CA1179254A - Subsea caisson - Google Patents
Subsea caissonInfo
- Publication number
- CA1179254A CA1179254A CA000411343A CA411343A CA1179254A CA 1179254 A CA1179254 A CA 1179254A CA 000411343 A CA000411343 A CA 000411343A CA 411343 A CA411343 A CA 411343A CA 1179254 A CA1179254 A CA 1179254A
- Authority
- CA
- Canada
- Prior art keywords
- caisson
- sea bed
- jetting
- soil
- wall
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000002689 soil Substances 0.000 claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 19
- 230000002706 hydrostatic effect Effects 0.000 claims abstract description 16
- 238000009434 installation Methods 0.000 claims description 10
- 238000005553 drilling Methods 0.000 claims description 6
- 230000002093 peripheral effect Effects 0.000 claims description 5
- 239000004020 conductor Substances 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 3
- 230000013011 mating Effects 0.000 claims description 2
- 230000035515 penetration Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 241000191291 Abies alba Species 0.000 description 2
- 230000014509 gene expression Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- NEHMKBQYUWJMIP-UHFFFAOYSA-N chloromethane Chemical group ClC NEHMKBQYUWJMIP-UHFFFAOYSA-N 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000009189 diving Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 230000036346 tooth eruption Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/18—Drilling by liquid or gas jets, with or without entrained pellets
- E21B7/185—Drilling by liquid or gas jets, with or without entrained pellets underwater
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/02—Surface sealing or packing
- E21B33/03—Well heads; Setting-up thereof
- E21B33/035—Well heads; Setting-up thereof specially adapted for underwater installations
- E21B33/037—Protective housings therefor
Abstract
ABSTRACT OF THE DISCLOSURE
A subsea caisson or silo for housing wellhead equipment and a method of installing it is disclosed. A
caisson which is sized to receive equipment that is to remain subsea has a closed top and open bottom. The caisson is lowered to the sea bed and hydrostatic pressure in the form of a suction jet is used to remove the internal soil. A rotatable cutter can be used if the seabed soil is too hard for effective hydrostatic removal.
A subsea caisson or silo for housing wellhead equipment and a method of installing it is disclosed. A
caisson which is sized to receive equipment that is to remain subsea has a closed top and open bottom. The caisson is lowered to the sea bed and hydrostatic pressure in the form of a suction jet is used to remove the internal soil. A rotatable cutter can be used if the seabed soil is too hard for effective hydrostatic removal.
Description
117~ 5 ~
Field of the Invention This invention relates to subsea caissons or silos for housing wellhead equipment and to protect that equipment from damage by ice, anchors, fishing gear or any other object in contact with the sea bed.
Background of the Invention Conventionally, sub sea wells have the wellhead at the sea bed and have connected to them either a blowout preventer during the pulling phase or a valve block assembly and flow line connector during the production phase. The wellhead and the associated equipment project somewhat above the sea bed and are thus vulnerable to damage. Anchors and fishing gear have caused damage to many sub sea wellheads to the extent that protection requirements are increasing. In the artic regions where the seabed is scoured by icebergs and ice pressure ridges, it has become common practice to place the wellhead in a dredged area referred to as a glory hole so that the equipment is below the ice scour depth.
One system presently in use is the sub-mudline or insert tree arrangement as proposed by Vetco and Cameron Oil Tools. These systems have the advantage of using the normal well conductor case as the caisson with the primary shutoff valves below the mudline which are therefore protected.
However, these valves are housed in a small diameter so that there is no easy access to rectify a failure. Moreover, the blowout preventer is still exposed during the drilling phase and, because the production tubing exits through the top of the casing, the wellhead assembly still protrudes 3~5~
significantly above the mudline, probably 6 or 7 feet.
To overcome some of these problems, it has been proposed to make a caisson large enough to contain the blowout preventer. United States patent 3,344,612 and 3,796,273 describe methods of installing such a caisson type. U.S. Patent 3,344,612 uses a jetting technique for caissons installed in a soft sea bed and Patent 3,796,273 uses a rotary drilling technique for hard sea beds. In this latter arrangement, the base of the caisson has cutting teeth on its surface and the complete caisson is rotated thereby boring its own hole. Although these techniques appear feasible, they require a drilling rig which is very expensive and must rely on cementing to ensure their soundness since the surrounding soil is highly disturbed. In the case of the rotating caisson, the feasibility of easily rotating such a large body when it nears its full penetration is questionable since there is a large surface area at a large radius.
United States Patent 3,380,256 proposes putting a complete drill rig in a caisson and sinking it by means of hydrostatic pressure. In this patent, the caisson skirt is pushed into the sea bed until the base of the caisson contacts the sea bed with the result that that part of the caisson with the wellhead equipment still protrudes above the sea bed. The technique of using hydrostatic pressure described in this patent has been used successfully in sinking suction anchors. The main limitation is the depth of penetration obtainable before the soil-resisting ~7'3~
force balances the force produced by the hydrostatic pressure.
Summary of the Invention The present invention overcomes many of the problems mentioned above relative to current caissons and their method of installation. In the present invention, the caisson is sized to suit the eguipment that is to remain subsea and is installed using hydrostatic pressure but with the caisson closed only at its upper end. Accordingly, the caisson is initially installed in the same manner as a suction anchor, but, unlike a suction anchor, the soil inside the caisson is removed either while the caisson is being run or after it has reached its correct depth. A base to the caisson is then installed. The installation of the base after the caisson is at its desired depth and thus allowing the caisson to be installed in a similar manner as a suction anchor, means that the installation can be done by a normal work boat rather than an expensive drill rig and does not tie up the drill rig if problems occur. Furthermore, the caisson is firmly installed in the sea bed and does not require additional cementing.
In some areas, the sea bed may provide too much resistance and prevent full penetration using only hydro-static pressure. If this occurs, a rotatable cutting device is utilized on the lower peripheral wall of the cylindrical ~ody of the caisson. Inasmuch as no base closure is initially used on the caisson body, the cutter only has to remove a small amount of subsea soil required for the caisson walls to pass through. The caisson is not rotated but only the ,S~
cutter so the torque required is considerably reduced over the conventional method referred to above and the hydrostatic pressure again is used to overcome vertical soil resistance.
The current method of drilling subsea wells in a cluster is to use a subsea template which is a structure placed on the sea bed that has holes or slots in it to accept wellheads. The template is usually plowed to the seabed and levelled. United States Patent 3,796,273 uses the idea of a template for multiple wells by setting the caissons into a template.
Accordingto the present invention, a number of caissons are joined together without the need for a template and the complete assembly is installed as an integral unit using hydrostatic pressure on each chamber.
~hould the addition of a soil cutter be required, the cutter described above for the single caisson is directly applicable to multiple units. The installation does not have to be manifolded but can be an option.
Preferably, the subsea soil on the interior of the caisson is removed as the caisson is being installed since this eliminates the soil friction on the inside of the caisson wall and permits deeper caisson penetration. One method is to provide a jetting device extending inwardly from the top cover to the lower end of the caisson and being directed downwardly therein. In this method, the soil is fluidized by the inwardly coming jet of water and is removed with the water through suction pumps, the inlet to which is situated coaxially in a detachable cover of the 3'~54 caisson body. In another embodiment, a plurality of jetting nozzles can be located adjacent the lower circumferential rim of the caisson body so that they not only assist the caisson wall penetration and effect the loosening of the inside soil but they are also directed angularly inwardly to prevent the jet of fluid and loosened soil from washing up on the outside of the caisson wall.
This ensures that the outside of the caisson is firmly held by the surrounding subsea soil.
Caisson systems proposed to date have not used a method of flowing the well to another facility or they suggest using flow lines exiting through the top of the caisson to a normal above-mudline connection method. The present invention utilizes a flowline connection port on the upper side wall of the caisson so that the flowlines can be connected below the mudline out of harm's way. Such a port can be equipped with a jetting device to wash soil away from the outside of the port and the flowline bundle as it is being pulled in.
The present invention utilizes a removable top closure which allows several tops to be used, depending on the circumstances of installation and use. The top with the suction pumps and associated equipment can be removed after the caisson is installed and used on other installations.
After the production equipment is installed on the caisson, at least two alternative tops can be fitted. If the equipment is to be used wet, i.e. to be accessed by divers, then a light debris protection cover is used. On the other ~7 ~
hand, if a dry, one-atmosphere installation is required, then a cover suitable for resisting hydrostatic pressure is installed and which would have a marine mating surface and hatch suitable for use by diving bells or submarines to land on and transfer people to the interior of the caisson.
According to one broad aspect, the invention relates to a method of securing the caisson in the seabed, the caisson having a detachable top cover and an open bottom, the method comprising the steps of; providing jet and suction means within the confines of the caisson; lowering the caisson to the seabed surface so that the peripheral open bottom wall of the caisson engages the surface of the seabed; orienting the jetting device toward the lower end of the caisson and actuating the same to fluidize soil within the caisson and removing said soil and jetting fluid via suction means whereby the caisson is lowered into said seabed by hydro-static pressure so that the top of the caisson is below the scour line; and removing the cover, jet and suction means.
According to another broad aspect, the invention relates to a caisson for installation in a seabed comprising an elongated cylindrical housing having an open bottom and replaceable top closure, means in the top closure are provided for the entry of jetting and suction means for removing subsea soil from within the caisson so as to lower it by hydrostatic pressure; and means are provided on the inner wall of said caisson for locking and sealing a permanent base therein.
~1~7~
Brief Description of the Drawings The invention is illustrated by way of example and the accompanying drawings in which Figures 1 through 9 inclusive are elevation drawings showing the sequence of installation of the caisson in subsea soil;
Figure 10 is a sectional view of the caisson wall showing the locking and sealing detail for the enclosure;
Figure 11 is a sectional view through the caisson wall showing the arrangement for mounting the cutter on the base of the caisson;
Figure 12 is a plan view of a cluster of caissons interconnected to a manifold caisson; and Figure 13 is an elevation view of the apparatus of Figure 12.
Descri tion of the Preferred Embodiment p Referring to Figure 1, the caisson 10 has an elongated cylindrical body with a continuous curved wall 12, an open bottom 14 and a top closed by a replaceable cover 16. The top 16 is secured by cables or the like 18 for lowering the caisson 10 to the seabed 20. Jettins and suction means consisting of an elongated jet nozzle 22 and suction inlet 24 are mounted in the top cover 16 as illustrated. The caisson 10 is lowered until the lower peripheral edge 26 engages the surface of the seabed in the glory hole and the subsea soil within the confines of the caisson is loosened and fluidized by the incoming water from jet 22 and the material is evacuated by a vacuum pump in the mother ship through the suction inlet 24, thereby causing the ambient water pressure to drive the caisson into the sea bottom as shown in Figure 2. When the subsea soil has been removed from the interior of the caisson, the jet means 22 and suction manifold 24 as well as the top cover 16 are removed from the caisson lO as shown in Figure 3.
A temporary drilling guide 28 is then lowered into the confines of the caisson lO, the guide 28 resting on an inwardly directed, circumferential lip 30 on the inside of the caisson wall adjacent its lower end. The drill stem 32 is then lowered through the guide and a hole 34 can be drilled for a conductor of given size. The temporary guide is then removed as shown on Figure 5 and the caisson can be flushed and cleaned.
As shown on Figures 6 and 7, a permanent base 36 is then installed in the lower end of the caisson 10, the base 36 being locked onto the inwardly directed lip as shown in Figure lO. The annular rim of the base 36 includes a shoulder 38 which rests on the lip 30 and a pocket 40 located above the shoulder 38 includes an expandable seal 42 which engages the inner wall of the caisson lO to seal the base therewith. Upward movement of the base is prevented by means of a lock ring 44 located in a lower pocket 46, the lock ring 44 engaging the underside of the inwardly directed lip 30.
After the base 36 is installed, the hole is drilled for casing 48 of given diameter with the returns going through a separate pipe 50 to the sea surface. A wellhead is then installed through the riser 60 and, as shown in Figure 7, 9~S4 g the riser is subsequently removed and a blowout preventer 62 is lowered to the wellhead as shown in Figure 8. Subsequently, a Christmas tree 64 is installed on the wellhead as seen in Figure 9, and flow lines 66 are attached to the Christmas tree 64, a debris cover 68 is installed and the flow lines 66 are passed through a port 70 in the upper side wall of the caisson 10. It will be appreciated that the debris covers 68 can be removed for wet access to the wellhead or a sealed entrance, not shown, can be applied to the caisson for dry access through submersible vehicles.
Figure 11 illustrates an arrangement for applying a cutter to the lower terminal edge of the silo 10 for use in areas where the seabed may provide too much resistance and prevent full penetration of the caisson using only hydro-static pressure. As mentioned earlier, in view of the fact that no base closure is used in the caisson when it is initially inserted in the subsea soil, the cutter has only to remove a small amount of the soil required for the caisson walls to pass through. Accordingly, the caisson wall 10 may be provided adjacent its lower end with a lip 72 having support means 74 for aligning and supporting a drive shaft 76 that passes downwardly through the top 16 of the caisson from exterior motor means 78. The lower end of the shaft 76 is provided with a pinion gear 80 which engages gear teeth 82 on the inner peripheral rim of an annular cutter body 84 which is mounted for rotation on the lower edge of the caisson 10 by means of rollers 86. As seen in Figure 11, the lower end of the cutter 84 is provided with suitable teeth 88 for 1179~5~
cutting into the subsea soil.
In a further embodiment of the present invention, a number of caissons are joined together without the need for a template and the complete assembly can be installed as an integral unit using hydrostatic pressure on each caisson chamber. Turning to Figure 12 and 13, a plurality of caissons lOa through lOd inclusive may be connected together by a structural tie plate 90 and interconnected to a central manifold silo 92. Silo lOd is the only well illustrated as completed for the purposes of clarity, a plurality of such wellhead caissons feeding into the manifold caisson 92 from which an export flow line 94 is used for delivery from the assembly. As seen in Figure 13, the wellhead 60 feeds the product via lines 96 through connectors 98, a valve 100 and choke 102 to a production line manifold 104 which receives product from all of the production caissons. The product subsequently exits through a vertically oriented manifold line 106 and diverter 108 to the export flow line.
While the present invention has been described in connection with specific embodiments thereof and in specific use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.
The terms and expressions which have been employed in this specification are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof. It is recognized - 117~ 4 that various modifications are possible within the scope of the invention claimed.
Field of the Invention This invention relates to subsea caissons or silos for housing wellhead equipment and to protect that equipment from damage by ice, anchors, fishing gear or any other object in contact with the sea bed.
Background of the Invention Conventionally, sub sea wells have the wellhead at the sea bed and have connected to them either a blowout preventer during the pulling phase or a valve block assembly and flow line connector during the production phase. The wellhead and the associated equipment project somewhat above the sea bed and are thus vulnerable to damage. Anchors and fishing gear have caused damage to many sub sea wellheads to the extent that protection requirements are increasing. In the artic regions where the seabed is scoured by icebergs and ice pressure ridges, it has become common practice to place the wellhead in a dredged area referred to as a glory hole so that the equipment is below the ice scour depth.
One system presently in use is the sub-mudline or insert tree arrangement as proposed by Vetco and Cameron Oil Tools. These systems have the advantage of using the normal well conductor case as the caisson with the primary shutoff valves below the mudline which are therefore protected.
However, these valves are housed in a small diameter so that there is no easy access to rectify a failure. Moreover, the blowout preventer is still exposed during the drilling phase and, because the production tubing exits through the top of the casing, the wellhead assembly still protrudes 3~5~
significantly above the mudline, probably 6 or 7 feet.
To overcome some of these problems, it has been proposed to make a caisson large enough to contain the blowout preventer. United States patent 3,344,612 and 3,796,273 describe methods of installing such a caisson type. U.S. Patent 3,344,612 uses a jetting technique for caissons installed in a soft sea bed and Patent 3,796,273 uses a rotary drilling technique for hard sea beds. In this latter arrangement, the base of the caisson has cutting teeth on its surface and the complete caisson is rotated thereby boring its own hole. Although these techniques appear feasible, they require a drilling rig which is very expensive and must rely on cementing to ensure their soundness since the surrounding soil is highly disturbed. In the case of the rotating caisson, the feasibility of easily rotating such a large body when it nears its full penetration is questionable since there is a large surface area at a large radius.
United States Patent 3,380,256 proposes putting a complete drill rig in a caisson and sinking it by means of hydrostatic pressure. In this patent, the caisson skirt is pushed into the sea bed until the base of the caisson contacts the sea bed with the result that that part of the caisson with the wellhead equipment still protrudes above the sea bed. The technique of using hydrostatic pressure described in this patent has been used successfully in sinking suction anchors. The main limitation is the depth of penetration obtainable before the soil-resisting ~7'3~
force balances the force produced by the hydrostatic pressure.
Summary of the Invention The present invention overcomes many of the problems mentioned above relative to current caissons and their method of installation. In the present invention, the caisson is sized to suit the eguipment that is to remain subsea and is installed using hydrostatic pressure but with the caisson closed only at its upper end. Accordingly, the caisson is initially installed in the same manner as a suction anchor, but, unlike a suction anchor, the soil inside the caisson is removed either while the caisson is being run or after it has reached its correct depth. A base to the caisson is then installed. The installation of the base after the caisson is at its desired depth and thus allowing the caisson to be installed in a similar manner as a suction anchor, means that the installation can be done by a normal work boat rather than an expensive drill rig and does not tie up the drill rig if problems occur. Furthermore, the caisson is firmly installed in the sea bed and does not require additional cementing.
In some areas, the sea bed may provide too much resistance and prevent full penetration using only hydro-static pressure. If this occurs, a rotatable cutting device is utilized on the lower peripheral wall of the cylindrical ~ody of the caisson. Inasmuch as no base closure is initially used on the caisson body, the cutter only has to remove a small amount of subsea soil required for the caisson walls to pass through. The caisson is not rotated but only the ,S~
cutter so the torque required is considerably reduced over the conventional method referred to above and the hydrostatic pressure again is used to overcome vertical soil resistance.
The current method of drilling subsea wells in a cluster is to use a subsea template which is a structure placed on the sea bed that has holes or slots in it to accept wellheads. The template is usually plowed to the seabed and levelled. United States Patent 3,796,273 uses the idea of a template for multiple wells by setting the caissons into a template.
Accordingto the present invention, a number of caissons are joined together without the need for a template and the complete assembly is installed as an integral unit using hydrostatic pressure on each chamber.
~hould the addition of a soil cutter be required, the cutter described above for the single caisson is directly applicable to multiple units. The installation does not have to be manifolded but can be an option.
Preferably, the subsea soil on the interior of the caisson is removed as the caisson is being installed since this eliminates the soil friction on the inside of the caisson wall and permits deeper caisson penetration. One method is to provide a jetting device extending inwardly from the top cover to the lower end of the caisson and being directed downwardly therein. In this method, the soil is fluidized by the inwardly coming jet of water and is removed with the water through suction pumps, the inlet to which is situated coaxially in a detachable cover of the 3'~54 caisson body. In another embodiment, a plurality of jetting nozzles can be located adjacent the lower circumferential rim of the caisson body so that they not only assist the caisson wall penetration and effect the loosening of the inside soil but they are also directed angularly inwardly to prevent the jet of fluid and loosened soil from washing up on the outside of the caisson wall.
This ensures that the outside of the caisson is firmly held by the surrounding subsea soil.
Caisson systems proposed to date have not used a method of flowing the well to another facility or they suggest using flow lines exiting through the top of the caisson to a normal above-mudline connection method. The present invention utilizes a flowline connection port on the upper side wall of the caisson so that the flowlines can be connected below the mudline out of harm's way. Such a port can be equipped with a jetting device to wash soil away from the outside of the port and the flowline bundle as it is being pulled in.
The present invention utilizes a removable top closure which allows several tops to be used, depending on the circumstances of installation and use. The top with the suction pumps and associated equipment can be removed after the caisson is installed and used on other installations.
After the production equipment is installed on the caisson, at least two alternative tops can be fitted. If the equipment is to be used wet, i.e. to be accessed by divers, then a light debris protection cover is used. On the other ~7 ~
hand, if a dry, one-atmosphere installation is required, then a cover suitable for resisting hydrostatic pressure is installed and which would have a marine mating surface and hatch suitable for use by diving bells or submarines to land on and transfer people to the interior of the caisson.
According to one broad aspect, the invention relates to a method of securing the caisson in the seabed, the caisson having a detachable top cover and an open bottom, the method comprising the steps of; providing jet and suction means within the confines of the caisson; lowering the caisson to the seabed surface so that the peripheral open bottom wall of the caisson engages the surface of the seabed; orienting the jetting device toward the lower end of the caisson and actuating the same to fluidize soil within the caisson and removing said soil and jetting fluid via suction means whereby the caisson is lowered into said seabed by hydro-static pressure so that the top of the caisson is below the scour line; and removing the cover, jet and suction means.
According to another broad aspect, the invention relates to a caisson for installation in a seabed comprising an elongated cylindrical housing having an open bottom and replaceable top closure, means in the top closure are provided for the entry of jetting and suction means for removing subsea soil from within the caisson so as to lower it by hydrostatic pressure; and means are provided on the inner wall of said caisson for locking and sealing a permanent base therein.
~1~7~
Brief Description of the Drawings The invention is illustrated by way of example and the accompanying drawings in which Figures 1 through 9 inclusive are elevation drawings showing the sequence of installation of the caisson in subsea soil;
Figure 10 is a sectional view of the caisson wall showing the locking and sealing detail for the enclosure;
Figure 11 is a sectional view through the caisson wall showing the arrangement for mounting the cutter on the base of the caisson;
Figure 12 is a plan view of a cluster of caissons interconnected to a manifold caisson; and Figure 13 is an elevation view of the apparatus of Figure 12.
Descri tion of the Preferred Embodiment p Referring to Figure 1, the caisson 10 has an elongated cylindrical body with a continuous curved wall 12, an open bottom 14 and a top closed by a replaceable cover 16. The top 16 is secured by cables or the like 18 for lowering the caisson 10 to the seabed 20. Jettins and suction means consisting of an elongated jet nozzle 22 and suction inlet 24 are mounted in the top cover 16 as illustrated. The caisson 10 is lowered until the lower peripheral edge 26 engages the surface of the seabed in the glory hole and the subsea soil within the confines of the caisson is loosened and fluidized by the incoming water from jet 22 and the material is evacuated by a vacuum pump in the mother ship through the suction inlet 24, thereby causing the ambient water pressure to drive the caisson into the sea bottom as shown in Figure 2. When the subsea soil has been removed from the interior of the caisson, the jet means 22 and suction manifold 24 as well as the top cover 16 are removed from the caisson lO as shown in Figure 3.
A temporary drilling guide 28 is then lowered into the confines of the caisson lO, the guide 28 resting on an inwardly directed, circumferential lip 30 on the inside of the caisson wall adjacent its lower end. The drill stem 32 is then lowered through the guide and a hole 34 can be drilled for a conductor of given size. The temporary guide is then removed as shown on Figure 5 and the caisson can be flushed and cleaned.
As shown on Figures 6 and 7, a permanent base 36 is then installed in the lower end of the caisson 10, the base 36 being locked onto the inwardly directed lip as shown in Figure lO. The annular rim of the base 36 includes a shoulder 38 which rests on the lip 30 and a pocket 40 located above the shoulder 38 includes an expandable seal 42 which engages the inner wall of the caisson lO to seal the base therewith. Upward movement of the base is prevented by means of a lock ring 44 located in a lower pocket 46, the lock ring 44 engaging the underside of the inwardly directed lip 30.
After the base 36 is installed, the hole is drilled for casing 48 of given diameter with the returns going through a separate pipe 50 to the sea surface. A wellhead is then installed through the riser 60 and, as shown in Figure 7, 9~S4 g the riser is subsequently removed and a blowout preventer 62 is lowered to the wellhead as shown in Figure 8. Subsequently, a Christmas tree 64 is installed on the wellhead as seen in Figure 9, and flow lines 66 are attached to the Christmas tree 64, a debris cover 68 is installed and the flow lines 66 are passed through a port 70 in the upper side wall of the caisson 10. It will be appreciated that the debris covers 68 can be removed for wet access to the wellhead or a sealed entrance, not shown, can be applied to the caisson for dry access through submersible vehicles.
Figure 11 illustrates an arrangement for applying a cutter to the lower terminal edge of the silo 10 for use in areas where the seabed may provide too much resistance and prevent full penetration of the caisson using only hydro-static pressure. As mentioned earlier, in view of the fact that no base closure is used in the caisson when it is initially inserted in the subsea soil, the cutter has only to remove a small amount of the soil required for the caisson walls to pass through. Accordingly, the caisson wall 10 may be provided adjacent its lower end with a lip 72 having support means 74 for aligning and supporting a drive shaft 76 that passes downwardly through the top 16 of the caisson from exterior motor means 78. The lower end of the shaft 76 is provided with a pinion gear 80 which engages gear teeth 82 on the inner peripheral rim of an annular cutter body 84 which is mounted for rotation on the lower edge of the caisson 10 by means of rollers 86. As seen in Figure 11, the lower end of the cutter 84 is provided with suitable teeth 88 for 1179~5~
cutting into the subsea soil.
In a further embodiment of the present invention, a number of caissons are joined together without the need for a template and the complete assembly can be installed as an integral unit using hydrostatic pressure on each caisson chamber. Turning to Figure 12 and 13, a plurality of caissons lOa through lOd inclusive may be connected together by a structural tie plate 90 and interconnected to a central manifold silo 92. Silo lOd is the only well illustrated as completed for the purposes of clarity, a plurality of such wellhead caissons feeding into the manifold caisson 92 from which an export flow line 94 is used for delivery from the assembly. As seen in Figure 13, the wellhead 60 feeds the product via lines 96 through connectors 98, a valve 100 and choke 102 to a production line manifold 104 which receives product from all of the production caissons. The product subsequently exits through a vertically oriented manifold line 106 and diverter 108 to the export flow line.
While the present invention has been described in connection with specific embodiments thereof and in specific use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.
The terms and expressions which have been employed in this specification are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof. It is recognized - 117~ 4 that various modifications are possible within the scope of the invention claimed.
Claims (10)
1. A method of securing a caisson in a sea bed, said caisson having a detachable top cover and an open bottom, said method comprising the steps of:
a) providing jet and suction means within the confines of the caisson;
b) lowering the caisson to the sea bed surface so that the peripheral open bottom wall of the caisson engages the surface of the sea bed;
c) orienting the jetting device toward the lower end of the caisson and actuating the same to fluidize soil within the caisson and removing said soil and jetting fluid via the suction means whereby said caisson is lowered into said sea bed by hydrostatic pressure so that the top of said caisson is below the scour line; and d) removing said cover, jet and suction means.
a) providing jet and suction means within the confines of the caisson;
b) lowering the caisson to the sea bed surface so that the peripheral open bottom wall of the caisson engages the surface of the sea bed;
c) orienting the jetting device toward the lower end of the caisson and actuating the same to fluidize soil within the caisson and removing said soil and jetting fluid via the suction means whereby said caisson is lowered into said sea bed by hydrostatic pressure so that the top of said caisson is below the scour line; and d) removing said cover, jet and suction means.
2. A method according to claim 1 including further steps of:
e) placing a temporary guide in the lower end of said caisson and utilizing said guide for drilling a conductor into said sea bed;
f) removing said guide and installing a permanent base in said caisson and attaching a riser to said conductor;
g) installing a wellhead through said riser; and h) securing a blow-out preventer onto said wellhead.
e) placing a temporary guide in the lower end of said caisson and utilizing said guide for drilling a conductor into said sea bed;
f) removing said guide and installing a permanent base in said caisson and attaching a riser to said conductor;
g) installing a wellhead through said riser; and h) securing a blow-out preventer onto said wellhead.
3. A method according to claim 1 including connecting a flow line through the side wall of the caisson; and installing a debris cover on said caisson.
4. A method according to claim 1 wherein the jetting means is located circumferentially of the inner wall of the caisson and directed inwardly thereof.
5. A caisson for installation in a sea bed comprising an elongated cylindrical housing having an open bottom and a replaceable top closure; means in said top closure for the entry of jetting and suction means for removing sub sea soil from within said caisson so as to lower it by hydrostatic pressure; and means on the inner wall of said caisson for locking and sealing a permanent base therein.
6. A caisson according to claim 5 including a disk cutter mounted circumferentially on the lower terminal end of the caisson wall and means for rotating said cutter about said lower terminal end.
7. A caisson according to claim 5 wherein the jetting means comprises a single nozzle extending centrally downwardly of the caisson body to fluidize the sea bed soil therein.
8. A caisson according to claim 5 wherein the jetting means comprises a plurality of circumferentially spaced jetting devices adjacent the lower terminal end of the caisson wall, said jetting devices being directed angularly inwardly.
9. A caisson according to claim 5 wherein the replaceable top closures consist of a first closure for use in installing the caisson in the sea bed, a further closure for use as a debris cover and a further cover for converting a wet caisson to a one-atmosphere dry chamber with suitable marine mating surfaces.
10. A caisson according to claim 5 including a flow line exit on the upper side wall of the caisson body.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411343A CA1179254A (en) | 1982-09-14 | 1982-09-14 | Subsea caisson |
| US06/531,682 US4558744A (en) | 1982-09-14 | 1983-09-13 | Subsea caisson and method of installing same |
| GB08324660A GB2133060B (en) | 1982-09-14 | 1983-09-14 | Subsea caisson |
| NO83833291A NO833291L (en) | 1982-09-14 | 1983-09-14 | Submersible container for wellhead equipment as well as methods for using the container |
| DK419583A DK419583A (en) | 1982-09-14 | 1983-09-14 | DRINKING BOX FOR DRILLING EQUIPMENT AND PROCEDURE ON ITS APPLICATION ON THE SEA |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411343A CA1179254A (en) | 1982-09-14 | 1982-09-14 | Subsea caisson |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179254A true CA1179254A (en) | 1984-12-11 |
Family
ID=4123582
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411343A Expired CA1179254A (en) | 1982-09-14 | 1982-09-14 | Subsea caisson |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1179254A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001065050A1 (en) * | 2000-02-29 | 2001-09-07 | Harald Strand | Foundation for suction in installation of conductor casing |
| WO2017048941A1 (en) | 2015-09-15 | 2017-03-23 | Noble Drilling Services Inc. | Method for excavating a mud line cellar for subsea well drilling |
-
1982
- 1982-09-14 CA CA000411343A patent/CA1179254A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001065050A1 (en) * | 2000-02-29 | 2001-09-07 | Harald Strand | Foundation for suction in installation of conductor casing |
| US6692194B2 (en) | 2000-02-29 | 2004-02-17 | Harald Strand | Method for installing a conductor casing through a suction substructure |
| WO2017048941A1 (en) | 2015-09-15 | 2017-03-23 | Noble Drilling Services Inc. | Method for excavating a mud line cellar for subsea well drilling |
| EP3353368A4 (en) * | 2015-09-15 | 2019-05-01 | Noble Drilling Services, Inc. | Method for excavating a mud line cellar for subsea well drilling |
| US10364609B2 (en) | 2015-09-15 | 2019-07-30 | Noble Drilling Services Inc. | Method for excavating mud line cellar for subsea well drilling |
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| Date | Code | Title | Description |
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| MKEC | Expiry (correction) | ||
| MKEX | Expiry |