Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02197584 1999-11-23
1 FIELD OF THE INVENTION
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.
6
7 BACKGROUND OF THE INVENTION
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;
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CA 02197584 1999-11-23
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.
3
CA 02197584 1999-11-23
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.
13
14 SUMMARY OF THE INVENTION
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
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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.
21 DESCRIPTION OF THE DRAWINGS
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;
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CA 02197584 1999-11-23
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.
14
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.
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CA 02197584 1999-11-23
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
7
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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
40
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).
8
