Method And Device For Connecting A Riser To A Target Structure
The present invention relates to a method for connecting a free end of an at least partially submerged riser to a target structure, the method comprising: (a) connecting the riser by the free end thereof to a riser support assembly; (b) positioning the target structure near the riser support assembly; (c) connecting a lifting assembly, with the free end (24) of the riser; (d) moving the riser by the free end thereof from the riser support assembly toward the target structure by the lifting assembly; and (e) connecting the riser with the target structure. The present invention also relates to a riser support assembly for connecting a riser by a free end thereof with a target structure.
The present invention relates to a method and device for connecting a riser to a target structure. Risers are widely applied in the offshore industry in oil and/or gas fields at sea. An oil and/or gas well is located at a seabed level. The product, e.g. oil and/or gas, is produced by the well and is transported to a structure at the water level. From the structure, the product is transported further on, for instance by means of another pipeline to a shore. The product may also be temporarily stored in a storage facility close to, or on the structure. In order to transport the product to the structure, the well is connected to the structure by a pipeline for conveying the product to the structure.
During the installation of oil and/or gas field, a pipeline is laid connecting the well with the structure located at the water surface. Such a pipeline usually has a first part which rests on the seabed, and a second part which rises from the seabed towards the structure at the water level. The second part of the pipeline is known in the field of the art as a “riser”.
Typically, the riser follows a curved trajectory from the seabed towards the riser support assembly. At the seabed level, the riser has a substantially horizontal orientation. Near the riser support assembly, the riser may have a substantially vertical orientation.
DESCRIPTION OF THE PRIOR ARTIn a known method of installation of a riser, a transfer of a product riser and a transfer of a number of anchor lines from a first, temporary buoy to a second, permanent buoy are combined. The product riser is produced and installed by a pipe-laying vessel, located at the water surface. The first buoy is anchored to the seabed by at least a first and a second anchor line. The product riser connected by a free end thereof to the first buoy. The riser may stay in this position for a considerable period of time, until a second, permanent mooring buoy is put in place.
When the second buoy is ready, it is positioned in a desired position, close to the first buoy. The first and the second buoy are connected to one another via a member which can take up tension forces. A tug boat is provided for pulling the second buoy away from the first buoy. Then, the anchor lines are detached one by one from the first buoy and connected to the second buoy. During the time period in which at least one of the anchor lines is detached, the combination of the first and second buoy is no longer anchored in a stable and secure way, and is in risk of drifting away from the desired location. The tug boat is provided for keeping the buoys in place.
Subsequently, the second anchor line is transferred from the first buoy to the second buoy. During this operation, the tug boat also keeps the first and second buoy in place en prevents drifting away of the first and second buoy.
Then, the product riser is transferred from the first buoy to the second buoy. This is performed by using a cable which is connected to a winch on the second buoy. The free end of the cable is connected to a free end of the product riser. When the product riser is detached from the first buoy, the cable is pulled by the winch, transferring the product riser from the first buoy to the second buoy.
A drawback of the above mentioned method is that it is a complicated procedure, requiring a tug boat
Further, the combination of transferring the anchor lines and the product riser at the same time provides the drawback that the first buoy is no longer anchored to the seabed at the end of the operation and is to be moved away by the tug boat. A reverse operation of transferring the product riser back to the first buoy cannot be performed without re-anchoring the first buoy back to the seabed.
SUMMARY OF THE INVENTIONIt is an object of the present invention to provide a method and device for connecting a riser to a target structure which is substantially free of the above mentioned drawbacks.
It is a further object of the invention to provide a method and device for connecting a riser to a target structure, which is relatively fast, reliable and simple to perform.
It is in particular an object of the present invention to provide a method and device of connecting a riser to a target structure, wherein a free end of the riser can temporarily be positioned in a predetermined way during a time period in which the target structure is not yet present and connected to the target structure when the target structure is present at its desired position.
Thereto the method according to the invention comprises the steps of:
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- (a) connecting the riser by the free end thereof to a riser support assembly;
- (b) positioning the target structure near the riser support assembly;
- (c) connecting a lifting assembly with the free end of the riser;
- (d) moving the riser by the free end thereof from the riser support assembly toward the target structure by the lifting assembly; and
- (e) connecting the riser with the target structure.
With the method according to the invention, risers can be installed when the target structure is not yet present at the time of installation of the riser itself.
The word “riser” may refer to a production, injection, communication and/or control riser for conveying oil and/or gas or another product. A production or injection riser is constructed to convey a product, such as oil or gas or water or any fluid, from the seabed to the target structure or vice versa from the target structure to the well. The word riser may also refer to a communication and/or control riser. A communication and/or control riser is constructed to transmit signals from the target structure to devices on the seabed, such as for instance the wells, or controllable valves. Also, signals may be transmitted by the riser from the oil well and/or other devices on the seabed to the target structure, for controlling the devices on the seabed.
Other types of risers also exist, for instance risers that are used to convey water from the target structure toward the seabed, for injection of the water in the well. Other types of riser are well control risers.
The words “target structure” are to be interpreted broadly and can indicate a wide range of structures, floating or resting on the seabed. A number of non-limiting examples of target structures are provided hereinafter.
The words “lifting assembly” are to be understood as to indicate a wide range of lifting assemblies. The lifting assembly may be a crane or a winch or a drilling tower, or another device. The lifting assembly may be positioned on the target structure or on a separate vessel or structure.
The riser support assembly indicates any construction configured for supporting a riser by a free end thereof. The riser support assembly preferably comprises a buoyancy device for providing a required buoyancy for supporting the riser.
Preferably, the target structure and the riser support assembly are maintained in their respective positions independently from one another.
In this way the riser support assembly and the target structure may be accurately positioned with respect to one another.
Preferably, the target structure comprises the lifting assembly. This provides the advantage of obviating the need for providing a separate vessel with a lifting assembly. The moving of the riser can be conducted from the target structure itself, which is simple and reliable.
Preferably, the riser support assembly is anchored to the seabed by a first anchoring device.
The anchoring device advantageously keeps the riser support assembly in a fixed position.
Preferably, the target structure is anchored to the seabed by a second anchoring device which is an independent device from the first anchoring device. In this way, advantageously the step of transferring the anchoring device of the riser support assembly to the target structure can be left out of the procedure.
Preferably, the riser support assembly is directly connected to the first anchoring device throughout steps (a), (b), (c), (d) and (e). This provides the advantage of having a simple and reliable positioning of the riser support assembly throughout steps (a), (b), (c), (d) and (e).
Preferably, during step (b) the target structure and the riser support assembly are connected by a connecting means. With the connecting means, a horizontal distance between the riser support assembly and the target structure can be reduced, providing easier transfer of the riser.
Preferably, the target structure and the riser support assembly are not connected to one another.
Preferably, during step (b) the target structure and the riser support assembly are moved towards one another by reducing the length of the connection means. Also, the length of the mooring lines of the target structure can be adjusted, thereby moving the target structure toward the riser support assembly. This may be a substantial horizontal movement. Advantageously, the target structure and the riser support assembly can be positioned very close to one another, facilitating the transferal of the riser from the target support assembly to the target structure.
Preferably, the riser support assembly is positioned at a predetermined depth under the water surface when the riser is suspended from the riser support assembly. This facilitates an eventual positioning of the riser support assembly close to the target structure.
Preferably, the riser support assembly is positioned at a depth at which the riser support assembly is substantially free from influences from wind and waves at the water surface. This provides the advantage of a stable support for the riser with relative low dynamic forces exerted on the riser support assembly and the riser.
Preferably, in step (b) the target structure is at least temporarily positioned substantially above the riser support assembly. This provides the advantage that the riser can be moved from the riser support assembly to the target structure in a substantially vertical direction. This enables a simple lift operation by the lifting assembly.
Preferably, the depth at which the riser support assembly is positioned is greater than the draught of the target structure. This enables the positioning of the riser support assembly under the target structure.
Preferably, the method according to the invention comprises a further step (f) of removing the riser support assembly. Advantageously, the riser support assembly may be reused at another location.
Preferably, prior to step (a) the riser is suspended by the free end thereof from a pipe-laying vessel and in step (a) the riser is transferred from the pipe-laying vessel to the riser support assembly. This enables the pipe-laying vessel to start another operation elsewhere, and obviates the need for the pipe-laying vessel to wait for a substantial amount of time for late arrival of the target structure.
Preferably, in step (a) the riser support assembly is moved towards the pipe-laying vessel, for transferring the riser from the pipe-laying vessel to the riser support assembly.
Preferably, the target structure is chosen from a group of floating structures, comprising: a TLP, a Spar, a Semi-submersible, an FPSO, an FPDSO, an FPWSO, a storage barge, an FSO, an FSU. For these structures and other structures, the method according to the invention provides a reliable way of connecting the riser to the target structure.
Different riser configurations exist to provide a reliable connection between the pipeline on the seabed and the target structure. Preferably, the riser comprises rigid sections. Alternatively the riser comprises only flexible pipe sections. The riser can also be of a hybrid type comprising rigid sections and flexible sections.
Preferably, in step (a) at least two risers are connected to a single riser support assembly. This provides the advantage of needing only a limited number of riser support assemblies, in some cases only one.
Preferably, a first riser support assembly and a second riser support assembly are provided, wherein the first riser support assembly and second riser support assembly are connected by a mooring connecting means for maintaining a predetermined distance between the first and second riser support assembly.
This embodiment advantageously prevents damage to the riser support assemblies. The mooring connecting means may be a wire or a line, a cable or a rigid bar, or another connecting means known in the art.
Alternatively, the riser support assemblies may be positioned at a sufficient large distance from one another. The riser support assemblies may comprise fenders to prevent damage at contact between the riser support assemblies.
Alternatively, two or more riser support assemblies are integrated into to a large riser support assembly. A large riser support assembly can support a number of risers, thereby further simplifying the construction.
Preferably, the lifting assembly is chosen from a group of lifting assemblies, comprising: a pull-in device with chain jacks, a winch, a crane and a drill tower. These lifting assemblies have a lifting power that is sufficient to move the riser from the riser support assembly to the target structure.
Preferably, the target structure is anchored to the seabed using a second anchoring device. This provides the advantage of a secure anchoring of the target structure, while obviating the need for detaching the first anchoring device from the riser support assembly.
Preferably, the lifting assembly is connected to the riser by a remotely operated vehicle (ROV) The lifting assembly comprises a lifting means such as a cable or a wire or another lifting means known in the art. The ROV will assist to connect underwater the lifting means and the riser with the advantage of diverless operations.
The invention also relates to a riser support assembly for connecting a riser by a free end thereof with a target structure, the riser support assembly comprising:
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- a buoyancy device for providing a predetermined buoyancy to the riser support assembly;
- a suspending device configured for suspending the riser by the free end thereof from the riser support assembly;
- a first anchoring device for anchoring the riser support assembly to the seabed.
With the riser support assembly, a riser can be connected to a target structure in a reliable and simple way.
Preferably, the riser support assembly is constructed for allowing an upwards movement of the riser relative to the riser support assembly. In this way the lifting assembly can lift the riser from the riser support assembly without hindrance, for instance when the riser support assembly is positioned substantially underneath the target structure.
Preferably the riser support assembly comprises a recess configured for receiving the riser therein. Advantageously, the riser is positioned in the recess, thereby exerting a downwards pulling force on the riser support assembly substantially on the center of the riser support assembly, when viewed from above. The riser support assembly will subsequently stay in a stable orientation.
Preferably, the recess is a channel which, in use, extends substantially through the buoyancy device, preferably in a substantially vertical direction. This provides the advantage that the free end of the riser will extend on the upper side of the riser support assembly, allowing easy access to the riser from above, for instance for connecting a connecting means thereto.
Preferably, the riser support assembly has a substantially elongated form.
Preferably, the substantially elongated form extends in a substantially horizontal direction. In this way, space is created for suspending more than one riser from the riser support assembly.
Preferably, the buoyancy device comprises a first buoyancy means and a second buoyancy means, wherein the first and second buoyancy means are connected with one another by means of a bridging body. This provides the further advantage of enabling a configuration of a large riser support assembly.
Preferably, the bridging body comprises the suspending device. An integration of the bridging body and the suspending device provides the advantage of a simple design and ease of construction.
Preferably, the suspending device is configured for suspending a number of risers therefrom. This provides the advantage that less riser support assemblies will need to be installed when a relatively large number of risers is present.
Often, a number of oil and/or gas wells are located in a same oil and/or gas field at relatively close distances with respect to one another. In that case, a number of riser may rise from the wells and be suspended from a single riser support assembly.
Preferably, the first anchoring device comprises a mooring line and an anchoring means, the anchoring means being chosen from a group of anchoring means, comprising: a piled foundation, a suction pile and a gravity foundation. These anchoring means have shown to be reliable for these purposes.
Preferably, the anchoring means are configured for bearing a substantially upwardly directed force which is exerted on the anchoring means by the mooring line. On the first anchoring means an upwards force may be exerted by the buoyancy device. Therefore, the anchoring means preferably allows for an upwardly directed force.
Preferably, the first anchoring device comprises a mooring line, the mooring line being chosen from a group of mooring lines, comprising: a tendon, a polyester line, a steel wire and a chain. These mooring lines have shown to be reliable.
The word tendon indicates a rigid and stiff pipe, used for vertical mooring and high loads. Preferably the tendon comprises pipe section which are screwed to one another. These tendons technology is well known and has been used to moor Tension Leg Platforms (TLP) to the seabed.
The claims and advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.
BRIEF DESCRIPTION OF THE DRAWINGSHereinafter the present invention will be illustrated in more detail by a drawing. Herein shows:
FIGS. 20 shows a side view of an alternative embodiment of moving the buoyancy device and the target structure towards one another;
The riser 6 may be manufactured from well-known construction materials such as steel or titanium. Preferably, the riser 6 is a Steel Catenary Riser (SCR). The riser 6 may also be manufactured from a synthetic material, or a composite material. It is also possible that the riser is a flexible riser. The riser 6 may also be a hybrid curved riser comprising rigid sections and flexible sections (not shown).
In the same way, the risers 6a, . . . , 6f are laid on the sea bed, possibly connected on one end thereof with a respective well.
Then, the target structure 2 is positioned in its desired position. The mooring lines 8a, . . . , 8l are picked up from the seabed by an installation vessel (not shown). The mooring lines 8a, . . . , 8l are then connected at their free end to the target structure 2.
In the same way, the risers 6a, 6f are picked up from the seabed and connected on a respective free end 24a, . . . , 24f thereof to the target structure 2.
Turning to
The riser support assembly 20 comprises a buoyancy device 28 and an anchoring device 29. The anchoring device 29 comprises a mooring line 14 and an anchoring means 30, the mooring line 14 being connected with a first end to the buoyancy device 28 and with a second end to the anchoring means 30, anchored in the seabed at an anchoring point 12. An indicating buoy 32 is connected with a line to the riser support assembly 20 and floats at the water surface 34, for indicating the position of the riser support assembly 20.
The anchoring means 30 may be a piled foundation, a suction pile, a gravity foundation. Preferably, the anchoring means 30 is configured to resist a substantially upwardly directed vertical force exerted on it by the mooring line 14.
The mooring line 14 can be a tendon, a light weight line such as a polyester line, a steel wire or a chain.
The buoyancy device 28 may be completely under the water surface 34 or partially above the water surface 34 when there is no riser 6 suspended from the riser support assembly 20. When the riser 6 is suspended from the riser support assembly 20, the buoyancy device 28 will be under the water surface 34 at a depth 41 where there is no influence from wind and/or waves.
When the riser 6 is connected to the riser support assembly 20, the mooring line 14 may extend along a substantially straight line or may extend along a catenary line.
The riser 6 has at the free end 24 thereof a lifting connector 40 for connecting the riser 6 to a lifting assembly (not shown), in order to lift the riser 6 from the buoyancy device 28. Further, at the free end 24 of the riser 6 a first collar 42 is provided for suspending the riser 6 from the buoyancy device 28. A second collar 44 is provided to hang the riser 6 from the target structure (not shown).
The riser support buoy 28 has a suspending device 31 for suspending the riser 6 therefrom. The suspending device comprises a contact area 33, wherein the collar 42 engages the buoyancy device 28.
A number of risers 6a, 6b, 6c, 6d, 6e are suspended from the riser support assembly 20. Each riser has at the free end 24 thereof a suspending device 46 in the form of a hook 46a, 46b, 46c, 46e for suspending the respective risers 6 from the buoyancy device 28. A person skilled in the art will appreciate that many other embodiments such a suspending device 46 are possible, without departing from the scope of the invention.
Turning to
In
Alternatively, in order to prevent contact between the buoyancy devices 28, a sufficient large distance between the buoyancy devices may also be provided. Also fenders on the buoyancy devices 28 may be provided in order to avoid damage during contact. Another possibility of avoiding damage to the buoyancy devices 28 is to integrate a number of buoyancy devices into a single large buoyancy device 28.
The anchoring means 30a, 30b, 30c . . . 30h are positioned on the other side of the target structure as the respective corresponding buoyancy devices 28a, . . . 28h.
The risers 6a, 6b, 6c, . . . 6h extend in different directions, and are connected to the target structure 2 on different sides thereof.
Mooring connecting means 54 connect buoyancy devices 28a, with 28e, 28b with 28c, 28d with 28h, and 28g with 28f. Other ways of connecting the buoyancy devices 28a . . . 28h with one another are also possible.
When the target structure 2 is in the desired position, the riser 6 can be transferred to the target structure.
If a number of risers 6 are to be connected to the target structure 2, the target structure may be moved from one desired position to the next one, picking up a riser 6 in each position. After the risers 6 are connected to the target structure 2, the target structure 2 is moved to its final position.
The buoyancy device 28 can be left in this position, allowing a reverse operation of transferring the riser 6 from the target structure 2 onto the riser support assembly 20. Alternatively the riser support assembly 20 may be removed and reused in another location. The riser support assemblies 20 may be disconnected from the anchoring means 30 by a remote operated vehicle (ROV, not shown), known in the art. Partial flooding of the buoyancy device 28 may be performed prior to disconnecting from the buoyancy device 28. The ROV may also be used to assist in connecting the connection line 62 to the buoyancy device 28.
In an alternative embodiment, the riser 6 is lifted off the riser support assembly 20 by a support vessel (not shown) and moved towards the target structure 2 by the support vessel. The support vessel requires a high capacity winch to lift the heavy riser (possibly weighing in the order of 2000-6000 kiloNewton).
A number of risers 6 are positioned on the side 83 of the target structure 2. Hydraulic rams 78a, 78b are provided for moving the pull-in device in the directions of arrows relative to the target structure A pulling rig skid base 81 is provided for skidding on the skidding rails 78a, 78b. In this way, a single pull-in device 63 can be used to sequentially pull in a number of risers 6a, 6b, 6c towards the target structure 2.
It will be obvious to a person skilled in the art that numerous changes in the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.
Claims
1. A method for connecting a free end of an at least partially submerged riser to a target structure, the method comprising:
- (a) connecting the riser by the free end thereof to a riser support assembly;
- (b) positioning the target structure near the riser support assembly;
- (c) connecting a lifting assembly with the free end (24) of the riser;
- (d) moving the riser by the free end thereof from the riser support assembly toward the target structure by the lifting assembly; and
- (e) connecting the riser with the target structure.
2. The method of claim 1, wherein the target structure and the riser support assembly are maintained in their respective positions independently from one another.
3. The method of claim 1 or 2, wherein the target structure comprises the lifting assembly.
4. The method of claim 1, wherein the riser support assembly is anchored to the seabed by a first anchoring device.
5. The method of claim 4, wherein the target structure is anchored to the seabed by a second anchoring device which is an independent device from the first anchoring device.
6. The method of claim 1, wherein the riser support assembly is directly connected to the first anchoring device throughout steps (a), (b), (c), (d) and (e).
7. The method of claim 1, wherein during step (b) the target structure and the riser support assembly are connected by a connecting means.
8. The method of claim 7, wherein during step (b) the target structure and the riser support assembly are moved towards one another by reducing a length of the connection means.
9. The method of claim 1, wherein the riser support assembly is positioned at a predetermined depth under the water surface when the riser is suspended from the riser support assembly.
10. The method of claim 9, wherein the riser support assembly is positioned at a depth at which the riser support assembly is substantially free from influences from wind and waves at the water surface.
11. The method of claim 1, wherein in step (b) the target structure is at least temporarily positioned substantially above the riser support assembly.
12. The method of claim 1, comprising a further step (f) of removing the riser support assembly.
13. The method of claim 1, wherein prior to step (a) the riser is suspended by the free end thereof from a pipe-laying vessel and in step (a), the riser is transferred from the pipe-laying vessel to the riser support assembly.
14. The method of claim 13, wherein in step (a) the riser support assembly is moved towards the pipe-laying vessel, for transferring the riser from the pipe-laying vessel to the riser support assembly.
15. The method of claim 1, wherein the target structure is chosen from a group of floating structures, comprising: a TLP, a Spar, a Semi-submersible, an FPSO, an FPDSO, an FPWSO, a storage barge, an FSO, an FSU.
16. The method of claim 1, wherein the riser is chosen from a group of risers, comprising: a steel catenary riser, a lazy wave riser with buoyancy elements, a steep wave riser, and a flexible riser.
17. The method of claim 1, wherein the riser is manufactured from a material, chosen from a group of materials, comprising: steel, titanium, a synthetic material, and a composite of a metal and a synthetic material.
18. The method of claim 1, wherein the riser comprises flexible pipe sections.
19. The method of claim 1, wherein at least two risers are connected to the target structure.
20. The method of claim 19, wherein in step (a) at least two risers are connected to a single riser support assembly.
21. The method of claim 19 or 20, wherein a first riser support assembly and a second riser support assembly are provided, and wherein the first riser support assembly and second riser support assembly are connected by a mooring connecting means for maintaining a predetermined distance between the first and second riser support assembly.
22. The method of claim 21, wherein the mooring connecting means are selected from a group of mooring connecting means, comprising: a flexible mooring connecting means and a rigid mooring connecting means.
23. The method of claim 1, wherein the lifting assembly is chosen from a group of lifting assemblies, comprising: a pull-in device with chain jacks, a winch, a crane and a drill tower.
24. The method of claim 1, wherein the target structure is anchored to the seabed using a second anchoring device.
25. The method of claim 1, wherein the lifting assembly is connected to the riser by a remotely operated device.
26. A riser support assembly for connecting a riser by a free end thereof with a target structure, the riser support assembly comprising:
- a buoyancy device for providing a predetermined buoyancy to the riser support assembly;
- a suspending device configured for suspending the riser by the free end thereof from the riser support assembly;
- a first anchoring device for anchoring the riser support assembly to the seabed.
27. The riser support assembly of claim 26, wherein the suspending device is constructed for allowing an upwards movement of the riser relative to the riser support assembly.
28. The riser support assembly of claim 26 or 27, wherein the riser support assembly comprises a recess configured for receiving the riser therein.
29. The riser support assembly according to claim 28, wherein the recess is a channel which, in use, extends substantially through the buoyancy device, preferably in a substantially vertical direction.
30. The riser support assembly according to claim 26, wherein the riser support assembly has a substantially elongated form.
31. The riser support assembly according to claim 30, wherein the substantially elongated form extends in a substantially horizontal direction.
32. The riser support assembly according to claim 26, wherein the buoyancy device comprises a first buoyancy means and a second buoyancy means, wherein the first and second buoyancy means are connected with one another by means of a bridging body.
33. The riser support assembly according to claim 26, wherein the bridging body comprises the suspending device.
34. The riser support assembly according to claim 26, wherein the suspending device is configured for suspending a number of risers therefrom.
35. The riser support assembly according to claim 26, wherein the first anchoring device comprises an mooring line and an anchoring means, the anchoring means being chosen from a group of anchoring means, comprising: a piled foundation, a suction pile and a gravity foundation.
36. The riser support assembly according to claim 35, wherein the anchoring means are configured for bearing a substantially upwardly directed force which is exerted on the anchoring means by the mooring line.
37. The riser support assembly according to claim 26, wherein the first anchoring device comprises a mooring line, the mooring line being chosen from a group of mooring lines, comprising: a tendon, a polyester line, a steel wire and a chain.
38. The riser support assembly according to claim 26, having at least one riser suspended therefrom.
Type: Application
Filed: Jul 8, 2005
Publication Date: Apr 17, 2008
Inventors: Peter Salome (Boskoop), Robert Narold (Hoofddorp), Robert Hovinga (Av 'S Gravenzande), Ion Coppens (Oegsigeesi)
Application Number: 11/632,307
International Classification: E21B 17/01 (20060101);