U.S. patent application number 10/487049 was filed with the patent office on 2004-12-02 for annulus monitoring system.
Invention is credited to Laureano, Marcio P, Robertson, Thomas.
Application Number | 20040238178 10/487049 |
Document ID | / |
Family ID | 26246447 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238178 |
Kind Code |
A1 |
Laureano, Marcio P ; et
al. |
December 2, 2004 |
Annulus monitoring system
Abstract
Apparatus and a system for accessing one or more of the annuli
defined between casing strings in a subsea wellhead that are
usually sealed for the production stage of the well. Access to an
annulus (30) is made via the wall of the wellhead housing (12) at a
location where is communicates with the annulus. The access is a
passageway (31) having a first opening in communication with the
annulus and a second opening either at the external surface of the
wall or at a location on the inner surface of the wall above the
casing hangar seal for the inner casing (14), which is not in
communication with the annulus apart from the passageway. An
isolation valve (32) communicates with the passageway and with
apparatus for monitoring or controlling pressure of flow in the
annulus. The passageway may be used with an open lower end to the
annulus during drilling stages for material transfer and during
production stage to monitor/control a sealed annulus.
Inventors: |
Laureano, Marcio P;
(Osteras, NO) ; Robertson, Thomas; (Aberdeen,
GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Family ID: |
26246447 |
Appl. No.: |
10/487049 |
Filed: |
June 30, 2004 |
PCT Filed: |
August 19, 2002 |
PCT NO: |
PCT/GB02/03809 |
Current U.S.
Class: |
166/368 ;
166/89.1 |
Current CPC
Class: |
E21B 33/076 20130101;
E21B 33/035 20130101; E21B 33/043 20130101; E21B 33/047
20130101 |
Class at
Publication: |
166/368 ;
166/089.1 |
International
Class: |
E21B 033/035 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2001 |
GB |
0120140.9 |
Oct 17, 2001 |
GB |
0124943.2 |
Claims
1. A wellhead housing assembly for a subsea wellhead, the assembly
comprising a wellhead housing that is adapted to receive a
plurality of casing strings therewithin with an annular passage
defined between respective adjacent casing strings, and in which
the wall of the wellhead housing has a penetration with a first
opening on its inner surface in a location that will communicate
with one annular passageway formed by a pair of adjacent casing
strings, the penetration extending to a second opening on a surface
portion of the wellhead housing wall that will not be in
communication with any annular passageway between casing
strings.
2. A wellhead housing assembly according to claim 1 in which the
second opening of the penetration is on the exterior of the
wellhead housing.
3. A wellhead housing assembly according to claim 2 in which the
penetration extends through the wellhead housing wall substantially
radially.
4. A casing string assembly according to claim 2 in which the
penetration extends through the wellhead housing wall at an angle
inclined longitudinally from radial.
5. A casing string assembly according to any preceding claim in
which the penetration is below a location for a casing hangar seal
for the casing string defining the inner wall of the annular
passageway.
6. A wellhead housing assembly according to any preceding claim 1
in which a plurality of penetrations are provided each with a first
opening located to communicate with an annulus defined by
respective different pairs of adjacent casing strings.
7. A wellhead housing assembly according to claim 1 in which the
second opening of the penetration is on the interior of the
wellhead housing above a location for a casing hangar seal for the
casing string defining the inner wall of the annular passageway
8. A wellhead housing assembly according to claim 7 in which second
end of the penetration communicates with a location where the
wellhead housing defines an annulus with an isolation sleeve.
9. A wellhead housing assembly according to claim 7 or claim 8 in
which the penetration comprises a series of bores including one
bore extending in the axial direction.
10. A wellhead housing assembly according to any preceding claim
further comprising an isolation valve in communication with the
passageway.
11. A wellhead housing assembly according to claim 10 in which the
isolation valve is integral with the wellhead housing.
12. A pressure monitoring/control system for a subsea wellhead
arrangement including a wellhead housing assembly according to any
preceding claim and means for monitoring and/or controlling
pressure or flow within the annular passage.
13. A subsea wellhead arrangement having a plurality of casing
strings disposed coaxially with respective adjacent casing strings
defining an annular passage therebetween, and in which a
respectively outward one of adjacent casings strings has a
passageway in its wall with a first opening communicating with the
annulus and a second opening connecting to apparatus for monitoring
or controlling pressure or flow within the annular passage.
14. A subsea wellhead arrangement according to claim 12 in which
the respectively outward one of the casings defining the annular
passageway is open at its lower end and material is routed via the
open end and passageway.
15. A subsea wellhead arrangement according to claim 14 in which
the material is drill cuttings routed for reinjection to the
formation.
16. A subsea wellhead arrangement according to claim 14 in which
the material is mud in a mud-lift system.
17. A subsea wellhead arrangement according to claim 13 in which
flow in the annulus is used to drive a pump.
18. A subsea wellhead arrangement according to claim 12 or claim 13
in which there are a adjacent annular passageways defined between
three concentrically disposed casings and an additional penetration
to connect the annuli is made in the common casing.
19. A subsea wellhead arrangement according to any preceding claim
in which a bore in the wellhead housing interconnects two annular
passageways between casing strings.
20. A subsea wellhead arrangement according to claim 18 in which
the bore has a first opening between the seals for a first pair of
casing strings and a second opening between seals for a second pair
of casing strings.
21. A pressure monitoring/control system for a subsea wellhead
arrangement including an inner pipe surrounded by an outer pipe and
defining an annular passage therewith, the inner and outer pipes
being adapted to withstand internal and external pressure and the
annular passage being filled with fluid to prevent compression,
characterized in that a penetration communicates at one end with
the annular passage and at its other end is connected via a
pressure isolation valve to means for monitoring and/or controlling
pressure or flow within the annular passage.
22. A system according to claim 21 in which the penetration is in
the wellhead housing with said one end at a level communicating
with the annulus.
23. A system according to claim 21 in which the end of the
penetration communicating with the annulus is below a casing seal
for the inner pipe and above a casing seal for the outer pipe.
24. A system according to claim 21 in which the inner pipe is a
well casing and the outer pipe is a barrier casing and the means
for monitoring connects to a component at the subsea wellhead.
25. A system as claimed in claim 21 in which the penetration is
radial with respect to the well bore.
26. A system as claimed in any of claims 21 to 25, in which a
second isolation valve is connected in series with said pressure
isolation valve.
27. A system as claimed in any one of claims 21 to 26, in which the
isolation valve or valves are operable hydraulically, with
provision for ROV override.
28. A system as claimed in any one of claims 21 to 27, in which
there is a rigid connection between the isolation valve and the
monitoring/control feature.
29. A system as claimed in claim 28, in which there is an alignment
key between an outer housing and a system support structure to
ensure aligned engagement of the rigid connection and the support
structure.
30. A system as claimed in any one of claims 21 to 27, in which
there is a flexible connection between the isolation valve and the
monitoring/control feature.
31. A system as claimed in any one of claims 21 to 30, in
combination with means to control/monitor fluid pressure within the
annulus between the well casing and the outer barrier pipe, whereby
to increase the allowable pressure within the well casing.
32. A system as claimed in any one of claims 21 to 31, in which
there is another pipe surrounding the outer barrier pipe, so
forming a second annulus surrounding the annulus aforesaid, and in
which there is a second penetration leading to another isolation
valve by which the pressure in the second annulus may be
monitored/controlled.
33. A pressure monitoring/control system according to any of claims
21 to 32 in which the isolation valve is integral with the wellhead
housing.
34. A pressure monitoring/control system according to claim 21 in
which the penetration has a portion that extends axially within the
housing to a further annulus near to the top of the wellhead
arrangement.
35. A system as claimed in claim 21 in which part of the
penetration in the wellhead housing is directed radially upward and
outward with respect to the well bore.
36. A system as claimed in claim 34 or claim 35, in which a second
isolation valve is connected to an outflow from the further annulus
in series with the isolation valve aforesaid.
37. A system as claimed in any of claims 21 to 36 in which the end
of the penetration communicating with the annular passage is formed
between the casing hangers for the well casing and the next outer
casing.
38. A system as claimed in claim 34 in which the isolation valve in
the wellhead housing is a small bore gate valve with metal to metal
sealing.
39. A system as claimed in claim 34 in which the further annulus is
between a tree isolation sleeve and a connector body.
40. A system as claimed in claim 39, in which a port is formed in
the connector body and the outlet includes the second isolation
valve.
41. A system as claimed in any of claims 21 to 40, in which the
isolation valve or valves are operable hydraulically.
42. A system as claimed in any of claims 21 to 41, in combination
with means to control/monitor fluid pressure within the annulus
between the well casing and the outer barrier pipe, whereby to
increase the allowable pressure within the well casing.
Description
[0001] This invention relates to subsea wellheads and to casings
for such wellheads.
[0002] More particularly it concerns providing a way of accessing
an annular passageway (or annulus) defined between concentric
casings, and to a pressure monitoring and/or control system for the
annulus The casings may be part of a series of casing strings. The
pressure control may include movement of materials and the access
may be used at the drilling or completion stage or during
production.
[0003] Well casing emerging from subsea deposits of oil and/or gas
is required to contain well fluids under high pressures. The well
casing may typically be of 103/4" OD (approx 273 mm) pipe. The well
casing is secured to a well casing hanger within the wellhead and
coaxial with the well bore. The well casing is surrounded by a
further casing, which forms an outer barrier of an annulus formed
between the two casings. The further casing may be of 13 3/4"
(approx 356 mm) OD pipe. This further casing may also be surrounded
by other casings. During drilling the casings are open at the top
and bottom, but they are generally sealed at various stages prior
to production. Access to the innermost annulus is maintained via
the top and valves but there is not sufficient space to provide
such access to other annuli.
[0004] To prevent collapse under subsea pressure the annuli between
the successive concentric casings are filled with fluid, which may
be for example gas, drilling mud or water. The fluid is generally
injected into the annulus via the open annulus access of the top
during the completion phase of the well when the casings are
sealed. For the avoidance of doubt, in this specification the
expression fluid covers any flowable substance which may be gas or
liquid, or suspensions or slurry. If leakage from production occurs
or there is other ingress of fluid into an annulus there can be a
build up of pressure. Presently, if this occurs the casings have to
be pulled up, which requires the well to be shut down. It is being
found that as drilling goes to deeper formations, the resulting
higher temperatures and pressures increases the instances of
pressure build up.
[0005] There are also other circumstances where the balance of
pressures on the casings changes. On the inside there is high
pressure from the reservoir and on the outside deep sea pressure.
During the course of production pressure may change, for example
reducing pressure due to natural depletion of the reservoir, which
may also be accompanied by changing temperatures; in the example
just mentioned, a temperature drop. Such pressure changes can
result in a differential pressure increase, collapsing or bursting
of casings or damage to the formation.
[0006] Thus it is desirable at the production stage to be able to
monitor pressure within an annulus between concentric casings
and/or to be able to bleed, circulate or inject fluids in order to
change or restore the annulus pressure to a particular level. It is
also desirable to be able to utilise the annuli for movement of
material, either as part of drilling, after drilling or during
production.
[0007] There are also instances where the ability to pressurize an
annulus may enable design changes to casing thickness. Also
respective concentric annuli may be held at different pressure
levels.
[0008] According to the invention there is provided a wellhead
housing assembly for a subsea wellhead, the assembly comprising a
wellhead housing that is adapted to receive a plurality of casing
strings therewithin with an annular passage defined between
respective adjacent casing strings, and in which the wall of the
wellhead housing has a penetration with a first opening on its
inner surface in a location that will communicate with one annular
passageway formed by a pair of adjacent casing strings, the
penetration extending to a second opening on a surface portion of
the wellhead housing wall that will not be in communication with
any annular passageway between casing strings.
[0009] The invention also provides a pressure monitoring/control
system for a subsea wellhead arrangement including an inner pipe
surrounded by an outer pipe and defining an annular passage
therewith, the inner and outer pipes being adapted to withstand
internal and external pressure and the annular passage being filled
with fluid to prevent compression, characterized in that a
penetration communicates at one end with the annular passage and at
its other end is connected via a pressure isolation valve to means
for monitoring and/or controlling pressure or flow within the
annular passage.
[0010] The inner pipe may be a well casing and the outer pipe a
barrier casing.
[0011] The penetration may be radial with respect to the bore
radius of the pipe, or it may be inclined upwardly and have a
portion extending in the general axial direction into another
annulus at the top of the wellhead assembly.
[0012] The penetration may extend through the casing wall or run
between two location on the inner surface of the wall on opposite
sides of the seal for the casing defining the inner wall of the
annular passageway.
[0013] Pressurizing the annulus may also be used to circulate
fluids or to route material, for example drill cuttings for
reinjection back into the formation, or to route returns in
mud-lift systems.
[0014] The invention is now described by way of example with
reference to the accompanying drawings, in which:
[0015] FIG. 1 is a schematic cross section of a conventional well
assembly at a drilling stage;
[0016] FIG. 2 is a schematic cross section of a subsea wellhead at
seabed level showing access to an annulus via a casing wall;
[0017] FIG. 3 is a modification of the subsea wellhead of FIG. 2
showing two valves;
[0018] FIG. 4 is a further modification of the wellhead showing
penetrations to two annuli;
[0019] FIG. 5 is a schematic cross section of a wellhead showing an
alternative penetration route;
[0020] FIG. 6 is a schematic diagram of the wellhead of FIG. 5
showing a valve layout, and
[0021] FIG. 7 is a schematic diagram of a well assembly at a
drilling stage showing use of a penetration according to the
invention in a mud lift system
[0022] FIG. 1 shows the schematic layout of a well. Extending from
a platform 100 is a marine riser 101 within which is a drill pipe
102. When drilling is complete the drill pipe is recovered to the
surface and the casings are left hanging from the subsea wellhead.
At this stage the casings will be sealed at the top but may be open
at the bottom.
[0023] At mudline or seabed level a series of casing strings extend
down into the formation. The more outward casing strings are
suspended at the level of a subsea wellhead 10 on the seabed. Above
the casing strings is a blowout preventer.
[0024] The invention generally relates to accessing one or more of
the annuli defined between casing strings at the subsea wellhead
level that at present are sealed for the production stage of the
well. Access provided in this way may also be used at earlier
stages and to provide additional functions. Access via the top of
the casings is unavailable due to space considerations and the
technology established for providing casing hangars and sealing.
Access in the invention involves a radial or laterally extending
penetration of the casing outside the annulus or more conveniently
of the wellhead housing where it is in communication with the
annulus. The penetration may go completely through the casing or
provide a bore through to an accessible location on the inner
surface of the casing that is above the hangar/seal for the casing
defining the inside of the annulus.
[0025] Referring now to FIG. 2, the wellhead arrangement 10 has a
frame 11 installed on the seabed. The wellhead arrangement 10 has a
wellhead housing 12, typically this housing may be 183/4"
(approximately 476 mm).
[0026] Extending down to the seabed strata from the wellhead
housing 12 are four coaxial casings, termed herein as well casing
14, outer barrier pipe 15, casing 16 and conductor 17. The casings
are supported on casing hangars in the generally known manner. The
drawing shows hangar packoff 21 engaging with wellhead housing 12
to support well casing 14 and hangar packoff 22 engaging lower down
wellhead housing 12 to support outer barrier pipe 15. A well bay
insert 18 also coaxial and concentric with the wellhead housing and
casings locates the wellhead and casings within the frame 11. It is
usually the case that several casings are supported by the wellhead
housing, it may be more than the number illustrated in the
drawings.
[0027] It will be appreciated that the sizes of the casings may be
any of those appropriate, for example conductor casing 17 may be 30
inches (approximately 762 mm), casing 16 may then be 20 inches (508
mm), barrier pipe 15 being 14 inches (356 mm) and the well casing
being 103/4 inches (273 mm), with the wellhead housing 12 being
183/4 inches (476 mm).
[0028] Between adjacent casings there is an annulus of free space
which is filled with a fluid such as gas, sea water, methanol or
drilling mud, or other such substance as conditions demand. The
annulus between well casing 14 and outer barrier pipe 15 is shown
shaded and with reference 30.
[0029] It is customary for the casings to be sealed to one another
both at the top, where it prevents egress of gas or other
substances that might otherwise escape from the annulus, and also
at the end within the seabed strata. This sealing is done at the
end of the drilling process.
[0030] In the embodiment shown a radial penetration 31 is made in
the wellhead housing 12, and it will be seen that at this point the
annulus between casings 14 and 15 extends upwards above the seal of
hangar 22 to become an annulus between the wellhead housing and the
casing 14. An isolation valve 32 is provided integral with the
wellhead housing 12 and this leads to an access port. The isolation
valve 32 has a remotely or directly actuated valve operating
arrangement outstanding from the body of the valve. These
mechanisms may be of any appropriate type, for example the valve
may be an hydraulic valve. The valve may be operable by a ROV.
[0031] FIG. 3 shows a second embodiment in which a second isolation
valve 34 is connected in series with the isolation valve 32. The
second isolation valve 34 also has a remote or direct operating
arrangement with provision for ROV over ride. Hard piping may lead
down from the single or second isolation valve and loop round the
wellhead housing 12 to a connection point. Various
monitoring/control features relating to the well output may be
connected to the connection point.
[0032] As well as monitoring conditions in the annulus, excess
pressure in the annulus can be relieved via the isolation valve or
valves, or the annulus between the casings 14 and 15 can be
pressurised by pumping a fluid medium (e.g. methanol) through the
valve or valves, and via the penetration 31, into the annulus.
Pressurisation of the annulus outside the well casing 14 may allow
higher pressures to be contained within that casing. The invention
provides ability to top up pressure to compensate for outward
leakage, change of state or pressure reduction due to temperature
variation, or to reduce pressure in the corresponding converse
circumstances.
[0033] In order to position the penetration and isolation valves
with respect to the external layout it may be necessary to provide
an alignment mechanism. This is particularly the case if the
connections use rigid pipes. In the embodiments shown orientation
between the template 11 and the conductor housing 20 and also
between the conductor housing 20 and the wellhead housing 12 is
achieved by alignment keys.
[0034] Alternatively a flexible conduit may lead off from the
isolation valve 32 (or 34) to pressure monitoring/control features
elsewhere on the wellhead arrangement 10 or on associated
equipment. The wellhead housing 12 is installed complete with
annulus monitoring valve and flexible hose. A welded connection
attaches the casing 16 to the bottom of the wellhead. Only rough
orientation is required.
[0035] It is possible for pressure in different ones of the annuli
between casings to be monitored or adjusted, or for more than one
annulus, possibly even all, to be so monitored or controlled. FIG.
4 shows an arrangement where the annulus between casings 15 and 16
is monitored and/or adjusted via a second penetration 41. At the
level of penetration 41 through the wellhead housing 12, the
wellhead housing forms an extension of the annulus between casings
15 and 16, it being above the suspension hangar for casing 16, but
it is also below the seal for casing 15 and so isolated from the
more inward annulus between casings 14 and 15. It will be
appreciated that as the progressively more outward casing strings
are hung at progressively lower levels, a penetration to access
them will also be at a lower level, intermediate the casing hangars
of the respective casings that form the annulus.
[0036] When there are a plurality of penetrations to different
annuli they do not all have to be provided with the same
facilities. For instance it may be required only to monitor one or
more while others may need to have pressure controls. The provision
of a penetration may in some cases be used to pressurise only at
the completion/sealing stage with lesser monitoring only equipment
being installed subsequently.
[0037] In the embodiments described above the penetration is radial
though it could be inclined and an alignment framework is required.
Also additional connections between the subsea tree and the
alignment framework are required. In an alternative embodiment
shown in FIGS. 5 and 6 the additional connections can be avoided by
extending the penetration passageway to a void that is created
between an isolation sleeve (reference 40) and the wellhead
housing.
[0038] As in previous embodiments, the wellhead assembly 10 has a
wellhead housing 12, well casing 14 and outer barrier pipe 15.
[0039] As can be seen in FIG. 5, as the wellhead body 12 extends
upwardly beyond the casing hangar 22 there is an upper annulus
defined between the wellhead body 12 and an isolation sleeve 40. In
this embodiment a passage is created through the wellhead body from
the annulus between casings 14 and 15 and into the upper annulus.
This enables the monitoring and pressure adjustment mechanism to be
located higher up and avoid extra connections to the tree.
[0040] In FIG. 5, the first part of the passageway from the annulus
between casings 14 and 15 has an opening in the same location on
the inside of the wellhead housing as previous embodiments. This
time bore 31 is upwardly inclined and communicates with an access
port additionally provided on the wellhead housing. A valve 43,
such as a small bore gate valve is provided within bore 31 to
isolate the pressure of the annulus. The port and this location for
the valve are option. Penetration through the wall of the wellhead
is not needed but blocking a through bore with a port may be a more
convenient way of providing the passageway.
[0041] The passageway then continues through further communicating
bores 44, 45 and 46 to the upper annulus and then via bore 48 to
valves and connections at the top of the wellhead assembly. The
arrangement shown is a convenient way to drill the bores, however
all that is required is to provide a looped passage from the inner
surface of the wellhead housing below packoff 21 to the inner
surface of the wellhead housing above packoff 21. Thus the
configuration, number and inclination of the bores may vary.
[0042] FIG. 6 shows schematically the bores and valves of the
assembly. Hydrocarbon fluids emerge from the well bore to an outlet
50 via a primary master valve 51 and primary wing valve 52. When
isolation valve 43 is open the monitoring and control of the
annulus pressure is via valve 53 and, optionally, other valves
shown generally at 54.
[0043] Valves controlling full flow of hydrocarbon fluids and
access to the annulus between casings 14 and 15 can be applied both
to Side Valve Trees (also known as Horizontal Trees or Spool Trees)
and conventional trees.
[0044] The specific example of the invention described above with
reference to FIGS. 5 and 6 has the advantages that it eliminates
the use of additional connections and isolation valves between the
wellhead system and the subsea tree system. It does not add any
extra operations to the conventional running/installation
procedures for the tree or wellhead as it is usual to have test
ports in this annulus, for example to test the connection between
the Subsea Xmas Tree and the Subsea wellhead. Thus this
communication will in this embodiment additionally have the
application of monitoring the annulus, once the closure/isolation
mechanism is left open in the wellhead.
[0045] The embodiment of FIGS. 5 and 6 may also be used in
combination with lower level penetrations to one or more annulus at
lower levels as described in respect of the embodiment of FIG. 4.
Likewise a looped passageway from between other pairs of packoffs
to above packoff 21 may also be provided. Isolating valves and
onward separate routing would be required if more than one annulus
is connected to the annulus between the wellhead housing and
isolation sleeve.
[0046] It will be appreciated that the embodiments described are
all situated below the Blowout preventor and therefore do not
interfere with the construction of that part of the assembly.
[0047] The invention has been described so far generally within the
context of coaxial casings that have, or will be, sealed at their
top and at the base of the more outward casing so as to form an
enclosed, sealed annulus. While it is most probable that top seals
will always be in place, there need not always be a lower seal.
This then offers the possibility of monitoring pressure that is in
communication with seabed strata or of applying pressure or
introducing fluid or material to the formation via the open end of
the annulus. The open lower end of the casing may have modified
structure or openings for specific purposes.
[0048] FIG. 7 shows a so called `mud lift` system employing a
modification of the invention used during drilling.
[0049] Mud lift systems have been proposed for deep drilling where
the weight of mud in the marine riser as shown in FIG. 1 is too
great to be supported by the formation. To overcome this there have
been proposals to seal the marine riser at the subsea wellhead
level and only have seawater in the riser above that level. It is
then proposed to pump the mud via a mud return to the surface.
However such systems have not yet evolved due to the complexity of
routing the mud from the riser. Proposals for this routing have
been located within the blowout preventer (BOP) which is both
complex and requires redesign of the BOP.
[0050] The present invention proposes providing a penetration 31 as
previously described and connecting the penetration to the mud lift
system. In a further modification (not shown), a penetration may be
provided to route the mud into a casing outside the marine riser,
or even back into the marine riser if the load is supported at the
level of the seal.
[0051] The arrangements described in respect of FIG. 7 may also be
used to transfer material in the reverse direction. For example
after drilling, drill cuttings may be reinjected back into the
formation. This reinjection may alternatively be performed between
other casings, with open lower ends providing access to the
formation.
[0052] After use for mud lift and/or reinjection as the case may
be, the same penetration may be used at the production stage for
monitoring, control or other functions.
[0053] A further embodiment of the invention may establish multiple
penetrations into an annulus so as to provide a flow path. Such a
flow path may be used to drive a pump located in the annulus.
Adjacent annuli may be interconnected by a penetration in their
common casing (at a lower level) and then penetrations as described
above to each of the annuli used as respective inward and outward
flow paths.
[0054] Interconnection of casing annuli via a looped penetration in
the wellhead housing is also possible in a manner similar to the
connection shown between the casing 14 and 15 annulus and the upper
annulus in FIG. 5.
* * * * *