U.S. patent application number 10/471329 was filed with the patent office on 2004-08-05 for power connection to and/or control of wellhead trees.
Invention is credited to Appleford, David Eric, Lane, Brian William.
Application Number | 20040149446 10/471329 |
Document ID | / |
Family ID | 9910335 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040149446 |
Kind Code |
A1 |
Appleford, David Eric ; et
al. |
August 5, 2004 |
Power connection to and/or control of wellhead trees
Abstract
A hydrocarbon extraction system (1) comprises a host facility
(2), a wellhead tree (3) and a retrievable electrical power
connection/control module (4). The module has a load (12) and is
connected to the host facility and the tree via first and second
wet mateable connectors (6, 8) respectively. The module also has
qwitchgears (14, 15) controlled by the load for isolating the load
from the host facility or the tree. The host facility is arranged
to provide power to the module, and to the tree via the module when
the switchgears (14, 15) are closed, and the load (12) of the
module is arranged to control the via one (15) of the closed
switchgears.
Inventors: |
Appleford, David Eric;
(Epping, GB) ; Lane, Brian William; (Essex,
GB) |
Correspondence
Address: |
SUMMA & ALLAN, P.A.
11610 NORTH COMMUNITY HOUSE ROAD
SUITE 200
CHARLOTTE
NC
28277
US
|
Family ID: |
9910335 |
Appl. No.: |
10/471329 |
Filed: |
March 12, 2004 |
PCT Filed: |
March 6, 2002 |
PCT NO: |
PCT/GB02/01030 |
Current U.S.
Class: |
166/366 ;
166/368; 166/65.1 |
Current CPC
Class: |
E21B 33/0385 20130101;
H01R 13/523 20130101; E21B 43/017 20130101; E21B 33/0355
20130101 |
Class at
Publication: |
166/366 ;
166/368; 166/065.1 |
International
Class: |
E21B 043/01 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2001 |
GB |
0105856.9 |
Claims
1. A retrievable electrical power connection/control module (4) for
a hydrocarbon extraction system (1), comprising: first
disconnectable connection means (8) arranged to connect the module
to at least one wellhead tree (3) and second disconnectable
connection means (6) arranged to connect the module to a host
facility (2); power/control means (12) arranged to provide power
and/or control operation of at least one said wellhead tree via the
first connection means; and. isolating means (14,15) for isolating
the power/control means from at least one said wellhead tree.
2. A module as claimed in claim 1, wherein the power/control means
(12) is arranged to receive power and/or control signals from the
host facility (2) and to supply it to at least one said wellhead
tree.
3. A module as claimed in claim 1 or 2, wherein the isolating means
(14,15) is arranged to isolate the power control means (12) from
the host facility (2).
4. A module as claimed in claim 1, 2 or 3, including voltage
reduction means (16) for receiving electrical power at a first
voltage level from the host facility (2) and supplying electrical
power at a second lower voltage level to at least one said wellhead
tree (3).
5. A module as claimed in any preceding claim, wherein the
isolating means comprises at least one switchgear (14,15), the or
each switchgear arranged to be controlled from the power control
means (12) of the module (4).
6. A hydrocarbon extraction system (1) comprising a host facility
(2), at least one wellhead tree (3), at least one retrievable
electrical power connection/control module (4) as claimed in any
preceding claim, the or each module being electrically
disconnectably connected to the host facility by its second
connection means (6) and to the at least one tree by its first
connection means (8), the host facility being arranged to provide
power to the or each module and the power/control means (12) of any
said module being arranged to provide power and/or control to at
least one said tree via said first connection means (8).
7. A system as claimed in claim 6, including power isolating means
for enabling the power/control means (12) to supply power or
negligible or no power to said at least one tree.
8. A system as claimed in claim 7, wherein each module (4) has a
module based part (83) of the power isolating means, and each
wellhead tree (3) has a tree based part (84a-e) of the power
isolating means.
9. A system as claimed in claim 6, 7 or 8, wherein the
power/control means (12) includes power means (82) for supplying
power from the module (4) to said at least one tree (3).
10. A system as claimed in claims 7 or 9, wherein the power/control
means includes control means (85) for controlling the power means
(82) and/or the power isolating means (83,84a-e).
11. A system as claimed in any one of claims 6 to 10, wherein the
power/control means (12) is arranged to send control signals to at
least one said tree (3) in parallel to the power.
12. A system as claimed in any one of claims 6 to 11, including a
system module including said retrievable module (4) and being
remote from the at least one tree (3).
13. A system as claimed in any one of claims 6 to 12, wherein at
least one said module (21,41,51,61) is connected by said first
disconnectable connection means (8) to a plurality of said trees
(28,29;43-46;54,55;65-6- 7) in parallel.
14. A system as claimed in any one of claims 6 to 13, wherein at
least one said tree (28,43,54,65) is connected to a plurality of
said modules (21,22;41,42;51-53;61,62) in parallel.
15. A system as claimed in anyone of claims 6 to 14, wherein a
plurality of said modules (41,42,51-53,61-64,71a-d) are connected
in series with the host facility (27) to form a circuit.
16. A system as claimed in any one of claims 6 to 15, wherein at
least one said tree (28,43,54,65,72) is connected in series between
two said modules (21,22;41,42;51,53;61,62;71).
17. A system as claimed in claim 15, wherein at least one said tree
(43,54,65,72) is connected in parallel to a plurality of said
modules (41,42;51-53;61,62;71).
18. A system as claimed in any one of claims 6 to 17, including a
plurality of modules and module isolating means for isolating at
least one module so that the isolated module (22,42) or modules can
be removed without cutting off the supply of electrical power to
any of the trees (28,29,43-46) or any of the remaining modules
(21,41) of the system.
19. A system as claimed in claim 18, wherein the host facility (27)
has a host facility based part (25,26) of the module isolating
means.
20. A system as claimed in claim 18 or 19, wherein each wellhead
tree (28,29,43-46) has a tree based part (34a,34b;35a,35b;49) of
the module isolating means.
21. A system as claimed in claim 18, 19 or 20, wherein each module
(41,42) has a module based part (48) of the module isolating
means.
22. A system as claimed in any one of claims 18 to 21, wherein
parts (25,48,49) of the module isolating means electrically
adjacent to the module (41) to be removed are arranged to isolate
the module.
23. A system as claimed in any one of claims 18 to 22, wherein the
module isolating means is arranged to isolate a plurality of
serially adjacent modules.
24. A system as claimed in any one of claims 18 to 23, wherein the
module isolating means and/or the power isolating means comprises
switchgears.
25. A system as claimed in any one of claims 6 to 24, wherein at
least one said tree (3) has a parallel supply of power from a said:
module (4) and an emergency shut down facility (90a-d) for closing
at least one valve (80a-d) in the tree (3) when there is an absence
of the parallel supply of power.
26. A hydrocarbon extraction system (1) comprising: a host facility
(2) for supplying electrical power; at least one retrievable
electrical power connection/control module (4); at least one
wellhead tree (3) remote from the or each module; and means (12)
for powering/controlling at least one said tree including means for
transmitting the electrical power from the host facility to the
tree and/or transmitting electrical control signals from the module
to at least one said tree.
27. A method of powering/controlling a wellhead tree (3) in a
hydrocarbon extraction system (1) including the step of supplying
at least one said tree (3) with electrical power and/or electrical
control signals from a remote retrievable power/control module
(4).
28. A method as claimed in claim 27, including the step of
supplying the module (4) with power and/or control signals from a
host facility (2).
29. A method as claimed in claim 27 or 28, wherein at least one
said tree (3) is supplied with control signals in parallel to the
electrical power.
30. A method as claimed in claim 29, including the steps of: (a)
activating the module (4) to supply negligible or no power to at
least one said tree (3); (b) activating power isolating means to
enable the module (4) to be able to supply power to at least one
said tree (3); and (c) activating the module to supply power from
the module (4) to at least one said tree (3).
31. A method as claimed in claim 30, including before step (a) the
step of activating the power isolating means to isolate the module
(4) from at least one said tree (3).
32. A method as claimed in claim 30 or 31, including after step
(c), the steps of: (d) activating the module (4) to supply
negligible or no power to at least one said tree (3); and (e)
activating the power isolating means to isolate the module (4) from
at least one said tree (3).
33. A method as claimed in claim 32, wherein step (e) includes
activating a module based part (83) of the power isolating means
before a tree based part (84a-e) of the power isolating means.
34. A method as claimed in any one of claims 30 to 33, wherein step
(b) includes activating a tree based part (84a-e) of the power
isolating means before a module based part (83) of the power
isolating means.
35. A method as claimed in any one of preceding claims 30 to 34,
including controlling the activating steps by control means (85) in
the retrievable module (4).
36. A method as claimed in any one of claims 28 to 35, including
transmitting electrical power at a first voltage from the host
facility (2) to voltage reduction means (16) and transmitting
electrical power at a second lower voltage from the voltage
reduction means to at least one said tree (3), and transmitting
said electrical control signals from control means (12) in the
retrievable module (4) to at least one said tree (3).
37. A method as claimed in any one of claims 28 to 35, including
transmitting electrical power and control signals from the host
facility (2) to said at least one tree (3), and reducing the
voltage between the host facility (2) and said at least one tree
(3).
Description
[0001] The present invention relates to power connection to and/or
control of wellhead trees, such as those trees used in an
underwater oil/gas field. Conventional oil/gas fields have a
plurality of wells which remove the oil/gas from reservoirs beneath
the seabed. Each well has a wellhead tree on the seabed, the trees
being linked to a host facility via flow lines. Each wellhead tree
incorporates a number of main valves which are often powered by
hydraulically operated actuators. Most of the valves are emergency
shut-down (ESD) valves, although some may be variable positional
flow control valves also known as chokes. The ESD valves are
normally operated in either fully open or fully closed positions.
It is usual for each valve to be operated in turn.
[0002] If the trees are in close proximity to the host facility and
few in number, they may be powered and controlled directly from the
host facility. However, trees are often not close to the host
facility and consequently each tree is equipped with its own
control pod which contains the means for actuating the valves in
the trees. These valves may be actuated by electric solenoid
actuators or by hydraulically operated control valve actuators
where both these systems require physical communication with the
host facility. The tree valves are generally hydraulic and the
control pod will generally have hydraulic connections with these
valves in order to operate them. Such hydraulic connections have
cleanliness/maintenance issues. If a control pod fails as a result
of a component within it failing, for example, or due to the
failure of an associated wet mateable connector between the control
pod and the tree, then the tree ceases to operate as required and
consequently production is lost whilst replacement or repairs are
carried out.
[0003] It is an object of the present invention to improve the
arrangement for powering/controlling wellhead trees.
[0004] According to one aspect of the present invention there is
provided a retrievable electrical power connection/control module
for a hydrocarbon extraction system, comprising:
[0005] first disconnectable connection means adapted to connect the
module to at least one remote wellhead tree and second
disconnectable connection means adapted to connect the module to a
remote host facility;
[0006] power/control means adapted to provide power/control
operation of at least one said wellhead tree via the first
disconnection means; and
[0007] isolating means for isolating the power/control means from
at least one said wellhead tree.
[0008] One such retrievable electrical power connection/control
module is able to provide power/control operation of a number of
remote trees instead of there being a control pod for each tree.
The module can control all the functions of the tree.
[0009] The retrievable module permits high voltages (e.g. 11/24KV)
to be used between the host facility and such a module with there
being a benefit of low losses over long step-out distances. It also
enables relatively low voltages (e.g. 400V) to be used between the
retrievable module and the wellhead tree or trees to which it is
connected and also avoids the problems of using hydraulics. By
having the control means in the retrievable electrical power
connection module, this avoids local control equipment on the trees
resulting in simpler and more reliable trees.
[0010] The power/control means may be adapted to receive power
and/or control signals from the host facility and supply it to said
at least one tree.
[0011] It may be desirable for the isolating means to isolate the
power/control means from the host facility. The isolating means may
comprise at least one switchgear, the or each switchgear adapted to
be controlled from the power/control means of the module.
[0012] The module may include voltage reduction means for receiving
electrical power at a first voltage level from the host facility
and supplying electrical power at a second lower voltage level to
at least one said wellhead tree.
[0013] There may be provided a hydrocarbon extraction system
comprising a host facility, at least one wellhead tree, at least
one retrievable electrical power connection/control module as
previously described, the or each module being electrically
disconnectably connected to the host facility by its second
connection means and to the at least one tree by its first
connection means, the host facility being adapted to provide power
to the or each module and the power/control means of any module
being adapted to provide power and/or control at least one said
tree via said first connection means.
[0014] The system may include power isolating means for enabling
the power/control means to supply power or negligible or no power
to said at least one tree. Each module may have a module based part
of the power isolating means, and each wellhead tree may have a
tree based part of the power isolating means.
[0015] It may be desirable for the power/control means to include
power means for supplying power from the module to said at least
one tree. The power/control means may include control means for
controlling the power means and/or the power isolating means.
[0016] The hydrocarbon extraction system may include a system
module remote from the at least one tree including the retrievable
electrical power connection/control module.
[0017] At least one module may be connected by the first
disconnectable connection means to a plurality of trees in
parallel. At least one tree may be connected to a plurality of
modules in parallel.
[0018] It may be desirable for a plurality of modules to be
connected in series with the host facility to form a circuit. At
least one tree may be connected in series between two modules. A
plurality of the trees connected in series may be connected between
two modules. At least one tree may be connected in parallel to a
plurality of modules.
[0019] Conveniently, the system may include a plurality of modules
and module isolating means for isolating at least one module so
that the isolated module or modules can be removed without cutting
off the supply of electrical power to any of the trees or any of
the remaining modules of the system. The host facility may have a
host facility based part of the module isolating means. Each
wellhead tree may have a tree based part of the module isolating
means. Each module may have a module based part of the module
isolating means. Preferably, parts of the module isolating means
adjacent to the module to be removed are adapted to isolate the
module. The module isolating means may be adapted to isolate a
plurality of serially adjacent modules. The module isolating means
and/or the power isolating means may comprise switchgears.
[0020] According to another aspect of the present invention there
is provided a hydrocarbon extraction system comprising:
[0021] a host facility for supplying electrical power;
[0022] at least one retrievable electrical power connection/control
module;
[0023] at least one wellhead tree remote from the or each module;
and
[0024] means for powering/controlling at least one said tree
including means for transmitting the electrical power from the host
facility via the module to at least one said tree and/or
transmitting electrical control signals from the module to at least
one said tree.
[0025] According to yet another aspect of the present invention
there is provided a method of powering/controlling at least one
wellhead tree in a hydrocarbon extraction system including the
steps of supplying at least one said tree with electrical power
and/or electrical control signals from a remote retrievable
electrical power connection/control module.
[0026] The method may include the steps of:
[0027] (a) activating the module to supply negligible or no power
to at least one said tree;
[0028] (b) activating power isolating means to enable the module to
be able to supply power to at least one said tree; and
[0029] (c) activating the module to supply power from the module to
at least one said tree.
[0030] The method may include the step of activating the power
isolating means to isolate the module from at least one said tree
before step (a).
[0031] There may be the additional step (d) after step (c) of
activating the module to supply negligible or no power to at least
one said tree, and the additional step (e) of activating the power
isolating means to isolate the module from at least one said
tree.
[0032] Step (b) may include the step of activating a tree based
part of the module isolating means before a module based part of
the module isolating means. Step (e) may include the step of
activating the module based part of the module isolating means
before the tree based part of the module isolating means.
[0033] The various activating steps may be controlled by a control
means in the retrievable module.
[0034] The power isolating means may be switches/relays which are
operated at no or negligible power, which means that reliability
issues regarding switching at high power are avoided.
[0035] The control may be effected without using pressurised fluid
control signals.
[0036] Electrical power may be transmitted at a first voltage from
a host facility to voltage reduction means and transmitted at a
second lower voltage from the voltage reduction means to the tree,
and electrical control signals may be transmitted from a control
means in a retrievable module to the wellhead tree. Alternatively,
electrical power at a first voltage and control signals may be
transmitted from a host facility to voltage reduction means and
electrical power at a second lower voltage and control signals from
the voltage reduction means may be transmitted to the tree.
[0037] Embodiments of the present invention will now be described,
by way of example, with reference to the accompanying drawings, in
which:
[0038] FIG. 1 is a schematic diagram of a substantially underwater
system including a retrievable module according to a first
embodiment of the invention;
[0039] FIG. 2 is a schematic circuit diagram of the substantially
underwater system;
[0040] FIGS. 3 and 4 show a schematic diagram of a modified
substantially underwater system in accordance with an aspect of the
invention; and
[0041] FIGS. 5 to 9 show schematic diagrams of further modified
substantially underwater systems in accordance with further aspects
of the invention; and
[0042] FIGS. 10 and 11 are modifications of FIG. 2.
[0043] Referring to FIG. 1 of the accompanying drawings, a
substantially underwater system 1 is shown. A top side host
facility 2 is connected to a wellhead tree 3 via a retrievable
module 4 or control pod in a substantially autonomous system module
on the seabed (not shown) remote from the tree. The host facility
provides the source of power for both the retrievable module 4 and
the tree, the module 4 forming part of an electrical power
connection to the tree. The host facility 2 has a switchgear 5
which is connected to an underwater mateable connector 6 on one
side of the module by an integrated power/control cable 7. The
opposite side of the module 4 also has an underwater mateable
connector 8 that is connected to an underwater mateable connector 9
on the wellhead tree 3 by another integrated power/control cable
10, the module mateable connectors 6,8 enabling the module to be
retrieved. The tree 3 has a load 11 to which the tree connector 9
is connected.
[0044] The module 4 has a load 12 connected to an integrated
power/control cable 13 which links the two connectors 6,8 of the
module together. The load 12 is electrically isolatable from the
mateable, connectors 6 and 8 by first and second switchgears 14 and
15 respectively, each switchgear being controlled by the load 12.
Accordingly, the first switchgear 14 connects the load with the
host facility 2 and the second switchgear 15 connects it to the
wellhead tree 3.
[0045] Each power/control cable or umbilical 7,13,10 comprises a
three-phase power supply cable, each including three supply lines
7a,13a,10a;7b,13b,10b; 7c,13c,10c as illustrated in the simplified
circuit diagram shown in FIG. 2. The power supply line 7a,13a,10a
forms a series connection from the host facility switchgear 5 to
the tree load 11 through the module 4. The power supply line
7b,13b,10b also forms a series connection from the host facility
switchgear 5 to the tree load 11 through the module 4 as does the
power supply line 7c,13c,10c. The module load 12 is connected
across the power supply lines 13a,13b,13c as shown. The host
facility switchgear 5 and the module switchgears 14,15 effect the
switching of all three power supply lines. The module also includes
a transformer 16 for reducing high voltage input from the host
facility 2, the transformer being across the power supply lines
between the module's mateable connector for the host facility and
the first switchgear 14.
[0046] The retrievable module 4 has a control pod which is divided
into two compartments by means of a bulkhead. The two compartments
house the control electronics, which forms part of the module load
12, and the switchgears 14,15 respectively. The control electronics
controls the normal running of the module 4 and the connected
wellhead tree 3 and the module load 12 is in communication with the
host facility 2 from where it may, for example, be reprogrammed or
be instructed to shut down the tree. The control pod is constructed
as a pressure vessel and has penetrators for cables from outside
the pod to connect to the control electronics and switchgear.
[0047] In normal use, the host facility switchgear 5 and the two
module switchgears 14,15 are closed so that the module load 12 and
the tree load 11 receive power from the host facility 2 and so that
the module load is able to electrically control the wellhead tree 3
via the closed second switchgear 15.
[0048] Referring to FIG. 3, a more complex substantially underwater
system 20 is shown, the system being similar to the underwater
system 1 described in FIGS. 1 and 2 except where noted. The system
20 has first and second substantially autonomous seabed modules
21,22, the load 23,24 of each module being connected to separate
switchgears 25,26 of a host facility 27. The system 20 also has
first and second wellhead trees 28,29, the load 23,24 of each
module being interconnected with the load 30,31 of each wellhead
tree 28,29. Each module 21,22 and each tree 28,29 has a pair of
parallel switchgears 32a,32b;33a,33b;34a,34b;35a,35b connected to
its respective load 23,24,30,31, the pair of switchgears for each
module and each wellhead tree being controlled by its respective
load, although the switchgears of the trees may also or instead be
controlled by either of the modules. One 32a of the pair of
switchgears of the first module 21 is connected via an integrated
power/control cable 36 to one 34a of the switchgears of the first
tree 28 and the other 32b of the pair of switchgears of the first
module is connected via another integrated power/control cable 37
to one 35a of the switchgears of the second tree 29. The pair of
switchgears 33a,33b of the second module 22 are similarly connected
to the other switchgears 34b,35b of both the trees 28,29 via
integrated power/control cables 38,39 respectively.
[0049] The electrical connectors are such that the load 23,24 of
each module 21,22 can control either or both of the trees 28,29.
For example, the load 23 of the first module 21 can control the
first tree 28 and the load 24 of the second module 22 can control
the second tree 29. This is achieved by having the first module
first switchgear 32a closed and the first module second switchgear
32b opened and the second module first switchgear 33a opened and
the second module second switchgear 33b closed. Also, the host
facility switchgears 25,26 and the tree switchgears 34a and 35b
need to be closed. In a similar way the first module load 23 can
control the second tree 29 and the second module load 24 can
control the first tree 28 by having the first module first
switchgear 32a opened and the first module second switchgear 32b
closed and the second module first switchgear 33a closed and the
second module second switchgear 33b opened.
[0050] If one module needs to be retrieved, the switchgears can be
set so that the two trees can be controlled by the load of the
other module with the trees still being provided with power from
the host facility 27. For example, to retrieve the second module
22, as illustrated in FIG. 4, the second switchgear 34b in the
first tree 28 and the second switchgear 35b in the second tree 29
are opened and the second switchgear 26 in the host facility 27 is
opened, causing the second module 22 to be isolated. The first
switchgears 34a,35a in the first and second trees 28,29 remain
closed as do the pair of first module switchgears 32a,32b to which
they are respectively connected. Hence, both trees 28,29 are able
to be controlled by the load 23 in the first module and receive
power from the host facility 27 via the closed first host facility
switchgear 25. The second module 22, being isolated, can then be
retrieved, whilst permitting the remaining module and trees to
continue to operate. Once retrieved the second module 22 may be
inspected/adjusted before being lowered back or a separate
replacement module may be lowered and installed in the place
hitherto occupied by the second module.
[0051] In a similar way, the first module 21 can be isolated and
retrieved with both wellhead trees 28,29 being controlled by the
load 24 in the second module 22 and the trees receiving power from
the host facility 27 via the second switchgear 26 of the host
facility.
[0052] In a like manner a single module could be connected to two
or more trees. Alternatively, plural modules could be connected to
a single tree. Further alternatives include two or more modules
connected to two or more trees.
[0053] Also, one or more trees may be removed by first being
isolated by the relevant switchgears, and at the same time
permitting the remaining trees and modules to continue to
operate.
[0054] In FIGS. 5 to 9, other possible alternative substantially
underwater systems are shown.
[0055] The system 40 shown in FIG. 5 is similar to the system 20
shown in FIGS. 3 and 4 except that each module 41,42 is adapted to
be connected to four wellhead trees 43,44,45,46, each module having
four parallel switchgears 47a,47b,47c,47d, each one of these
switchgears being provided for a respective tree. In addition, the
two modules 41,42 are connected in series between the two
switchgears 25,26 of the host facility 27 to form a circuit and
each module has an additional switchgear 48 for the series
connection to the power supply of the load of the adjacent module.
The host facility switchgears 25,26 are adapted to isolate the
modules 41,42 from the power supply at the host facility 27, and
from control signals which may be sent from the host facility. By
having the modules 41,42 connected in series between the two host
facility switchgears 25,26, either of the modules may be isolated
by operating the host facility switchgear and the module switchgear
48 on adjacent opposite sides of the module to be removed and the
tree switchgear 49 adjacent to the module to be removed. Hence, a
module is able to be recovered without affecting power to the trees
43,44,45,46 or to the remaining module nor effecting the control of
the trees by the remaining module.
[0056] In a like manner two or more modules could be connected to
any number of trees.
[0057] The system 50 shown in FIG. 6 is similar to the system 40
shown in FIG. 5 except that there are three modules 51,52,53 in
series and two wellhead trees 54,55. Each module 51,52,53 is
adapted to be connected to the two trees 54,55 and each tree has
three parallel switchgears 56a,56b,56c, with there being one
switchgear for each module. Although three modules are provided
only two power/control cables need to extend from the host facility
27 to the subsea location where the modules and trees are
installed.
[0058] FIG. 7 shows an arrangement of four modules 61,62,63,64
connected in series between the two host facility switchgears 25,26
with three wellhead trees 65,66,67 being interconnected with the
first two modules 61,62 and another three wellhead trees 68,69,70
being interconnected with the third and fourth modules 63,64. The
first two modules 61,62 and the trees 65,66,67 comprise one of two
system groups and the third and fourth modules 63,64 and the trees
68,69,70 comprise the other system group. A module in one system
group is able to power and/or control any tree in the other group
via the power/control link 73 between the second and third modules
62,63. Thus, if say the first 61 or fourth module 64 is to be
removed the substantially underwater system can continue
production.
[0059] Grouping of modules and trees interconnected in a like
manner could alternatively be used. For example, any number of
groups could be used with each group containing any number and
preferably a plurality of modules and trees.
[0060] FIG. 8 illustrates an arrangement where a number of modules
71a-d are connected in series between the two host facility
switchgears 25,26. A number of wellhead trees 72a-e are connected
in series and are connected to two of the modules, the series of
trees being parallel to the modules in series. Thus, there is a
complete ring circuit for power and/or control of the trees 72 from
the modules 71 with duplicate power and/or control supplies from
the host facility. With such an arrangement, isolation of any
module or tree for removal purposes can be effected by opening the
two serially adjacent switchgears on opposite sides of the
particular module or tree, whilst permitting the remaining modules
and trees to continue to operate. If, say, the switchgear 25 fails,
the power/control continues to the modules and trees from the
switchgear 26 via the ring circuit. If, say, module 71 a is
removed, although the ring circuit is broken, supply continues via
switchgear 26. Also, if the load 12 within the module 71 a for
controlling the trees fails, control would be supplied by any one
of the other modules via a clockwise route around the ring circuit
via module 71d.
[0061] In a like manner any number, and preferably a plurality, of
modules could be connected to any number, and preferably a
plurality, of trees.
[0062] The arrangement of FIG. 9 is similar to FIG. 8 except that
there are two groups of trees 72, each tree of a group being
connected to other trees in the group in series, each group being
connected in parallel to the modules and being connected to
different modules. If a module is removed, the trees connected
thereto are able to receive control signals from the load of a
remaining adjacent module and the trees and the remaining modules
are still able to receive power from host facility, control
signals/power being received via any intervening modules or trees.
In a like manner the system may include any number of groups, each
group comprising any number, and preferably a plurality, of modules
connected to any number, and preferably a plurality, of series
connected trees.
[0063] Referring to FIG. 10, a modified schematic circuit diagram
of the arrangement shown in FIG. 2 is illustrated. The wellhead
tree 3 includes five valves 80a-e, such as choke valves, which are
each actuated by an associated valve actuator comprising a motor
81a-e. Also, the retrievable module 4 has a three-phase drive
system 82 which receives its power from the host facility (not
shown) via the power/control cable 7 including the three supply
lines 7a-c. The drive system 82 is connected via the three
power'supply lines 10a-c carried by the integrated power/control
cable 10 between the module and the tree, to each valve actuator
motor 81a-e in parallel. The drive system has an associated low
power switch/relay 83 across the three power supply lines 10a-c
between it and the tree. Each motor 81a-e also has an associated
simple low power switch/relay 84a-e. The module 4 also includes a
control system 85 which is connected by parallel control lines
86a-e carried by the integrated power/control cable 10, each
control line 86a-e connecting to a respective switch/relay 84a-e in
the tree. The control system controls the speed and direction of
operation of the valve actuators in the tree. The control system 85
is also connected to the drive system 82 by a control line 87. It
also is connected to the host facility by a control line 88 carried
by the integrated power/control cable 7 to the host facility.
[0064] The drive system 82, the switch/relay 83 and the control
system 85 are all contained within the retrievable control pod or
module 4. This ensures that these, components with a propensity for
failure are contained within the retrievable control pod and can be
readily replaced.
[0065] The control system 85 is so configured to ensure that the
switches 84a-e are only operated when the drive system 82 is not
providing power to the power/control cable 10 between the module 4
and the tree 3.
[0066] When, for example, valve 80a is required to be operated, all
the switches/relays 83, 84a-e are initially open and the drive
system 82 is set by the control system 85 to ensure that there is
negligible/no power on the supply lines 10a-c. The control system
85 then closes the switch/relay 84a associated with the valve 80a
and then the drive system's switch/relay 83. By closing the
switches/relays in this order, any of the switches/relays in the
tree are prevented from being damaged by any residual power,
ensuring that any possible damage is confined to the readily
retrievable control pod 4 in the system module. The drive system is
then instructed by the control system 85 to provide the required
power to the motor 81a to operate the valve 80a. Once the valve has
been operated, the drive system 82 is actuated to ensure that there
is negligible/no power on the supply lines 10a-c. The control
system 85 then causes the switch/relay 83 to be opened and then the
valve switch/relay 84 to be opened.
[0067] The other valves 80b-e of the tree 3 are operated in a
similar manner.
[0068] Referring to FIG. 11, a modification of the arrangement of
FIG. 10 is shown in which the tree 3 additionally has an emergency
shut-down (ESD) facility 90a-d on four of the valves 80a-d. The ESD
facility comprises part of the valve actuator and does not require
the valve motor 81a-e to operate to facilitate closure of the
valve. Each ESD facility 90a-d is connected to a common ESD supply
from an ESD control device 91 in the control pod 4 via a supply
line 92 in the integrated power/control cable 10. The ESD control
device 91 is controlled by signals from the host facility supplied
via the control system 85 in the control pod 4 and receives its
power from the drive system 82 via a supply line 93.
[0069] When there is an absence of the ESD supply from the ESD
control device 91, then this causes the valves 80a-d to
automatically close.
[0070] The arrangements in FIGS. 10 and 11 can easily be
incorporated into substantially underwater systems described with
reference to FIGS. 3 to 9, and may constitute an invention
independently of the other features referred thereto.
[0071] The systems described are all electric. Electrical systems
can operate over greater distances/deeper levels, transmit
emergency signals instantaneously, such as to shut down a wellhead
tree, and are cheaper than existing systems. The systems use
industry standard networking protocols to signals sent from the
seabed modules to the trees or from the host facility to the seabed
modules and/or trees which enables a signal to be received by the
intended recipient tree or module to be interpreted as a control
signal for that particular tree or module.
[0072] The system of retrievable modules and wellhead trees may
comprise any suitable arrangement for the particular oil/gas field
being exploited. While the invention has been described in the
context of a sub-sea hydrocarbon field it could also be used in
other environments and, in particular, environments in which access
is not readily available such as in swamps or marshes.
[0073] It is to be understood that each cable, such as cables
7,10,36-39, shown by a single line in the FIGS. 1 and 3 to 9 may
comprise three lines (e.g. 7a,7b,7c;10a,10b,10c), each line
carrying one phase of a three phase electrical supply and running
parallel to each other as shown for example in FIG. 2. Any of the
integrated power/control cables or umbilicals 7,13,10 may be
replaced by separate power and control lines.
[0074] There does not have to be a discrete umbilical or discrete
lines between a module and a tree, as this could be replaced by an
intervening unit, such as a termination block, to which at least
one module and at least one tree is connected by at least one
umbilical or power and control lines. The intervening unit may be a
docking manifold in which cross-linking between at least one tree
and at least one module is hard wired. A single umblicial may
connect at least one module to the docking manifold and another
single umblicial may connect at least one tree to the docking
manifold. At least one module and at least one tree may be
connected together by a "loomed" umbilical.
[0075] The integrated power/control cable between a module and a
tree may be used to additionally carry chemical injection fluid
into the tree. A retrievable module may comprise a retrievable
subsea power and control pod which may be contained within a system
module.
[0076] Any of the arrangements described in the Figures may be
modified to provide single phase electrical supply.
[0077] Unless otherwise stated, connectors referred to are to be
taken as electrical connectors.
[0078] While emergency shut down valves have been described as
being closed upon actuation, the present invention would be equally
applicable to valves which are opened upon actuation.
* * * * *