US20040262010A1

US20040262010A1 - Horizontal tree assembly

Info

Publication number: US20040262010A1
Application number: US10/874,714
Authority: US
Inventors: Lionel Milberger
Original assignee: Dril Quip Inc
Current assignee: Dril Quip Inc
Priority date: 2003-06-26
Filing date: 2004-06-22
Publication date: 2004-12-30
Also published as: WO2005001233A2; WO2005001233A3

Abstract

A horizontal spool tree assembly includes a spool body or housing 12 and a tubing hanger 18, 118, 218, 318 supporting a tubing string in a well. An internal tree cap 20, 120, 220, 320 is provided within the central bore in the spool body. In some embodiments, the tree cap includes a central bore in communication with a production bore through the tubing hanger and the lateral bore extending to a production port in the spool body. First and second closure members may be provided in the tree cap.

Description

RELATED CASE

This invention claims priority from U.S. Ser. No. 60/482,727 filed on Jun. 26, 2003.

1. Field of the Invention

The present invention relates to horizontal trees used in the construction of subsea wells. The horizontal tree provides lateral access to the various internal flow passages of the well, such as the flow passage associated with the production fluids and the annular passage between concentric tubulars in the completed well. The top of the horizontal tree is accessible to blowout preventors, risers, and other equipment that extends vertically to the surface of the water above the subsea completion for use in completing, treating or reworking the well.

2. Background of the Invention

Subsea wells are frequently completed with a “horizontal tree”, i.e., a production system which contains one or more hangers in a spool body with a lateral production passageway in fluid communication with a production tubing string, and a tree cap above the tree hanger. A port through the spool body passes production fluids from the production tubing laterally through the spool body and then to the surface via a production flow line. Retrievable plugs may be installed in the bores of both the tree cap and the tubing hanger. Exemplary prior art is disclosed in U.S. Pat. Nos. 5,544,707, 5,706,893, 6,050,339, 6,039,119, 6,227,300, 6,470,968 and 6,650,339. Relevant publications are U.S. 2001/0011593, 2002/000322, 2002/0000315, 2003/0089501 and WO01 /73259.

Various types of equipment and techniques have been proposed for the workover of horizontal spool tree wells. Workover operations are conventionally performed utilizing a floating drilling rig with a subsea BOP connected to the top of the horizontal spool tree, and a drilling riser connected to the top of the BOP. When a big bore riser and a BOP stack are placed on top of the tree, various types of workover operations may be performed, including pulling and reinstalling the tubing. One or more workover strings provide fluid communication with the horizontal spool tree assembly, with the workover fluid passing to the tubing annulus. A running tool may be used to seal off the top of the tubing hanger and to pull a plug if one is provided in the top of the tubing hanger to close off the tubing string.

Workover porting of the tubing annulus may be accomplished utilizing a valve in a flow line extending through the tubing hanger for fluid communication with the tubing annulus. Valves external of the spool body or within the spool body have alternatively been used to route the tubing annulus line around the tubing hanger to various locations within the spool body.

Horizontal spool trees also desirably provide a crossover line between the production line and the annulus line. If for some reason the production line needs to be shut down, flow may be diverted through the crossover line to the annulus line and then to the production platform. The crossover flow line is thus located closely adjacent the horizontal spool tree assembly, and conventionally is located within twelve feet of the production bore.

Horizontal spool trees also include an annulus port and an annulus line which conventionally extends from the spool tree assembly to the production platform. The annulus line enables excessive annulus pressure to be bled off, thereby maintaining a desired pressure differential between the interior and the exterior of the tubing string.

The disadvantages of the prior art are overcome by the present invention, and a horizontal spool tree with improved porting is hereafter disclosed.

Summary of the Invention

In one embodiment, the horizontal spool tree assembly includes a spool body defining a spool body central bore for receiving a tubing hanger, with the tubing hanger having a production bore extending axially therethrough for fluid communication between the production tubing string and a lateral port extending from the production bore in the tubing hanger and in communication with a lateral production port.through the spool body. A tree cap positioned above the tubing hanger has a vertical bore therein, and includes first and second closure members each received within the vertical bore in the tree cap for closing off flow through the tree cap. A sleeve-shaped guide extends substantially from a lower face on the tree cap to an upper face on the tubing hanger and has the guide passageway aligned with the tubing hanger production bore and the vertical bore in the tree cap.

In another embodiment, the tubing hanger has a lateral port extending from the production bore in the tubing hanger and in communication with the lateral port through the spool body. A tree cap positioned within the central bore of the spool body above the tubing hanger has a vertical bore therein. A crossover flow path extends laterally through at least a portion of the spool body between upper and lower seals on the tree cap and then laterally through a portion of the tree cap and downward into the spool body central bore. The crossover flow path is in selective fluid communication with the annulus line. A first closure member may be provided within the production bore of the tubing hanger or in the vertical bore in the tree cap, and a second closure member may be provided within the vertical bore in the tree cap.

In another embodiment, a tubing hanger has a production bore extending axially therethrough. A tree cap is positioned within the central bore of the spool body and has a vertical bore therein and a lateral bore extending from the vertical bore to a production port through the spool body. The first and second closure members are each provided within the vertical bore in the tree cap above the lateral bore for closing off flow through the tree cap.

These and further features and the advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a horizontal spool tree assembly with a lateral production port in the tubing hanger. [0015]
FIG. 2 is another embodiment of a horizontal spool tree assembly with a lateral production port in the tubing hanger and a crossover flow path extending through a portion of the tree cap. [0016]
FIG. 3 is another embodiment of a horizontal spool tree assembly with a lateral bore in the tree cap in communication with a production bore in the tubing hanger. [0017]
FIG. 4 is an alternate embodiment of horizontal spool tree assembly with an annulus line extending vertically through the tubing hanger and a lateral port in the tree cap in communication with the production line. [0018]

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a horizontal tree indicated generally at [0019] 10, constructed in accordance with the teachings of the present invention. The tree 10 includes a tree housing 12 connected to the upper end of a production casing 14. The horizontal tree 10 is positioned at the bottom of a body of water with the production casing 14 extending through the bottom of the water and into a subterranean petroleum bearing formation, in customary fashion.
A [0020] production tubing string 16 is suspended internally from the tree housing 12 by a tubing hanger 18. Annular, elastomeric seals 18 a and 18 b, spaced axially from each other, provide sealing engagement between the tubing hanger 18 and the surrounding wellhead housing 12. The top opening of the tree housing 12 is closed at its upper end by a tree cap 20. The tree cap 20 may be removed to permit vertical access from above the well during the completion or workover process. Two tree cap valves 22 and 24 close the vertical entrance to the tree. Two valves are employed to meet the regulatory restrictions requiring a working and a backup closure for sealing fluid containing passages in the submerged well structure. The valves 22 and 24, like all other vertically accessible valves in the illustrated embodiments, may be wireline retrievable plugs or may be in-place, remotely operated valve devices that can be opened or closed from the surface to provide access or to limit flow through the tree passages. Both plugs and valves are referred to herein as closures.
Access into the [0021] production tubing 16 is made possible by removal of tree cap 20, and removal or spacing of retrievable plugs 22 and 24. Annular, elastomeric ring seals 20 a and 20 b provide a leak proof connection between the tree housing 12 and the tree cap 20. One or more axially spaced seals between the tree cap and the housing 12 are preferably provided.
The [0022] tree cap 20 may be connected with a tubular guide 20 c that extends between the tree cap 20 and the tubing hanger 18 to assist in directing tools into the inside of the tubing string 16 during workover and completion procedures.
Communication of fluids from within the [0023] tubing 16 is provided via a central tubing hanger production bore and a horizontal or lateral port 18 c extending laterally through the tubing hanger between the axially spaced seals 18 a and 18 b. An annular communication space 25 formed between the tubing hanger 18 and the wellhead housing 12, and disposed axially between the two spaced seals 18 a and 18 b, provides 360° communication with a laterally extending port 12 a through the tree housing 12. The annular space 25 ensures communication between the production tubing 16 and the tree housing port 12 a regardless of the circumferential orientation of the port 18 c relative to the port 12 a. Although not expressly illustrated in the various figures, such a communication space may be provided at any juncture of radial ports that communicate between relatively rotatable components. Axially spaced seals on either side of the ports may be used to maintain sealing integrity between the two engaged components.
[0024] Dual production valves 26 and 28 control the opening of the port 12 a for flow between the production tubing string 16 and the production flow line 30.
The top of the production tubing string communicates through an annular space [0025] 32 with a lateral port 12 b formed in the sidewall of the tree housing 12 vertically between the tree cap 20 and the tubing hanger 18. Communication from the tubing string 16 to the port is permitted via a lateral port 20 d formed in the side of the guide 20 c, with port 20 d generally aligned with lateral port 12 b. A valve 34 regulates fluid communication between the annular space 32 and a flow line connector 36.
A [0026] lateral annulus port 12 c extending through the tree housing 12 communicates an annular space 40 between the production casing string 14 and the production tubing string 16, with an external valve 42 used to regulate the flow into a T-Connector 44 connected to the flow line 36. A valve 46 connected to the T-Connector 44 regulates communication with annulus flow line 48. The flow line 48 may be in communication with either the production fluids in the tubing 16 during a crossover operation or with the annulus fluids in the annular area 40, depending upon the open or closed condition of the various valves 34, 42, 46, 26 and 28.
The [0027] guide 20 c extends at least substantially between a lower surface or substantially planar face of a tree cap 20 and an upper surface or face of the tubular hanger 18. As noted above, the guide 20 c assists in directing tools into the interior of the tubing string 16, and also acts to prevent the buildup of debri in the annular space 32 between the tree cap and the tubular hanger. The embodiment shown in FIG. 1 advantageously includes the guide 20 c secured to the cap 20, although in other embodiments the guide could extend substantially upward from the tubing hanger 18 to serve its intended purpose. The guide 20 c is provided with port 20 d which may be directed toward the lateral port 12 b in the side of housing 12. The central passageway in the sleeve-shaped guide preferably has a diameter substantially equal to the diameter of the vertical tubing hanger production bore.
FIG. 1 discloses an assembly which uses a horizontal tree with a lateral port [0028] 18 c in the tubing hanger communicating with the interior of the tubing 16, and aligned with the lateral port 12 a in the housing 12 for passing production fluids to production line 30. Advantageously, the first and second vertically spaced plugs 22, 24 are provided within the body of the tree cap 20, and are sealed to the vertical bore through the tree cap. By providing both plugs or closure members in the tree cap rather than providing one or both plugs in the tubing hanger, the vertical spacing between the lowermost plug 24 and the lateral passage 18 c in the tubing hanger is increased, thereby providing a sizable vertical cushioning space between the lowermost plug and the side outlet port in the tubing hanger. Moreover, by providing both plugs 22, 24 in the tree cap, the seats for both plugs may be retrieved to the surface, inspected, and repaired if necessary without affecting the tubing hanger 18 or the production tubing 16 below the tubing hanger 18.
Flow paths within the assembly as shown in FIG. 1 provide for alternative production through the [0029] annulus line 48 should a problem develop in production line 30. For that application, valves 26, 28 and 42 may be closed and valves 34 and 46 opened. Crossover flow passes vertically through the tubing hanger, out port 12 b, through line 36, and to annulus line 48. The production bore in the tubing hanger 18 has a substantially uniform diameter bore so as not to restrict fluid flow.
[0030] Flow line 36 also provides fluid communication for workover fluids from the annular space 32, with a BOP conventionally positioned above the housing 12 and the tree cap 20 removed. Valves 34 and 42 may thus be opened and valve 46 closed to pass workover fluids from choke and kill lines to the annular space 32 and then to annulus 40 surrounding the tubing string 16. The vertical production bore in the tubing hanger is conveniently sealed off by a running tool sealed to the tubing hanger during a work-over operation.
FIG. 2 illustrates a form of the invention indicated generally at [0031] 110 that is similar to that previously illustrated in FIG. 1. The components of the embodiment in FIGS. 2-4 carry reference characters that are magnitudes of 100 higher than the most closely related component in FIG. 1. This convention is used throughout the following description whereby the reference characters used in the drawings will identify corresponding components and will differ by a magnitude of 100 in each of the drawing figures.
The [0032] embodiment 110 of FIG. 2 includes a lateral flow passage 120 e that extends through the tree cap 120 for crossover flow. Passage 120 e has a vertical passage portion that opens to a lower face of the cap 120, and a lateral passage portion extending radially outward from the vertical passage portion. Passage 120 e does not intersect the vertical bore in the tree cap. The passage 120 e communicates from the internal space 132 through a lateral tree housing port 112 b and through a valve 134 to the flow line 136. When plug 124 is removed and the valve 134 is open, the passage 120 e allows production fluids from the tubing 116 to flow to the annulus flow line 148.
The valve (plug) [0033] 124 is carried in the top of the tubing hanger 118 so that the space 132 may remain isolated from the production fluids in the tubing 116 until the valve 124 has been removed or opened. By comparison, the assembly of FIG. 1 permits continuous communication between the tubing 116 and the housing space 132.
As with the embodiment of FIG. 1, the communication between the internal [0034] tree housing space 132 and the annulus 140 may be controlled by the opening valves 134 and 142, and the closing valve 146. Similarly, communication of the fluids from the annulus 140 to the annulus line 148 may be regulated by the opening of the valves 142 and 146, and closing valve 134.
A primary feature of the [0035] assembly 110 is its ability to prevent production fluids and pressure from communicating with the area 132 by setting the retrievable plug valve 124 (or closing the in-place valve 124).
It will be understood that the communication between the [0036] flow passage 120 e in the tree cap 120 may be assisted by providing an annular communication space in the area between the axially spaced seal ring 120 a and 120 b as previously described so that circumferential orientation of the flow passage 120 e with respect to the port 112 b does not affect the flow of fluids into the port 112 b.
The FIG. 2 embodiment includes one [0037] plug 122 in the tree cap 120, and another plug 124 in the tubing hanger 118. Fluid in the annulus 140 is in fluid communication with lateral port 112 c. If production line 130 becomes disabled, valves 126 and 128 may be closed and plug 124 removed. Production fluid from tubing 116 then flows through the production port in the tubing hanger, then through the passageway 120 e in the tree cap 120, with passageway 120 e having a port within a lower surface of the tree cap 120 and thereby being in fluid communication with the space 132. The production bore in the tubing hanger and the crossover flow path within the tree cap are each in fluid communication with the central bore in the spool body between the tubing hanger and the tree cap. The crossover passageway thus extends vertically through a portion of the tree cap 120, then horizontally through a portion of the tree cap and between the pair of seals 120 a, 120 b to the lateral port 112 b. With valves 134 and 146 open and valve 142 closed, crossover production fluid flows to annulus line 148.
With the tree cap removed and [0038] valves 134 and 142 open and valve 146 closed, workover fluids may be passed from choke and kill lines through port 112 b and to the annulus 140 via external line 136. The lower plug 124 in the tubing hanger could alternatively be provided in the vertical bore of the tree cap below closure 122, in which case the running tool may seal off the production bore in the tubing hanger. The design as shown in FIG. 2 is substantially simpler than the design disclosed in U.S. Pat. No. 6,650,339, wherein the annulus passageway extends into a plug within the central through passageway in the tree cap.
FIG. 3 illustrates a form of the invention, indicated generally at [0039] 210, in which no lateral porting is provided through the tubing hanger 218. All communication of the production fluids and the annular fluids is achieved without having to communicate through a lateral passage formed in the tubing hanger 218. Communication of the production fluids in the tubing string 216 is through a lateral port 220 g in the tree cap 220.
[0040] Dual valves 226 and 228 in the port 212 a regulate the flow of production fluids into the production flow line 230. The radial passage 220 g is positioned axially intermediate the annular elastomeric seal rings 220 b and 220 e.
The embodiment of FIG. 3 is particularly significant in that the requirement for lateral passages through the [0041] tubing hanger 218 has been eliminated. The system 210 in FIG. 3 eliminates the requirement for port seals in the tubing hanger by providing a sealed communication from the tubing string 216 to the flow line 230 through the tree cap 220. A feature of the tree 210 is that it is unnecessary to remove the tubing hanger and suspended tubing when it becomes necessary to repair leakage in the seals sealing the tubing hanger to the inside of the tree housing. Thus, with reference to FIG. 2, if the seals 118 a or 118 b become inoperative, it is necessary to retrieve the tubing hanger 118 and attached tubing string to the well surface to effect the repair.
By providing a [0042] seal 220 i between the tree cap 220 and the hanger 218, and by providing a production flow path extending laterally from a bore in the tree cap to the production line 230, all the essential seals in the tree assembly may be retrieved to the surface and inspected and replaced without retrieving the tubing hanger 218. The tubing hanger 218 is shown with a seal 218 b for sealing with the housing 212 which is desired during the completion phase. During the production phase, however, the seal 218 may leak and the operator need not pull the tubing hanger 218 to replace the seal 218 b.
An advantage to the FIG. 3 design is that the 90° bend in the flow of production fluid from the central axis of the [0043] tubing string 216 to the lateral port 226 in the tree 220 is provided entirely within the tree cap. Corrosion and wear acting on the tree cap may be controlled and seals replaced by pulling the tree cap, with it being unnecessary to remove the tubing hanger 218 from the well.
During workover, the tree cap is removed. Fluid from the choke and kill lines may pass through the [0044] passageway 212 b and past the open valves 234 and 242, and into the annulus 240 about the tubing string 216. A running tool connects to the tubing hanger and seals the vertical production bore in the tubing hanger from workover fluids. A crossover line is not shown in FIGS. 3-4, but could extend from between the production valves, e.g. 326, 328, to the annulus valve 342.
The sleeve [0045] 212 c secured to the lower end of the tree cap 220 thus seals directly to the tubing hanger 218, and preferably to a cylindrical pocket in the upper end of the tubing hanger with seal 220 i. In an alternative design, the sleeve 212 c could be fixed to and extend upwardly from the tubing hanger, and sealed with the tree cap 220. Preferably, however, the seal between the tree cap and the tubing hanger is supported on the tree cap, so that it may be retrieved with the tree cap. The sleeve-shaped guide preferably has a central guide passageway diameter substantially equal to the tubing hanger production bore, and may extend downward to seal in a pocket in the tubing hanger.
FIG. 4 of the drawings illustrates an embodiment, indicated generally at [0046] 310, wherein a longitudinal flow passage 318 e is provided across the tubing hanger 318. The passage 318 e permits communication between the annulus 340 and the tree housing space 332 between the top of the tubing hanger and the bottom of the tree cap. The space 332 is isolated from such fluid by annular seal rings 320 i and 320 e that cooperate with the seal ring 318 a to isolate the space 332.
A retrievable plug or an in-[0047] place valve 355 may be positioned within the vertical passage 318 e. Similarly, a removable plug or an in-place valve 357 may be positioned within the central production bore in the tubing hanger 318 to control or regulate fluid flow into or out of the production tubing 316. When the tubing string is landed during the completion of the well, the valve 355 is in its open position, (or if a plug valve is used, the plug valve is removed from its sealing position in the passage 318 e while the tubing string is being landed) to prevent a pressure differential from developing across the tubing hanger that could prevent proper seating.
The [0048] valves 355 and 357 need not be included as part of the tubing hanger assembly 310. When the valves are absent, communication between the production tubing fluid and the annulus fluid is prevented by the seal ring 320 i. If desired, two or more spaced seal rings 320 i may be provided each for sealing with the tubing hanger.
An important feature of the embodiment of FIG. 4 is that vertical access to the annulus [0049] 340 is made possible during the landing and retrieval of the tubing hanger 318 without having to communicate through a lateral flow passage through the tubing hanger or through the tree housing.
The FIG. 4 design thus provides a [0050] flow path 318 e through the tubing hanger for communicating between the annulus 340 below the tubing hanger and the annular cavity 332 between the tubing hanger and the tree cap. The assembly 310 otherwise is similar to the embodiment shown in FIG. 3. A pair of plugs 322, 324 are provided in the bore of the tree cap, and sleeve 320 c connected to the tree cap is sealed to the tubing hanger by seal 320 i. A plug or valve 355 is provided along with flow path 318 e for controlling annular flow from above to below the tubing hanger. The flow line 318 e thus effectively replaces the line 36 shown in FIG. 31 by providing a flow path from above the tubing hanger to the annulus below the tubing hanger. Workover fluid from choke and kill lines may thus pass downward through passageway 318 e in the tubing hanger to the annulus 340, with valve 355 open. Valve 357 preferably is a temporary plug which may be placed within the bore of the tubing hanger before the tree cap is installed, and may then be completely removed from the bore in the tubing hanger after installation of the tree cap. A similar plug may be installed in the production bore of the tubing hanger before the tree cap is installed in the FIG. 1 and FIG. 3 embodiments.
While preferred embodiments of the present invention have been illustrated in detail, it is apparent that other modifications and adaptations of the preferred embodiments will occur to those skilled in the art. The embodiments shown and described are thus exemplary, and various other modifications to the preferred embodiments may be made which are within the spirit of the invention. Accordingly, it is to be expressly understood that such modifications and adaptations are within the scope of the present invention, which is defined in the following claims. [0051]

Claims

1. A horizontal spool tree assembly for controlling fluid flow through a production tubing string within a subsea well, the production tubing string defining a tubing annulus surrounding the tubing string, the tree assembly comprising:

a spool body defining a spool body central bore for receiving a tubing hanger therein, the spool body including an annulus passageway extending laterally through at least a portion of the spool body for fluid communication between the tubing annulus and an annulus line;

the tubing hanger adapted to support the production tubing therefrom, the tubing hanger having a tubing hanger production bore extending axially therethrough for fluid communication between the production tubing string and a lateral port in the tubing hanger extending from the production bore and in communication with a production port extending laterally through at least a portion of the spool body to a production line;

a tree cap positioned within the central bore of the spool body above the tubing hanger and having a vertical bore therein; and

first and second closure members each received within the vertical bore in the tree cap for closing off flow through the tree cap.

2. A horizontal spool tree assembly as defined in claim 1, further comprising:

a sleeve-shaped guide extending at least substantially between a lower face on the tree cap to an upper face on the tubing hanger and having a central guide passageway aligned with the tubing hanger production bore and the vertical bore in the tree cap.

3. A horizontal spool tree assembly as defined in claim 2, wherein the sleeve-shaped guide has a side port therein substantially aligned with a crossover port in the spool body, the crossover port being selectively in fluid communication with the annulus line.

4. A horizontal spool tree assembly as defined in claim 2, wherein the sleeve-shaped guide is secured to the tree cap, and extends downward into a pocket in the tubing hanger.

5. A horizontal spool tree assembly as defined in claim 2, wherein the central guide passageway in the sleeve-shaped guide has a diameter substantially equal to the tubing hanger production bore.

6. A horizontal spool tree assembly as defined in claim 1, further comprising:

a workover flow path extending at least partially through the spool body and fluidly connecting the central bore in the spool body above the tubing hanger to the tubing annulus.

7. A horizontal spool tree assembly as defined in claim 6, further comprising:

a workover valve controlling fluid flow along the workover flow path.

8. A horizontal spool tree assembly as defined in claim 1, further comprising:

a production valve positioned on the spool body for controlling fluid flow from the production port through the spool body to the production line.

9. A horizontal spool tree assembly as defined in claim 1, further comprising:

the production bore in the tubing hanger having a substantially uniform diameter bore so as not to restrict fluid flow.

10. A horizontal spool tree assembly as defined in claim 1, further comprising:

two or more axially spaced seals for sealing between the tree cap and the spool body.

11. A horizontal spool tree assembly for controlling fluid flow through a production tubing string within a subsea well, the production tubing string defining a tubing annulus surrounding the tubing string, the tree assembly comprising:

a tree cap positioned within the central bore of the spool body above the tubing hanger and having a vertical bore therein;

a crossover flow path extending from the spool body central bore upward through a portion of the tree cap, laterally through a port in the tree cap, through at least a portion of the spool body between upper and lower seals on the tree cap, and then through a crossover flow line in selective fluid communication with the annulus line;

a first closure member within one of the production bore in the tubing hanger and the vertical bore in the tree cap; and

a second closure member within the vertical bore in the tree cap for closing off flow through the tree cap.

12. A horizontal spool tree assembly as defined in claim 11, wherein the crossover flow path extends laterally through the spool body.

13. A horizontal spool tree assembly as defined in claim 11, further comprising:

14. A horizontal spool tree assembly as defined in claim 11, further comprising:

a production valve positioned on the spool body for controlling fluid flow from the lateral production port through the spool body to the production line.

15. A horizontal spool tree assembly as defined in claim 11, further comprising:

the production bore in tubing hanger having a substantially uniform diameter bore so as not to restrict fluid flow.

16. A horizontal spool assembly tree assembly as defined in claim 11, wherein the production bore in the tubing hanger and the crossover flow path within the tree cap are each in communication with the central bore in the spool body between the tubing hanger and the tree cap.

17. A horizontal spool tree assembly for controlling fluid flow through a production tubing string within a subsea well, the production tubing string defining a tubing annulus surrounding the tubing string, the tree assembly comprising:

the tubing hanger adapted to support the production tubing therefrom, the tubing hanger having a tubing hanger production bore extending axially therethrough for fluid communication between the production tubing string and a production port through the spool body to a production line;

a tree cap positioned within the central bore of the spool body and having a vertical bore therein in fluid communication with the tubing hanger production bore, the tree cap having a lateral bore therein extending from the vertical bore in the tree cap to the production port through the spool body; and

first and second closure members each received within the vertical bore in the tree cap above the lateral bore in the tree cap for closing off flow through the tree cap.

18. A horizontal spool assembly tree assembly as defined in claim 17, wherein a workover flow path extends from the spool body central bore above the tubing hanger laterally outward through at least a portion of the spool body and to the tubing annulus.

19. A horizontal spool assembly tree assembly as defined in claim 17, wherein a workover flow path extends from the spool body central bore above the tubing hanger through a vertical bore in the tubing hanger offset from the production bore in the tubing hanger and then to the tubing annulus; and

a valve member positioned along the vertical bore in the tubing hanger.

20. A horizontal spool tree assembly as defined in claim 17, further comprising:

a sleeve-shaped guide extending at least substantially from a lower face on the tree cap to an upper face on the tubing hanger and having a central guide passageway aligned with the tubing hanger production bore and the vertical bore in the tree cap.

21. A horizontal spool tree assembly as defined in claim 20, further comprising:

the sleeve-shaped guide being secured to the tree cap and having a lower seal for sealing with the tubing hanger.

22. A horizontal spool tree assembly as defined in claim 21, wherein the sleeve-shaped guide is secured to the tree cap, and extends downward into a pocket in the tubing hanger.

23. A horizontal spool tree assembly as defined in claim 20, wherein the central guide passageway in the sleeve-shaped guide has a diameter substantially equal to the tubing hanger production bore.