Wells – Submerged well – Wellhead
Reexamination Certificate
2002-04-17
2003-11-04
Pezzuto, Robert E. (Department: 3671)
Wells
Submerged well
Wellhead
C166S338000, C166S344000, C166S088100, C166S089100
Reexamination Certificate
active
06640902
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to subsea wellheads for oil and gas wells, and in particular to a nested stack-down casing hanger configuration which allows the pressure in the intermediate casing annuli to be monitored without penetrating the outer pressure containing housing or casing walls which separate the annuli from the external environment. Although the present invention has particular utility with respect to subsea wells, the invention is also applicable to land and offshore surface drilled wells.
In order to conform to various regulations and to protect life, property, and the environment, it is common practice on surface drilled wells to monitor the pressure in the various casing annuli for sustained casing head pressure (SCP). Pressure containing side outlets are provided in the casing and tubing heads, through which the annulus pressure can be measured. However, because such side outlets themselves create potential leak points, and because of the difficulty in detecting leaks, side penetrations in subsea wellhead housings are usually avoided. Exceptions are made in the regulations for high pressure subsea wells, such that it is required only to monitor pressure in the production annulus. In fact, such body penetrations are actually prohibited by some regulations. In any event, body penetrations in subsea wellheads could create potential hazards greater than those originally addressed by annulus monitoring.
Despite the difficulties inherent in monitoring annulus pressure in subsea wells, regulations have been proposed which would require that the pressure be monitored in every annulus in the well. Thus there is a need for a method of monitoring annulus pressure which does not require penetration of the pressure containing casings or housings. Even in the absence of such regulations, such a method would be most useful and desirable. Several prior art methods for monitoring annulus pressure in subsea wells are described in U.S. Pat. Nos. 5,544,707 and 4,887,672. A more complete discussion of the various regulations and the state of the prior art with respect to annulus pressure monitoring is presented in copending U.S. patent application Ser. No. 09/776,065, which is commonly owned herewith and the entirety of which is hereby incorporated by reference for all purposes.
Typical prior art wellhead systems have utilized a “stack-up” casing hanger configuration. In this type of system, the hanger for each successively smaller diameter casing string is landed on top of the hanger for the next larger casing string. Each hanger is locked and sealed to the wellhead housing bore above the next lower hanger. Thus, as each hanger is installed in the wellhead housing, the next lower hanger (and the associated annulus) becomes inaccessible.
For the purposes of illustration, a typical stack-up subsea wellhead system is shown in FIG.
1
. The wellhead system comprises a conductor housing
12
attached atop conductor pipe
18
and locked into permanent guide base
10
. The wellhead housing
14
is landed in the conductor housing
12
and includes wellhead bore
16
. Second intermediate casing hanger
32
is landed in the wellhead housing
14
and supports second intermediate casing string
42
. Hanger
32
is provided with annulus access port
36
, which allows for fluid communication between the wellhead bore
16
and the “C” annulus
50
after installation of hanger
32
. After the hanger
32
is landed in the wellhead housing
14
, pack-off
34
is installed between hanger
32
and the wellhead housing
14
, preventing further communication with access port
36
.
First intermediate casing hanger
26
is then landed atop second intermediate casing hanger
32
and supports first intermediate casing string
40
. Hanger
26
is provided with annulus access port
30
, which allows for fluid communication between the wellhead bore
16
and the “B” annulus
48
after installation of hanger
26
. After the hanger
26
is landed on hanger
32
, pack-off
28
is installed between hanger
26
and the wellhead housing
14
, preventing further communication with access port
30
.
Production casing hanger
20
is then landed atop first intermediate casing hanger
26
and supports production casing string
38
. Hanger
20
is provided with annulus access port
24
, which allows for fluid communication between the wellhead bore
16
and the production or “A” annulus
46
after installation of hanger
20
. The “A” annulus is located between the production casing string
38
and the production tubing, shown in phantom at
44
. After the hanger
20
is landed on hanger
26
, pack-off
22
is installed between hanger
20
and the wellhead housing
14
, preventing further communication with access port
24
. As is apparent from the figure, once all the casing hangers have been installed in the wellhead housing
14
, access to the “B” and “C” annuli is prevented.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other disadvantages in the prior art are overcome by providing a wellhead system which comprises a wellhead housing and a plurality of concentric casing strings, each of which is suspended from a corresponding casing hanger. The casing hanger for the radially outermost casing string is supported in said wellhead housing and the casing hanger for each successively smaller casing string is supported in the casing hanger for the next radially larger casing string. Each casing string defines a corresponding annulus which surrounds said casing string and is located below the casing hanger for said casing string. Furthermore, at least one casing hanger comprises a bypass port or similar means for providing fluid communication between the annulus below said casing hanger and an area above said casing hanger.
Thus, the wellhead system of the present invention comprises a “stack-down” casing hanger configuration. In this type of system, the hanger for each successively smaller diameter casing string is landed or “nested” within the hanger for the next larger casing string. This approach allows the pack-off for each casing hanger to be retrieved independently, thus allowing fluid communication to be established with any of the casing annuli after all of the casing strings and hangers have been installed. Thus the pressure in each annulus may be monitored while the well is in production mode.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar components in the various embodiments.
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patent: 3937251 (1976-02-01), Ahlstone et al.
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patent: 4794988 (1989-01-01), van Bilderbeek
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patent: 5127478 (1992-07-01), Miller
patent: 5366017 (1994-11-01), Voss, Jr.
patent: 5544707 (1996-08-01), Hopper et al.
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patent: 6039119 (2000-03-01), Hopper et al.
patent: 6513596 (2003-02-01), Wester
patent: 2 285 077 (1995-06-01), None
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patent: 2 358 204 (2001-07-01), None
patent: 2 364 538 (2002-01-01), None
Baten Robert B.
MacFarlane David
McBeth Russell E.
Skeels Harold B.
Smedley Marcus A.
Beach Thomas A.
FMC Technologies Inc.
Query, Jr. Henry C.
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