Note: Descriptions are shown in the official language in which they were submitted.
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SUBSEA MANIFOLD SYSTEM
The present invention relates to a subsea hydrocarbon production hub, and
to a subsea hydrocarbon production system incorporating such a hub, which are
particularly useful when oil or gas is to be produced from a plurality of
fields where
at least one is a remote "satellite" field.
It is well-known that when hydrocarbons (oil and/or gas) are to be produced
from a sub-sea reservoir, a top-side facility, such as a production platform
or vessel
is provided on the surface and well-head is provided on the sea bed. The well-
head
is located at the top of the well, through which oil and/or gas may flow from
the
underground reservoir. The well-head is equipped to control the well and has
valve
and arrangements to prevent leakage from the reservoir.
The well-head is connected to the top-side facility by means of a production
and/or injection flow line running along the sea bed, often for tens of
kilometers,
and a riser extending upwardly to the top-side facility, also referred to as a
platform.
Through these, the oil/gas flows to the top-side facility. Also, from the top-
side
facility, risers for gas lift, gas injection or water injection are connected
to the well-
head, either via subsea manifolds or directly to the dedicated wells.
In addition, dedicated umbilicals provide power, control and
communications, as well as the supply of chemicals, such as hydraulic fluids
and
MEG (mono ethylene glycol), which is used as anti-freeze to prevent the
formation
of hydrates.
There will typically be a number of well-heads grouped comparatively close
together. Rather than having separate risers leading to each, a manifold is
normally
provided on the sea bed. This will have risers connecting it to the top-side
facility to
provide the previously-mentioned services. In turn, there are separate
connections
from the manifold to each of a plurality of well-heads. One example of such a
manifold system is disclosed in US 2011/0132615.
Another known situation is for a so-called satellite field to be developed and
produced from the same topside facility. When this is to be done, it can
either be
achieved by a daisy-chained solution via other templates or by connecting each
new satellite field directly to the topside facility. The conventional
arrangement is to
provide a so-called riser base in association with each wellhead and for the
riser
base to be connected to the topside facility.
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Figure 1 illustrates such a conventional arrangement where a topside
facility, in this case the platform, is connected to a standard manifold and
to a
number of satellite fields.
Referring to that figure, the platform 1 is shown schematically as having two
regions, 2 and 3. Region 2 provides for connection to standard manifold 4 by
means of umbilical 5 which includes various conduits. (In the diagram, C
indicates
conduits for control, power and fluids (hydraulic, chemicals and barrier
fluids). WI
indicates water or gas injection, and LP/ HP indicate low pressure/ high-
pressure
production respectively.) Manifold 4 is in turn connected to a number of wells
6
(shown here as nos. 1, 2 and 3) by means of connectors 7.
Platform 1 also has a region 3 for connection to satellite fields. These
fields
will typically have been developed subsequent to the initial fields. The
satellite fields
are shown adjacent to the other fields in the figure, but in reality they will
be
dispersed over a large area of the seabed, often tens of kilometers away. Each
satellite field has a riser base 8, 9, 10 connected to the platform by means
of risers
and umbilicals 11, 12, 13. The riser bases are in turn connected to various
satellite
fields 14, 15 and 16 by means of connections 17, 18 and 19.
It will be understood from the figure that each satellite field normally
requires
dedicated riser(s) between the satellite field and the topside facility, which
each
must include production lines and provide for injection of gas and water. In
addition,
there must be umbilical(s), providing conduits for control, power, MEG and
various
fluids. Accordingly, between two and four riser slots are needed at the
topside
facility for each satellite field.
Taking these factors together, the result is that for each single new field,
very significant new costs are involved. Whilst these costs may be
economically
justifiable where the satellite fields in question contain significant
reserves of
producible hydrocarbons, the development of more marginal fields will not be
commercially attractive. In addition, there is a physical limit on the number
of
available riser slots at the top site facility.
The present invention aims to address this problem in order to enable
production from more marginal satellite fields.
Viewed from a first aspect there is provided a modular, subsea hydrocarbon
production hub comprising a primary manifold and one or more co-located
extension structure(s), the primary manifold having first connections for
connection
to at least a riser and an umbilical from a top-side facility, and second
connections
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for connection to at least one extension structure, wherein at least one of
the
extension structure(s) comprises a secondary manifold having first connections
connected to the second connections of the primary manifold, second
connections
for connection to at least one further extension structure, and third
connections for
connection to at least one wellhead or template, the secondary manifold
providing
for a flow of produced hydrocarbon from the at least one wellhead or template
to
the top-side facility via the primary manifold and the riser, and facilitating
electrical
and/or hydraulic control from the top-side facility via the primary manifold
and the
umbilical.
The use of such a modular hub facilitates communication between a large
number of subsea wells and the surface platform via a small number of risers
and
umbilicals. Furthermore, the modular configuration means that if additional
capacity or functionality is required, for example to produce from new
satellite wells
or to provide additional subsea processing, then this can be provided simply
by
connecting further extension structures to the hub. For example, extension
manifolds or processing equipment may be connected directly to on spare
connections on the primary manifold or an extension structure.
In the present context, the term "co-located" is intended to mean that the
modular components of the hub (the primary manifold and the extension
structures)
are located in a group or cluster proximate one another in the context of an
offshore
hydrocarbon production facility, e.g. below a platform. Thus, they are
proximate at
least relative to a satellite well site, which will be remotely located, often
tens of
kilometers away. In various embodiments, this could for example be understood
to
include components within the safety zone surrounding the riser (typically a
500
meter radius around the riser base, or primary manifold in this case). More
typically
the components of the hub will be closer together and the distance between
individual components would typically be well under 100m, and usually under
50m.
In some embodiments, the components may be directly adjacent and/or
mechanically inter-connected (in addition to the fluid/control connections),
e.g.
bolted together or rigidly connected in some other manner.
In various embodiments, the primary manifold may provide connection to
the secondary manifold (or other extension structure) in respect of any or all
of the
following services, which will typically connect to the riser: hydrocarbon
production,
water injection, gas injection, gas lift. Additionally (or alternatively) it
may provide
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any or all of the services provided via the umbilical, such as control, power
and/or
service fluids (hydraulic, chemicals, barrier fluids).
Typically, the primary manifold will itself be connected to a wellhead and/or
template and indeed, either or both manifolds may be connected to a plurality
of
wellheads and/or templates. Thus, the primary manifold may also have third
connections for connection to at least one wellhead or template. In some
implementations, the hub may be installed at an initial well site, and then
expanded
using extension structures to connect subsea to new satellite sites as they
are
found or become viable.
The facilitation of control is preferably provided by the provision of
conduits
and/or conductors within the riser/umbilical/connector that distribute one or
more
(and preferably all of) the following services: injection gas and water,
electrical
power, electrical control signals, communication, chemicals and/or hydraulic
power.
Corresponding conduits and connections may then be provided within the primary
manifold to allow distribution of these services to the secondary manifold(s).
Most
preferably, each of these services is provided to the hub.
Thus, by means of the invention, satellites can be added to the overall
production system without any increase in the number of risers connected to
the
top-side facility. Alternatively, where a large number of satellite fields are
added, the
increase in the number of risers/umbilicals is significantly reduced compared
to the
prior art. This minimises the number of topside modifications and reduces the
overall cost of producing from such satellite fields.
Preferably, the one or more extension structures include a plurality of
secondary manifolds. As discussed above, the modular configuration permits
simple enlargement of the capacity of the hub to permit new well sites to be
connected and produced. The modular hub is not limited to any specific
configuration, and in various embodiments at least two of the secondary
manifolds
may be connected to the primary manifold or to another extension structure in
series, i.e. as a daisy chain, or in parallel, e.g. in as spokes. The specific
configurations available will of course depend upon the individual design of
the
components of the hub and how many ports are available for the second
connections on each modular component.
The hub, and particularly the primary manifold of the hub, preferably also
provides valving arrangements so that flow of each of the various production
lines
may be controlled. (Likewise, switching arrangements may be provided for
electrical
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power, communications and control.) This may be necessary, either to open and
close connection ports when secondary manifolds are connected/disconnected, or
for control purposes during operation Such valves may be remotely operated
from
the surface, automatically operated (e.g. safety cut-off systems) or operable
by
ROV. Preferably each conduit within the hub may be closed by means of a valve
and preferably a valve is provided in association with each connection port
thereof.
The invention of course also extends to the hub when installed. Thus, in a
second aspect, the present invention also provides a hydrocarbon production
system comprising a top-side production platform connected by means of a riser
and an umbilical to a hub on the sea floor as described above, the hub being
in turn
connected subsea to one or more wells, wherein hydrocarbons produced from each
of the wells flow to the platform via a secondary manifold of the hub, the
primary
manifold of the hub, and the riser, and wherein one or more of service fluids,
electrical control signals, electrical power and injection fluids are
transmitted to
each of the wells via first the primary manifold and then a secondary
manifold.
It will therefore be seen that, in a particularly preferred embodiment, there
is
provided a production platform connected by means of a riser and an umbilical
to a
primary manifold on the sea floor. The primary manifold is in turn connected
to one
or a plurality of secondary manifolds that expand the capacity of the hub. The
secondary manifolds are themselves connected to wellheads and hydrocarbons
produced from those wellheads flows via the secondary manifold, the primary
manifold and then, via a riser, to the platform. At the same time, fluid,
electrical
control signals, electrical power and/or injection fluids are transmitted to
the
wellhead via first the primary manifold and then via the secondary manifold.
Optionally, the primary manifold, a secondary manifold or one or more of the
other extension structures may provide ancillary services. Such services may
include: processing of produced fluids, such as separation of oil from water
and/or
gas, oil, gas and water treatment; boosting the fluid by means of a pump or
compressor; measuring one or more of the different fluid streams.
For example, an external pumping unit may be provided in an extension
structure which may be used to increase the pressure of produced fluids in
order to
maintain or increase the production from the satellite field. The pumping unit
may
be connected to second connections of the primary manifold or an extension
structure.
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In another example, one of the extension structures may comprise a
separator unit. The separator unit may be connected to second connections of
the
primary manifold or an extension structure. The separator unit may separate
water
from a hydrocarbon stream before the hydrocarbon stream is passed to the
riser.
This reduces the quantity of water raised unnecessarily to the surface, The
separated water may be discharged to sea or may be re-injected into a well.
The
separator unit may additionally or alternatively separates a hydrocarbon gas
phase
from a hydrocarbon liquid phase. The gas phase can be used to provide gas
lift.
The liquid phase can be used as a driving medium for an ejector.
Alternatively, the
gas and liquid phases may be separated to facilitate pumping to the surface as
separate phases, which may simplify the pumping equipment required.
Preferably, means is provided for connection of an external pump/pressure
module (to boost pressure of production from satellite fields). To achieve
this, most
preferably, the second connections include ports that are suitable both for
connection to secondary manifold and also for connection to such units.
Although the invention has been described in the context of both a riser and
umbilical being provided between the top-side facility and the subsea
manifold,
other aspects of the invention may involve only a riser or an umbilical, or
pluralities
of one or the other.
The invention also extends to a method of hydrocarbon production
comprising the use of the system, or hub of any of the above aspects of the
invention.
Viewed from a third aspect, the present invention also provides a method of
connecting a subsea wellhead to a top-side production platform via a modular,
subsea hydrocarbon production hub connected to the platform via a riser and an
umbilical, the method comprising: connecting a secondary manifold to the
subsea
hub; and connecting the wellhead subsea to the extension manifold of the hub
such
that hydrocarbons produced from the wellhead flow to the platform via the hub
and
the riser, and one or more of service fluids, electrical control signals,
electrical
power and injection fluids are transmitted to the wellhead via the hub and the
umbilical.
In accordance with this method, a new satellite well or template can be
added to an existing subsea hydrocarbon production facility by simply
installing a
modular extension structure to the hub and connecting the new satellite to the
extension structure. This avoids the need for new dedicated risers and
umbilicals
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to be connected from the platform to the site, thereby reducing costs and tie-
offs
required at the platform, and potentially making new sites economically
viable.
The method may further comprise (remotely) controlling a valving
arrangement and/or switching equipment within the hub to permit flow of
hydrocarbons and/or control to and from the new extension structure.
The method may further comprise connecting one of more functional units to
the hub, for example to enable processing of the hydrocarbons produced by the
satellite well. This may be required where the satellite well has a different
composition to existing wells and may require different processing to existing
wells,
e.g. a higher water or acid gas composition or the like.
Embodiments of the invention will now be described, by way of example
only, and with reference to the accompanying drawings:
Figure 1 is a of view of a conventional system for producing hydrocarbons
from main and satellite fields;
Figure 2 is schematic view of the first embodiment of the invention showing
a primary manifold connected to two secondary manifolds and a pumping unit;
Figure 3 is a schematic view of another of embodiment of the invention
which differs from that of figure 2 in that a further pumping unit is shown in
the
position of one of the extension structures;
Figure 4 is a schematic view of a still further embodiment in which a
separator is provided in connection with the primary manifold;
Figure 5 a schematic diagram of a possible application of the invention to a
complex oil field situation;
Figure 6 is a schematic view of the network and valves in the primary
manifold;
Figure 7 is a perspective view corresponding to figure 6;
Figure 8 is a perspective view of a hub including the primary manifold and a
pumping unit; and
Figures 9 is a sectional view of an umbilical for use with the hubs of the
various embodiments.
With reference to figure 2, there is shown a first embodiment of the invention
20. A host platform 21, at the surface, is connected to a subsea hub 36, on
the
seabed, by means of risers and umbilicals 23. These correspond to the
risers/umbilicals 5 in figure 1. Accordingly, they provide for control, power
and fluids
(hydraulic, chemicals and/or barrier) (C), low pressure production (LP), high
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pressure production (HP) and injection of water (or gas) injection (WI). Gas
lift may
also be provided (not shown). The hub 36 comprises a primary manifold or
"mother
structure" 22 that receives the risers and umbilicals 23 from the surface. The
primary manifold 22 is in turn connected to a plurality of wells 24 (nos. 1, 2
and 3)
by means of connectors 25, again similarly to figure 1. These are shown as
providing production (P), water injection (WI) and control (C), though any or
all of
the above-mentioned services may also be provided.
The present embodiment 20 differs significantly from the prior art system
shown in figure 1 in that the hub 36 has a modular configuration and can be
extended after installation using extension structure that increase the
capacity or
capabilities of the primary manifold 22.
In figure 2, the hub 36 comprises two secondary or extension manifolds 26,
30, which are examples of such extension structures. The first extension
manifold
26 is connected to the primary manifold 22 by means of connections 27. The
first
extension structure 26 is adjacent to the primary manifold 22, generally
within about
50 meters and in some cases physically adjoining the primary manifold 22 with
preferably rigid connections 27 The first extension manifold 26 provides
connections to wells 29 (nos. 4 and 5) by means of connections 28. These
correspond to connections 25 and 7, thus providing production P, water
injection WI
and control C, though any of the other above-mentioned services may be
provided.
The first extension manifold 26 is in turn connected to an adjacent second
extension manifold 30 by means of connections 31, which can be identical to
connections 27. The second extension structure 30 is in turn connected to
further
satellite wells 32 by means of connections 33.
Only two extension manifold are shown in figure 2. However, it will be
appreciated that a third extension manifold may be connected to the second
extension manifold 30. Likewise further such structures may be daisy-chained
together, or connected in parallel.
In addition to being connected to the extension manifold, primary manifold22
is shown as being connected to a pumping unit 34 by means of conduits 35. The
pumping unit 24 is an extension structure that serves to pressurise the
produced
fluids to enable them to be transported to the platform 21 in cases where one
more
of the produced wells is at insufficiently high pressure.
As will be discussed further below, the primary manifold 22 and extension
structures 26, 30, 34, have ports, which are used for connection to various
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connectors, in a standard manner. Accordingly a modular system is provided
whereby standardised extension structures, may be connected to the subsea hub
36 as desired.
The hub 36 thus provides for communication between a large number of
subsea wells 24, 29, 32 and the surface platform 21 via a small number of
risers
and umbilicals 23. If additional capacity or functionality is required, for
example to
produce from new satellite wells, then this can be provided by simply
connecting
further extension manifolds or other functional units to the hub 36.
The provision of additional subsea functionality is illustrated in figure 3
where a second embodiment 40 is shown. This corresponds to the first
embodiment except that in place of second extension manifold 30, the hub 36 is
provided with a further pumping unit 41. Thus, the primary manifold 22 is
connected
both to the second pumping unit 41(indirectly via the first extension manifold
26)
and to the first pumping unit 42.
Another example of the provision of additional subsea functionality is
illustrated in figure 4, where the third embodiment 50 is shown. This differs
from the
second embodiment 40 in that, in place of first pumping unit 42, the hub 36 is
provided with a separator unit 51. The use of a subsea separator unit 51
permits
improved efficiency of the hub in this embodiment 50.
Produced hydrocarbons often contain substantial amounts of water. This
may include formation water that was trapped in the reservoir, or water
injected
during production. The separator unit 51 separates water from produced fluids
so
that water is not wastefully transported to the platform 52. This both
relieves the
riser, as a smaller quantity of fluid must be transported to the surface, as
well as
reducing the amount of topside water processing required at the processing
platform, where space is often limited. The water can be either discharged
into the
sea (subject to appropriate processing, for example using a further extension
structure), or re-injected into an injection well.
As pure phases of liquid and/or gas are more controllable with respect to
throttling, boosting and transporting than a two-or three phase mixture, the
separator unit 51 can also separate liquid phase and gas phase hydrocarbons
from
one another. The gas phase may be pressurized as used as lift gas to increase
production from a well. Alternatively or in addition, the preferably gas-free
liquid
phase may be used as a driving medium for an ejector. Ejectors can be used to
boost production of an existing well or to restart a "dead" well.
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Note that in any of figures 2 to 4, the ancillary unit(s) may be provided in
addition to the plural extension structures shown in figure 2; for clarity
only a limited
number of components are illustrated.
Figure 5 shows a possible application of the invention to areas having a
number of hydrocarbon producing fields connected to the platform.
Here, production platform 61 is above the original well site and is connected
directly to the initial subsea template 62 in a conventional manner.
Previously, the
platform 61 would have been connected directly to the satellite subsea
templates
63 and 64 (for example, with reference to figure 1, manifold 4 might have been
at
the initial site and riser bases 8, 9 and 10 might have been at satellite
sites A, B
and C). However, implementing the invention has the result that a subsea hub
65 is
instead provided in direct connection with the platform 61. The satellite
templates
63 and 64 connect subsea to the hub 65, instead of being connected directly to
the
platform.
This facilitates a reduction in the number of risers and umbilicals required
to
connect these templates 63, 64 to the platform 61. Additionally, the invention
enables satellite fields C, D, E, which would previously have been
economically
unviable, to be produced. Using the present invention, an extension manifold
and
any other required extension structures can be added to the hub 65, and
production
templates 66, 67 and 68 can be installed and connected to the extension
manifold
of the hub 65. Field C is to be produced initially, with fields D and E being
added
later (hence they are shown in phantom).
The application of the invention to this oil field provides a number of the
advantages described previously. In particular, there is a reduced need for
riser
hang-offs at the production platform 61. It also makes it easier to provide
subsea
water separation and pressure boosting, again as previously described.
Furthermore, the use of a modular construction permits the capacity of the hub
65
to be increased to allow further satellite wells to be produced, without the
need for
new risers or umbilicals to directly connect the satellite well to the
platform 61.
Details of the primary manifold and extension structures are described now
with reference to figures 6 to 8.
Schematic pipework diagram 6 shows a hub 70 having a primary manifold
71, an extension manifold 72 and a pumping unit 73. The physical arrangement
of
the pipework and valves, etc. may be seen from figures 7 and 8.
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The arrows at the upper part of figure 6 represent connections to the
umbilical and riser which lead to the production platform. Produced oil is
shown at
81 and 86, electrical control inputs at 82 and 83, water input at 84, and
hydraulic
control input at 85.
The connections to the various external units are shown at the lower part of
the figure. Production input is at 87, 89 and 93, hydraulic fluid at 88 and
92, with
water outlets at 90 and 91. It will also be seen that there are provided flow
paths
between each of the respective inputs and outputs and that control valves are
provided in each line.
Connections 94 and 95 permit the connection of an external pump 73, with
connections 96, 97 and 98 providing injection water, hydraulic and production
connections for future use.
Pumping unit 73 comprises an input and output conduit for connection to the
primary manifold 71, plus an internal pump and a control valve.
Figure 8 shows the pipework of figure 7 mounted to a support cradle and
connected to the external pumping unit 73, thus corresponding to figures 6 and
7.
Figure 9 illustrates a cross-section through an umbilical used to connect the
hub to the platform. It provides the following services:-
36x MEG tubes
6x low pressure hydraulic fluid tubes
6x high pressure hydraulic fluid tubes
6x chemicals tubes
2x barrier fluid tubes
4x spares hydraulic fluid tubes
33x FO cables
10x electrical quads (3-phase and earth)
4x spares electrical quads
2x HV triads 12 kV, 120 mm2
In use, the various control valves provided at the hub and elsewhere will
normally be operated by remotely operated vehicles. However, certain safety
critical valves may be controlled remotely and all by means of automatic
operation
based at the hub.
