U.S. patent application number 12/766511 was filed with the patent office on 2010-12-30 for production of hydrocarbons.
Invention is credited to Ton Coppens.
Application Number | 20100326667 12/766511 |
Document ID | / |
Family ID | 43379464 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100326667 |
Kind Code |
A1 |
Coppens; Ton |
December 30, 2010 |
PRODUCTION OF HYDROCARBONS
Abstract
The present invention relates to a floating production platform
for oil and/or gas production in a marine environment, the floating
production platform comprising: a floater for providing buoyancy,
the floater having suitable motion characteristics for supporting a
dry tree riser, at least one riser support point constructed and
arranged for supporting at least one dry tree riser which extends
between the floating production platform and a seabed, a rotary
communication assembly constructed and arranged for providing
communication between the floating production platform and a vessel
for: transferring a product fluid coming out of the at least one
riser to the vessel, and/or transferring other fluids between the
floating production platform and the vessel, and/or transferring
electrical power via one or more electrical lines between the
floating production platform and the vessel, transferring control
signals via one or more electrical lines or fibre optic lines
between the floating production platform and the vessel, the rotary
communication assembly comprising: a circumferential communication
line which in top view extends around the at least one riser
support point, bridge communication line being in connection with
the circumferential communication line at one end and comprising an
end coupling at the other end for connection with the vessel, the
bridge communication line constructed to bridge a gap between the
floating production platform and the vessel, wherein the bridge
communication line is movable along the circumferential
communication line such that when in use the vessel weathervanes
around the floating production platform, the bridge communication
line rotates around the floating production platform with the
weathervaning vessel, such that the rotary communication assembly
maintains communication between the riser and the vessel.
Inventors: |
Coppens; Ton; (Oegstgeest,
NL) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.;624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Family ID: |
43379464 |
Appl. No.: |
12/766511 |
Filed: |
April 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61172545 |
Apr 24, 2009 |
|
|
|
Current U.S.
Class: |
166/355 ;
114/230.1; 166/369 |
Current CPC
Class: |
B63B 21/507 20130101;
B63B 27/24 20130101 |
Class at
Publication: |
166/355 ;
166/369; 114/230.1 |
International
Class: |
E21B 43/01 20060101
E21B043/01; B63B 21/00 20060101 B63B021/00 |
Claims
1. Floating production platform for oil and/or gas production in a
marine environment, the floating production platform comprising: a
floater for providing buoyancy, the floater having suitable motion
characteristics for supporting a dry tree riser, at least one riser
support point constructed and arranged for supporting at least one
dry tree riser which extends between the floating production
platform and a seabed, a rotary communication assembly constructed
and arranged for providing communication between the floating
production platform and a vessel for transferring a product fluid
coming out of the at least one riser to the vessel, and/or
transferring other fluids between the floating production platform
and the vessel, and/or transferring electrical power via one or
more electrical lines between the floating production platform and
the vessel, and/or transferring control signals via one or more
electrical lines or fibre optic lines between the floating
production platform and the vessel, the rotary communication
assembly comprising: a circumferential communication line which in
top view extends around the at least one riser support point, a
bridge communication line being in connection with the
circumferential communication line at one end and comprising an end
coupling at the other end for connection with the vessel, the
bridge communication line constructed to bridge a gap between the
floating production platform and the vessel, wherein the bridge
communication line is movable along the circumferential
communication line such that when in use the vessel weathervanes
around the floating production platform, the bridge communication
line rotates around the floating production platform with the
weathervaning vessel, such that the rotary communication assembly
maintains communication between the riser and the vessel.
2. Floating production platform of claim 1, comprising at least one
drilling derrick, wherein in top view the circumferential
communication line extends around the at least one drilling
derrick.
3. Floating production platform of claim 1, wherein the
circumferential communication line comprises: an annular swivel
comprising an inner ring comprising a inner fluid conduit and an
outer ring comprising an outer fluid conduit, the inner fluid
conduit being in fluid connection with the supply opening, wherein
the inner ring and outer ring are rotatable relative to one another
and wherein the inner fluid conduit and the outer fluid conduit are
in fluid connection with one another, wherein the bridge
communication line is connected to the outer fluid conduit, or a
reel, wherein the bridge communication line and the circumferential
communication line form an ongoing line which is flexible and is
spooled partly on the reel and extends partly from the reel to the
vessel.
4. Floating production platform of claim 1, wherein the floating
production platform comprises a plurality of riser support points
and wherein the circumferential communication line extends around
the plurality of riser support points.
5. Floating production platform claim 1, wherein the floating
production platform comprises primary drilling equipment and
primary production equipment and wherein in top view the
circumferential communication line extends around the primary
drilling equipment and primary production equipment.
6. Floating production platform of claim 1, wherein in top view the
circumferential communication line extends substantially along an
outer circumference of the floating production platform.
7. Floating production platform of claim 1, wherein the rotary
communication assembly is constructed to allow rotation of the
vessel around the floating production platform over a plurality of
revolutions.
8. Floating production platform of claim 1, comprising a plurality
of circumferential communication lines above one another in order
to allow a plurality of fluid connections between the floating
production platform and the vessel.
9. Floating production platform of claim 1, wherein the
circumferential communication line is shaped by a reel which is
substantially flat and comprises a vertical rotation axis.
10. Floating production platform of claim 1, wherein the floater is
a turret like construction constructed to be positioned in a
moonpool of a vessel.
11. Combination of the floating production platform of claim 1 and
a vessel, wherein the at least one bridge communication line is
connected at one end to the floating production platform and at the
other end to the vessel.
12. Combination of claim 11, comprising a rotary mooring assembly
constructed to bear a mechanical load and configured to allow
weathervaning of the vessel about the floating production platform,
the rotary mooring assembly comprising: one end which is connected
with the floating production platform, an opposite end which is
connected with the vessel, a rotary coupling at the end which is
located at the floating production platform, which rotary coupling
is constructed to allow weathervaning of the vessel around the
floating production platform, the rotary mooring assembly being
constructed for maintaining the vessel at a substantially
controlled distance from the floating production platform.
13. Combination of claim 11, wherein the floating production
platform comprises primary production equipment and wherein the
vessel comprises auxiliary production equipment and supplies which
are auxiliary to the primary production equipment on the floating
production platform.
14. Combination of claim 11, wherein the circumferential
communication line comprises a first reel, and wherein the vessel
comprises at least one second reel, wherein the at least one bridge
communication line is spooled on both reels, allowing a part of the
bridge communication line which is spooled from the reel on the
floating production platform during weathervaning to be spooled
onto the second reel on the vessel and vice versa, thereby
maintaining the length of the bridge communication line between the
floating production platform and the vessel substantially the
same.
15. Combination of claim 11, wherein the circumferential
communication line comprises a reel for spooling the bridge
communication line, allowing a part of the bridge communication
line to be spooled from the reel during weathervaning of the vessel
around the floating production platform, and wherein an end of the
bridge communication line is connected to a discharge point on the
vessel, wherein the circumferential communication line and the
discharge point are constructed to allow an excess length of the
bridge communication line to be suspended in the water between the
floating production platform and the vessel.
16. Combination of claim 11, wherein the floating production
platform is a Tension leg Platform (TLP), a Spar or a Dry Tree Unit
(DTU) and the vessel is a Floating Production, Storage and
Offloading (FPSO) vessel or a Floating Production and Offloading
(FPO) vessel.
17. Combination of claim 11, the rotary communication assembly
comprising a return fluid line configured for transferring a fluid
back to the floating production platform, wherein the production
platform comprises a support point for supporting a riser of an
export pipeline which extends from the floating production platform
to a remote location, the combination being configured to convey
oil and/or gas from the vessel back to the floating production
platform through the return fluid line and subsequently through the
export riser and the export line to a remote location.
18. Method for producing oil and/or gas, the method comprising: 1.
providing a floating production platform for oil and/or gas
production in a marine environment, the floating production
platform comprising a floater for providing buoyancy, the floater
having suitable motion characteristics for supporting a dry tree
riser, at least one riser support point constructed and arranged
for supporting at least one dry tree riser which extends between
the floating production platform and a seabed, a rotary
communication assembly constructed and arranged for providing
communication between the floating production platform and a vessel
for: transferring a product fluid coming out of the at least one
riser to the vessel, and/or transferring other fluids between the
floating production platform and the vessel, and/or transferring
electrical power via one or more electrical lines between the
floating production platform and the vessel, and/or transferring
control signals via one or more electrical lines or fibre optic
lines between the floating production platform and the vessel, the
rotary communication assembly comprising: a circumferential
communication line which in top view extends around the at least
one riser support point, a bridge communication line being in
connection with the circumferential communication line at one end
and comprising an end coupling at the other end for connection with
the vessel, the bridge communication line constructed to bridge a
gap between the floating production platform and the vessel,
wherein the bridge communication line is movable along the
circumferential communication line such that when in use the vessel
weathervanes around the floating production platform, the bridge
communication line rotates around the floating production platform
with the weathervaning vessel, such that the rotary communication
assembly maintains communication between the riser and the vessel,
2. providing a vessel and mooring the vessel to the floating
production platform via a mooring assembly which allows
weathervaning of the vessel about the floating production platform,
and coupling the rotary communication assembly to the vessel, 3.
conveying substantially untreated oil and/or gas hydrocarbons
upwards through the production riser to the floating production
platform, 4. transferring the oil and/or gas through the rotary
communication assembly from the floating production platform to the
vessel.
19. Oil or gas, obtained via the method of claim 18.
20. Vessel constructed and arranged to be connected to the floating
production platform of claim 1, the vessel comprising: a coupling
for connection with the bridge communication line of the rotary
communication assembly of claim 1, a mooring assembly coupling for
coupling with a rotary mooring assembly.
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of production of
hydrocarbons (oil and/or gas) from subsea wellheads in a deep water
marine environment. Hydrocarbons are found in subsea hydrocarbon
formations in ever increasing water depths. It becomes increasingly
difficult to produce these hydrocarbons. The hydrocarbons generally
must be conveyed upwards from the seabed to the water level through
a riser. The riser connects the subsea wellheads at the seabed to
the supporting floating platform. These risers are in themselves
complex and costly structures. The riser is often suspended from a
floating platform. Generally, risers may have a catenary form or a
straight form. A catenary form is typical for a wet tree system. A
straight vertical form is typical for dry tree systems.
[0002] Dry Tree Risers and Wet Tree Risers
[0003] US2006021756 discloses the concept of dry trees versus wet
trees very well. The following text is a quote from this
document.
[0004] A variety of designs exist for the production of
hydrocarbons in deep to ultra-deep waters, i.e. depths greater than
1300 meter. Generally, the preexisting designs fall within one of
two types, namely, wet tree or dry tree systems. These systems are
primarily distinguished by the location of pressure and reservoir
fluid flow control devices. A wet tree system is characterized by
locating the trees atop a wellhead on the seafloor whereas a dry
tree system locates the trees on the platform in a dry location.
These control devices are used to shut in a producing well as part
of a routine operation or, in the event of an abnormal
circumstance, as part of an emergency procedure.
[0005] In wet tree systems, these control devices are located
proximate to a subsea wellhead and are therefore submerged. The
primary function of the tree is to shut-in the well, in either an
emergency or routine operation, in preparation for workover or
other major operations.
[0006] Dry tree systems, in contrast, place the control devices on
a floating platform out of the water, and are therefore relatively
dry in nature. Having the production tree constructed as a dry
system allows operational and emergency work to be performed with
minimal, if any, ROV assistance and with reduced costs and
lead-time. The ability to have direct access to a subsea well from
a dry tree is highly economically advantageous. The elimination of
the need for a separate support vessel for maintenance operations
and the potential for increased well productivity through the
frequent performance of such operations are beneficial to well
operators. Furthermore, the elimination of a dedicated workover
riser and the associated deployment costs will also result in a
substantial savings to the operator.
[0007] Historically, dry tree systems have been installed in
conjunction with tension leg platforms (TLP's) or spar-type
platforms that float on the surface over the wellheads and have
minimal heave motion impact upon the risers.
[0008] Dry tree platforms have a large central well bay for the
surface trees. The size is dictated by well count and spacing.
Topsides equipment has to be arranged around the well bay. The
surface trees are designed for full reservoir shut-in pressures. A
large production manifold is provided on deck, and a skidable rig
is required for individual well intervention.
[0009] Compared with the wet tree development, the dry tree
development offers a number of advantages, which include:
[0010] Easy access for inspection and maintenance.
[0011] Minimum loss of production due to maintenance/workover
operations.
[0012] Higher level of reliability.
[0013] In addition, a Dry Tree Unit (DTU, also referred to as Dry
Completion Unit, DCU) offers a permanent platform for drilling,
workover operation, and hosts limited or full production
facilities.
[0014] Motions
[0015] In a marine environment, weather conditions can be harsh.
Wind, waves, currents exert forces on any floating platform and
cause movements thereof.
[0016] Catenary risers have an advantage in that large motions of
the platform can be followed by the catenary riser without damaging
the catenary riser. Floating platforms such as semi-submersibles,
barges and vessels have been used to suspend catenary steel or
flexible risers, connecting the platform with the subsea wet-tree
wellheads. This type of floater moves more in waves, but is in
general less costly than the TLP's or Spar platforms.
[0017] However, a dry tree riser is substantially rigid and does
not extend in a catenary form, but extends upwards from the seabed
to the sea level along a substantially straight line. Thus, motions
of a floating platform at the water level can not be followed very
well, and a dry tree riser requires a relatively stable support
point at the sea level.
[0018] An important aspect in implementing the dry tree solution is
to ensure that the riser supporting mechanism can accommodate the
platform movement. A DCU hull concept should have desirable motion
characteristics. For this reason, the TLP's and SPARs are
considered to be suitable DCU hull concepts. The TLP's and SPARs
are designed using different principles to suppress motions and
accommodate riser movements. The TLP relies upon the high tendon
stiffness in the vertical direction so that its heave, roll and
pitch natural periods are designed well below the wave excitation
period. As a result, the dynamic amplification of vertical motion
is almost nonexistent, i.e. the platform has small heave, roll and
pitch motions. In the horizontal direction, the TLP is relatively
compliant to the environment, and wind and wave generated slow
drift motion can be significant. The TLP horizontal movement
introduces a static vertical movement called set down. The
attractive feature is that the top tensioned risers respond in a
similar way to that of the tendons, and the platform set-down
actually helps to reduce the riser stoke.
[0019] On the other hand, the SPAR is moored by catenary or
taut-leg mooring lines and compliant to waves in both the vertical
and horizontal directions. The motion natural periods are designed
to be greater than the excitation period. By using deep draft and
avoiding the wave excitation period, the SPAR has relatively small
wave induced motions. The riser stroke of the SPAR is mainly caused
by the platform horizontal excursions. Even though the SPAR's riser
stroke is significantly larger than that of the TLP, it is
accommodated by the specially designed riser buoyancy cans, which
isolate the riser vertical movement from that of the platform.
[0020] The motion characteristics of conventional floaters (barge,
vessel) are not as good as those of the TLP and SPAR. An
alternative is a deep draft semi-submersible, having motions
characteristics approaching the SPAR.
[0021] Costs of Floating Production Platforms
[0022] The TLP, SPAR and other floaters are all capable of carrying
the full range of topsides facilities weights. Among the concepts,
the TLP is most sensitive to topsides weight increase as it has to
be accompanied by an increase of tendon sizes in order to maintain
the same motion natural periods. This in turn requires a larger
hull size to support the tendons. An increase in size leads to an
increase in costs. A large TLP is therefore very costly. The costs
of a SPAR also increase substantially with an increase in size.
[0023] Thus, floating production platforms which are very stable
and show good motion characteristics are relatively expensive to
construct. On the other hand, inexpensive floating platforms
(barge, normal ship hull) exist which are suitable for carrying
equipment for producing oil and gas. However, these inexpensive
floating platforms have poor motion characteristics, and thus are
less suitable for supporting dry tree risers.
[0024] Well Intervention
[0025] US2006021756 discloses the concepts of well intervention
very well. The text below is a quote from this document.
Requirements for workover and servicing of wells are relevant in
the design of floating production platforms. All wells require
routine or unplanned interventions for maintenance, data gathering,
or reservoir management. These interventions can be categorized by
frequency and duration. Frequency is a function of many variables
including specific reservoir characteristics, well construction,
completion type, and reliability of subsea and subsurface
equipment.
[0026] Heavy intervention operations require production tubing
removal and a drilling rig, marine riser, and BOP to perform safe
operations. Causes include tubing failure, casing failures, gravel
pack or sand screen failure, production isolation, and replacing
wellhead connectors.
[0027] Light intervention operations are those where downhole
service is performed through the wellbore. This includes all slick
line, wireline, and coiled tubing work that can be performed
without pulling production tubing. Operations include routine
production logging, well stimulation, paraffin/asphaltene/hydrate
remediation, changeout of downhole values, and reperforations.
[0028] Minor workovers are intervention services performed through
flowlines or umbilicals, such as pigging, bullheading scale, or
hydrate inhibitors, into a wellbore. Also, there are services
performed external to the wellbore such as remotely operated
vehicle services, control-pod and choke-module changeout on subsea
trees, manifold and jumper inspections, etc.
[0029] Well interventions from a DTU, with drilling/workover
facilities and direct vertical access into the wellheads, is easier
and very competitive over working from a floater supporting
(catenary) risers to wet-trees at subsea well heads. This is an
advantage of dry tree risers. Therefore, in the field of the art,
dry tree risers are a preferred choice in several situations.
[0030] Temperature Considerations
[0031] Other issues are also important. Ultra-deepwater presents
flow assurance challenges to both wet and dry tree platform well
systems. Production risers in the water column dominate overall
hydraulic and thermodynamic system performance.
[0032] Wax (or paraffin) may form in a pipeline such as a riser
when the temperature of the fluid drops below a certain point. This
may clog up a pipeline carrying oil or gas. The clogging may be
irreparable and permanently make the pipeline useless. The
temperature requirements are important in the design of risers and
are a driver in the development of so-called dry tree risers.
[0033] Well system architecture for both wet and dry platforms
incorporate design features to mitigate and remediate blockage due
to formation of wax and hydrates. Features include insulation, dual
flow paths, supplemental dead oil circulation, chemical injection,
and blockage remediation via coiled tubing.
[0034] A dry tree production riser can be double walled for
superior temperature maintenance performance in view of single
walled risers. Insulation of catenary risers is very expensive and
complex and generally results in inferior temperature maintenance
characteristics.
[0035] Other Design Considerations
[0036] Furthermore, various other requirements are relevant in the
design of floating production platforms, such as: the need for a
short time-to-first-oil, the desire for the possibility of
pre-drilling of number of wells prior to the start of production, a
desire for a pre-installation of production risers, the need for
increased safety with respect to hurricanes, blow-outs, the need
for a possibility of fast transfer of people to and from the
production platform, the desire for the possibility of a phased
field development, from early production to full field development,
with extension of number of wells and risers
[0037] Moreover, there is a tendency in the field of the art to
develop more marginal fields. To reduce risk of how a field will
produce it is an option to have only a few wells drilled and during
early production one learns more of how the field, being a subsea
hydrocarbon formation, behaves and more wells can be drilled to
stimulate field pressures and/or for additional hydrocarbon output.
From early production, with a number of wells and risers and
limited investments, the decision can be taken to drill additional
wells and install additional risers. Dry tree units (DTUs) having a
drilling derrick are capable of carrying out these further
extension from early production to full field development, without
the use of a drilling vessel or riser installation vessel, as is
the case for wet trees.
[0038] The different requirements have led to various
configurations for producing hydrocarbons in deep water. Because of
the complex and often conflicting requirements, the different
configurations vary widely. Some examples are discussed below.
DESCRIPTION OF THE PRIOR ART
[0039] U.S. Pat. No. 4,436,048 (Gentry et al) discloses one
alternative. FIG. 12 shows a turret 72 positioned in a moonpool of
a vessel 50. A derrick 71 is provided at another moonpool 60 for
maintenance activities. A riser section 38 is suspended from an
underwater floater 39 and connected via a yoke 41 and a flowline
bundle 41 to the turret 72.
[0040] A disadvantage of the system of U.S. Pat. No. 4,436,048 is
that during workover operations, the riser should be connected to
the service moonpool 60. However, the vessel 50 is a regular vessel
having poor motion characteristics. Motions of the vessel 50 may
damage the riser during maintenance. Further, the connection
operation of the riser to the service moonpool itself is
cumbersome. Further, the presence of a separate turret 72 and a
separate service moonpool is a disadvantage.
[0041] U.S. Pat. No. 5,857,808 (de Baan) shows another solution. A
surface collection vessel 100 is provided having an opening 102 for
a turret assembly 130. A problem associated with U.S. Pat. No.
5,857,808 is that the vessel has poor motion behaviour. This
renders the use of dry tree risers impossible and necessitates the
use of catenary risers which allow more movement of the end point
at the surface. Catenary risers have a greater risk of temperature
drops and thus clogging of the riser. The preferred option of a dry
tree riser is not possible with the solution of U.S. Pat. No.
5,857,808.
[0042] Furthermore, because catenary risers are used and not dry
tree risers, no maintenance activities can be carried out on the
wells.
[0043] A further disadvantage of U.S. Pat. No. 5,857,808 is that
the vessels 100 can only weathervane about the turret 130 in a
limited fashion. For greater angles of rotation, disconnecting of
the lines between the turret and the vessel is required, see also
column 3, line 25 of U.S. Pat. No. 5,857,808.
[0044] U.S. Pat. No. 6,338,505 shows a swivel construction for use
on a vessel moored to a single point mooring or a turret. A
disadvantage of the system of U.S. Pat. No. 6,338,505 is that
workover or maintenance activities are not possible on a well. When
the swivel is applied on the vessel, the poor motion
characteristics of the vessel limit the system to the use of
catenary risers, including the temperature problems and paraffin
development that are associated with catenary risers.
[0045] U.S. Pat. No. 6,968,899 discloses a system comprising a
vessel 50 such as an FPDSO which envelops a turret 51. A small
workover rig 56 is positioned on the turret 51. A swivel 53 is
positioned on the turret above the workover rig 56.
[0046] U.S. Pat. No. 6,968,899 discloses that this system can be
used with vessels, see column 1, line 65. In this embodiment, a
disadvantage of the system of U.S. Pat. No. 6,968,899 is that it
can only use catenary risers, including the temperature problems
and paraffin development that are associated with catenary risers.
This is due to the fact that vessel 50 has poor motion
characteristics that make it unsuitable for the use with other
kinds of risers in most operating conditions.
[0047] U.S. Pat. No. 6,968,899 also discloses that this system can
be used with a semi-submersible. A disadvantage of such a system is
that it is extremely costly. A semi-submersible which houses all
production equipment and drilling equipment on board needs to be
extremely large and automatically becomes very expensive.
[0048] U.S. Pat. No. 7,171,479 discloses a system comprising a
vessel 12, which comprises a turret 16. On the turret, a
drilling/workover rig 60 is mounted. A disadvantage of this system
is that in case a dry tree riser is used, the operating conditions
are limited to good weather conditions. This is due to the poor
motion characteristics of the vessel 12. In most operating
conditions, the system of U.S. Pat. No. 7,171,479 is limited to the
use of a catenary riser.
[0049] Another known concept uses a Dry Tree Unit (DTU) in the form
of a Tension leg platform or a Spar. A TLP or a Spar provides
excellent motion characteristics and thus is suitable for dry tree
risers. However, if a full production unit is installed on a dry
tree unit, the Dry Tree Unit becomes very large and thus very
expensive.
[0050] Another known design comprises a combination of a dry tree
unit (DTU) and a separate FPSO. OTC11927--Dry Completion Units for
West Africa Field Development, FIG. 1, discloses such a system
[0051] The advantage of this design is that the unit which supports
the dry trees and requires excellent motion characteristics is
relatively small, which limits the costs. The Dry Tree Unit may be
a Tension Leg Platform or a Spar. The unit which carries the
greater portion of the production and drilling equipment is a
simple vessel such as an FPSO, which is relatively cost-effective.
An umbilical connection comprising various different lines connects
the DTO to the FPSO. Only a small number of key components of the
entire facility are located on the relatively expensive DTU.
[0052] A disadvantage is the relatively large distance between the
DTU and the FPSO, which makes operations difficult. Time lags and
other practical problems arise during operation of this
configuration.
[0053] Another disadvantage of this design is that the connection
is fragile. Furthermore, weathervaning is difficult because the
umbilical can become intertwined with the tension legs or with the
dry tree risers of the TLP, which makes the design vulnerable.
[0054] Another known concept is disclosed in U.S. Pat. No.
4,490,121 which shows an FPSO with a disconnectable buoy. A
disadvantage of this system is the difficulty in maintenance and
workover operations on the wells.
[0055] WO2008012358 discloses another variant comprising an FPSO
and a spar-like construction. A disadvantage of this system is the
low temperature performance of the catenary risers and the lack of
maintenance capability.
OBJECTS OF THE INVENTION
[0056] It is an object of the invention to provide a working
alternative to the prior art.
[0057] It is an object of the invention to provide a system which
allows the use of dry tree risers in different operating conditions
and which is relatively cost-effective.
[0058] It is an object of the invention to provide a system for
producing hydrocarbons which allows disconnecting of a substantial
part of the production equipment in case of bad weather without a
risk of temperature drop and wax forming in the risers.
THE INVENTION AND ITS EMBODIMENTS
[0059] In order to achieve at least one object, the invention
provides a floating production platform for oil and/or gas
production in a marine environment, the floating production
platform comprising: [0060] floater for providing buoyancy, the
floater having suitable motion characteristics for supporting a dry
tree riser, [0061] at least one riser support point constructed and
arranged for supporting at least one dry tree riser which extends
between the floating production platform and a seabed, [0062]
rotary communication assembly constructed and arranged for
providing communication between the floating production platform
and a vessel for: [0063] transferring a product fluid coming out of
the at least one riser to the vessel, and/or [0064] transferring
other fluids between the floating production platform and the
vessel, and/or [0065] transferring control signals via one or more
electrical lines between the floating production platform and the
vessel, [0066] the rotary communication assembly comprising: [0067]
a circumferential communication line which in top view extends
around the at least one riser support point, [0068] a bridge
communication line being in connection with the circumferential
communication line at one end and comprising an end coupling at the
other end for connection with the vessel, the bridge communication
line constructed to bridge a gap between the floating production
platform and the vessel, wherein the bridge communication line is
movable along the circumferential communication line such that when
in use the vessel weathervanes around the floating production
platform, the bridge communication line rotates around the floating
production platform with the weathervaning vessel, such that the
rotary communication assembly maintains communication between the
riser and the vessel.
[0069] In one embodiment, the present invention has an advantage in
that the vessel may be located at a short distance from the
floating production platform. This simplifies operations.
[0070] The weathervaning capability of the vessel allows operations
in different weather conditions. The floating production platform
can be kept small, because a substantial part of the equipment can
be located on the vessel. Dry tree risers can be used, because the
floating production platform has the required dynamic behaviour for
supporting one or more dry tree risers.
[0071] The circumferential communication line and bridge
communication line may be configured to transfer fluids, electrical
power and control signals. Fluids may be transferred in both
directions. The invention provides a simple and robust
communication between the floating production platform and the
vessel. The circumferential communication line defines an opening
of substantial size which allows the placement of one or a
plurality of riser support points and possibly related equipment
within the contours of the circumferential communication line when
viewed from above. For instance, a deck may be provided within the
opening when viewed in top view. On the deck, the riser support
points and other equipment may be positioned.
[0072] Because the circumferential communication line extends
around the riser support point, the riser itself does not hinder
the weathervaning of the vessel. Generally, a plurality of riser
support points is located within the opening formed by the
circumferential communication line.
[0073] Generally, the rotary communication assembly comprises a
product fluid line for conveying the product coming from the riser
from the floating production platform to the vessel. In use, the
product fluid line is in fluid connection with the free end of the
riser.
[0074] Generally, in an embodiment, a plurality of fluid lines and
other lines will extend between the floating production platform
and the vessel. Some fluids are transferred to and from the
floating production platform, i.e. in both directions.
[0075] The circumferential communication line may be located below
the free end of the riser, at the same level as the free end of the
riser, or above the free end of the riser. The circumferential
communication line may have an annular form. When the
circumferential communication line is located below the free end of
the riser, the riser may extend through the circumferential
communication line.
[0076] The circumferential communication line may be circular or
substantially circular, square, hexagonal, or have another
form.
[0077] The vessel may be an FPSO. Because the vessel is a separate
vessel from the floating production platform, it can be used at
other sites earlier or later in time. A separate installation of
the floating production platform is possible, prior to the arrival
of the vessel.
[0078] Furthermore, in an embodiment disconnecting of the vessel
from the floating production platform is possible without wax
forming, because the dry tree risers have adequate temperature
control. Other advantages may also exist, such as that an
accommodation may be located on the vessel, at a distance from the
risers. This reduces the risk of injuries to personnel in case of a
blow-out. A helicopter deck may be located on the vessel. This may
reduce the risk of damage to the risers in case of a helicopter
crash. The separate configuration also provides an escape route to
the floating production platform in case of fire or flooding on
board the vessel.
[0079] Generally, the vessel will be an elongate, ship-shape
vessel. These kinds of vessels are reliable and cost-effective in
construction. Other forms are also possible
[0080] In an embodiment, the floating production platform comprises
a workover rig or a coiled tubing device for performing workover
operations on the dry tree risers, in particular to remove wax
(paraffin).
[0081] In an embodiment, the floating production platform comprises
at least one drilling derrick, wherein in top view the
circumferential communication line extends around the at least one
drilling derrick.
[0082] In an embodiment, the circumferential communication line
comprises: [0083] an annular swivel comprising an inner ring
comprising an inner fluid conduit and an outer ring comprising an
outer fluid conduit, the inner fluid conduit being in fluid
connection with the rise, wherein the inner ring and outer ring are
rotatable relative to one another and wherein the inner fluid
conduit and the outer fluid conduit are in fluid connection with
one another, wherein the bridge communication line is connected to
the outer fluid conduit, or [0084] a reel, wherein the bridge
communication line and the circumferential communication line form
one ongoing line which is flexible and is spooled partly on the
reel and extends partly from the reel to the vessel.
[0085] A swivel may allow an unlimited number of rotations of the
vessel around the floating production platform. A swivel
construction is also possible for electric power lines. In this
embodiment, one or more circular electrical tracks are provided and
slider contacts are provided which make contact with the circular
track. This swivel construction can also be used for control
lines.
[0086] A reel is a reliable system and can comprise several
windings of lines, which allows multiple rotations of the vessel
around the floating production platform. Generally, the
weathervaning action will not require a substantial number of
rotations of the vessel about the floating production platform and
a reel will allow a sufficient number of windings. The line on the
reel may be a bundle of different lines, sometimes referred to as
an umbilical.
[0087] In an embodiment, in top view the floating production
platform is substantially circular. If both the circumferential
communication line and the floating production platform are
circular, a simple construction is possible which allows easy
weathervaning. The floater may also be substantially circular. The
circumferential communication line may extend along the outer
perimeter of the floater or along the outer perimeter of a topside
construction which is supported by the floater.
[0088] In an embodiment, the circumferential communication line
extends around a plurality of riser support points. In this way a
plurality of risers can be connected to the vessel.
[0089] In an embodiment, the circumferential communication line
extends, in top view, around primary drilling equipment and primary
production equipment. Thus, the equipment is conveniently placed
inside the circumferential communication line.
[0090] In an embodiment, in top view the circumferential
communication line extends substantially along an outer
circumference of the floating production platform.
[0091] In an embodiment, the floating production platform is a
Tension Leg Platform (TLP). TLP's are reliable structures which
have excellent dynamic behaviour and are suitable for supporting
dry tree risers. Because a substantial part of the equipment can be
positioned on board the vessel, the TLP can be kept relatively
small. The TLP will have connection points for connecting tendon
legs to the seabed.
[0092] In an embodiment, the floating production platform is a
Spar. Spars are also known structures which have good dynamic
behaviour and are suitable for dry tree risers. Because a
substantial part of the equipment can be positioned on board the
vessel, the Spar can be kept relatively small. Typically, the Spar
will have mooring points for connecting mooring lines to the
seabed.
[0093] It is also possible to provide a semi-submersible vessel as
the floating production platform. The semi-submersible will
comprise a DP system for position control and orientation
control.
[0094] In an embodiment, the floating production platform is a Dry
Tree Unit (DTU). Other kinds of Dry Tree Units than a Spar or a TLP
may also be used, such as a deep draft semi-submersible. Deep draft
semi-submersibles have also good motion characteristics which
approach the low Spar motions.
[0095] In an embodiment, the rotary communication assembly is
constructed to allow rotation of the vessel around the floating
production platform over an angle of at least 180 degrees.
[0096] In an embodiment, the rotary communication assembly is
constructed to allow rotation of the vessel around the floating
production platform over a plurality of revolutions.
[0097] In an embodiment, the floating production platform comprises
a plurality of circumferential communication lines above one
another in order to allow a plurality of fluid lines and other
communication lines to extend between the floating production
platform and the vessel. In this way, a plurality of lines can be
provided between the floating production platform and the vessel,
while maintaining the weathervaning capability.
[0098] In an embodiment, the circumferential communication line
comprises a reel which is substantially flat and comprises a
vertical rotation axis. A flat reel having a vertical rotation axis
is a simple way of providing the circumferential communication
line.
[0099] In an embodiment, the floater is a turret like construction
constructed to be positioned in a moonpool of a vessel. This allows
the vessel to be constructed such that it extends around or
substantially around the floating production platform, when viewed
in top view.
[0100] The present invention also relates to a combination of the
floating production platform according to the invention and a
vessel, wherein the at least one bridging communication line is
connected at one end to the floating production platform and at the
other end to the vessel.
[0101] In an embodiment, the combination comprises a rotary mooring
assembly constructed to bear a mechanical load and configured to
allow weathervaning of the vessel about the floating production
platform, the rotary mooring assembly comprising: [0102] one end
which is connected with the floating production platform, [0103] an
opposite end which is connected with the vessel, [0104] a rotary
coupling at the end which is located at the floating production
platform, which rotary coupling is constructed to allow
weathervaning of the vessel around the floating production
platform, the rotary mooring assembly being constructed for
maintaining the vessel at a substantially controlled distance from
the floating production platform.
[0105] With the rotary mooring assembly, a sturdy mechanical
coupling between the floating production platform and the vessel is
provided.
[0106] In an embodiment, the vessel is substantially separate from
the floating production platform.
[0107] In an embodiment, the floating production platform comprises
primary production equipment and the vessel comprises auxiliary
production equipment and supplies which are auxiliary to the
primary production equipment on the floating production
platform.
[0108] This arrangement allows the floating production platform to
be kept relatively small, while the vessel is constructed
relatively large. Overall, this is a cost-efficient
configuration.
[0109] In an embodiment, the floating production platform
comprises: [0110] a heat control device for
paraffin/asphaltene/hydrate remediation to maintain wells after
disconnect of the vessel and/or [0111] a small accommodation for
crew. In an embodiment, the auxiliary production equipment on the
vessel comprises one or more components chosen from a group
comprising: [0112] a well stimulation device with water, gas and/or
chemical injections [0113] separation equipment for separating oil
from water, [0114] storage equipment for storing water, sand and/or
sulphur which is separated from oil, [0115] pressure reduction
equipment for reducing a pressure in the oil and/or gas, [0116]
heating equipment for generating heat for heating the one or more
production risers, [0117] large accommodation for a crew, [0118]
fluid supply equipment for well maintenance, [0119] power
generator/power supply.
[0120] These components are relatively bulky and heavy and would
result in a costly floating production platform if they were
positioned on the floating production platform. Due to the
positioning on the vessel, overall costs can be limited.
[0121] In an embodiment, the floating production platform comprises
primary drilling equipment comprising at least one drilling
derrick, wherein the vessel comprises auxiliary drilling equipment
comprising at least one component chosen from a group comprising
[0122] mud supply equipment for providing mud to the drilling
derrick, [0123] drilling fluid equipment for providing drilling
fluid to the drilling derrick.
[0124] These drilling components are relatively bulky and heavy and
would result in a very costly floating production platform if they
were positioned on the floating production platform. Due to the
positioning on the vessel, overall costs can be limited.
[0125] In an embodiment, the circumferential communication line
comprises a first reel, and the vessel comprises at least one
second reel, wherein the at least one communication line is spooled
on both reels, allowing a part of the fluid line which is spooled
from the reel on the floating production platform during
weathervaning to be spooled onto the second reel on the vessel and
vice versa, thereby maintaining the length of the fluid line
between the floating production platform and the vessel
substantially the same.
[0126] With the reel on board the vessel, the communication line
can have the same length at any weathervaning angle. This prevents
entanglement of the communication line or damage thereto. As will
be apparent the communication lines can be a fluid line, a power
line, a different line or a bundle of different lines.
[0127] In an embodiment, the circumferential communication line
comprises a reel for spooling the bridge communication line,
allowing a part of the bridge communication line to be spooled from
the reel during weathervaning of the vessel around the floating
production platform, wherein an end of the bridge communication
line is connected to a discharge point on the vessel, wherein the
circumferential communication line and the discharge point are
constructed to allow an excess length of the bridge communication
line to be suspended in the water between the floating production
platform and the vessel.
[0128] In an embodiment, the suspended part of the bridge
communication line has a substantially catenary or U-shaped
form.
[0129] In an embodiment, the rotary mooring assembly is somewhat
flexible in that it allows a limited variation in distance between
the floating production platform and the vessel in addition to the
weathervaning capability.
[0130] The flexibility reduces the forces exerted by the vessel on
the floating production platform.
[0131] In an embodiment, the rotary mooring assembly is constructed
to maintain the vessel at a fixed distance from the floating
production platform.
[0132] A fixed construction provides the advantage of no variations
in distance between the floating production platform and the vessel
which simplifies various operations.
[0133] In an embodiment, the vessel comprises a dynamic positioning
system. The dynamic positioning system reduces the forces on the
rotary mooring assembly and improves the position keeping of the
vessel. In some embodiments, the position keeping of the DTU is
also improved, especially in strong currents.
[0134] In an embodiment, the floating production platform is a
Tension leg Platform (TLP) and the vessel is a Floating Production,
Storage and Offloading (FPSO) vessel. This configuration provides a
substantially complete and cost-efficient production facility.
[0135] In an embodiment, the floating production platform is a
Tension leg Platform (TLP) and the vessel is a Floating Production
and Offloading (FPO) vessel. In this configuration, the produced
oil and/or gas can be exported to a remote location via an export
flowline which is suspended from the floating production platform.
No storage is required on board the vessel.
[0136] In an embodiment, the rotary communication assembly
comprises a connecting/disconnecting coupling for connecting and
disconnecting the vessel from the floating production platform,
allowing: [0137] the vessel to be removed to a remote location in
times of bad weather or for other reasons and/or [0138]
installation of the floating production platform at a site prior to
an installation of the vessel.
[0139] In an embodiment, the rotary communication assembly
comprises a return product fluid line configured for transferring a
product fluid back to the floating production platform, wherein the
production platform comprises a support point for supporting a
riser of an export pipeline which extends from the floating
production platform to a remote location, the combination being
configured to convey oil and/or gas from the vessel back to the
floating production platform through the return fluid line and
subsequently through the export riser and the export line to a
remote location.
[0140] The present invention further relates to a method for
producing oil and/or gas, the method comprising the steps of:
[0141] 1. providing a floating production platform for oil and/or
gas production in a marine environment, the floating production
platform comprising: [0142] a floater for providing buoyancy, the
floater having suitable motion characteristics for supporting a dry
tree riser, [0143] at least one riser support point constructed and
arranged for supporting at least one dry tree riser which extends
between the floating production platform and a seabed, [0144] a
rotary communication assembly constructed and arranged for
providing communication between the floating production platform
and a vessel for: [0145] transferring a product fluid coming out of
the at least one riser to the vessel, and/or [0146] transferring
other fluids between the floating production platform and the
vessel, and/or [0147] transferring control signals via one or more
electrical lines between the floating production platform and the
vessel, [0148] the rotary communication assembly comprising: [0149]
a circumferential communication line which in top view extends
around the at least one riser support point, [0150] a bridge
communication line being in connection with the circumferential
communication line at one end and comprising an end coupling at the
other end for connection with the vessel, the bridge communication
line constructed to bridge a gap between the floating production
platform and the vessel, wherein the bridge communication line is
movable along the circumferential communication line such that when
in use the vessel weathervanes around the floating production
platform, the bridge communication line rotates around the floating
production platform with the weathervaning vessel, such that the
rotary communication assembly maintains communication between the
riser and the vessel,
[0151] 2. providing a vessel, mooring the vessel to the floating
production platform via a mooring assembly which allows
weathervaning of the vessel about the floating production platform,
and connecting the at least one bridge communication line to the
vessel,
[0152] 3. conveying untreated oil and/or gas hydrocarbons upwards
through the production riser to the floating production
platform,
[0153] 4. transferring the oil and/or gas through the rotary
communication assembly from the floating production platform to the
vessel.
[0154] In an embodiment, the method comprises treating polluted
hydrocarbons such as oil and/or gas on board the vessel. The
treatment on board the vessel saves payload on the floating
production platform which results in a lighter floating production
platform
[0155] In an embodiment, the method comprises providing: [0156] a
return fluid line configured for transferring a fluid back to the
floating production platform, and providing, [0157] an export
support point on the floating production platform for supporting a
riser of an export line which extends from the floating production
platform to a remote location, [0158] an export line comprising an
export riser suspended from the export support point, the method
comprising: [0159] transferring the treated oil and/or gas from the
vessel back to the floating production unit through the return
fluid line, [0160] conveying oil and/or gas through the export
riser and the export line to a remote location.
[0161] In this embodiment, no storage is required and the end
product is directly transported away from the production facility
to a remote location.
[0162] The present invention further relates to oil or gas,
obtained via the method according to the invention.
[0163] The present invention further relates to a vessel
constructed and arranged to be connected to the floating production
platform of the invention, the vessel comprising: [0164] a
communication line coupling for connection with the bridging
communication line of the rotary communication assembly, [0165] a
mooring assembly coupling for coupling with a rotary mooring
assembly.
[0166] The invention is explained in more detail in the text, which
follows with reference to the drawing, which shows a number of
embodiments, which are given purely by way of non-limiting
examples. In the Figures, like numbers denote like elements.
LIST OF FIGURES
[0167] FIG. 1A shows a diagrammatic side view of a combination of a
floating production platform and a vessel according to the
invention.
[0168] FIG. 1B shows a diagrammatic side view of a embodiment of
the embodiment of FIG. 1A comprising stacked reels.
[0169] FIG. 2A shows a diagrammatic top view of another embodiment
of the floating production platform according to the invention.
[0170] FIG. 2B shows a schematic aerial view of the variant of FIG.
2A.
[0171] FIG. 3A shows a side view in cross-section of a part of
another embodiment of the floating production platform according to
the invention.
[0172] FIG. 3B shows a side view of a cart for a fluid swivel
conduit of the embodiment of FIG. 3A.
[0173] FIG. 4 shows a diagrammatic side view of another embodiment
a floating production platform and a vessel according to the
invention and shuttle tanker,
[0174] FIG. 5A shows a diagrammatic side view of another
combination of a floating production platform and a vessel
according to the invention.
[0175] FIG. 5B shows a diagrammatic side view of yet another
combination of a floating production platform and a vessel
according to the invention.
[0176] FIG. 6 shows a diagrammatic side view of another combination
of a floating production platform and a vessel according to the
invention.
[0177] FIG. 7 shows a diagrammatic side view of yet another
combination of a floating production platform and a vessel
according to the invention.
[0178] FIG. 8 shows a diagrammatic side view of another combination
of a floating production platform and a vessel according to the
invention.
[0179] FIG. 9 shows a diagrammatic side view of another combination
of a floating production platform and a vessel according to the
invention.
[0180] FIG. 10A shows a diagrammatic side view of another
combination of a floating production platform and a vessel
according to the invention.
[0181] FIG. 10B shows another diagrammatic side view of the
floating production platform and a vessel of FIG. 10A.
DETAILED DESCRIPTION OF THE FIGURES
[0182] FIG. 1A shows a floating production platform 10 (FPP)
according to the invention. The floating production platform 10 is
connected to a vessel 12 via the rotary communication assembly 14
and via a rotary mooring assembly 16.
[0183] The floating production platform floats at the water line
18. The floating production platform may be a Tension Leg Platform
(TLP), or may be a different kind of platform. The floating
production platform 10 comprises a floater 20, which is
substantially circular above the waterline. The floating production
platform 10 can be moored to the seabed by means of mooring lines
102 and/or by means of tendon legs 24 (or tethers) extended
downwards to the seabed. The floater 20 can consist of one large
column with a central moonpool 79, or of multi columns. The floater
20 may have a tubular form with a vertical through passage (also
referred to as moonpool), or a substantially tubular form. The
moonpool 79 may have a circular form, but may also have another
form, such as a square or rectangular form, or another form.
[0184] A plurality of risers 28 extend downward from the floating
production platform 10 to the seabed. The risers 28 extend through
a wellbay in the floater 20 and are connected to the floating
production platform 10 at respective riser support points 48. The
support points 48 generally comprise hydro-pneumatic tensioner
systems mounted on the platform deck. Other systems are also
possible and are known in the field of the art. The support points
48 comprise suspender-like members which connect the risers 28 to
the floating production platform. `Trees` are generally positioned
at the upper end of the risers 28. The trees comprise couplings via
which different lines are connected with the risers 28 such as
product fluid, chemical injection fluid, water injection.
[0185] The risers 28 are dry tree risers which extend according to
a substantially straight line downward to the seabed. The dry tree
risers 28 allow workover operations to be performed on the well
from the floating production platform 10.
[0186] On the floater 20, a topside construction 32 is mounted. The
topside construction 32 extends above the water level 18 and
provides space for various components. The topside construction 32
comprises different decks 36.
[0187] A drilling derrick 30 is provided on the floating production
platform 10. The drilling derrick 30 comprises the known components
of a hoisting assembly and a drive for rotating a drill string
34.
[0188] The Rotary Communication Assembly (RCA) 14 comprises three
circumferential communication lines 38A, 38B, and 38C.
[0189] For the product coming from the risers, the circumferential
communication line is in connection with the risers via a manifold
to which each riser is connected. The product flows from the risers
merge at the manifold and are subsequently directed as a single
flow to the circumferential communication line 38.
[0190] Other lines also connect the floating production platform
with the vessel, such as power lines for electrical power, control
lines for control signals and other fluid lines for other fluids
such as high pressure water and gas for gas injection, which fluids
are also essential for the working of the entire facility.
[0191] The RCA further comprises three bridge lines 40A, 40B, 40C.
Each bridge communication line 40 extends from a respective point
42 on the respective circumferential communication line 38 to a
discharge point 44 on the vessel 12.
[0192] Each circumferential communication line 38 extends along the
outer perimeter of the floating production platform 10. The
circumferential communication lines 38 are circular, but may also
have another form, such as an oval, a triangular form, a square or
polygonal form. As will be discussed below, a spiral form is also
possible. The circumferential communication lines 38 extend in a
substantially horizontal plane, wherein each circumferential
communication line 38 extends at a different level.
[0193] Each circumferential communication line 38 defines an
opening 46. The openings 46 are located above one another and are
large. The openings 46 are large enough for a plurality of riser
support points 48 to be located within the opening, i.e. to be
surrounded by the circumferential communication lines 38.
[0194] The drilling derrick 30 is normally located above the
surrounded by the circumferential communication lines 38. Further,
primary drilling equipment and primary production equipment is on
board the floating production platform 10 and is positioned above
or below the circumferential communication lines or is, in top
view, also positioned in the opening 46, i.e. surrounded by the
circumferential communication lines 38.
[0195] In this embodiment, the circumferential communication lines
38 are spooled on respective reels 49. The reels can also be
horizontally positioned, separate or stackable, as shown in FIG.
1B. The bridge lines 40 extend to respective reels 49 on the vessel
12. The reels 49 are constructed to take in excessive lengths of
the bridge communication lines 40 or to provide extra length of
bridge communication lines 40, depending on the direction of
rotation of weathervaning.
[0196] From the reels 49, further connecting lines run to equipment
50 installed on board the vessel 12. The equipment 50 comprises
auxiliary drilling equipment 52 and auxiliary production equipment
54.
The auxiliary drilling equipment 52 on board the vessel comprises:
[0197] mud supply equipment for providing mud to the drilling
derrick, [0198] drilling fluid equipment for providing drilling
fluid to the drilling derrick. The auxiliary production equipment
54 on the vessel comprises: [0199] separation equipment for
separating oil from water, [0200] storage equipment for storing
dirty water, sand, sulphur and other contaminations separated from
the crude oil or gas, [0201] pressure reduction equipment for
reducing a pressure in the oil and/or gas, [0202] heating equipment
for generating heat for heating the one or more production risers,
[0203] accommodation for a crew, [0204] fluid supply equipment for
well maintenance, [0205] power generator/power supply.
[0206] Further, an accommodation, a helicopter deck, and other
facilities are provided on the vessel 12. Also storage of other
products, i.e. ammonium, as by-product from the processed
hydrocarbons can be stored in storage 56 on board the vessel 12 and
the crude oil can be stored in the vessel 12. The vessel 12 may be
referred to as an FPSO.
[0207] The vessel 12 is a low-cost ship-shape vessel or barge,
whereas the floating production platform 10 is a costly Spar or
TLP. Because a substantial part of the equipment is located on
board the vessel 12, the floating production platform 10 can be
designed relatively small. The combined configuration therefore is
cost-effective.
[0208] The vessel 12 may be equipped with a dynamic positioning
(DP) system 58 for position control not only of the vessel 12, but
also controlling the position of floating production platform 10
and the DP also controls the forces in the rotary mooring assembly
16.
[0209] The rotary mooring assembly 16 comprises an annular rail 60
extending around the floating production platform 10 and mounted to
the floating production platform 10. A slider or roller 62 is
mounted to the annular rail 60 and movable along the rail 60. A
hinge 64 is provided, which connects one end 65 of a beam 66 to the
roller 62. The opposite end 65 of said beam 66 is connected via to
a dead weight 68 which is suspended via another beam 70 from a
suspension point 72. A hinge 71 is provided to allow for some
rotation of the dead weight 68. The suspension point 72 is
supported by a frame 74 which extends over the bow or stern 76 of
the FPSO 12.
[0210] The mooring assembly 16 allows rotation of the vessel 12
around the floating production platform 10. Further, the mooring
assembly allows some variation in distance between the floating
production platform 10 and the vessel 12. When the distance
increases, the beam 70 is inclined from the vertical, creating a
return force via the dead weight. The return force returns the
distance to the required distance. The opposite effect is attained
when the distance between the floating production platform 10 and
the vessel 12 decreases.
[0211] In use, the floating production platform 10 may be installed
months before the vessel 12 is positioned in place. Some wells can
be predrilled and other wells can be additional drilled if needed
from the floating production platform 10, and the wells can be
commissioned one by one. At a certain point in time, the vessel 12
is positioned in place and connected to the floating production
platform 10 via the rotary communication assembly 14 and the rotary
mooring assembly 16.
[0212] As production continues, a need for maintenance operations
of the wells may arise. These can be carried out from the floating
production platform 10 with the drilling derrick 30 or with other
equipment on board the floating production platform 10.
[0213] On regular intervals, a shuttle tanker (not shown) can be
moored at the vessel 12 for offloading hydrocarbons from the
storage on board the vessel 12. The shuttle tanker then transports
the hydrocarbons to another off-loading location or harbour for
further processing.
[0214] In times of bad weather, the vessel 12 can be uncoupled from
the floating production platform 10 and moved to a safe location.
This removal does not necessary lead to wax deposition in the
risers, because dry tree risers have good temperature control using
the production control equipment on the floating production
platform 10 to prevent a drop in temperature in the risers 28 and
wells, limiting risk of wax deposition.
[0215] Also, when the fields have no more producible hydrocarbons,
the vessel 12 can be removed and upgraded for use at the same or at
another site.
[0216] FIG. 1b shows a substantially same embodiment as FIG. 1a,
but in FIG. 1B the reels 49 are oriented horizontally, i.e. have a
vertical axis.
[0217] FIG. 2A shows the configuration in top view and FIG. 2B in
an aerial view. The circumferential communication line 38 extends
in a spiral form around the riser support points 48 in the well bay
45. The product and other lines connect the dry tree on top of each
riser with the process equipment on the floating production
platform 10 or vessel 12. Each tree on top of each riser 28 is
connected via product and other lines to one or more supply
openings 78 of the circumferential communication line 38 on deck
36. The supply opening 78 is stationary with respect to the risers
28 and the riser support points 48.
[0218] From the supply opening 78, the circumferential
communication line 38 extends in one or multiple windings around
the reel 47. This can be a spiral form. The bridge communication
line 40 is the part of the fluid line which extends to the vessel
12. When the vessel 10 weathervanes in clockwise direction around
the floating production platform 10, the bridge communication line
40 is spooled off the reel 47 and is wound onto the reel 49. When
the vessel 12 weathervanes in anti-clockwise direction around the
floating production platform, the bridge communication line 40 is
spooled from the reel 49 and onto the reel 47.
[0219] Because the bridge communication line 40 originates from an
outer perimeter of the floating production platform 10, there is no
or little risk of obstruction of any equipment to the bridge
communication line 40. There is also no or little risk of
entanglement of the bridge communication line 40 with any other
object such as a mooring line of the floating production platform
10 or the risers 28.
[0220] FIGS. 3A and 3B show another embodiment of the invention.
The floating production platform 10 is shown having a moonpool 79
through which a riser 28 extends upwards. The riser support point
48 is provided for providing support for the riser 28. Often, only
lateral support is provided, since dry tree risers are generally
equipped with buoyancy devices 86 around the riser. Thus, dry tree
risers 28 are often free standing and only need lateral
support.
[0221] The circumferential communication line 38 comprises a fluid
swivel conduit 83 which comprises an inner non rotatable ring 80
and an outer ring as sliding door 82. The inner fluid conduit 81
and the fluid swivel conduct 83 are in fluid communication with one
another via supply opening 89. The sliding door ring 82 is pulled
outward to seal-off the fluid conduit swivel 83 to the seals of
restrainers 87 by means of carts 84, positioned on deck 36 on a
circular track around the topside 32. The fluid swivel 83 allows an
unlimited number of rotations of the vessel 12 around the floating
production platform 10.
[0222] FIG. 4 shows another embodiment, wherein the floating
production platform 10 is a Truss Spar. Spars are known to have
good dynamic characteristics and are suitable for supporting dry
tree risers. Fluid swivels are provided as circumferential
communication lines 38. The Truss Spar comprises a floater 20, a
truss 23 and a stabilizing weight 21 at a lower end of the
Spar.
[0223] Three fluid swivels 38 are provided above one another,
forming a swivel stack. The swivels 38 are circular and extend
around the outer perimeter of the floating production platform
10.
[0224] FIGS. 5A and 5B show embodiments comprising a floating
production platform 10 and a vessel 12, wherein the rotary mooring
assembly 16 comprises a fixed distance yoke. The rotary mooring
assembly comprises the annular rail 60, the rollers 62, the hinge
64, a rotary device (swivel) 67 to allow the vessel to roll, and a
beam 88 connected to the vessel 12 via a hinge 90. The embodiment
of FIG. 5A has horizontal beams 22 which extend outwardly away from
the floater 20. The ends of the beams 22 are constructed as a
connection point for the tendon legs 24. The embodiment of FIG. 5B
is substantially the same as the embodiment of FIG. 5A, but does
not have the beams 22. Here, the tendon legs 24 are connected to
the tubular floater 20 directly.
[0225] FIG. 6 shows another embodiment of the invention, wherein
the vessel 12 does not comprise a substantial storage for end
product, but a return fluid line is provided from the vessel 12 to
the floating production platform 10, here being a multi column TLP,
moored to the seabed with tendon legs 24. The return fluid line is
configured in the same way as the fluid line from the floating
production platform 10 to the vessel 12. A bridge communication
line is provided and a circumferential communication line is
provided. At the floating production platform 10, the
circumferential communication line is connected to an export riser
96 which extends downward to a seabed 98 and which exports the
product to a remote location.
[0226] In use, the hydrocarbons are transferred from the floating
production platform 10 to the vessel 12. The hydrocarbons are
subsequently treated on board the vessel 12, are subsequently
returned to the floating production platform 10 and are
subsequently exported through the export riser 96.
[0227] FIG. 7 shows an embodiment which is similar to the
embodiment of FIG. 1, but with a Truss Spar as the floating
production platform 10, with mooring lines 102 and truss 23
connected to the floater 20.
[0228] FIG. 8 shows an embodiment wherein the rotary mooring
assembly 16 comprises a catenary chain, wire or cable 100. The
catenary chain is connected to a roller 62 which is mounted for
rotation on annular rail 60.
[0229] The floating production platform is a Spar which is moored
to the seabed via mooring lines 102.
[0230] The vessel 12 is kept at an approximately constant distance
from the floating production facility 10, using its dynamic
positioning system with thrusters 58.
[0231] FIG. 9 shows an embodiment wherein the floating production
platform 10 is configured as a turret-like construction and
positioned in a moonpool 104 of a vessel 12. The rotary
communication assembly 14 is substantially the same as in other
embodiments. However, the rotary mooring assembly is different, in
that the floating production platform 10 is kept in position
because of a substantial form fit between the floating production
platform 10 and the moonpool 104 of the vessel. In this
configuration, the dry tree risers 28 have a curve to allow heave
motions of the vessel in waves. The risers 28 may be Compliant
Vertical Access Risers (CVAR).
[0232] FIG. 10A shows an embodiment wherein the bridge lines 40
extend from a respective point 42 on the respective circumferential
communication line 38 to a discharge point 44 on the vessel 12. An
end of the bridge communication line is connected to a discharge
point on the vessel 12. No reels are provided on the vessel 12 for
spooling an excess length of the bridge line 44. In this
embodiment, the suspended length of the bridge lines 40 varies with
the weathervaning of the vessel 12, as is shown in FIG. 10B.
Preferably the floating production platform 10 is moored with
tendon legs 24, to avoid contact with the suspended lines 40.
[0233] The circumferential communication line 38 and the discharge
point 44 are constructed to allow any excess length of the bridge
communication line 38 to be suspended in the water between the
floating production platform 10 and the vessel 12 in a
substantially catenary or U-shaped form. The size of the suspended
part varies in dependence of the position of the vessel.
[0234] It will be obvious to a person skilled in the art that
numerous changes in the details and the arrangement of the parts
may be varied over considerable range without departing from the
spirit of the invention and the scope of the claims.
* * * * *