GB2372062A - A method of installing a ROV deployed tree cap for a subsea tree - Google Patents

Abstract

A method of installing a Christmas tree cap (28) on a subsea Christmas tree which has a projecting upper hub (10) to receive the cap (28), involves lowering and latching the cap (28) to the tree. The tree cap (28) has an outer latch (36) for latching onto the outer peripheral surface of the upper hub (10) and a fluid operated inner latch (76) for latching onto the inner peripheral surface of the upper hub (10) and a seal plate (68) for sealing the production (13) and annulus (15) bores. To connect the cap (28) to the tree, the cap (28) is lowered onto the hub (10) and the cap (28) latched to the outer surface of the hub (10). The seal plate (69) moves downwardly relative to the tree cap (28) against the projecting hub (10) of the Christmas tree to seal the production (13) and annulus (15) bores. Finally the seal plate (68) is latched to the inner surface of the hub (10) using the fluid operated latches (76). The cap (28) can be made of a lightweight plastic material.

Description

APPLICATION FOR PATENT TITLE: ROV DEPLOYED TREE CAP FOR A SUBSEA TREE AND METHOD OF INSTALLATION BACKGROUND OF THE INVENTION Reference to Related Provisional Application This application claims the benefit of provisional application serial no.

60/067, 434 filed December 3,1997.

Field of the Invention This invention relates generally to the field of equipment and methods of installation thereof of subsea wellhead equipment. In particular, the invention concerns a ROV deployed cap for a Xmas tree for a subsea well and the method of installing and retrieving the tree cap.

Background and Objects of the Invention Prior tree caps have been installed by using a drill pipe connector arrangement.

Prior tree cap design has been elaborate, almost a piece of art. Extensive machining and weight issues became the norm. An extra trip of the drill pipe was required simply to retrieve or lower the tree cap. As the offshore oil industry moves to deeper and deeper depths, the time that it takes to lower or retrieve the tree cap with drill pipe will cost a well operator thousands of dollars in rig time alone.

Accordingly, a primary object of the invention is to provide a light weight ROV installable tree cap for a subsea Xmas tree.

Another object is to provide a method of installing and retrieving the tree cap by using pressure fluid apparatus for stabbing the cap in place on the production hub and for retrieving the cap.

SUMMARY OF THE INVENTION It is important that the tree cap when installed by a ROV (Remotely Operated Vehicle) onto a subsea Xmas tree, have the capability to stab the production and annulus seal stabs into the pockets of the tree re-entry hub. According to a preferred embodiment of the invention, two spring loaded pins latch onto the O. D. (outer diameter) hub profile of the re-entry hub initially locking the tree cap to the hub.

Pressure is applied on top of the seal plate, and the seal stabs into place. During this operation, the reaction force is taken by the spring loaded latch pins. Next, pressure is applied on top of the piston which extends the locking segments out into the I. D. (inner diameter) groove of the re-entry hub, thereby locking the tree cap to the re-entry hub.

Force generated by pressure below the seal stabs is transferred to the hub via the seal plate and the locking segments. Thus, the locking sequence is a two step process. The normal retrieval operation for removal of the cap from the Xmas tree includes applying fluid pressure for releasing the locking segments and for lifting the seal plate from sealing relation. Then, the latch pins are retracted and the cap is lifted by the ROV gripping a release handle.

The tree cap is arranged and designed to receive a fluid coupler installed by the ROV to provide pressure fluid to the cap for forcing the seal plate into firm stabbing position with the Xmas tree production hub and to provide high pressure fluid to a piston for forcing the locking segments into a releasably locked position with the production hub. During the retrieval operation, pressure fluid is normally provided to the piston to move the piston out of the locking position of the locking segments. Then, pressure fluid is applied beneath the seal plate to move the seal plate out of sealing relation with the production hub. Next, the spring loaded latch pins are retracted from engagement with the production hub to permit removal of the cap by lifting of the release handle on the cap.

The tree cap is designed to have a weight under about 100 pounds when submerged so that it may be easily handled by a ROV. The tree cap utilizes various plastic components which have densities approximately the same as seawater. The body of the tree cap is formed of a lightweight non-metallic plastic material to define a pair of generally parallel sides connected by upper and lower ends. The lower end has a suitable opening for mounting of a metallic sealing member therein. The upper end of the non-metallic body has a plurality of mounting positions for various control elements. Handles extend upwardly from the control elements for grip. ig by manipulator arms of a ROV for controlling the installation and retrieval of the tree cap.

Other objects, features, and advantages of the invention will be apparent from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The objects, advantages, and features of the invention will become more apparent by reference to the drawings which are appended hereto and wherein like numerals indicate like parts and wherein an illustrative embodiment of the invention is shown, of which: Figure I is a sectional view of the ROV deployed tree cap comprising the present invention shown in an installed position on the production hub of a subsea Xmas tree; Figure 2 is a top plan of the ROV deployed tree cap shown in Figure I removed from the subsea production hub; Figure 3 is a front elevation of the tree cap shown in Figure 2; Figure 4 is an end elevational view of the tree cap shown in Figures 2 and 3; Figure 5 is an enlarged section taken generally along line 5-5 of Figure 3; Figure 6 is an enlarged section taken generally along line 6-6 of Figure 3; Figure 7 is an enlarged fragment of Figure 1 showing fluid lines for actuation of the piston for camming locking segments into a releasably locked position on the tree hub ; Figure 8 is an enlarged fragmentary view of Figure 1 showing the locking segments cammed outwardly by the piston into locking engagement with an internal groove of the production tree hub; Figure 9 is an enlarged sectional view of a latch pin for initially engaging the outer grooved profile of the production tree hub; Figure 10 is a sectional view of a needle valve assembly for controlling the hydraulic fluid flow to the seal plate for retrieval of the tree cap from the subsea tree hub; Figure 11 is a perspective of the lightweight molded plastic body of the tree cap with all of the separate members removed therefrom; Figure 12 is a view similar to Figure 1 but showing the tree cap in an initial position on the production tree hub with only a pair of latch pins engaging the tree hub; and Figure 13 is a view similar to Figure 12 but showing the tree cap in an intermediate position with the seal plate in a landed position on the production hub and the tubular seal members projecting from the seal plate stabbed and sealed within the production bore and annulus bores of the tree hub.

DESCRIPTION OF THE INVENTION Referring now particularly to Figure 1, a Xmas tree production hub is shown generally at 10 having an outer annular groove 12, an inner horizontal landing shoulder 14, an inner annular groove 16 above landing shoulder 14, and an upper planar end surface 18. Hub 10 has a production bore 13 and an annulus bore 15 therein. An outer funnel guide shown generally at 20 is supported on a flange 22 extending from hub 10 and has an inner tapered guide surface 24. Y-shaped slots 26 extend in a generally vertical direction, and a pair of opposed upper slots 25 is provided along the upper surface of funnel guide 20.

The lightweight ROV deployed tree cap is shown generally at 28 in an installed position on hub 10 of the Xmas tree. Tree cap 28, as will be explained below, has been lowered into the sea with an ROV by suitable tethers from a surface location as well known. The ROV is disengaged from the tethers at about one hundred feet above the mudline. The ROV manipulator arm then grasps a handle on tree cap 28 to disengage tree cap 28 from the tethers and then lowers the tree cap into funnel guide 20.

Tree cap 28 has a body generally indicated at 30 as shown particularly in Figure 11 formed of a non-metallic lightweight material such as polypropylene which is a thermoplastic polymer. Other plastic and composite materials may be used in forming body 30, such as fiberglass, polyethylene, or polyurethane, for example. Body 30 may be cast, molded or formed from a sheet material. The integral one piece non-metallic body 30 is shown in Figure 11 before any of the various separate elements or members are mounted thereon. The utilization of a lightweight body permits a lightweight tree cap having a submerged weight of less than about 100 pounds, while the tree cap weighs about 225 pounds out of water. Body 30 has a pair of generally parallel

opposed sides 27 connected by an upper end 29 and a lower end 31. A lower opening 33 is provided in lower end 31. Various mounting positions or bases 35 are provided in openings or slots along upper end 29. Body 30 has extensions 32 (see Figure 1) which are received within the Y-slots 26 of funnel guide 20 for initial alignment of body 30 with hub 10. Upper arms 34 register with upper surfaces 25 of funnel guide

20 for further alignment of body 30 with hub 10. The density of the solid lightweight material of body 30 approximates the density of seawater. Since tree cap 28, including all of the members mounted thereon, has a submerged weight of less than about 100 pounds, an ROV can easily maneuver tree cap 28.

A pair of opposed generally identical latch pins 36 are mounted within bores 37 in body 30 as shown in Figures 1 and 9 with the ends of pins 36 received within outer annular groove 12 of hub 10 in latched relation. Spring 38 urges pin 36 outwardly. A flexible cable or rope 40 has an enlarged end 42 fitting within a central bore 44 of pin 36 and is adapted to contact annular shoulder 46. The upper end of flexible cable 40 is looped about an indicator pin 47 which extends through an opening in body 30 for visual observation to determine the position of pin 36. Indicator pin 47 is connected to an externally threaded rod 48 received within an internally threaded sleeve 50 connected to a handle 52. Upon rotation of handle 52, flexible cable 40 is pulled upwardly with enlarged end 42 contacting shoulder 46 to withdraw latch pin 36 from latching relation with production tree hub 10. Latch pin 36 is retained within bore 37 by retainer ring 54 and is continuously urged outwardly by spring 38.

Mounted within lower opening 33 (see Figure 11) in body 30 is a metallic sealing structure including an outer housing 58 fixed to body 30 by studs 59 (see Figure 3) and having an outer ring 60 with a downwardly extending outer flange secured by studs 62 (see Figure 1) to body 30 and adapted for fitting over the upper end 18 of hub 10. Mounted for reciprocal movement within fixed housing 58 is a seal plate assembly 64 comprising an upper cylindrical piston 66 having a lower seal plate 68 thereon including a pair of projecting tubular stab members or plugs 70,72 for stabbing and fitting in sealing relation with production bore 13 and annulus bore 15 of tree hub 10.

Suitable annular elastomeric seals 74 extend about tubular stab members 70, 72 for J effective sealing against bores 13 and IS. A pair of locking segments 76 are supported on the upper surface of plate 68 by retainer bolts 78 received within enlarged openings 80 as shown particularly in Figure 8. Position indicator rods 82 are secured to seal plate 68 to indicate the position of seal plate 68 and may be viewed in openings 84 in body 30 to determine if seal plate 68 is seated on shoulder 14 of hub 10 as shown in Figure 1. Figure 5 shows retaining means for releasably holding seal plate assembly 64 in an upper unsealed relation with hub 10. For releaseably retaining piston 66 and seal plate 68 in an upward position, spring urged retainer pins 81 fit within annular groove 83 until seal plate assembly 64 is forced downwardly by fluid pressure into sealing relation with hub 10 as shown by the position in Figure 5 and as will be explained further.

To lock locking segments 76 within annular groove 16 of hub 10, an annular piston 86 extends about inner solid piston 66, and a fluid chamber 88 is provided

adjacent the upper end of outer annular piston 86 as shown particularly in Figures 7 and qu 8. A pair of piston release rods 80 are secured at their lower ends to the upper end of

piston 86 and secured at their upper ends to a handle 92. Handle 92 is shown in a retracted position in Figure 1 to indicate that locking segments 76 are in locking relation with tree hub 10. When handle 92 is in a projected position as shown in Figures 12 and 13, piston 86 is withdrawn from engagement with locking segments 76 and locking segments 76 are removed from annular grooves 16 of tree hub 10. Handle 92 is not normally utilized to release piston 86 from engagement with locking segments 76 but may be used, such as in an emergency, for release of locking segments 76 to permit removal or retrieval of tree cap 28. Handle 92 is also utilized by manipulator arms of the ROV for lifting and maneuvering cap 28 As shown particularly in Figure 7, an hydraulic fluid passage 94 in solid piston 66 communicates with the upper end of fluid chamber 88, and hydraulic fluid passage 96 in solid piston 66 communicates with the lower end of fluid chamber 88. To supply fluid to fluid passages 94,96 a so-called hot stab fluid coupler 98 is releasably pushed by handle 99 within a bore in receptacle 100 in body 30 by an ROV manipulator arm. Fluid lines 102 from an ROV supply hydraulic fluid through fluid passages 104 of coupler 98 to suitable lines 106 to fluid passages 94,96. After tree cap 28 has been installed, hot stab coupler 98 is removed by the ROV by lifting of handle 99 and a dummy stab which is carried in a receptacle on tree cap 28 is positioned within the bore of receptacle 100 to keep foreign matter and the like from receptacle 100.

To retrieve tree cap 28 and to remove tubular seal members 70 and 72 from sealing engagement with production bore 13 and annulus bore 15 of tree hub 10, it may be necessary to apply fluid pressure beneath seal plate 68. For that purpose, a main fluid passage 108 is provided in solid cylinder 66 to production bore 13 and a branch fluid passage 110 is provided in solid cylinder 66 to annulus bore 15. High pressure hydraulic fluid is supplied from the ROV through a hot stab coupler 112 which is received within a bore in receptacle 114 in body 30 by pushing of handle 116 by an ROV manipulator arm. Hydraulic fluid line 118 from the ROV supplies fluid through fluid passage 120 in hot stab coupler 112. Fluid from fluid passage 120 is supplied through line 122 to a needle valve assembly shown generally at 124 in Figure 10. A fluid outlet line 126 from needle valve assembly 124 extends to main fluid passage 108 in cylinder 66. Needle valve assembly 124 shown in Figure 10 has a handle 128 secured to shaft 130 which is threaded within outer sleeve 132. The end of shaft 130 contacts needle plug 134 to control the flow of fluid from line 122 to line 126 and fluid passage 108.

Installation of Tree Cap 28 Tree cap 28 is shown in a final installed position in Figure 1. Figures 12 and 13 show initial and intermediate stages of installation with tree cap 28 being controlled by the manipulator arms of an ROV (not shown). Prior to tree cap 28 being in the position of Figure 12, tree cap 28 has been lowered subsea with an ROV by suitable tethers from a surface location. The ROV is disengaged from the tethers at about a hundred feet above the mudline. The ROV manipulator arm then grasps tree cap 28 by handle 92 to disengage tree cap 28 from the tethers and then lowers tree cap 28 into funnel guide 20. Tree cap 28 is aligned within funnel guide 20 by Y-shaped slots 26 and a pair of opposed upper slots 25 along the upper surface of funnel guide 20.

Extending arms 34 of cap 28 fit within slots 25.

After tree cap 28 is positioned within funnel guide 20 as shown in Figure 12 with ring 60 fitting over hub 10, low pressure fluid coupler 98 along with high pressure fluid coupler 112 are installed by the ROV by inserting couplers 98 and 112 from handles 99 and 116 within the respective receptacles 100 and 114. Seal plate 68 is spaced from landing shoulder 14 on tree hub 10, and indicator rods 82 are in the raised position to indicate that seal plate 68 is not seated. Retainer pins 81 as shown in Figure 5 are in engagement with groove 83 which releasably holds seal plate 68 in unseated relation. Also, handle 92 is in a raised position to indicate that annular piston 96 is not in locking engagement with locking segments 76. The spring loaded latch pins 36 retract as the tree cap 28 is lowered over hub 10 and then project outwardly into engagement with annular groove 12 on hub 10. Pressurized hydraulic fluid is then applied through line 96 from coupler 98 to fluid chamber 88 to urge the piston 66 and seal plate 68 downwardly relative to housing 58 while annular piston 86 reacts the fluid pressure. Seal plate 68 is then seated on shoulder 14 with indicator pins 82 being in a down position which can be easily observed. Tubular stab members 70,72 are stabbed and sealed within bores 13 and 15 by elastomeric seal rings 74. Locking segments 76 remain in an unlocked position and handle 92 remains in a projected relation indicating that annular piston 86 has not moved into locked relation with locking segments 76.

From the position of Figure 13 which shows the indicator rods 82 in a down position and with sealing plate 68 seated on shoulder 14, fluid is applied from coupler 98 through line 94 to move annular piston 86 downwardly to cam locking segments 76 outwardly within locking groove 16 in hub 10. In this position, indicator handle 92 is moved downwardly by indicator rods 90 to the position shown in Figure 1 which indicates that tree cap 28 is in the installed position. In the installed position, the hot stab couplers 98 and 112 may be removed by the ROV by gripping of handles 99 and

116 for pulling the couplers 98 and 112 from receptacles 100, 114 on body 30. Prior to removal of the fluid pressure couplers 98 and 112, the high pressure coupler 112 may be utilized to test, vent or inject chemicals for the production and annulus bores 13 and 15. A three-way valve on a ROV manifold is controlled for performing the test. After the tests have been completed, the fluid lines are vented and couplers 98 and 112 are removed. Dummy couplers are then inserted within receptacles 100,114 to prevent the entrance of debris and the like in the receptacles. The fluid couplers 98 and 112 are positioned within suitable parking receptacles on the tree frame for future use, such as retrieval or removal of tree cap 28.

Retrieval Tree Cap For removal or retrieval of tree cap 28 from the installed position shown in Figure 1, the dummy stab members are removed from the low pressure and high pressure receptacles 100 and 114. Then, the low pressure and high pressure fluid couplers 98 and 112 are removed from their parking receptacle openings and are then pushed downwardly by manipulator arms of the ROV into receptacles 110 and 114.

Fluid is then applied through coupler 98 and fluid passage 96 to lift piston 86 upwardly from engagement with locking segments 76. Indicator rods 90 and handle 92 move upwardly to indicate that latch members 76 have been unlatched. Locking segments 76 are now free to retract. Next, high pressure fluid is applied through coupler 112 and line 122 to needle valve 124, and thence through fluid lines 108 and 110 to move seal plate 68 upwardly. Locking segments 76 are cammed inwardly to an unlatched position, and seal plate 68 moves upwardly until tubular seal members 70 and 72 are out of sealing relation with production bore 13 and annulus bore 15. Indicator rods 82 may be visually observed to indicate the position of seal plate 68 and associated tubular seal members 70 and 72.

Latch pins 36 are in engaged position with annular groove 12. For removal of latch pins 36, handles 52 are rotated by the manipulator arms of the ROV to pull flexible cables 40 upwardly with enlarged ends 42 contacting shoulders 46 thereby to retract pins 36 and remove pins 36 from groove 12. Upon removal of latch pins 36, handle 92 is gripped by a ROV manipulator arm and lifted upwardly for removal of tree cap 28 from hub 10.

From the above, an ROV deployable tree cap 28 has been provided including a plastic body 30 on which all of the operating elements and members of the tree cap 28 are mounted. Handles 52,92, 99, and 116 are easily accessible from upper end 29 of cap body 30 by manipulator arms of the ROV. Mounting bases 35 on body 30 provide for mounting and ROV accessibility of the various control elements utilized by the ROV. The seal plate assembly 64, locking segments 76, and annular piston 86 are formed of metal such as Inconel 718. However, the remaining non-pressure bearing elements and the outer housing may be formed of a lightweight plastic or composite material, preferably a high density, high molecular weight plastic material, such as polypropylene, for example. As a result, a tree cap 28 having a submerged weight less than about 100 pounds is provided. Since an ROV is capable of physically handling the tree cap 28, the tree cap may be removed and replaced subsea without having to make an extra trip with drill pipe.

According to another feature of the invention, a tree cap 28 may be initially stored on the tree frame. The tree cap may be removed from its storage position on the tree frame and installed on the tree hub 10, with the ROV. All such operations are accomplished rapidly with the ROV without an additional trip to the surface.

Alternatively, a spare tree cap may be stored on the tree frame. If another tree cap is damaged, the damaged tree cap is withdrawn from the tree hub, stored on the sea floor or on the tree frame, and the spare tree cap is installed on the tree hub 10, with the ROV.

The present invention and the best modes of practicing it have been described.

It is to be understood that the foregoing descriptions are illustrative only and that other means and techniques can be employed without departing from the full scope of the invention as described in the appended claims.

Claims (2)

Claims :

1. A method for installing a subsea Xmas tree cap on a subsea Xmas tree above the mudline; the subsea Xmas tree having a projecting upper hub to receive the tree cap including a production bore and an annulus bore, said upper hub having an outer peripheral surface and an inner peripheral surface, the method comprising the steps of : providing the tree cap with an outer latch means for latching onto the outer peripheral surface of said upper hub, a fluid operated inner latch means for latching onto the inner peripheral surface of said upper hub, and a seal plate for sealing the production bore and the annulus bore; lowering the tree cap onto said hub, latching said cap with said outer latch means onto the outer surface of said hub; moving said seal plate downwardly relative to said tree cap against said projecting upper hub of said xmas tree to provide a sealing relation with said production bore and annulus bore; and then latching said seal plate with said fluid operated inner latching means to the inner peripheral surface of said upper hub.

2. A method according to claim 1 including the steps of : providing fluid pressure means for moving said seal plate downwardly into sealing relation with said upper hub; and providing fluid pressure to said fluid operated inner latch means after said seal plate is in sealed relation to urge said fluid operated inner latch means into releasable locking position with said inner peripheral surface of said upper hub.