US3450201A - Extensible caisson for underwater well - Google Patents

Description

June 17, 1969 K A. IBLENKARN EXTENSIBLE CAISSON FOR UNDERWATER WELL Filed Aug. 3, 1967 Sheet of2 KENNETH A. BLENKARN INVENTOR.

ATTORNEY.

June 17, 1969 I ,K. A. BLENKARN 3,450,201

EXTENSIBLE CAISSON FOR UNDERWATER WELL Filed Aug. 3, 1967 Sheet 3 of 2 2 7e 78 f 4 70 j j H /82 A J L 4/- 68 o o J o o v 75 ';-62 j 74 72 64 z k j 69 Y 8O Q FIG. 3 84 KENNETH A. BLENKARN INVENTOR.

ATTORNEY United States Patent Ofi Patented June 17, 1969 ice EXTENSIBLE CAISSON FOR UNDERWATER WELL Kenneth A. Blenkarn, Tulsa, Okla, assignor to Pan American Petroleum Corporation, Tulsa, Okla, a corporation of Delaware Filed Aug. 3, 1967, Ser. No. 658,151 Int. Cl. E21b 33/035, 43/01; E02d 25/00 US. Cl. 166-5 9 Claims ABSTRACT OF THE DISCLOSURE This describes a telescopic or extensible underwater caisson having a cap enclosing its upper end. The caisson is placed over the well head of a well which has been drilled in the floor of a body of water. The caisson has an upper extensible portion which when extended reaches above the surface of the water. Workovers or other required maintenance of the well or well head can then be made through the extended caisson, the interior of which is then at atmospheric pressure. Anchor lines extend from the upper part of the upper section of the caisson to anclhors in the ocean floor spaced from the floor end of the caisson. When it is desired to perform maintenance on the well, the upper section of the caisson is extended, the cap removed and the anchor lines made taut. This is to maintain the upper end of the caisson relatively still while the maintenance operations are being conducted. If a sudden storm should appear, the anchor lines are let loose so that the upper end of the caisson can move freely and withstand great storms. Means can be added to the anchor lines to introduce damping for suppressing motion.

The invention relates to caissons set in the ocean fioor and through which wells are completed. It relates especially to extensible type underwater caissons in which the caisson, when extended, is provided with anchor lines which resist motion of the upper end of the caisson.

Background The search for oil and gas has, in recent years, led to exploration and drilling of wells for oil and gas in watercovered areas such as the continental shelf in the Gulf of Mexico. In the past, it has been a frequent method of completion to build a permanent platform which is supported above the surface of the body of water by a plurality of legs which extend to the ocean floor. The platform is usually made rather rigid so as to resist the force of the waves and storm winds. The method of completion is frequently used even when the well was originally drilled from a floating vessel. Such rigid platforms are rather expensive and as they extend above the surface of the water, they present a certain navigational Lhazard. It has been suggested that the well be completed on the ocean floor. This method presents a problem of servicing the well, which ultimately becomes necessary in all wells. It has further been suggested that a caisson be extended from the well to the surface and that the well be completed within the caisson. Such caisson would ordinarily present a certain navigational hazard so it has been further suggested that a telescopic type caisson be used. Then, when the caisson is not being used as a means of gaining entry to the well head for maintenance or workover, the upper section of the caisson can be retracted so that it is well below the surface of the water. Such extensible caissons could experience considerable motion at the top even in relatively mild water.

Brief description of the invention This invention relates to an extensible telescopic caisson supported vertically in a body of water. It is equipped such that the extensible portion when extended reaches above the water level so that maintenance of workover tasks can be performed through the caisson. Any water in the caisson when it is extended is pumped out so that the workover operations can be performed under atmospheric conditions. Mooring or anchor lines are provided for the caisson. Such anchor lines are provided to pre vent extensive caisson motion when the caisson is in its extended position and when workover operations are to be conducted. The anchor lines are connected to the upper portion of the upper section of the caisson. The anchor lines are of such length that when the caisson is in its collapsed position, or contracted position, the anchor lines are quite loose. When the caisson is in its extended position, the anchor lines are taut. 'Ilhe anchor lines are maintained in a taut position during workover operations so that the workers will be protected from excessive motion. If a storm should develop while the caisson is in its extended position, means are provided to release the anchor lines. Release of the anchor lines permits the caisson to give with the waves, thereby reducing the forces which act upon the caisson itself. When the storm subsides, the anchor lines are again made taut. The primary purpose of the anchor lines is to give stiffness rather than strength to the caisson.

Description of the drawings Other objects and a better understanding of the invention can be had from the following description taken in conjunction with the drawings in which:

FIGURE 1 illustrates the caisson in its contracted position wherein the upper end of the upper portion of the telescopic caisson is beneath the surface of the Water;

FIGURE 2 illustrates the caisson in its extended position wherein the upper end of the caisson is above the body of water; and

FIGURE 3 illustrates a locking device for locking the caisson in its extended position.

Attention is directed to FIGURE 1 which shows the caisson in its retracted position and to FIGURE 2 which shows the same caisson extended. Shown thereon is a body of water 10 having a surface 12 and a bottom 14. The caisson has an upper portion 16 which in FIGURE 1 extends down over a lower portion 18. Lower portion 18 is set in ocean bottom 14 and preferably cemented as by cement 20. The upper end of upper caisson section 16 is provided with a platform 22. The upper end of platform 22 is provided with a circular opening 24 which is covered (FIGURE 1) by a cap 26.

Cap 26 is provided with an air passage 28 therethrough which connects to an air supply hose 30. Air supply hose 30 is connected to buoy 32. The end of air supply hose 30 in buoy 32 is provided with a valve and connection means 34 so that a ship can move alongside the buoy 32 and connect a compressor or other [high pressure air source to connection 34. As will be seen, this high pressure air is used for raising the upper section of the caisson to the position shown in FIGURE 2. Other supply hose 76A and 78A are also provided and as will be seen supply air for operating the latching mechanism between the upper and lower caisson section.

Attention will now be directed toward the anchoring lines of the apparatus. This includes anchor lines 36 which are connected at one end to anchors 38 in the ocean floor. The other ends of anchor lines 36 are connected to winches 40 which are supported inside platform means 22. The length of anchor line 36 is such that it becomes taut upon the caisson being extended into the position shown in FIGURE 2. If the line is not as taut as desired, it can be tightened by winches 40. Ordinarily it will not be necessary to take in over a few feet on lines 36 to give them the desired tightness. Means are also provided for releasing the anchor lines quickly in the event a heavy sea builds up while the caisson is in its extended position of FIGURE 2. This can be accomplished by releasing the ends of the lines from winch 40 and attaching a buoy to the upper end of the line 36 so that it can be easily recovered when the storm subsides.

In some cases the natural catenary of the anchoring lines 36 may introduce too much spring into the system. If such is the case, buoyancy can be introduced along the anchor lines. Buoyancy properly placed along the line has the effect of making the anchor lines of essentially neutral buoyancy which eliminates catenary spring effects. One means of providing this buoyancy is to provide a number of individual buoys to the anchor line itself. Shown in the drawing are buoys 42, 44 and 46, spaced along one of the anchor lines 36. Any reasonable number of buoys can be used as required to give a neutral buoyancy along the line. Three are shown on one line 36 in the drawing. One would probably have the same number of buoys on each anchor line. Each buoy is provided with an air supply hose; however, only one buoy is so shown in the drawings to simplify it. Shown in the drawing is a buoy 44 which has an opening 48 in the lower side adjacent line 50 which is used to attach the buoy to anchor line 36. An air supply hose 52 is connected from the buoy 44 to float means 32. Alternatively, the air supply hose could be connected to platform 22 and not be operable until the platform or caisson were extended. This is illustrated by hose 52A in FIGURE 2 which goes to a compressor or other air source 54 on platform 22. When the caisson is extended, the various buoys are charged with air. The air displaces water through holes 48. An alternate possibility of providing neutral buoyancy of line 36 is to make line 36 of a re-inforced hose which has air under pressure to maintain the hose in a desired expanded position.

As shown in FIGURE 2, the lower section of the caisson extends over well head 56. Well head 56 is connected to tubing 58 which extends downwardly in the earth to a producing formation as is well known. The outlet from well head 56 goes through a pipe 60 which extends downwardly from well head 56 to adjacent the floor 14. There it goes laterally out through the wall of section 18.

Attention is next directed to FIGURE 3 which illustrates the locking and sealing mechanism between upper section 16 and lower section 18 of the caisson. The upper end of lower section 18 is provided with shoulder 62 having external seals 64. When the caisson is extended as shown in FIGURE 2 seal 64 forms a sealing contact with internal surface 66 of upper section 16. Above shoulder 62 on lower section 18 is a latching dog assembly. This includes dogs 68 which pivot about axis 70. Dogs 68 are controlled by a ram or rod 72 which is attached to piston 74. Air supply lines 76 and 78 are provided to cylinder 75 on opposite sides of piston 74. Thus, by controlling the air pressure in conduits 76 and 78, dog 68 can be driven outwardly or retracted. The lower end of upper caisson section 16 is provided with notches 80 which are adapted to receive dogs 68 when the dogs 68 are in an extended position, and at a proper relative elevation. Dogs 68 are also provided with springs 82 which are used for urging them outwardly.

The lower end of upper caisson section 16 is provided with an internal shoulder 84 which is provided with lip seal 86. Lip seal 86 seals with the exterior surface of lower caisson section 18. Seal '86 is to prevent entry of water into the caisson when it is in the retracted position. If seal 86 should fail, it would not hurt the operation of the device; it would merely let water enter the caisson when in the retracted position of FIGURE 1. Such water could be pumped out when the caisson was extended. When the caisson is extended, seals 64 give more complete sealing effectiveness to the extended caisson.

Attention will now be directed briefly to the operation of the extensible caisson. When it is desired to extend the caisson, a service ship approaches buoy 32 and makes an air supply connection to connection 34. Air under pressure is then injected through air supply hose 30 into the interior of the caisson. This air acts as a lifting mechanism and raises the upper section to above the water level. The latching mechanism of FIGURE 3 stops the upper movement by latching dogs 68 into notch 80. This latching serves a dual purpose. It stops the upper movement and later prevents the upper section from falling down. At the same time that air is injected into the interior of the caisson, air under pressure is injected through conduit 76. This forces dogs 68 outwardly. As the upper section 16 is raised by the air pressure, dogs 68 encounter sloping interior shoulder 69 and retracts the dogs against the air pressure in cylinder 75. Continued upward movement of caisson section 16 advances notch until it is opposite dog 68. At this time dog 68 enters notch 80 to effectively latch the upper section 16 in its extended position to lower section 18 so that the caisson takes the configuration of FIGURE 2. At this point there is a good seal between seal 64 and interior surface 66. If there is any water within the extended caisson, it is pumped out.

After the latching as described above has taken place, the air supply through hose 60 can be removed. In fact, at this time cap 26 can be removed. It is normally after the removal of cap '26 that any accumulated water is pumped out of the caisson. Once cap 26 is removed, workover operations can then proceed through the caisson.

When in the extended position, air can be supplied through hose 52 to buoy 44 (and the other buoys through their respective hoses) to give each anchor line 36 its desired buoyancy. If lines 36 are not quite tight enough, winches 40 are operated to obtain the necessary added tightness. &

It is to be remembered that anchor lines 36 are not intended to give strength to the extended caisson. It is primarily to give it stiffness. In water, say 300-400 feet in depth, a caisson, for example 4 feet in diameter and having one inch walls, would sway quite considerably at the surface. This motion is considered sufficient to prevent effective workover or other maintenance operations from being conducted by human beings. These anchor lines 36, when made tight, add stiffness to the extended caisson so that it does not have such excessive motion. These cables are not made especially strong. Thus, in the event of a storm or heavy sea, the cables are released and cap 26 replaced. The caisson is then free to move at the top and thus absorb energy and prevent the effect of large forces on the caisson. Lines 36 can be cut loose or otherwise freed from winches 40. This releasing of the anchor lines permits the caisson to be free to move. A recovery buoy is tied to the upper end before the lines are cast off. After the storm has subsided, released lines 36 are recovered and attached to winches 40 so that the desired stiffness of the caisson can again be attained. After the workover operations are completed, cap 26 is replaced and lines 30 connected to a buoy 32. Air is then supplied through conduit 78 to move piston 74 inwardly, thus releasing locking dog 68. If desired, pressure can be built up inside the caisson before the dog is released. This would tend to raise the caisson and permit release of the dog 68. Pressure is then released inside the caisson so that it slowly descends to the position of FIGURE 1. A stop 37 on lower member 18 stops the descent.

While the above invention has been disclosed with a certain degree of detail, it is possible to produce other embodiments and modifications thereof without departing from the spirit or scope of the invention.

I claim:

1. A method of operating a vertically extensible telescopic caisson having an upper section and a lower sec- 5 tion which is supported at its lower end from the ocean floor which comprises:

(a) raising the upper section of said caisson to above the surface of the water;

(b) making taut anchoring lines which extend from the upper end of said upper section to anchor in the ocean floor;

(c) performing working operations through said extended caisson;

(d) thereafter lowering said upper telescopic section of caisson and making said anchor lines loose.

2. A method as defined in claim 1 including anchoring the lower end of said anchoring lines as far from the base of said caisson as the depth of said water.

3. A method of operating said telescopic casing as defined in claim 1 in event of a strom including the following step taken timewise between steps (b) and (c) of claim 1 of releasing said anchor lines, and after the subsiding of the storm reconnecting said anchor lines to the upper section and again tightening said anchor lines.

4. A method as defined in claim 1 including the step of providing buoyancy along said anchor lines when said caisson is in its extended position.

5. A method as defined in claim 3 including the step of controlling the buoyancy along each said anchor line.

6. An offshore apparatus for use in the production of oil and gas which comprises:

a large diameter telescopic caisson having an upper section and a lower section, the [lower end of said lower section being securely anchored to the bottom of said 'body of water; the upper end of said upper section being above the body of water when in its extended position;

means for extending said upper section and including means for maintainingusaid upper section in its extended position;

anchoring lines extending from the upper end of said upper section of said caisson to anchors spaced from the base of said lower section;

winch means mounted on top of said upper section for tightening and paying out said anchor lines; sealing means between said upper section and said \lower section of said caisson.

7. An apparatus as defined in claim 6 in which buoyancy means are provided for each said anchor line intermediate the ends thereof and including means for controlling the buoyancy of such buoyancy means.

8. Anapparatus as defined in claim 6 in which said anchor lines are reinforced, flexible, hollow members.

9. An apparatus as defined in claim 7 including a well head positioned inside said lower section near the upper end thereof and further including a production line extending from said well head down to the lower end of said lower section and thence through the wall of said section to the lower exterior thereof.

References Cited UNITED STATES PATENTS CHARLES E. 'OCONNELL, Primary Examiner. R. E. FAVREAU, Assistant Examiner.

. U.S. Cl. X.R. 6181

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