US3605669A

US3605669A - Floating self-elevating platform

Info

Publication number: US3605669A
Application number: US881315A
Authority: US
Inventors: Tsi V Yu
Original assignee: Kerr McGee Corp
Current assignee: Kerr McGee Corp
Priority date: 1969-12-01
Filing date: 1969-12-01
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20
Also published as: GB1310142A; TR16905A; NL7012519A; ZA705508B; DE2041925A1; FR2061001A5

Abstract

A FLOATING VESSEL FOR MARINE OPERATIONS SUCH AS WELL DRILLING IN DEEP OFFSHORE WATERS. BUOYANCY AND STABILITY IN THE OPERATION POSITION ARE PROVIDED BY A PLURALITY OF ELONGATED COLUMNS LOCATED IN A STABILIZING PATTERN ABOUT THE VESSEL, AND A BARGE OR SHIP SUPPORING A WORKING PLATFORM VERTICALLY MOVABLE RELATIVE TO THE COLUMNS IS PROVIDED. THE BARGE SUPPORTING THE WORKING PLATFORM PROVIDES ADDITIONAL BUOYANCY AND STABILITY DURING RELOCATION OF THE VESSEL.

Description

Sept. 20, 1971 s v, u

FLOATING SELF-ELEVATING PLATFORM 3 Sheets-Sheet 1 Filed Dec. 1, 1969 INVENTOR TSI VAN YU BY WILLIAM G. ADDISON ATTORNEY Sept. 20, 1971 T51 v. u 3,605,669

FLOATING" SELF-ELEVATING PLATFORM Filed Dec. 1, .1969 3 Sheets-Sheet 2 AInygny 4-n' P INVENTOR TSI VAN YU BY WILLIAM G. ADDISON ATTORNEY Sept. 20, 1971 TSI v. YU 3,605,659

FLOATING SELF-ELEVATING PLATFORM Filed Dec. 1, 1969 3 Sheets-Sheet 3 INVENTOR TSI VAN YU BY WILLIAM G. ADDISON ATTORNEY United States Patent 3,605,669 FLOATING SELF-ELEVATING PLATFORM Tsi V. Yu, Oklahoma City, Okla., assignor to Kerr-McGee Corporation Substituted for abandoned application Ser. No. 678,878, Oct. 31, 1967. This application Dec. 1, 1969, Ser. No.

Int. Cl. B63b 35/00, 35/44 US. Cl. 114.5 y Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Platforms, both fixed and mobile, for performing marine operations such as well drilling in offshore waters are well known. Platforms of the mobile type, which are floated to a location and then either sunk to the underlying land bottom or partially submerged to a level above the land bottom and anchored into position have been used for many years. In some cases, drilling is done from a platform on a conventional ship which has been modified to allow drilling through an opening in the ship, or a platform is mounted bet-ween two vessels floating side by side. The use of a conventional ship as a drilling vessel has certain advantages, particularly with regard to stability while relocating, and also with regard to mobility, as the ship type structure is much easier and faster to relocate than are other types of mobile drilling platforms. Also, because of the nature of their design, a ship type vessel can get through narrow channels and canals which will not handle other types of mobile drilling platforms. However, the ship type vessel has a serious drawback when used to support a drilling platform. This disad vantage is its large exposure to wave forces, combined with an inherently low radius of gyration. This disadvantage results in excessive roll during operation, and in some cases results in damage to drilling equipment.

One of the most successful types of mobile platforms used to date is described in US. Pat. No. 3,246,476. This type comprises a unitary construction of a working platform fixed to the tops of a group of elongated, buoyant stabilizing columns spaced about the structure in a stabilizing pattern. The spacing and size of the stabilizing columns is selected so that the structure has a high degree of stability during submergence and and refloating operations. Another related type of floating structure, which includes a platform movable with respect to open-ended stabilizing columns, is described in US. Pat. No. 3,285; 213.

While these prior art devices have generally been quite satisfactory, a need still exists for a design which offers advantages over existing equipment.

SUMMARY OF THE INVENTION According to the present invention, a structure is provided which combines the best features of the different prior art designs, and at the same time eliminates the undesirable features of existing designs. The structure includes at least three elongated, buoyant stabilizing col umns movable vertically with respect to a working platform. The working platform preferably comprises the 3,6fl5,669 Patented Sept. 20, 1971 top portion of a barge member having the general configuration of a ship, which barge also provides additional buoyancy and stability during relocation of the structure.

The stabilizing columns are fluid tight, at least throughout the portion that will be in contact with the body of water that the device is operating in, except that valved openings may be included to facilitate ballasting and deballasting of the columns using conventional means and techniques. The stabilizing columns are vertically movable with respect to the barge or appendages thereof, and may be locked to the platform at one or more locations by any suitable means. Guide means attached to the structure facilitate vertical movement of the columns relative to the platform. Preferably, means are provided to prevent rotation of the columns With respect to the platform, and stop means may also be provided near the tops of the columns to prevent them from falling completely through the platform.

The design of the present invention provides a stable structure without the necessity of additional stabilizing means such as ballast chambers or the cable-supported ballast mass required by prior art structures which utilize open-ended columns. It is only necessary, as described more completely in the aforementioned US. Pat. No. 3,246,476, to make the stabilizing columns of sufficient size, and locate them in a stabilizing pattern a sufficient distance from the center of the structure, to provide moments of inertia of the water plane areas of the structure of sufficient magnitudes to establish the metacenter of the structure above the center of gravity for every anticipated operating condition of the structure. The above requirement is essential to the stability of the device because the center of gravity of the structure may be above the center of buoyancy during many of its operating conditions, and without adequate water plane areas located in a stabilizing pattern, the structure would be dangerously unstable. When the center of gravity of the structure is below the center of buoyancy, the size and location of the water plane areas is not critical, as the structure is then stable due to a pendulum effect. However, when the center of gravity is above the center of buoyancy, as will be the case when the barge is elevated above the water and a heavy drilling rig is mounted on the platform, the requirement of water plane areas located in a stabilizing pattern about the structure is critical, and unless the moments of inertia of these water plane areas about any axis of heel are sufiicient to establish the metacenter of the structure above the center of gravity, the structure will be inherently unstable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a structure constructed in accordance with the present invention, the structure being illustrated in the operating condition.

FIG. 2 is a front elevational view of a structure constructed in accordance with the invention, the structure being shown in the towing or relocating condition.

FIG. 3 is a front elevational view of the structure shown in FIG. 2, the structure being shown with the barge floating and the columns lowered.

FIG. 4 is a front elevational view of the structure shown in FIG. 2, the structure being shown with the barge portion raised to just above the water level.

FIG. 5 is a front elevational view of the structure shown in FIG. 2, the structure being shown with the barge portion elevated to the operating level.

FIG. 6 is a front elevational view of another embodi ment of the invention showing the barge portion in the floating condition and part of the columns being carried above the water level.

FIG. 7 is a side elevational view showing a means for locking a column to the platform.

FIG. 8 is a front elevational view showing a means for moving a column relative to the barge portion of the structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to one embodiment of the invention, the platform is elevated solely by means of deballasting the columns after it has been locked to the previously ballasted and lowered columns. It is not necessary that prior art jacking equipment or rack and pinion means capable of supporting and elevating the full weight of the barge be provided. However, as a matter of safety and convenience, it may be desirable to include means for restraining or controlling the movement of the columns With respect to the platform. Such means might, for example, be light weight jacking means similar in operation to the heavy duty types used to elevate platforms in conventional prior art jackup type rigs. These light Weight jacking means need only be capable of providing enough restraint to movement of the columns relative to the platform to prevent undesired movement caused by wave action during the times that the columns are being raised or lowered relative to the platform. The jacks may be used in conjunction with a notched rail or rows of openings in the columns.

According to another embodiment of the invention, the columns may be raised and lowered by conventional elevating devices such as heavy duty hydraulic jacking means or rack and pinion means. The inclusion of these elevating devices provides additional flexibility of operation, and when used in conjunction with ballasting and deballasting, permits the columns to be raised or lowered while maintaining the platform a fixed distance above the water level. This is useful as a means of controlling the T011 period of the structure, which should always be different from the wave period to prevent undesirable amplification of roll. The period of roll of the vessel may also be varied by adding ballast to or removing ballast from h barge itself. This changes the center of gravity of the structure and thereby varies the roll period of the vessel' It is obvious from the above discussion that the stabilizing columns must provide enough buoyancy to float the structure with the barge portion out of the water.

If the structure is to be used for drilling of wells, appropriate drilling and auxiliary equipment is provided on the barge and platform portions of the structure. Also, living quarters, a heliport, storage facilities and other supporting equipment may be provided.

The design of the structure is such that it has a high order of stability during movement or relocation of the structure, which may be accomplished by towing, or by suitable self-propulsion means. The barge and the stabilizing columns are preferably deballasted during relocation, with the result that the structure is partially supported by the buoyancy of the barge portion, and partially supported by the buoyancy of the columns, except that in one particular embodiment, to be described below, the structure may be floated by the barge portion alone during relocation.

Following is a description of the method of raising and lowering the barge solely by means of adding and r moving ballast. After reaching a selected working location, the columns are ballasted, for example, by pumping sea water into the interior of the fluid tight columns. This causes the columns to sink through the openings in the barge or other appended structure affixed to the barge portion, and when the columns have settled to the desired level, they are locked into place. Subsequent deballasting of the columns causes the entire structure to rise as a unit. The columns provide enough buoyancy that the barge portion can be elevated sufficiently above the water level to be clear of normal wave action.

At this point, or in some cases before the ballasting and deballasting is performed, suitable anchoring means may be utilized to maintain the structure above a fixed point of the underlying seabed. Alternatively, the structure may be maintained in position above a fixed point by suitable dynamic positioning systems.

After the barge is elevated and the anchoring means are in place, or the dynamic positioning system is function ing, a marine operation, such as drilling or servicing a well, is performed. After completion of the operation, ballast is added to the columns, causing the entire device to begin to submerge. When the barge portion has reached its normal floating level, the means locking the columns to the platform are released, and deballasting of the columns is begun. The columns should have a neutral buoyancy at this point to prevent sudden upward or downward movement when the locking means are released. Complete deballasting of the columns results in their being raised to the towing position, and the entire cycle can then be repeated. The use of restraining means, such as hydraulic jacks, is very useful during the times that the columns are being ballasted or deballasted, since this lets the columns move against a predetermined load, and prevents hazardous unrestrained back and forth relative movement due to Wave action or other causes.

The operation as described above is in some Ways similar to that described in US. Pat. No. 3,285,213. However, this particular prior art patent describes stabilizing columns which are open at the bottom ends, with the result that the apparatus is supported on columns of compressed air. There are disadvantages inherent in such a device if it is to be operated in adverse weather conditions which could produce high wind and Wave forces, as the columns of compressed air could act as a spring and quickly aggravate any overturning tendency induced by Wind or waves, with catastrophic results. Also, it is difficult, if not impossible, to maintain such a device level when it is unevenly loaded.

In the embodiment wherein elevating means suflicient to lift the entire barge out of the water are provided, it is simply a matter of driving the columns down into the water until the submerged portions of the columns provide enough buoyancy to float the entire structure with the barge out of the water. Continued operation of the ele vating means after this point will raise the barge above the water level. Ballasting and deballasting of the columns is not necessary in this embodiment, but in some cases will be desired to provide additional control of the operation.

With reference to FIG. 1 of the drawings, a floating structure designated generally as 10 is shown. The structure has a barge portion 12, stabilizing

columns

14 and 16 located at the fore and aft ends, respectively, of barge 12, and stabilizing

columns

18 and 20 located on either side of barge 12. The barge 12 is shown with a deck 22 and a working platform 24 mounted thereon. A derrick 26 is supported by the working platform 24, and drilling rig equipment such as a drawworks, pumps, motors, and related equipment is indicated generally at 28. A stop means 30 is shown near the top of each of the

columns

14, 16, 18, and 20.

Columns

14, 16, 18 and 20 are shown passing through

column machinery housings

32, 34, 36 and 38 respectively, and

column machinery housings

36 and 38 are shown rigidly attached to the barge 12 by means of

structural appendages

40 and 42 respectively. The column machinery housings may also serve as guide means for the columns. Anchor lines 44 are shown extending from barge 12. A buoyancy tank 46 is shown attached to the lower end of column 14.

With reference to FIGS. 2, 3, 4 and 5, the structure 10 is shown in various stages of operation. FIG. 2 shows the barge 12 in a floating condition with the

columns

14, 18 and 20 raised to the towing position. As shown, the buoyancy tank 46 attached to the lower end of column 14 rests against the bottom of barge 12, while the buoyancy tanks 46 attached to the lower ends of

columns

18 and 20 rest against

column machinery housings

36 and 38. The buoyancy tanks 46 are preferably streamlined or elongated in the direction of the longitudinal axis of barge 12 for minimum resistance or drag during relocation o structure 10.

FIG. 3 shows the condition of the structure 10 after it has reached a working location and after the

columns

14, 18 and 20 have been lowered until the stop means 30 near the tops of the columns have contacted the

column machinery housings

32, 36 and 38. At this point in the operation the columns can be locked into place by any suitable means (not shown).

FIG. 4 shows the structure 10 after the columns have been locked into place and partially deballasted. The barge 12 is shown just as it emerges from the water, at which point the total stability of the structure is provided by the columns.

FIG. 5 shows the structure in a completely deballasted condition with the barge 12 raised well above the water level. The structure in this condition is floated by the submerged portions of the columns and attached buoyancy tanks.

FIG. 6 shows a modification of the invention in which side mounted

columns

48 and 50 are mounted to the barge in such a manner that the columns and their attached buoyancy tanks can be elevated above the water level when the structure is floating. This further reduces resistance to movement of the structure through the water, and in addition enables the structure to move down narrow canals which could not accommodate the structure as shown in FIG. 2.

It will be obvious that a structure in accordance with the invention could have all of its stabilizing columns pass through housings appendaged outboard of the barge portion, provided that at least three columns are supplied in a stabilizing pattern about the structure.

The process of operating a structure as shown in FIGS. 1 through 6, in the embodiment described previously where the barge is elevated by ballasting and deballasting, involves floating it to a location as shown in FIG. 2, and then adding ballast to the columns to cause them to sink to the position shown in FIG. 3.

When fully lowered, the colunms may rest against the top of the

housings

32, 34, 36 and 38 by means of stop members 30. The columns are then locked to the platform and its appendages by any suitable means, and the columns are deballasted. As shown in FIG. 4, as ballast is removed from the columns, the entire structure, with the barge securely fixed to the top portions of the columns, begin to rise in the water. Since the columns alone have sufiicient buoyancy when deballasted to support the structure with the barge portion completely out of the water, the barge and platform will be elevated above the water level. The barge is further elevated with continuing deballasting, and the final stage of the operation is illustrated in FIG. 5, which shows the barge elevated sufliciently above the water level to clear a preselected level of wave action.

The device may be maintained at the working location (such as directly above a drilling site) by conventional means, which might be large sea anchors of a dynamic positioning system comprising a series of outboard motors arranged about the device.

After drilling a well or otherwise completing an operation with the barge elevated, the raising process is reversed, and the device is returned to the towing or moving position for relocation. For example, ballast is pumped into the columns and/or the barge portion until the barge reaches its normal floating level. Usually it is preferred to lower the device by ballasting the colunms, rather than the barge portion, as this gives the structure a lower center of gravity and, therefore, is much safer. Also, it would not be desirable for the columns when submerged to have maximum buoyancy, because when the locking means holding the barge and platform to the top of the colunms are released, the columns would tend to spring upward, with resulting hazards.

After the barge is lowered to its normal floating level, the locking means holding the barge to the column tops are released, and the columns are deballasted. The columns then rise through the guide means until they reach the towing condition. While it is possible to tow the structure with the barge out of the water, and this might be desirable for short moves during calm weather, it is ob- 'viously much safer to first lower the barge into the water.

FIG. 7 shows a suitable locking means for securing the barge to the columns. The locking means includes a pin 52 slidably mounted in a sleeve 54 which is secured to the barge deck 22. Pin 52 is actuated by a hydraulically actuated piston rod 56 for insertion into opening 58 in a column.

While the invention is illustrated in the drawings with four stabilizing columns, it is only essential that at least three columns be provided, and that the columns be of suflicient size, and be located in a stabilizing pattern a suflicient distance from the central portion of the structure, to provide adequate buoyancy and stability during any planned use of the device. The stabilizing columns need not be all the some size, and need not be spaced uniformly about the center of the structure, but in most cases this would be the preferred design.

As mentioned above, in some cases it will be preferred to include elevating means for raising the barge, instead of relying strictly on deballasting of the structure. Such elevating means might be conventional heavy duty jacks, or might be of the rack and pinion type as illustrated in FIG. 8. As shown, a motor 60 drives a spur gear 62 through a gear reduction system 64. Spur gear 62 is adapted to mesh with rack 66 mounted on the column. In practice, two or more racks would be mounted on each column to distribute the load. The elevating means may also serve as locking means for securing the columns to the barge at a selected position.

The embodiments described above illustrate the invention, but are not to be considered as limiting the scope thereof. It has been shown that the structures in accordance with this invention are mobile, and can be moved from location to location, either by towing or by selfpropulsion, much more easily than the prior art columnstabilized devices. Also, the structures in accordance with the invention, when in the operating or raised condition, are much less susceptible to rolling due to wave action than are the prior art drilling ships, due to the smaller surfaces presented to the waves. It is also apparent that structures in accordance with the invention are stable, due to the size and spacing of the stabilizing columns, even when the barge portion is raised above the water level and the center of gravity of the structure is above the center of buoyancy due to a heavy load carried on the barge.

What is claimed is:

1. A buoyant structure capable of being floated in a body of water for movement to a location comprising:

(a) buoyant barge means having a working platform thereon, said barge means being elongated in the direction of its longitudinal axis to reduce water resistance during said movement to a location;

(b) at least three elongated, watertight stabilizing columns each being provided with means for vertical movement;

(c) means on the structure, including an opening therethrough for each column, for guiding the columns through said vertical movement, at least one of said columns and its opening being located in an appendage disposed outwardly from and rigidly connected to the barge means;

((1) means for securing the columns to the structure at at least one predetermined position thereon, the lower ends of the columns, when in their lowered positions, extending into the body of water to a distance above its mud line; and

(e) means for raising the barge means above the surface of the body of water, the structure being capable of floating while in such position;

said openings for the columns being positioned in such manner that the columns guided thereby provide the sole stabilization for the structure by maintaining the center of gravity of the structure below its metacenter when the barge means is positioned above the surface of the body of water.

2. A buoyant structure as defined in claim 1, wherein the barge means has the general configuration of a ship.

3. A buoyant structure as defined in claim 1, including enlarged bouyancy tanks attached to the lower ends of at least one of the columns.

4. A buoyant structure as defined in claim 1, including means for varying the period of roll of the structure, said means comprising means for controllably varying the center of gravity of the structure while maintaining the stabilizing columns fixed with respect to the barge means.

5. A buoyant structure as defined in claim 1, wherein the center of gravity of the buoyant structure is above the center of buoyancy of the buoyant structure at least when the barge means is elevated to a working level above the surface of the body of water.

6. A buoyant structure as defined in claim 1, including means for raising the buoyant structure to position the barge means above the surface of the body of water.

7. A buoyant structure as defined in claim 1, including elevating means adapted to vary the position of the columns with respect to the barge when the barge is above the water level.

8. A buoyant structure as defined in claim 7, including means for varying the period of roll of the structure, said means including means capable of maintaining the barge a fixed height above the water level while varying the position of the colunms with respect to the barge.

9. A buoyant structure as defined in claim 7, wherein at least one of the columns may be raised completely out of the Water while the barge is floating.

References Cited UNITED STATES PATENTS 2,947,148 8/1960 Young 6l46.5 3,294,051 12/ 1966 Khelstovsky l140.5D 3,318,275 5/1967 Field l14-O.SD 3,349,740 10/1967 Field ll40.5D

TRYGVE M. BLIX, Primary Examiner US. Cl. X.R. 61-46.5