Intervention system and apparatus

Abstract

A ball valve apparatus includes a housing defining a housing inlet and a housing outlet and a valve cartridge mounted within the housing and defining a cartridge flow path extending between a cartridge inlet and a cartridge outlet, wherein the cartridge inlet is arranged in fluid communication with the housing inlet and the cartridge outlet is arranged in fluid communication with the housing outlet. A ball valve member is mounted within the valve cartridge and is rotatable to selectively open and close the cartridge flow path. A leak chamber is defined between the housing and the cartridge for containing fluid leakage from the valve cartridge.

Claims

1. A ball valve apparatus, comprising: a housing defining a housing inlet and a housing outlet; a valve cartridge comprising a cartridge housing which defines a pressure housing operable to retain pressure inside the cartridge housing, the valve cartridge being mounted within the housing and defining a cartridge flow path extending between a cartridge inlet and a cartridge outlet, wherein the cartridge inlet is arranged in fluid communication with the housing inlet and the cartridge outlet is arranged in fluid communication with the housing outlet; a ball valve member mounted within the cartridge housing and being rotatable to selectively open and close the cartridge flow path; a valve actuator arrangement mounted within the valve cartridge for actuating the ball valve member between open and closed positions; and a leak chamber defined between the housing and the cartridge housing for containing fluid leakage from the valve cartridge.

2. The ball valve apparatus according to claim 1, deployable through a rotary table provided on a surface vessel.

3. The ball valve apparatus according to claim 1, wherein the leak chamber is defined by an annular space between an outer surface of the valve cartridge and an inner surface of the housing.

4. The ball valve apparatus according to claim 1, wherein the cartridge housing comprises multiple housing components sealingly secured together.

5. The ball valve apparatus according to claim 1, wherein the valve cartridge comprises a valve actuator arrangement for use in actuating the ball valve member to move between open and closed positions.

6. The ball valve apparatus according to claim 5, wherein the valve actuator arrangement is hydraulically actuated by hydraulic pressure delivered via a hydraulic line connected or connectable to the ball valve apparatus.

7. The ball valve apparatus according to claim 5, wherein the actuator arrangement is operable by fluid flow along the cartridge flow path in a particular direction.

8. The ball valve apparatus according to claim 5, wherein the actuator arrangement comprises a piston member and a piston housing defined by the cartridge housing, wherein the piston member is reciprocally mounted within the piston housing.

9. The ball valve apparatus according to claim 8, wherein the piston comprises an annular piston arranged coincident and/or collinear with the cartridge flow path and around the ball valve member.

10. The ball valve apparatus according to claim 5, wherein the actuator arrangement comprises a biasing arrangement for biasing the valve member towards a closed position.

11. The ball valve apparatus according to claim 5, comprising a linkage arrangement connecting the ball valve member and the actuator arrangement, wherein the linkage arrangement is operable to convert a linear movement of the actuation arrangement to a rotational movement of the ball valve member.

12. The ball valve apparatus according to claim 1, wherein the valve cartridge is sealingly engaged with the housing in the region of one of both of the cartridge inlet and cartridge outlet.

13. The ball valve apparatus according to claim 1, comprising at least one of an inlet sealing arrangement for providing sealed fluid communication between the cartridge inlet and the housing inlet, and an outlet sealing arrangement for providing sealed fluid communication between the cartridge outlet and the housing outlet.

14. The ball valve apparatus according to claim 1, comprising an inlet sealing collar which spans an interface between the valve cartridge and the housing, wherein one end of the inlet sealing collar is received within the cartridge flow path, and an opposing end of the inlet sealing collar is received within an inlet bore of the housing, the inlet sealing collar comprising a first sealing member for sealing against the valve cartridge, and a second sealing member for sealing against the housing.

15. The ball valve apparatus according to claim 1, comprising an outlet sealing collar which spans an interface between the valve cartridge and the housing, wherein one end of the outlet sealing collar is received within the cartridge flow path, and an opposing end of the outlet sealing collar is received within an outlet bore of the housing, the inlet sealing collar comprising a first sealing member for sealing against the valve cartridge, and a second sealing member for sealing against the housing.

16. The ball valve apparatus according to claim 1, wherein the ball valve member is operable to cut or sever an object or apparatus present within the cartridge flow path at the time of closing of the ball valve member.

17. The ball valve apparatus according to claim 1, wherein the ball valve member is a first ball valve member, and the ball valve apparatus further comprises a second ball valve member, wherein the first and second ball valve members are axially arranged relative to each other.

18. The ball valve apparatus according to claim 1, comprising at least one sensor arranged to sense or monitor conditions within the leak chamber.

19. The ball valve apparatus according to claim 1, wherein the housing comprises one or more external connectors for use in connecting to other apparatus such that the housing facilitates connection of the ball valve apparatus within a larger system.

20. The ball valve apparatus according to claim 1, wherein at least one section of the housing defines part of an emergency disconnect assembly.

21. The ball valve apparatus according to claim 1, wherein the housing defines an inlet flow path in fluid communication with the cartridge flow path via the cartridge inlet, and an outlet flow path in fluid communication with the cartridge flow path via the cartridge outlet.

22. The ball valve apparatus according to claim 1, wherein the housing defines a port through a side wall thereof for facilitating fluid communication externally of the housing and by-passing the valve cartridge.

23. The ball valve apparatus according to claim 1, wherein opposing ends of the valve cartridge are installed against opposing support shoulders provided within the housing such that the valve cartridge is axially captivated between the opposing support shoulders within the housing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a longitudinal cross-section of a subsea intervention system according to an embodiment of the present invention;

(3) FIG. 2 is an enlarged view of a well control package of the subsea intervention system of FIG. 1;

(4) FIG. 3 illustrates a lower region of a stress joint portion of the subsea intervention system if FIG. 1;

(5) FIG. 4 is a view from above of the stress joint portion of FIG. 3;

(6) FIG. 5 is a cross-sectional view of an emergency disconnect package of a subsea intervention system in accordance with an alternative embodiment of the present invention;

(7) FIG. 6 is a cross-sectional view of a portion of a subsea intervention system in accordance with a further embodiment of the present invention;

(8) FIG. 7 is a cross-sectional view of a portion of a subsea intervention system in accordance with a further embodiment of the present invention;

(9) FIG. 8 is a diagrammatic illustration of a subsea intervention system in accordance with another embodiment of the present invention; and

(10) FIGS. 9A to 9J illustrate a running sequence for use in deploying the subsea intervention system of FIG. 1.

DETAILED DESCRIPTION

(11) A subsea light weight well intervention system, generally identified by reference numeral 10, in accordance with an embodiment of the present invention is illustrated in cross-section in FIG. 1. The system 10 comprises a connector, in the present embodiment an H4 type connector 12, which facilitates connection to a subsea production Christmas tree (not shown). As will be described in more detail below, the illustrated system 10 is set-up for mounting on and performing intervention operations through a horizontal Christmas tree.

(12) The system 10 includes a well control package 14 coupled to the H4 connector 12 via an adaptor 16. The adaptor 16 in the embodiment shown includes a central monobore 18 which is configured to facilitate interfacing with a horizontal Christmas tree. The adaptor 16 includes and a generally cylindrical section 20 which extends into the connector 12 with radial O-ring seals 22 providing sealing therebetween. The provision of such radial seals may permit sealing to be maintained in the event of relative axial movement between the connector 12 and adaptor 16.

(13) The adaptor 16 is secured to the well control package 14 via bolted flange connection 24, and similarly the adaptor 16 is secured to the H4 connector 12 via bolted flange connection 26.

(14) The system 10 further comprises a stress joint assembly 28 mounted above the well control package 14, wherein the stress joint assembly includes upper and lower connectors 30, 32 and a pipe section 34 extending therebetween. The pipe section 34 includes a wall thickness which tapers from a thick wall section adjacent to the lower connector 32, to a thinner wall section adjacent the upper connector 30. Such a tapering wall thickness permits a gradual stress relief, particularly bending stress relief, to be achieved over the length of the stress joint assembly 28.

(15) In the particular embodiment shown the pipe section 34 of the stress joint assembly 28 includes a lower wall section 34a which defines a substantially uniform wall thickness, and an upper wall section 34b which defines a tapering wall thickness.

(16) The upper connector 30 of the stress joint assembly facilitates connection to a riser (not shown) which extends to a surface vessel (also not shown). The lower connector 32 of the stress joint assembly facilitates connection with the rest of the intervention system 10.

(17) The intervention system 10 further comprises an emergency disconnect package 36 mounted intermediate the well control package 16 and the stress joint assembly 28. The emergency disconnect package 36 includes first and second connector portions 36a, 36b which are connected together in normal use as shown in FIG. 1, but which may permit disconnection in the event of an emergency situation, such as in the event of a significant deviation of a surface vessel. In the event of such an emergency disconnect the well control package 14 remains connected to the well head system and thus continues to provide well control.

(18) The first connector portion 36a includes a connection profile 38 on an outer surface thereof, and the second connector portion 36b includes a plurality of dogs 40 which are activated by a piston 42 to selectively engage the connection profile 38. In the event of an emergency disconnect requirement, the piston 42 will stroke to de-support the dogs 40 and permit disconnection to be achieved. The first and second connector portions permit a high angle release to be achieved.

(19) The intervention system further comprises a retainer valve assembly 44 intermediate the stress joint assembly 28 and the emergency disconnect package 36. Specifically, the retainer valve assembly 44 is connected to the stress joint assembly 28 via the lower connector 32 of the stress joint assembly 28. Further, the retainer valve assembly is connected to the emergency disconnect package 36 via a hydraulic connector arrangement 46. In the example embodiment shown in FIG. 1 the retainer valve assembly includes a male connector portion 48 which is stabbed into a hydraulically actuated female connector portion 50 which is mounted on the emergency disconnect package 36 via flange connector 52.

(20) The retainer valve assembly 44 includes a ball valve 54 which is arranged to close in the event of an emergency disconnect, to retain fluids and any equipment in the connected riser and thus prevent release to the environment. In the embodiment shown the ball valve 54 is capable of shearing any equipment, such as coiled tubing or wireline, which might extend therethrough.

(21) A detailed description of the foil and construction of the well control package will now be provided, with additional reference to FIG. 2, which is an enlarged view of the intervention system 10 in the region of the well control package 14.

(22) The well control package 14 includes a ball valve apparatus 60 having an outer housing 62 which is split into an upper housing part 62a and a lower housing part 62b, connected together via a sealed flange connector 63. The housing 62 defines a structural housing and facilitates or accommodates load transfer when coupled within the entire system 10.

(23) A valve cartridge 64 is mounted within the housing 62 and is axially captivated between opposing shoulders 66, 68 provided within the respective housing parts 62a, 62b. Such axial captivation is achieved during assembly of the upper and lower housing parts 62a, 62b together.

(24) When the valve cartridge 64 is installed within the housing 62 an annulus 70 is established therebetween. As will be described in further detail below, this annulus 70 defines a leak chamber which collects and retains any fluid which may have leaked from the valve cartridge 64, thus providing a secondary barrier to leakage into the environment.

(25) The valve cartridge 64 defines a cartridge flow path 72 extending between a cartridge inlet 74 and a cartridge outlet 76, wherein the cartridge inlet 74 is arranged in fluid communication with a housing inlet 78 and the cartridge outlet 76 is arranged in fluid communication with a housing outlet 80. An inlet sealing collar 82 spans the interface between the cartridge inlet 74 and housing inlet 78. Similarly, an outlet sealing collar 84 spans the interface between the cartridge outlet 76 and housing outlet 80. Each sealing collar 82, 84 includes radial O-rings seals, and when in place the collars 82, 84 function to isolate the cartridge flow path 72, and indeed the flow path through the entire system 10, from the annulus 70. As such, any leakage from the seal collars 82, 84 can be addressed be retaining the leaked fluid within the annulus 70.

(26) The valve cartridge 64 is generally cylindrical and elongate in form, and comprises a cartridge housing 90 which is composed of multiple parts secured together via threaded collars 92. The connections between individual cartridge housing components is such that sealing is provided therebetween. Thus, in the event of any leakage at the connectors 92, any leaked fluid will become retained within the annulus 70.

(27) Although not illustrated in the drawings, the system further comprises a pressure sensor which is arranged to monitor pressure within the annulus 70, such that any leakage into the annulus 70 may be detected.

(28) In the embodiment illustrated the cartridge 64 comprises two axially arranged ball valve assemblies 94a, 94b mounted within the cartridge housing 90. Each ball valve assembly 94a, 94b includes a rotatable ball valve member 96a, 96b which comprises a through bore 98a, 98b. When each ball valve member 96a, 96b is rotated to align the respective through bores 98a, 98b with the cartridge flow path 72, the flow path 72 will be open and flow will be permitted. However, when each ball valve member 96a, 96b is rotated to misalign the through bores 98a, 98b from the cartridge flow path 72, as illustrated in FIGS. 1 and 2, the flow path 72 is closed and flow is prevented.

(29) In the embodiment illustrated each ball valve member 96a, 96b includes a leading cutting edge 100a, 100b which is capable of cutting an object, such as coiled tubing or wireline, which might extend through the well control package 14 at the time of closure of the ball valve members 96a, 96b. In such a case, the ball valve assemblies 94a, 94b may be considered to be shear and seal valves.

(30) Each ball valve assembly 94a, 94b includes an actuation arrangement 102a, 102b for selectively causing rotation of the respective ball valve members 96a, 96b. In the embodiment illustrated each actuation arrangement 102a, 102b includes a hydraulically operated piston sleeve 104a, 104b which is secured to a respective ball valve member 96a, 96b via a linkage mechanism (not shown). Further, each actuation arrangement 102a, 102b includes a baising spring 106a, 106b, specifically Bellville spring stacks, which provide a baising force on the respective piston sleeves 104a, 104b. In use, hydraulic pressure may be applied to the piston sleeves 104a, 104b to cause said sleeves to stroke and cause the ball valve members 96a, 96b to rotate towards their open positions via the linkage mechanisms, while also compressing or energizing the associated springs 106a, 106b. When hydraulic pressure is removed, either deliberately or in the event of an unintentional loss, the springs 106a, 106b act to return the respective pistons 104a, 104b and rotate the ball valve members 96a, 96b towards their closed positions. Thus, in the embodiment illustrated the ball valve assemblies 94a, 94b function as fail-closed assemblies.

(31) The provision of a valve cartridge 64 which is separate and distinct from the outer structural housing 62 can provide significant advantages. For example, the cartridge facilitates ease of assembly, and possible maintenance. Further, the separate cartridge can permit the presence of a secondary leak barrier, specifically the annulus 70 to be created.

(32) The well control package 14 further comprises a side port 110 in the side wall of the outer housing 62 at a location below the valve cartridge 64. This port can facilitate the ability to establish fluid communication with an associated well bore system even in the event of the valve cartridge 64 closing. In the example embodiment shown the port 110 is connected to a conduit 112 (via dual ball valves 114, 116), which can be arranged in fluid communication with a fluid source. Such an arrangement may permit a well kill fluid, for example, to be pumped into an associated well system, for example to regain well control.

(33) The well control package 14 further comprises an on-board hydraulic power system 120 which stores hydraulic power for use in an emergency system, such as when a remotely provided hydraulic power supply fails. Such an arrangement may define a dead-man safety system. Further, the well control package may comprise an ROV interface 122 to permit intervention by an ROV if necessary.

(34) Reference is again made to FIG. 1, in combination with FIGS. 3 and 4, wherein FIG. 3 is an enlarged view of a lower portion of the stress joint assembly 28, and FIG. 4 is a view of the stress joint assembly 28 from above. The intervention system 10 further comprises a control system 130 which is mounted around the stress joint assembly 28. The control system 130 includes a plurality of individual modules 132 which are circumferentially distributed around the pipe section 34 of the stress joint assembly 28, as most clearly illustrated in FIG. 4.

(35) The control modules 132 may comprise suitable hydraulic and/or electrical control systems required for proper operation of the well intervention system 10. In the specific embodiment shown the control system 130 includes four hydraulic accumulator modules 132a and two electrical control modules 132b. The electrical control modules 132b may be configured similarly or identically, which may provide a degree of redundancy within the system 10 in the event of failure of one of the modules 132b.

(36) In the embodiment illustrated the stress joint assembly 28 includes an annular support shoulder 134 extending from the lower wall section 34a of the stress joint pipe section 34. As described above, this lower wall section 34a is of a uniform wall thickness. The individual modules 132 are axially supported and connected to the stress joint assembly 28 via the annular support shoulder. Such an arrangement can permit the individual modules to be supported by the stress joint assembly 28 in a relatively compact manner. Further, as the annular support shoulder, and thus mechanical connection, is located at the portion of the stress joint pipe 34 which defines a uniform wall thickness, there will be minimal effect to the stress relief function of the adjacent tapering wall section 34b.

(37) Also, in the illustrated embodiment, the individual modules 132 are substantially evenly circumferentially distributed around the stress joint assembly. Such an arrangement may prevent any adverse bending loads being applied on the system 10.

(38) In the embodiment illustrated in FIG. 1, the retainer valve assembly 44 is connected to the emergency disconnect package 36 via a hydraulic connector arrangement 46, and specifically the retainer valve assembly 44 includes a downwardly facing male connector portion 48 which is stabbed into an upwardly facing hydraulically actuated female connector portion 50 which is mounted on the emergency disconnect package 36 via flange connector 52. However, in an alternative embodiment, as shown in FIG. 5, the connector arrangement, now illustrated by reference numeral 44a, includes a hydraulic connector 50a which is mounted on the retainer valve assembly 44, and a male connector portion 48a which is provided on the emergency disconnect package, specifically on the second connector portion 36b of the emergency disconnect package. As in the previous embodiment, this arrangement may permit the connector arrangement 46a to be broken to allow the upper stress joint assembly 28 and retainer valve assembly 44 to be retrieved to surface. However, as the hydraulic female connector portion 50a in the present embodiment is secured to the retainer valve assembly, this connector portion 50a can also be advantageously retrieved to surface and may be inspected, repaired or the like.

(39) Furthermore, by providing the male portion 48a on the emergency disconnect package 36, the additional flange 52 (FIG. 1) may be eliminated.

(40) In the embodiment described above the intervention system 10 is configured for use with a horizontal Christmas tree by use of a specific monobore adaptor 16. However, the system 10 may be utilized in combination with alternative wellhead infrastructure by use of an alternative adaptor and some possible reconfiguration of associated hydraulic lines. In one embodiment, as illustrated in FIG. 6, the same intervention system 10 (in this case the stress joint assembly 28 and retainer valve assembly 44 are not shown for clarity) as first illustrated in FIG. 1 may be utilized in combination with a vertical Christmas tree (not shown), by use of a specific adaptor 200 which replaces adaptor 16 (FIG. 1). Specifically, adaptor 200 is interposed between the well control package 14 and the tree connector 12. The adaptor 200 includes a primary bore 202 which is aligned with the bore extending through the intervention system 10 and establishes communication with a production wellbore, and a secondary bore 204 which is intended to communicate with a wellbore annulus. The fluid conduit 112 is fluidly coupled to the secondary bore 204 and may facilitate fluid communication into a wellbore annulus separately from the production bore. As illustrated in FIG. 6, the side wall port 110 is sealed by a cap plate 206.

(41) It should be noted that all features relating to the intervention system 10 of FIG. 6 are largely as presented in relation to FIG. 1, and as such no further description will be provided.

(42) FIG. 7 provides a further alternative use of the intervention system 10 (the stress joint assembly 28 and retainer valve assembly 44 again not shown for clarity) by employing a further alternative adaptor arrangement, in this case identified by reference numeral 300. It should be understood that the intervention system 10 largely remains as illustrated in FIG. 1, and as such no further detailed description will be given.

(43) In this embodiment the adaptor 300 includes a dual bore sub 302 which includes a primary bore section 304 and an annulus bore section 306. When the system 10 is secured in this case to a vertical Christmas tree, the primary bore section 304 is aligned with a primary production bore, and the annulus bore section 306 is aligned with a wellbore annulus. The annulus bore section 306 may comprise a valve assembly 307, such as a ball valve assembly.

(44) The adaptor 300 further comprises a bore selector sub 308 which is interposed between the well control package 14 and the dual bore sub 308. The bore selector sub may be provided in accordance with the bore selector disclosed in U.S. Pat. No. 6,170,578, the disclosure of which is incorporated herein by reference.

(45) The bore selector sub 308 includes a pivoting plate 310 which is mounted within the bore selector sub 308 to pivot about pivot point 312. An hydraulically operated actuator sleeve 314 is connected to the side of the plate 310 via a pin and slot arrangement 316, such that stroking of the sleeve 314 causes the plate 310 to pivot, thus providing bore selection to allow a tool or other component to be inserted into the selected bore (either bore 304 or bore 306) via the intervention system 10.

(46) In the embodiments described above, the intervention system is intended to be secured to a surface vessel via a riser. However, in other arrangements the intervention system may permit a wire-in-water type wireline intervention system to be established. Such an arrangement is diagrammatically illustrated in FIG. 8, reference to which is now made.

(47) In this embodiment the intervention system 10 is largely as first defined with reference to FIG. 1, and as such comprises an adaptor 16, well control package 14, emergency disconnect package 36, retainer valve 44 and stress joint assembly 28. No further detailed description of these components will be provided, except to say that in the diagrammatic illustration of FIG. 8 the system 10 is shown connected to a horizontal Christmas tree 350 which in turn is mounted on a well head 352. In the present embodiment the stress joint assembly 28 of the intervention system 10 is secured to a lubricator stack and a stuffing box 360 which permits sealed insertion of wireline 362 into the intervention system.

(48) It should be understood that the arrangements shown in FIGS. 6 and 7 may also be modified in the same manner as in FIG. 8 to provide a wire-in-water system. Reference is now made to FIGS. 9A to 9J which illustrate an exemplary procedure for deploying the system 10 first shown in FIG. 1.

(49) Referring initially to FIG. 9A, the deploying vessel includes a drill floor 400 which includes a rotary table 402. Located below the drill floor 400 is a cellar deck 404 which includes a moonpool 406 aligned directly below the rotary table 402. Such an arrangement is quite typical of many vessels, such as Category B type vessels, which may provide more readily availability and attract lower rental rates compared with other vessel types, such as Category C vessel types. This may present significant cost savings to an operator.

(50) During the initial deployment stage, as illustrated in FIG. 9A, a lower portion 10a of the system 10 is mounted on a skid 408 on the cellar deck 404. Specifically, the lower portion 10a of the system 10 includes the connector 12, adaptor 16, well control package 14, emergency disconnect package 36 and the female connector portion 50 of the hydraulic connector 46. An upper portion 10b, which includes the male stab-in connector 48, retainer valve 44 and stress joint assembly 28, is prepared for pick-up.

(51) During the subsequent step, as illustrated in FIG. 9B, the lower portion 10a of the system is moved to be positioned over the moonpool 406 and below the rotary table 402 via the skid system 408, and the upper system portion 10b is then picked-up and hoisted above the drill floor 400 and aligned with the rotary table, as illustrated in FIGS. 9C and 9D.

(52) The upper system portion 10b may then be lowered through the rotary table, which is permitted by the precise design of the system, and connection to an associated umbilical 410 made, as illustrated in FIG. 9E. In this respect this particular running sequence enabled by the particular system design 10 advantageously facilitates connection of the umbilical 410 to be made by personnel safely working at the level of the drill floor 400. In other systems in which passage of any part of an intervention system through a rotary table (which may be less than 126 cm (49.5 inches)) is not possible, such connections would need to be made by personnel working at significant height, for example above the cellar deck 404, via man-rider systems and the like, which exposes personnel to risk.

(53) Following this the upper system portion 10b may be lowered until the male connector portion 48 stabs into the hydraulic female connector portion 50, with the complete connected system illustrated in FIG. 9F. In this respect, the use of a hydraulic connector for establishing the connection between the upper and lower system portions 10a, 10b eliminates any requirement for personnel to work at height over the cellar deck 404.

(54) Subsequent to this, the entire system 10 may be lifted from the skid 408, as in FIG. 9G, with the skid 408 subsequently retracted, as in FIG. 9H. The system 10 may then be lowered further until the upper end may be hung via slips set in the rotary table 402, as shown in FIG. 9I. At this stage a first riser section 412 may be secured to the upper end of the system 10, again from the level of the drill floor 400. The system 10 may then be released from the slips in the rotary table 402, and subsequently lowered further, now passing through the moonpool 406, as shown in FIG. 9J. The system 10 may once again be suspended, this time via slips engaging riser section 412, permitting a further riser section 414 to be connected, again from the safe level of the drill floor 400. Also, personnel working on the drill floor 400 may readily and safely attach clamps 416 for securing the umbilical 410 to the riser section.

(55) This procedure may be repeated until the total water depth has been reached, and the system 10 can be landed on a Christmas tree.

(56) It should be understood that the embodiments described herein are merely exemplary, and that various modifications may be made thereto without departing from the scope of the invention.