US3702105A - Deep water drilling rig - Google Patents

Abstract

A deepwater float has a supporting platform and downwardly depending legs which carry buoyancy tanks arranged annularly with reference to the platform, or a single ring-shaped buoyancy tank. Tethers secure the float against lateral displacement with reference to a selected portion of the deepwater floor. Gyroscopic controls normally maintain the tethers at a length and the buoyancy at such positive value that the tethers are taut and the platform is at a selected distance above mean wave level; they increase the tether length and positive buoyancy in automatic response to an increase in the height of the mean wave level.

Description

United StatesPatent Feldman 1 Nov. 7, 1972 [54] DEEP WATER DRILLING RIG Primary Examiner-Trygve M. Blix [72] lnvemor' Samuel Attorney--Richard J. l-lolton, Kelvin B. Clarke, Joel [73] Assignee: The Lummus Company, Bloomfield, G. Ackerman and Bryant W. Brennan NJ. 22 Filed: March 17, 1971 [57] ABSTRACT Appl. No.: 125,297

A deepwater float has a supporting platform and downwardly depending legs which carry buoyancy tanks arranged annularly with reference to the platform, or a single ring-shaped buoyancy tank. Tethers secure the float against lateral displacement with reference to a selected portion of the deepwater floor. Gyroscopic controls normally maintain the tethers at a length and the buoyancy at such positive value that the tethers are taut and the platform is at a selected distance above mean wave level; they increase the tether length and positive buoyancy in automatic response to an increase in the height of the mean wave level.

4 Claims, 11 Drawing Figures PATENTEDNM 11922 sum 1 or 4 ZO/VE MEAN 7 WA 1 5 A 51/51 DEEP WATER DRILLING RIG BACKGROUND OF THE INVENTION The present invention relates generally to floating platforms, and more particularly to stabilized floating platforms for use in deep water.

Platforms or floats of the general type here under discussion are already known in the art. Broadly speaking they are used for a variety of applications, such as deep-water drilling for scientific purposes, oil drilling on the continental shelf, as location for offshore radar stations, and the like. As opposed to stationary platforms which must be anchored in the ocean floor, floating platforms offer significant advantages. The most obvious of these is, of course, their mobility which permits them to be moved to different locations as desired. In addition, however,their use greatly reduces the expense involved because rigid anchoring of platforms in the ocean floor is costly, and of course it is impossible once a certain water depth is exceeded.

With reference to the most mobile of platforms, namely ships, the floats in question have the advantage of greater steadiness and space availability.

All of these factors are important and becoming more so, because the applications involving the use of such floats, particularly drilling for oil offshore, are exhibiting a steady trend to moving into deeper and rougher waters. With the dwindling of world oil supplies this trend can be expected to accelerate still further in the future.

While much work has already been done in this field, certain disadvantages still remain, however. Thus, while the prior art floating platforms attempt to achieve stabilization with reference to the waves, they do not provide for repositioning in response to changes in the water level e.g. very high waves due to storm so that it is for instance possible for the prior-art platforms to be stabilized with reference to the waves but nevertheless to be flooded by them.

SUMMARY OF THE INVENTION It is, accordingly, an object of the invention to overcome the aforementioned disadvantages.

More particularly, it is an object of the invention to provide an improved platform of the type under discusson.

A further object of the invention is to provide such a platform which can be moved to desired locations without undue difficulties.

Still another object of the invention is to provide such a platform which affords exceptional stability under even the most adverse of circumstances.

In pursuance of the above objects, and others which will become apparent hereafter, my invention resides in a deepwater float which comprises, briefly stated, supporting platform means; buoyancy means connected to and downwardly spaced from the platform means; tethering means for tethering the platform means a buoy means so as to restrain them in water against transverse displacement with reference to a selected location; and control means controlling operation of the buoyancy means and the tethering means for changing the positioning of the float between a lower position in which the tethering means have a predetermined first length and the buoyancy means a predetermined first buoyancy requisite for maintaining the tethering means taut and the platform means at a selected first distance above mean wave height, and a higher position in which the tethering means have a predetermined second length and the buoyancy means a predetermined second buoyancy requisite for maintaining the tethering means taut and the platform means at a greater second distance above mean wave height.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional advantages and objects thereof, will be best understood from the following description of specific embodiments when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side elevational view illustrating my novel platform in accordance with one embodiment thereof;

FIG. 2 is a diagrammatic sectional view of line IIII of FIG. 1;

FIG. 3 is a fragmentary sectional detail view illustrating a ballast tank for my platform in accordance with another embodiment;

FIG. 4 is a horizontal section showing, on an enlarged scale, details of the ballast tank construction;

FIG. 5 is a diagrammatic view of a sensing device for activating the tethering cable control and the buoyancy control of my novel platform;

FIG. 6 is a diagrammatic top plan view illustrating auxiliary stabilizing planes and their associated controls;

FIG. 7 is a fragmentary somewhat diagrammatic illustration showing a propulsion arrangement for exerting position control over the platform when emergency conditions necessitate slackening of the tether cables;

FIG. 8 is a fragmentary somewhat diagrammatic view showing separate buoyancy means and tethering means for a drill rig used in conjunction with my novel platform;

FIG. 9 is a fragmentary somewhat diagrammatic view showing means somewhat similar to those of FIG. 8, but supporting the drill rig separately from the plat form, so that the same can be raised and lowered with reference'to the drill rig; I

FIG. 10 is a diagrammatic illustration of my novel platform in conjunction with an early warning system of buoys provided with sensors; and

FIG. 11 is a diagrammatic detail view of one of the buoys shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing firstly FIGS. 1 and 2, it will be noted that they illustrate one embodiment of my invention. For the sake of convenience the entire structure will hereafter be called a float, while the support structure which is to be kept above water and in stabilized condition, is indentified as the support platform.

With this in mind, reference numeral 1 will be seen to identify the support platform whose outline may be circular (see FIG. 2), quadratic, rectangular, or indeed of any desired shape. In FIG. 1 the platform 1 is seen to carry on its upper deck a tower la, for instance of the type used in drilling operations. It is evident, however, that the platform may carry any other type of structure naturally within the limits of its supporting capability or no structure at all if it is for instance intended as a touch-down field for aircraft.

Extending downwardly from supporting platform 1 are legs 2 which are connectedat different levels by cross braces 3. The number of legs 2 may vary, but it is obvious that there cannot befewer than three in a structure of the size here contemplated.

in the region of their lower ends the legs are connected with fluid-tight ballast tanks 4 whose configuration may be selected as desired. Again, no fewer than three of these tanks may be provided and they must be located radially outwardly of the periphery ofsupporting platform 1, as shown. If more than three legs 4 are provided, for instance six of them, they will be arranged in form of an annulus as is evident without explanation.

FIG'. 3 shows that it is also possible to utilize a single tank 40 of annular shape, connected at appropriate circumferentially spaced locations with the legs 2. Such a tank 4a, as indeed the tanks 4, may be subdivided into a plurality of compartments, each of which may be separately flooded with the seawater and evacuated by means of compressed air. Some of the tanks or compartments thereof may contain oil for release when it is desired to calm the wavesin the vicinity of the float. Details of the tank construction are shown in FIG. 4. As shown there, the interior of tank 4a is interiorly-subdivided by legs 2 into four separate compartments 4aa which, in the illustrated embodiment, are fluid-tightly separated from one another. Conduits 4b connect the respective compartments with one or more non-illustrated sources of pressurized gas via suitable valves; ballast valves 412!) permit flooding or evacuating of water in the respective compartments-4aa. Pressurizedgas sources, control valves connecting and disconnecting conduits 4b from them, and valves 4bb (also sometimes known as seacocks) are known to those conversant with this art and their construction is not a part of this invention.

Returning to FIGS. 1 and 2, it will be seen that at least three of the legs 2 are hollow and tether cables or chains 5 pass through them from the interior of supporting platform downwardly beyond the tanks 4 and to the ocean floor 16. The tethers 5 carry anchors 6 of suitable construction which will become embedded in the ocean floor and prevent lateral drifting of the float. It is desirable that the anchors 6, when embedded, be radially outwardly displaced with reference to a circle intersecting the lower ends of the legs 2, to provide for improved stability.

FIG. 2 showsthat the interior of the supporting platform 1 houses cable control units 7 whose number corresponds to the number of tethers 5. Each of the units 7 comprises a sheave 8 over which the respective tether 5 passes from the outlet opening 10 of the associated leg 2. From the sheave 8, which rotates about a horizontal axis 9, the tether passes to the drum 11 which rotates about an upright axis 12. The drums 11 may be driven by individual drives 14, by a common drive of suitable type. Of course, other types of tether take-up and payout equipment may also be utilized.

Reference numeral 13 identifies tether controls for the drives 14, or a single tether control device if only a single drive is utilized for all reels 11. The construction and operation of such control devices is known per se, and it will be appreciated that they serve to shorten or lengthen the paid-out tether to compensate for wind and wave activity. They receive signalsfrom a sensing device 17 which is responsive to changes in the activities of wind and/or waves (see FIG 5 for details) and which causes them to operate the drives 14 in a sense shortening or lengthening the tethers 5, as required.

As FIG. 5 shows, the signals from the sensingdevice also operate control valves which determine the admission of compressed air into the tanks 4, or the evacuation'of air and admission of water.

The various units in FIG. 5 have been shownonly diagrammatically, because in themselves they are fully well known to those skilled in the artQThe Wind Activity Detector may operate on the principle of an anemometer and measures changes in the wind activity. The Wave Activity Detector of course measures changes in wave height. Such devices are for instance discussed in Van Nostrands Scientific Encylopedia and in U.S. Navy technical manuals available to anyone through the Government Printing Office, to name just a few sources. Both units generate signals indicative of the strength of the activity detected, and these signals are detected by the Signal Detector and Amplifier which amplifies them and passes them to the Valve and Cable Control Unit. The various valves and cable or tether drives may be electromagnetically activatable, and signals to effect activation or de-activation originate from the Valve and Cable Control Unit to operate the valves and/or tether drives in dependency upon activity'detected by the Wind Activity Detector and/or Wave Activity Detector.

In operation of my novel construction, the height of the supporting platform 1 above sea level may nonnally be held to the level of supply-ship decks. At such a low level, which may be maintained at the moderate wave height associated with steady long-term winds, wind exposure loading of the float is reduced to a minimum, thereby insuring maximum stability. The paid-out length of the tethers 5 is selected in accordance with this requirement, and the buoyancy of the tanks 4 is so selected as to have a positive effect, i.e., to maintain the tethers 5 taut at all times.

Increasing wind activity and/or increasing wave height will be sensed by the sensing device 17 which is preset for a significant value at which adjustment in the positioning of the supporting platform 1 to a new clearance level above the waves is to be initiated. As soon as this value is reached and detected by the device 17, a signal is initiated by the latter, causing additional lengths of tethers 5 to be paid out and additional seawater to be expelled via compressed air from the tanks 4, until the new clearance level is reached. At this new level, again, the positive buoyancy will be such as to maintain the tethers 5 taut at all times.

For the sake of simplicity the equipment may be preset for two elevated levels above the lowest (normal) level, namely a highest level required to weather maximum disturbances and an intermediate level which may be determined on the basis of average disturbances in the area where the float is anchored. The particular level to which the float would be raised would of course be determined in dependence upon the data sensed by the device 17, it being obvious that if the data indicated a disturbance in excess of the average disturbance but less than the maximum disturbance, the float would nevertheless rise to the highest level.

It goes without saying, of course, that the control may be automatic in response to any changes in wind and/or wave activity whatever, in which case the float would undergo frequent and usually small level changes. In other words, responses in the controls may be programmed to meet force variables (wind and/or wave activity) with response variables.

Alternatively, and in order to simplify operational responses to disturbances, the supporting platform 1 may normally be positioned at a predetermined elevation (say, 40 feet) above mean wave level. This position would then be maintained at all weather conditions (subject of course to changes dictated by operational requirements) until an extreme disturbance occurs, such 'as information of an earthquake-induced tidal wave. Information of such type may be obtained by telecommunication or, as shown in FIGS. and 11, from a system of several early warning buoys which are anchored in the ocean at an appropriate distance from the float, about which they form a ring. Such buoys, described in detail in FIGS. 10 and 11, would contain sensing devices and transmitters capable of transmitting a signal to a receiver on the float, where the signal would be used to initiate level changes as previously described.

Receipt of information (in whatever fashion) of an approaching extreme hazard, would result in elevation of the float to its extreme upper position say 60 foot clearance of the underside of supporting platform 1 with reference to the waves by paying out the tethers 5 and blowing of the buoyancy tanks 4. The anchor tethers 5 would be slacked, rather than maintained taut, and positional control would be transferred to a ship-type propulsion system, as illustrated in and described with reference to FIG. 7 (which see).

If the float is used for drilling operations, the drill rig would be disconnected well below wave activity level and the underwater portion of the rig be buoyed by separate buoyancy tanks (see FIG. 9). A light tether would maintain a (slack) connection between the underwater portion of the rig and the platform 1.

As shown in FIG. 1, the maximum wave depth to be expected may be reasonably estimated to be on the order of 100 feet. This allows for a wave activity zone of i 50 feet. The length of legs 2 is then so selected that the tanks 4 are located in the quiet region of the water, i.e., approximately 150 feet below mean wave level.

FIG. 6 shows a diagrammatic top plan view of a support platform 60 provided with auxiliary stabilizing planes 62. In the illustration, three equi-angularly spaced recesses are formed in the structure of the round platform 60 (it will be appreciated that the platform need not be round, that the number of auxiliary planes may differ, and that they may be located elsewhere), and in each recess there is mounted for raising and lowering movement an auxiliary stabilizing plane 62. These planes may act in the manner of a sailboats keel or center board, and may diverge in fanshaped configuration downwardly into the water. Reference numeral 63 identified a part of the mounting structure for each plane 62, housing also the drive for raising and lowering it. It is advantageous to make the planes 62 individually operable and to power them separately, but other solutions are also possible.

FIG. 7 is a view somewhat similar to FIG. 1, but with such parts of FIG. 1 omitted which are not needed for an understanding of the embodiment. Like reference numerals identify like elements. I-Iere, thrusters are provided in the illustrated brace 3; such thrusters, usually operating with forcibly expelled seawater, serve for positional control and may be circumferentially distributed as desired.

FIG. 7 further shows a propeller mount 71 housing a drive which rotates propeller 72. The mount 72 is secured by mounting element 73 to brace 3 for turning movement about an upright axis so that it is oriented as desired to obtain thrust and thereby positional control over the platform -when emergency conditions necessitate slackening of the tether cables. The elements 71, 72 may be conventional ships propulsion units which are known to those skilled in the art. Clearly, they as well as the thrusters 70 may be located in positions other than those illustrated.

FIG. 8 is a view similar to FIG. 7, and identical reference numerals identify again identical components. I-Iere, however, the drill rig 81 is shown, guided in the mast la and composed of longitudinally arrayed coupled sections 81a. A requisite number of buoyancy floats 82 is connected with the drill rig 82 below the water level so as to support the drill rig entirely. Thus, the mast 81 has only a guiding and stabilizing function, while the supporting (buoyancy) function is provided by the floats 82 which may be of any desired and suitable construction. In this manner the level of the platform 1 may be raised and lowered as necessary or desired, without affecting the drill rig 81 itself. In other words: platform 1 may be raised and lowered with reference to the drill rig 81.

In FIG. 9 I have shown an embodiment similar to FIG. 8, with like reference numerals again identifying like elements. Here, however, it is desired to be able to uncouple the drill rig 91 from the platform or float structure in emergency conditions. The sections of the drill rig are identified with reference numeral 9 1a.

At a level which will be located beneath the maximum wave activity zone expected to be encountered, the portion 91a will be joined via a suitable (fluid-tight) coupling 92 to the lower portion 91b of the drill rig; the coupling is releasable and the portions 91a and 91b will automatically close against water intrusion when the coupling is separated. Portion 91b is provided with a float 93, and a light tether 94 connects the platform 1 (or other part of the main float) with the float 93 (or the portion of coupling 92 which is on portion 91b of drill rig 91).

In emergency conditions, coupling 92 is released so that platform 1 can move freely without endangering the lower portion 91b of drill rig 91.

In the embodiment of FIG. 10, the platform 1 has a receiver which receives signals from a plurality of buoys anchored at a predetermined distance here about 50 miles from the platform 1. The distance may of course vary. The buoys 100 each carry the wind/or wave activity detecting units of FIG. 5 and a suitable transmitter which transmits signals generated by these units, to the receiver on platform 1. Thus, FIG.

provides an early-warning system for the platform 1. If the direction from the float or platform to land is substantially the same as, or smaller than the predetermined distance, then no buoy need be provided in direction from the float towards land.

FIG. 1 l, finally shows one of the buoys 100 diagrammatically, but more in detail. Reference numeral 101 identifies a buoyance tank, for instance a ring-shaped sealed tube, which carries atop it a protective superstructure 102.. Mounted within the superstructure 102 which is provided with suitable apertures are a wave activity recorder 103 and a wind activity recorder. As already previously pointed out, such recorders are well known in the art, as are indeed the buoys 100 as a whole. The signals these recorders 103 and 104 generate are transferred to a small transmitter from whose broadcast antenna 105 they are broadcast to the receiver on the platform 1 (FIG. 10) which in turn may simply provide read-out information for the platform personnel, or may effect automatic control of requisite valves and tether drives to change the platform attitude as needed.

Depending from the tank 101 of buoy 100 are chains or similar holding elements 106 which are connected with a tether 107 whose lower end is fastened to an anchor 108 anchoring the buoy 100 on the ocean floor.

Naturally, the buoys 100 may also be constructed otherwise, and may carry other and/or different gear from that described. In accordance with established regulations such buoys will usually require registry with international maritime bodies; they may also be required to carry obstruction warning devices (e.g., bells, lights) in addition to the platform warning gear.

It will be understood that the elements described above, individually or in various combination, may also find a useful application in types of float structures other than the types described above.

The invention has been illustrated and described as embodied in a deepwater float; nevertheless, it is not intended to be limited to the details shown. Modifications and structural changes may be made without departing from the concept of the present invention. The foregoing fully reveals the essence of the present invention. Others therefore can, by applying current knowledge, adapt it without difficulty for other applications without omitting features that, from the viewpoint of prior art, fairly constitute essential characteristics of the generic of specific aspects of this invention. All

.such adaptations are therefore intended to be included within the meaning and scope of equivalence of the following claims.

What I claim as new, and what I desire to protect by Letters Patent, is set forth in the appended claims:

1. A deepwater float comprising: support platform means; buoyancy means connected to and downwardly spaced from said platform means; tethering means for tethering said platform means and buoyancy means so as to restrain them in water against transverse displacement with reference to a selected location; control means comprising winch means for lengthening and shortening said tethering means, buoyancy varying means for increasing and decreasing the buoyancy of said buoyancy means and sensing means for sensing changes in mean wave leve signaling and cooperating with said winch means and buoyancy varying means; said control means for automatically controlling operation of said buoyancy varying means and said winch means for varying the positioning of said float in response to sensed changes in the mean wave level between a normal lower position at a predetermined shorter tether length and lower buoyancy to maintain said tether taut, and a predetermined higher position at a predetermined longer tether length and higher buoyancy to maintain said tether taut.

2. A deepwater float as defined in claim 1, wherein said sensing means further comprise signal-receiving means provided on said float, cooperating with said winch means and buoyancy varying means, and a plurality of buoys anchored at predetermined distances from said float including signal-generating sensing devices operative for sensing changes in the mean wave level and for signaling such changes to said signalreceiving means.

3. A deepwater float as defined in claim 1, said buoyancy tank means comprising a circumferentially complete annular buoyancy tank having a general plane substantially paralleling the general plane of said platform means.

4. A deepwater float as defined in claim 1, wherein said sensing means comprise gyroscopic means.

Claims (4)

1. A deepwater float comprising: support platform means; buoyancy means connected to and downwardly spaced from said platform means; tethering means for tethering said platform means and buoyancy means so as to restrain them in water against transverse displacement with reference to a selected location; control means comprising winch means for lengthening and shortening said tethering means, buoyancy varying means for increasing and decreasing the buoyancy of said buoyancy means and sensing means for sensing changes in mean wave level signaling and cooperating with said winch means and buoyancy varying means; said control means for automatically controlling operation of said buoyancy varying means and said winch means for varying the positioning of said float in response to sensed changes in the mean wave level between a normal lower position at a predetermined shorter tether length and lower buoyancy to maintain said tether taut, and a predetermined higher position at a predetermined longer tether length and higher buoyancy to maintain said tether taut.

2. A deepwater float as defined in claim 1, wherein said sensing means further comprise signal-receiving means provided on said float, cooperating with said winch means and buoyancy varying means, and a plurality of buoys anchored at predetermined distances from said float including signal-generating sensing devices operative for sensing changes in the mean wave level and for signaling such changes to said signal-receiving means.

3. A deepwater float as defined in claim 1, said buoyancy tank means comprising a circumferentially complete annular buoyancy tank having a general plane substantially paralleling the general plane of said platform means.

4. A deepwater float as defined in claim 1, wherein said sensing means comprise gyroscopic means.

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