CA2197584E

CA2197584E - Wellhead assembly

Info

Publication number: CA2197584E
Application number: CA002197584A
Authority: CA
Inventors: Tony M. Lam; Keith D. Farquharson
Original assignee: Stream Flo Industries Ltd
Current assignee: Stream Flo Industries Ltd
Priority date: 1996-02-14
Filing date: 1997-02-14
Publication date: 2000-05-16
Anticipated expiration: 2017-02-14
Also published as: CA2197584C; CA2169503A1; CA2197584A1

Abstract

The tubing head adapter, blow-out preventer ("BOP") housing and flow tee of a wellhead Christmas tree are integrated to provide a unitary, integral structure forming a vertical bore. From the bottom up, the structure comprises: a tubing head adapter bottom connection, studded or flanged, for connecting with the flanged top connection of the tubing head; a BOP housing forming side openings communicating with the bore, for receiving the ram components of a blow-out preventer; a flow tee section forming at least one side opening communicating with the bore, for producing well fluid; and a tubing head adapter top connection for connecting with the balance of the Christmas tree. By incorporating the BOP housing and flow tee into the tubing head adapter and eliminating threaded connections, the length of the three components can be reduced up to 50% and structural strength is improved.

Description

2 This invention relates to that segment of a wellhead Christmas tree comprising

3 the tubing head adapter, production blow-out preventer and flow tee. More

4 particularly, if relates to combining these components into a unitary integral structure free of welds or threaded connections.

8 A conventional oilwell wellhead or Christmas tree is illustrated in Figure 1. The 9 wellhead comprises:
~ A tubular casing bowl, which is connected or mounted to the upper end 11 of the well casing. The bottom end of the casing bowl is threaded, for 12 screwing onto the externally threaded casing. It has side-opening 13 ports, or openings, to provide access to the annular space between 14 the casing string and the tubing string. At its upper end, the casing bowl has a flanged connection;
16 ~ A tubular tubing head, having flanged connections at both ends, 17 mounts on the casing bowl. The lower flanged connection of the tubing 18 head is bolted onto the casing bowl flanged connection. The internal 19 bore of the tubing head is formed to support a tubing hanger, from which the tubing string is suspended. Side-opening, internally threaded 21 ports are provided in the tubing head wall to provide access to the 22 annular space between the casing and tubing strings;

1 ~ A tubular tubing head adapter, having a flanged lower connection and a 2 threaded upper connection, is bolted onto the flanged upper connection 3 of the tubing head. The adapter provides a transition from a flanged 4 connection having a large nominal size to a threaded connection having a smaller nominal size;
6 ~ A tubular production blow-out preventer ("BOP") unit is mounted on the 7 adapter. This BOP unit comprises a housing, having top and bottom 8 threaded connections, and side-opening, internally threaded ports for 9 receiving the ram assemblies of the BOP unit; and ~ A tubular flow tee is mounted onto the BOP unit. The flow tee has 11 internally threaded top and bottom connections and a side-opening, 12 internally threaded port for connection with a flow line through which 13 fluid from the tubing string is produced.
14 In recent years, many oilwells have been equipped with rotary progressive cavity downhole pumps, for pumping the produced fluid. These pumps are powered 16 by a rotating rod string extending through the vertical through-bore of the wellhead 17 assembly. A frame is mounted to the flow tee. A stuffing box is positioned within the 18 frame and connected to the top connection of the flow tee. The stuffing box seals 19 around the polish rod of the rod string, which extends from the wellhead assembly.
The polish rod protrudes through the stuffing box and frame and is drivably engaged 21 by a drive assembly linking the polish rod with a motor.

1 The motor is offset from the axis of the wellhead assembly. Since the motor 2 vibrates, this introduces a cyclical bending moment which is applied to the wellhead 3 structure. This bending moment increases as the length of the tubing head 4 adapterIBOP unit/flow tee structure increases in length. As a result of these factors, failures have occurred, particularly at the connection between the tubing head 6 adapter and the BOP unit.
7 To our knowledge, the only prior solution offered in the industry to cope with 8 this problem has been to weld up the threaded connections, to thereby strengthen 9 them.
It is the object of this invention to provide a novel tubing head adapter/BOP
11 housing/flow tee structure which is more compact and better able to withstand cyclical 12 stresses induced by the rotary drive assembly.

In accordance with the invention, the BOP housing and flow tee are integrated 16 between and with the end connections of the tubing head adapter to provide a unitary 17 integral structure. The structure is formed from a single piece of steel, forged or cast.
18 More particularly, the structure forms a vertical bore and comprises:
19 . a bottom connection, studded or flanged or of the clamp and hub type, for connecting with the top connection of a tubing head;
21 . a BOP housing section forming side openings communicating with the 22 bore, for receiving the ram components of a blow-out preventer;
23 . a flow tee section forming at least one side opening communicating with 24 the bore, for producing well fluid; and 1 . a top connection, preferably studded and internally threaded, for 2 connecting with the balance or upper segment of the Christmas tree.
3 The structure connects directly to the tubing head, accommodates BOP
4 components, has outlets for directing the well fluid flow horizontally and has a connection for connecting with the upper segment of the Christmas tree, which in the 6 case of a well completed with a rotary pump would comprise a stuffing box and drive 7 frame.
8 The structure also lends itself to use with a dual completion wellhead as well 9 as a wellhead equipped for steam injection.
By forming the structure in this way, we have realized the following 11 advantages:
12 ~ A comparative vertical length saving of about 50% is achieved by 13 eliminating the threaded connections and the body of the tubing head 14 adapter. This brings the rotary drive assembly closer to ground surface, which is advantageous for servicing, and significantly reduces 16 the bending moment; and 17 ~ By not having the end-to-end threaded or flanged connections of the 18 prior art assemblies, the structure is stronger, and thus is better able to 19 support a rotary drive assembly.

22 Figure 1 is a side view of a prior art wellhead assembly;
23 Figure 2 is a view similar to Figure 1, showing a unitary adapter/BOP/flow tee 24 structure;

5 1 Figure 3 is a perspective view of the structure;
2 Figure 4 is a perspective, partly broken away view of the structure;
3 Figure 5 is a top plan view of the structure;
4 Figure 6 is a sectional side view taken along the line A--A of Figure 5;
Figure 7 is a sectional side view taken along the line B--B of Figure 5;

6 Figure 8 is a partly sectional side view of the structure equipped with clamp

7 and hub type top and bottom connections;

8 Figure 9 is a partly sectional side view showing the structure incorporated into

9 the wellhead of a well equipped with dual tubing strings;
Figure 10 is a partly sectional side view showing the structure incorporated into 11 a wellhead equipped for steam injection; and 12 Figure 11 is a side view, partly in section, showing the structure incorporated 13 into a wellhead having a stuffing box and rotary drive for the rod string.

DESCRIPTION OF THE PREFERRED EMBODIMENT
16 The tubing head adapter/BOP housing/flow tee structure 1 comprises an 17 integral or one-piece, tubular housing 2 forming a vertical bore 3 extending 18 therethrough. The housing 2 is not formed of tubular parts connected end to end by 19 threaded connections, but instead is formed from a single piece of steel.
As shown in Figure 11, the diameter of the bore 3 is about equal to the diameter of tubing 21 suspended from the wellhead.

1 The housing 2 comprises a flanged bottom connection. This bottom 2 connection 4 is adapted to connect to the flanged top connection 30 of a tubing head 3 31. The face 6 of the connection 4 forms a seal ring groove 7 extending around the 4 vertical bore inlet 8. The connection 4 also forms bolt holes 10 for receiving connecting studs 11.
6 A production BOP housing section 12 extends up from the bottom connection 7 4. As shown in the drawings, the BOP housing section 12 is contiguous with the 8 bottom connection 4, so that there is no neck between them. The section 12 forms 9 diametrically aligned side openings 13 communicating with the vertical bore 3. The side openings 13 are internally threaded and formed to receive the ram components 11 14 of a side-opening BOP to provide emergency shut-off means, if required.
12 A flow tee section 15 extends up from the BOP housing section 12. As shown 13 in the drawings, the BOP housing section 12 is contiguous with the flow tee section 15 14 so that there is no neck between them. The flow tee section 15 forms internally threaded side openings 16 communicating with the vertical bore 3. The side 16 openings 16 form flow tee outlet means for tieing in to a flow line (not shown) through 17 which well fluid is produced.
18 An internally threaded, studded top connection 17 extends up from and is 19 integral with the flow tee section 15. The face 18 of connection 17 forms a ring seal groove 19 and bolt holes 20 for studs 21.
21 In summary, the structure 1 is adapted to bolt to the top flanged connection 30 22 of a tubing head 31 and to connect to the lower end of the balance of the Christmas 23 tree, which commonly will be the frame and stuffing box of a rotary rod string drive 24 assembly. The structure facilitates provision of the functions of a tubing head 1 adapter, blow-out preventer and flow tee. As shown in Figure 4, the housing 2, above 2 the bottom connection 4, is substantially cylindrical, so that a side wall of substantially 3 consistent thickness is provided.
4 Figure 9 shows a modified structure 1 in use in a dual completion wellhead having two tubing strings 41, 42. In this case, the structure 1 is formed with two 6 isolated, laterally spaced apart, vertical bores 43, 44. A separate side opening 45 for 7 the BOP ram component communicates with each vertical bore. Similarly, a separate 8 flow tee opening 46 communicates with each vertical bore.
9 Figure 10 shows a modified structure in use in as part of a wellhead equipped for steam injection. In this case a vertical bore 50 is provided to communicate with 11 the tubing string 51. A side opening 52 for the BOP ram component communicates 12 with the vertical bore 50, as does a flow tee side opening 53. A second vertical bore 13 54 is provided to communicate with the steam injection line. The bore 54 has its own 14 side inlet 56. In summary, the structure 1 is again provided with a pair of laterally spaced apart, vertical bores 50, 54.
16 These modified structures show that the structure 1 has a flexible capability for 17 use with dual completions and steam injection.
18 Figure 11 shows the structure 1 incorporated into a wellhead 60 having a 19 stuffing box 61, rotary drive frame 62 and drive assembly 63. The drive assembly functions to rotate a rod string 64 which powers a progressive cavity downhole pump 21 (not shown).

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A structure integrating a blow-out preventer and flow tee between the end connections of a tubing head adapter, comprising:
a housing formed from a single piece of steel and defining a vertical bore therethrough, said housing comprising, a bottom connection for connecting with the top connection of a tubing head, a blow-out preventer housing section forming side openings, communicating with the vertical bore, for receiving the ram components of a blow-out preventer, a flow tee section forming at least one side opening, communicating with the vertical bore, for producing well fluid, and a top connection for connecting to an upper segment of a Christmas tree.

2. The structure as set forth in claim 1 wherein:
the bottom connection is studded, flanged or of the hub and clamp type.

3. The structure as set forth in claim 2 wherein:
the top connection is studded and internally threaded.

4. The structure as set forth in claims 1, 2, or 3 wherein the housing comprises, from bottom to top, the bottom connection, the blow-out preventer housing section, the flow tee and the top connection.

5. A structure integrating a production blow-out preventer, flow tee and tubing head adapter, for mounting to a tubing head forming part of a wellhead, comprising:
a housing formed from a single piece of steel and defining a vertical bore therethrough, said housing comprising, a bottom connection for connecting with the top connection of a tubing head, a blow-out preventer housing section forming side openings, communicating with the vertical bore, for receiving the ram components of a blow-out preventer, a flow tee section forming at least one side opening, communicating with the vertical bore, for producing well fluid, and a top connection for connecting to an upper segment of the wellhead, the blow-out preventer housing section being contiguous with the bottom connection so that there is no neck between them.

6. The structure as set forth in claim 5 wherein:
the blow-out preventer housing section is contiguous with the flow tee section so that there is no neck between them.

7. The structure as set forth in claim 6 wherein:
the housing above the bottom connection is substantially cylindrical so that a side wall of substantially consistent thickness is provided.

8. The structure as set forth in claim 5, 6 or 7 wherein:
the diameter of the vertical bore is about equal to the diameter of tubing to be suspended from the wellhead.

9. The structure of claim 5, 6 or 7 wherein:
the bottom connection is studded, flanged or has a hub.

10. The structure of claim 5, 6 or 7 wherein:
the bottom connection is studded, flanged or has a hub; and the top connection is studded and internally threaded.

11. The structure of claim 5, 6 or 7 wherein:
the housing defines a single, central vertical bore.

12. The structure of claim 5, 6 or 7 wherein:
the housing defines a pair of laterally spaced apart bores.

13. The structure of claim 5, 6 or 7 wherein:
the bottom connection is studded, flanged or has a hub; and the housing defines a single, central vertical bore.

14. The structure of claim 5, 6 or 7 wherein:
the bottom connection is studded, flanged or has a hub; and the housing defines a pair of laterally spaced apart bores.