and one of the well conduits of the tank 21. An auxiliary vessel 60 is shown as being moored along the side of the platform structure 10.

A cross section of the buoyancy and storage tank 21 is shown in greater detail in FIGURE 4. The tank 21 may be centrally positioned within the platform structure by means of support members 61 and 62, which may in the case of support member 62 extend entirely through the tank 21 to give greater rigidity to the tank. In addition to well conduits 23, 24 and 25, the tank 21 in FIGURE 4 is shown as being provided with three more well conduits 63, 64 and 65. The number of well conduits provided in the tank 21 would depend upon the size of the tank, the number of wells to be drilled from the platform structure, and the spacing desired between each of the wells. At spaced levels along the tank 21 the well conduits 23, 24 and 25 are preferably reinforced by support bars 66 and 67 to which they are welded.

In accordance with the present invention, the platform structure 10 (FIGURE 1) is fabricated on land and then either floated in the water and towed to the selected offshore location, or placed on a barge 68 (FIGURE 7) which is towed to the desired location by means of a tug 69. In the event that the barge 68 is employed, the barge is preferably provided with skid beams or a sloping skidway 70 on which the platform structure 10 is positioned and secured thereto. On arriving at the selected location, another vessel 60 may be employed to help pull the platform structure 10 off the skidway 70 of the barge 68 as shown in FIGURE 9, or then it may be pulled into the water by a block and tackle and hoist located on the barge 68. With the platform structure pulled into the water as illustrated in FIGURE 9, the buoyancy of the central storage tank 21 is suflicient to float the platform structure in the water. Since there may be a tendency for the platform structure to roll in the water on the longitudinal axis of the tank 21, at least one of the legs is preferably sealed top and bottom as previously described so as to serve as an auxiliary buoyancy tank. Thus, in the event that the platform structure 21 was to roll in the water, it would only roll until the buoyant leg came in contact with the surface of the water at which time the buoyant leg would serve as an outrigger and stabilize the platform structure against roll. A preferred arrangement is to have all of the legs buoyant to reduce possibility of the structure rolling.

With the platform structure shown in the position in FIGURE 9, Water would be pumped through hose 23 into the bottom of the tank 21 or the tank would be otherwise flooded until the platform structure settled bottom first to the ocean floor as shown in FIGURE 10, piles would then be driven through the legs of the platform structure and if desired cemented to the ocean floor. Subsequently, the tops of the piles would be cut off at the tops of the legs of the platform structure and preferably secured thereto as by welding. The deck section 38 would then be lowered into place on top of the upper end of the platform structure 10, as by means of a crane on vessel 60, as shown in FIGURE 11.

In FIGURE 12 two identical platform structures in accordance with the present invention are shown as being positioned on the ocean floor with piles having been driven through their legs and deck section provided on their upper ends. Platform structure 19a is provided on its upper deck with living quarters 49 or a storage shed that is connected to the other platform structure by means of a walkway 70. Drilling operations are being carried out on platform 10 from the derrick 53 mounted thereon.

After having drilled the desired number of wells from platform structure 10 (FIGURE 13) the derrick 53 was moved to platform structure 10a to carry on drilling operations while the living quarters or storage facility 49 were moved to platform structure 10. After completing the scheduled drilling from both platforms 10 and 10a, a production facility such as one employing separators 45 and 4-6 is mounted on the top of one of the platforms, in this instance platform 19a, while production fluid is piped from the wells drilled from platform 14) through conduit 71 extending between the two platforms 1t? and 19a.

One form of a production handling facility adapted to be mounted on the deck unit of a platform structure in accordance with the present invention is shown in FIG- URE 5 schematically with the legs and cross-bracing members of the platform cut away from the central storage and buoyancy tank 21 and with the well casings 23, 24 and 25 (FIGURE 1) omitted from the tank 21 (FIG- URE 5). The illustrated production facility in FIGURE 5 utilizes sea water displacement of oil within the storage tank 21 so that the tank is full of liquid at all times and hence not subjected to the stresses of an underwater tank which is partially empty.

With the oil floating on top of the water within the tank, the tank is provided with an oil discharge line 73 from the top thereof which extends upwardly through deck 34 and is adapted to be closed by a valve 74. This line may be 12 inches in diameter, for example, and beyond valve 7 4 is provided with a flexible hose 75 adapted to extend to an oil barge moored alongside the structure. Production fluid from one of the wells is received through conduit 76 and passes through an oil, gas and water separator 77 so that only oil is discharged through conduit '78 and down pipe 79-73 into the top of the tank 21. In the event that oil was being discharged from the tank 21 into a tanker alongside (not shown) a control valve 80 in the conduit 79 would be closed so that the flow of oil from the separator 77 and through line 78 would be directed through a side conduit 81 into a temporary oil storage tank 82.

In order to discharge oil from the storage tank 21 one or more suction pumps 83 and 84 are provided with suction tubes 85 and 86 whose lower ends extend down below the surface of the water 22. The discharge of the pumps 83 and 84 is normally through open conduits 87 and 88 into a water storage tank 89 having an overflow line 90 to control the'head of fluid and hence limit the pressure being applied to the storage tank 21. The water discharge line 91 from the water tank 89 is normally open at all times and extends to the bottom of the storage tank 21. can be bypassed by opening one of the norm-ally closed valves 92 or 93 in the discharge line from pumps 83 and at so that water is pumped directly down line 91 into the tank 21.

A third line 94 extending to the bottom of the tank 21 is preferably provided with the flow therethrough being controlled by normally closed valve 95. This is a purge line which is employed when it is desired to clean out sediment from the bottom of tank 21. In cleaning sediment from the tank 21, valve 95 would be open and water would be pumped from one of the pumps 84 and 83 down water line 91 to the bottom of the tank with the water then being discharged up purge line 94, through valve 95 to the sea.

By utilizing a single storage tank in the center of the offshore platform structure through which wells may be drilled, the largest storage capacity of oil is provided with a minimum surface being exposed to lateral forces tending to tip the platform structure over. At the same time it is possible to employ batter legs at the corners of the structure thus giving the structure much more stability than could be realized by straight legs. It is only by employing this combination of elements that it is possible to provide the greatest stability for a structure of any given height while at the same time being able to start drilling wells in a vertical direction and subsequently providing storage capacity for the produced oil from the wells drilled from the platform of the present invention.

We claim as our invention:

1. An offshore platform structure for extending from the bottom of a body of water to above the surface of the water comprising,

a plurality of tubular legs of 'a length greater than the water depth and cross-braced together in a framework having a configrn'ation with a closed periphery, said tubular legs slanting downwardly and outwardly from a center line through the platform structure whereby the base of the structure encloses a larger area than the top of said structure,

a large-diameter tank extending longitudinally substantially the length of the legs of the structure and crossbraced thereto in the center of the structure entirely within the framework formed by said legs, the top of the tank being below the top of said structure a distance sufficient to be below the most violent wave action when the structure is in position on the bottom of the body of water,

said tank being closed and having a buoyancy sufficient to float the entire structure in a body of water, the interior of the tank being open to movement of fluid in both directions substantially throughout its entire length,

at least one of the tubular legs being closed at the ends thereof providing an outrigger buoyancy tank in contact with the water preventing rotation of said platform structure about its longitudinal axis when floating in water,

a plurality of longitudinally-extending conduits carried in said tank and extending the length thereof,

removable closure means closing both ends of said conduits in a fluidtight manner so that the conduits form auxiliary buoyancy chambers,

said conduits being of a diameter suflicient to carry out well drilling operations therethrough,

If desired, the water storage tank 89 port means through the wall of said tank for flooding said tank from the lower end thereof thereby causing the tank and structure to tilt bottom down to a vertioal position within a body of water, and

first conduit means for admitting oil to said tank and second conduit means for admitting water to said tank to displace the oil therefrom.

2. The apparatus of claim 1 wherein the legs are closed top and bottom by removable closure means.

3. The apparatus of claim 1 wherein the centrallylocated tank of said platform structure is secured to said structure in a manner such that the upper end of the tank floats slightly higher out of the water than the lower end of the tank when said tank is in a substantially horizontal position.

4. The apparatus of claim 1 wherein the centrally- References Cited by the Examiner UNITED STATES PATENTS Kuss et 'al. 6146.5 X

Schaufele 6146.5 Crake 6l-46.5 X

Newcomb 61-46.5 Sandberg 6146.5

15 EARL J. WITMER, Primary Examiner.

JACOB SHAPIRO, Examiner.

Claims (1)

1. AN OFFSHORE PLATFORM STRUCTURE FOR EXTENDING FROM THE BOTTOM OF A BODY OF WATER TO ABOVE THE SURFACE OF THE WATER COMPRISING, A PLURALITY OF TUBULAR LEGS OF A LENGTH GREATER THAN THE WATER DEPTH AND CROSS-BRACED TOGETHER IN A FRAMEWORK HAVING A CONFIGURATION WITH A CLOSED PERIPHERY, SAID TUBULAR LEGS SLANTING DOWNWARDLY AND OUTWARDLY FROM A CENTER LINE THROUGH THE PLATFORM STRUCTURE WHEREBY THE BASE OF THE STRUCTURE ENCLOSES A LARGER AREA THAN THE TOP OF SAID STRUCTURE, A LARGE-DIAMETER TANK EXTENDING LONGITUDINALLY SUBSTANTIALLY THE LENGTH OF THE LEGS OF THE STRUCTURE AND CROSSBRACED THERETO IN THE CENTER OF THE STRUCTURE ENTIRELY WITHIN THE FRAMEWORK FORMED BY SAID LEGS, THE TOP OF THE TANK BEING BELOW THE TOP OF SAID STRUCTURE A DISTANCE SUFFICIENT TO BE BELOW THE MOST VIOLENT WAVE ACTION WHEN THE STRUCTURE IS IN POSITION ON THE BOTTOM OF THE BODY OF WATER, SAID TANK BEING CLOSED AND HAVING A BUOYANCY SUFFICIENT TO FLOAT THE ENTIRE STRUCTURE IN A BODY OF WATER, THE INTERIOR OF THE TANK BEING OPEN TO MOVEMENT OF FLUID IN BOTH DIRECTIONS SUBSTANTIALLY THROUGHOUT ITS ENTIRE LENGTH, AT LEAST ONE OF THE TUBULAR LEGS BEING CLOSED AT THE ENDS THEREOF PROVIDING AN OUTRIGGER BUOYANCY TANK IN CONTACT WITH THE WATER PREVENTING ROTATION OF SAID PLATFORM STRUCTURE ABOUT ITS LONGITUDINAL AXIS WHEN FLOATING IN WATER, A PLURALITY OF LONGITUDINALLY-EXTENDING CONDUITS CARRIED IN SAID TANK AND EXTENDING THE LENGTH THEREOF, REMOVABLE CLOSURE MEANS CLOSING BOTH ENDS OF SAID CONDUITS IN A FLUIDTIGHT MANNER SO THAT THE CONDUITS FORM AUXILIARY BUOYANCY CHAMBERS, SAID CONDUITS BEING IN A DIAMETER SUFFICIENT TO CARRY OUT WELL DRILLING OPERATIONS THERETHROUGH, PORT MEANS THROUGH THE WALL OF SAID TANK FOR FLOODING SAID TANK FROM THE LOWER END THEREOF THEREBY CAUSING THE TANK AND STRUCTURE TO TILT BOTTOM DOWN TO A VERTICAL POSITION WITHIN A BODY OF WATER, AND FIRST CONDUIT MEANS FOR ADMITTING OIL TO SAID TANK AND SECOND CONDUIT MEANS FOR ADMITTING WATER TO SAID TANK TO DISPLACE THE OIL THEREFROM.

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