Note: Descriptions are shown in the official language in which they were submitted.
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
CELLULAR TENDONS FOR TLP
FIELD OF THE DISCLOSURE
100011 Embodiments disclosed herein relate to a tendon system for use with
tension leg
platforms crui. More specifically, embodiments disclosed herein relate to a
tendon
system that includes Cellular Tendon arrangement as the main body of at least
one tendon
or tendon module or a portion of one tendon or tendon module, designed and
configured
to enable use of the tendon, and thus use of TLPs, in ultra-deep waters and/or
for heavy
topsides, or to improve constructability and transportation and installation
and/or project
cost for any water depth.
BACKGROUND
[0002] One type of offshore drilling and production platform is a tension
leg platform,
generally called a TLP, which utilizes tendons to support the platform. The
tendons have
lower terminations that connect to pilings on the sea floor. The upper ends
connect to top
connectors on the platform. The platform is de-ballasted after connection to
the top
connector, placing the tendons in tension.
[0003] One type of tendon includes a main body that is a single steel
tubular formed of
multiple segments connected together with mechanical connections. The pipes in
the
tendon segments have hollow interiors that are sealed from sea water to
provide
buoyancy. Bulkheads may be located within the interior, dividing the hollow
interior in
separate compartments sealed from each other. Use of conventional single steel
pipe
design for the tendon main body has technical and practical limitations in
meeting the
combined stiffness and the tension-collapse resistance requirements, limiting
the depth
and topside payload at which conventional tendon systems may be used,
[0004] U.S. Pat. No. 6,851,894 discloses tubular sections having three
different wall
thicknesses. The upper section has a greater diameter but lesser wall
thickness than an
intermediate section, and the intermediate section has a greater diameter but
lesser wall
thickness than the lower section.
[0005] As TLP platforms are located in deeper waters, providing steel
tubular tendons
that can resist the hydrostatic pressure becomes an increasingly difficult
problem. For
2
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
example, US7422394 discloses use of a tendon having a varied diameter,
decreasing in
diameter with depth, and limiting the diameter to thickness ratio at depth to
overcome
crushing force and hydrostatic pressure increases.
[0006] Various methods have been proposed to overcome this hindrance to use
of TLPs
in extremely deep water. For example, another type of tendon is a solid cable,
formed of
composite fibers, such as carbon fibers (often called a tether). Typically, a
composite
tendon, such as disclosed in US7140807, has an elastomeric jacket that
encloses several
bundles of fibers. A spacer or filler fills the interior space surrounding the
fibers. Steel
terminations are located on the ends of the separate rods or sections of a
composite
tendon for connecting the sections to each other.
[0007] Composite fiber tendons are generally smaller in diameter than steel
tubular
tendons and weigh less. However, they are less buoyant, such as their specific
gravities
being around 0.85 where 1.00 is considered neutral. Having solid interiors,
composite
fiber tendons are able to withstand high hydrostatic pressures. However, the
lack of
buoyancy limits the usefulness of composite fiber tendons in very deep water
because a
larger and more buoyant hull for the TLP is required in order to maintain the
required
tension at the bottom connector. Also, fatigue of the upper portion of a
composite fiber
tendon can be a concern because of the high bending moments caused by TLP
lateral
motion. US4990030 discloses use of composite fibers in the interior of a steel
pipe
section, which may provide the buoyancy, but as noted above, the use of the
single pipe
would be unsuitable for deep waters due to the high hydrostatic pressures.
SUMMARY OF THE DISCLOSURE
[00081 In one aspect, embodiments disclosed herein relate to a cellular
tendon system
that may be used to moor a floating structure to a seabed. The tendon system
may
include a top tendon section configured to attach to a floating structure and
a tendon
bottom section configured to attach to a foundation. The tendon system may
also include
an upper transition unit connected to the top tendon section, and a bottom
transition unit
connected to the tendon bottom section. One or more tendon modules may be
disposed
intermediate the upper and bottom transition units, at least one tendon module
including a
tendon main body system comprising at least two pipe strings connected
proximate their
3
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
upper ends to a first module transition unit, which can be the same or
different than the
upper transition unit, and proximate their bottom ends to a second module
transition unit,
which can be the same or different than the bottom transition unit. A tension
leg platform
may be moored to seabed using such a tendon system.
[0009] In another aspect, embodiments disclosed herein relate to a cellular
tendon system
that may include a top tendon section configured to attach to a floating
structure and a
tendon bottom section configured to attach to a foundation. The tendon system
May also
include an upper transition unit connected to the top tendon section, and a
bottom
transition unit connected to the tendon bottom section. A tendon main body
system
including at least two pipe strings is connected proximate their upper ends to
the upper
transition unit and proximate their bottom ends to the bottom transition unit.
The tendon
system may be fully assembled onshore and transported to an offshore location,
where it
may be submerged and connected at its top end to a floating structure and at
its bottom
end to a foundation in the seabed. The floating structure may be, for example,
a tension
leg platform.
[0010] In another aspect, embodiments disclosed herein relate to a method
of assembling
a tendon system. The method may include assembling a tendon main body section
having two or more pipe strings. The two or more pipe strings may be connected
at their
top end and bottom ends to a tendon top segment and a tendon bottom segment,
which
may be, for example, configured to connect to a floating structure, a
foundation, or
another tendon module.
[0011] In another aspect, embodiments disclosed herein relate to a hybrid
tendon system,
including: an upper tendon module and a lowermost tendon module. The upper
tendon
module includes a top tendon section configured to attach to a floating
structure. The
lowermost tendon module includes a bottom transition unit configured to attach
to a
foundation. At least one of the tendon modules include a tendon main body
system
comprising at least two pipe strings connected proximate their upper ends to
an upper
transition unit and proximate their bottom ends to a lower transition unit. A
tension leg
platform may be moored to a seabed using such a tendon system.
4
=
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO 17964/023002
[0012] In another aspect, embodiments disclosed herein relate to a method
of mooring a
floating structure. The method may include: transporting a tendon system
according to
embodiments herein from an onshore assembly location to an offshore location;
submerging the tendon system; connecting the tendon system to a foundation and
connecting the tendon system to the floating structure.
[0013] Other aspects and advantages will be apparent from the following
description and
the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0014] Figure 1 is an elevation view of a tension leg platform anchored
with tendons
according to embodiments herein.
[0015] Figure 2 is a side view of a tendon according to embodiments herein.
[0016] Figure 3 is a top cross-sectional view of a tendon according to
embodiments
herein.
[0017] Figure 4 is a detail view of a portion of the tendon illustrated in
Figure 2.
[0018] Figure 5 is an elevation view of a tension leg platform anchored
with hybrid
tendons according to embodiments herein.
[0019] Figure 6 is a side view of a lower portion of a tendon according to
embodiments
herein.
=
[0020] Figure 7 is a side view of a lower portion of a tendon according to
embodiments
herein.
[0021] Figures 8-10 are cross-sectional views of a tendon or portion
thereof according to
embodiments herein.
DETAILED DESCRIPTION
[0022] Embodiments disclosed herein relate to a tendon system for use with
a tension leg
platform (m)). More specifically, embodiments disclosed herein relate to a
tendon
system having at least one cellular tendon main body portion designed and
configured to
enable use of the tendon, and thus use of TlYs, in ultra-deep waters and/or
with heavy
topside payload.
CA 02857910 2014-07-30
=
PATENT APPLICATION
ATTORNEY DOCKET NO. 179641023002
[0023] In a Tension Leg Platform (TLP), the tendons maintain the platform
position and
control the Tu) dynamic motions in various environmental conditions to meet
the
operational requirements. An individual tendon consists of three major parts:
a tendon top
segment (Ti S), or top section, for top interface at the platform, a tendon
bottom segment
(TBS), or bottom section, to connect to the tendon foundation at the seafloor,
and a main
body that links between the two. The main body may be formed, according to
embodiments herein, using one or more tendon modules.
[0024] Tendons according to embodiments herein include one or more tendon
modules
including a tendon main body section that has multiple metallic or composite
tubular
members or strings, bundled together, acting as the main body of the
respective module
of a tendon system for a Tension Leg Platform (UP). These "cellular" tendons
have
unique features which enable the use of UP technology and application in
hydrocarbon
production in ultra-deep water and/or with heavy topside payload. Where the
use of
conventional tendons is technically and practically possible, the advantages
of the cellular
tendon over conventional tendons reside in the technical robustness, and,
depending on
platform geographical and economical characteristics, local fabrication, and
cost savings.
[0025] The cellular tendon system includes the tendon main body, and for a
single-
module tendon system, an upper transition unit to interface with the tendon
top interface,
and a bottom transition unit to interface with the tendon bottom connection.
Unlike the
single carbon steel pipe used as the main body in a conventional tendon
design, a cellular
tendon consists of multiple metallic or composite tubular strings that are
bundled together
acting as one single body. Each individual string consists of multiple tubes
or pipe
segments connected to each other at the ends of the tubes, such as by welding
or
mechanical connections. The strings may be arranged in parallel and assembled
on-shore.
[0026] Centralizers or frames may be used to bundle the strings together.
Buoyancy
modules are used partially or fully along the cellular tendon length to
provide buoyancy
necessary for the installation of the tendons. The rrs and TBS are assembled
onshore
and connected to the cellular tendon top transition unit and bottom transition
unit,
respectively. The cellular tendons, once fully assembled, may then be towed
out to the
site, upended, and installed.
6
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
[0027] A tendon
system according to embodiments herein, such as a single-module
tendon system described further below with respect to Figures 1-4, may include
a top
tendon section configured to attach to a floating structure, such as a TLP,
and a tendon
bottom section configured to attach to a foundation in the seabed. An upper
transition
unit may be connected to the top tendon section, and a bottom transition unit
may be
connected to the tendon bottom section. The tendon main body system includes
at least
two pipe strings connected proximate their upper ends to the upper transition
unit and
proximate their bottom ends to the bottom transition unit.
[0028] A tendon
system according to embodiments herein, such as a multiple-module
tendon system described further below with respect to Figures 5-7, may include
a top
tendon section configured to attach to a floating structure, such as a UP, and
a tendon
bottom section configured to attach to a foundation in the seabed. The tendon
main body 1
system includes two or more modules, including an upper tendon module, a
lowermost
tendon module, and optionally one or more intermediate tendon modules. At one
of the
tendon modules includes a tendon main body system that includes at least two
pipe
strings connected proximate their upper ends to a first module transition unit
and
proximate their bottom ends to a second module transition unit.
[0029] The pipe
strings are connected to the upper and bottom transition units such that
the pipe strings are mechanically coupled. The coupling (connection) may be
made by
welding or other means of mechanical coupling such as treated connections. For
example, the pipe strings may be welded to the upper and bottom transition
units at the
upper and lower ends of the individual pipe strings, respectively.
Alternatively, the upper
and lower ends of the pipe strings may be mechanically coupled to the upper
and bottom
transition units, respectively.
[00301 The pipe
strings may be formed from steel, aluminum, or composite materials.
The inner and outer diameter of the pipe in the pipe strings may be constant
throughout
the length of the pipe string in some embodiments. In other embodiments, the
inner
diameter, the outer diameter, or both, may vary along the length of the pipe
string. For
example, in some embodiments, the outer diameter of the pipes in the pipe
string may
7
CA 02E57,910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
remain constant, while the inner diameter decreases with depth, the thickness
of the pipe
thereby increasing with depth. Other variations in pipe diameter and thickness
are also
possible. The outer diameter and wall thickness may be selected for each point
along the
length of a tendon to carry tension from the buoyant and partially submerged
TLP (which
consists of a nominal tension plus tension variations due to functional and
environmental
loads), to maintain a necessary tendon stiffness, to achieve a desired
buoyancy, and to
withstand the crushing forces of the surrounding sea,
10031] The tendon
main body system may include one or more centralizers disposed
along a length of the pipe strings. The centralizers may be, for example,
metallic or non-
metallic plates configured to space the pipe strings and arrange each the pipe
strings in a
parallel configuration (substantially parallel, in some embodiments, as
manufacturing
process tolerances may provide for some minor deviation from parallel). The
centralizers
may also be connected to the pipe strings or otherwise configured such that
the pipe
strings are mechanically coupled. In this manner, the individual pipe strings
form a
single operative unit. In some embodiments, the centralizers may include a non-
ferric
material associated with a metallic guide frame, described further below.
[0032] To reduce
consequences of flooding of the pipe strings, a plurality of bulkheads
may be mounted in the pipe strings. The bulkheads may form sealed compartments
so
that leakage at any point along the length of a pipe section will flood only
one
compartment. The remaining sealed compartments would maintain sufficient
buoyancy
to support the weight of the tendon. Bulkheads may be placed according to the
choice of
the designer. The bullchearls may be located at the end of a designated joint
of pipe, or at
selected intervals, for example. Bulkheads may be secured in a variety of
manners, and in
some embodiments are secured by welding or mechanic locks.
[0033] The tendon
main body system may also include one or more buoyancy modules
disposed around at least a portion of the pipe strings. In some embodiments,
buoyancy
modules may be disposed around the individual pipe strings in the tendon main
body; in
other embodiments, the buoyancy modules may be disposed around the set of pipe
strings
=-= forming the
tendon main body. In some embodiments, the buoyancy modules may be
8
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
formed from two or more sections disposed around respective portions of the
pipe strings,
and may be fastened to the pipe strings via non-ferric or metallic straps. For
example, the
buoyancy modules may be bundled to the pipe strings using metal straps or
straps made
of high-strength synthetic fiber or fabric, with a mechanical lock connecting
the ends.
[00341 The tendon main body system may also include one or more buoyancy
arrest
collars connected to the pipe strings. The buoyancy arrest collars may be
provided to
constrain the buoyancy modules to the cellular tendon. In some embodiments,
the
buoyancy arrest collar includes one or more mechanic parts configured to
engage
corresponding profiles in the buoyancy module.
[0035] The physical requirements of the tendons may vary with depth. Thus,
in some
embodiments, the tendon may be formed by two or more modules. In some
embodiments, for example, the tendon may include an upper tendon module and a
lower
tendon module; in other embodiments, the tendon may include an upper tendon
module, a
lower tendon module, and one or more intermediate tendon modules. As the
design
requirements (crush strength, etc.) of the shallower tendon modules may be
lower than
those used at depth, a hybrid tendon according to embodiments herein may
include, for
example, an upper tendon module, which may be a conventional tendon, such as a
single-
string tendon, and a lower tendon module or modules, which may be cellular
tendons as
described herein. In other embodiments, the tendon may include multiple
cellular tendon
modules. Where multiple cellular tendon modules are used along the length of
the
tendon, the design and physical requirements of the segments may be adjusted
for
operating depth.
100361 A hybrid tendon system according to embodiments herein, for example,
may
include an upper tendon module and one or more lower tendon modules, including
a
lowermost tendon module. The upper tendon module may include a top tendon
section
configured to attach to a floating structure. The upper tendon module may also
include a
lower tendon section configured to attach to one of the lower tendon modules,
such as to
an upper portion of an intermediate tendon module or the lowermost tendon
module.
9
CA 02857910 2014-07-30
=
=
PATENT APPLICATION
ATTORNEY DOCKET NO. 7964/023002
[0037] The lower tendon modules may be configured to attach at
their upper ends via an
upper transition unit to either (a) the lower tendon section of the upper
tendon module or
(b) a lower tendon section of an axially higher lower tendon module. The lower
tendon
modules may also be configured to attach at their lower ends via a lower
transition unit to
either (a) a foundation or (b) an upper tendon section of an axially lower
tendon module.
The one or more lower tendon modules may be formed of a cellular tendon
system,
similar to that as described above, having a tendon main body system including
at least
two pipe strings connected proximate their upper ends to the upper transition
unit and
proximate their bottom ends to the lower transition unit.
[0038] The above described tendons may be used to secure any
variety of floating
platform to a seabed.
[0039] Figure 1 is an elevation view of a floating platform 1,
such as a Tu), moored to
seabed 2 using tendon systems according to embodiments herein. Platform 1 may
have a
plurality of columns 4, and a horizontal section 6 may extend between the
columns 4.
Columns 4 and horizontal pontoons 6, to provide buoyancy, and may be adapted
to be
selectively ballasted with water. Platform 1 may also include one or more
decks 8 for
supporting a variety of equipment for offshore operations, such as drilling
and/or
production, such as through top tensioned risers 10.
[0040] Upper tendon supports 12 are mounted to platform 1 at each
column 4 for
attachment to an upper end 13 of each tendon 14. A minimum of two tendons 14
may be
used to support at each tendon support 12, and thus a platform 1 with four
corners would
have at least eight separate tendons 14. The lower end 16 of' each tendon 14
is secured to
1
a piling or foundation 18.
1
[0041] Figure 2 illustrates a tendon 14 according to embodiments
herein. Tendon 14
includes a tendon top segment 20, tendon main body section 22, and a tendon
bottom
segment 24. The top of the uppermost pipe segment in tendon top segment 20 may
be
terminated with a connector assembly 25, commonly referred to as a length
adjustment
joint (LAJ) that is arranged and designed to connect to the TLE. hull.
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. L1964/023002 .=
.=
[0042] The top of
tendon main body section 22 is axially connected to the bottom of
tendon top segment 20, and the bottom of tendon main body section 22 is
axially
connected to the top of tendon bottom segment 24. The bottom of the tendon
bottom
segment 24 is terminated with a connector assembly 27, commonly referred to as
a
bottom latch assembly that is arranged and designed to be received and locked
into a
piling 18 or other foundation structure on the seabed.
[0043] Tendon main body section 22 includes multiple (i.e., two or
more, small
quantities for large diameter seam pipes and large quantities for small
diameter seamless
pipes) metallic pipe strings 38. Each individual pipe string is formed from
multiple pipe
sections (segments, stands, or joints) welded or mechanically coupled end-to-
end.
Alternatively, tendon main body section 22 may include multiple composite pipe
sections.
[0044] To
facilitate connection of tendon main body section 22 to top and bottom
segments 20, 24, an upper transition unit 26 and a bottom transition unit 28
may be used.
Transition units 26, 28 may include tapered sections 30, 32 expanding in
diameter from
the diameter of the tendon top segment and the tendon bottom segment,
respectively,
terminating at a large diameter section 34, 36. Large diameter sections 34, 36
are sized
appropriately for connection with the main body section 22. The top and bottom
of pipe
strings 38 forming main body section 22 may be welded or mechanically
connected to
transition units 26, 28, respectively.
[0045] For example, pipe strings 38 may be attached to the upper
transition unit 26 that
interfaces with the tendon top segment 20, The pipes in the pipe strings 38
are welded to,
or mechanically connected to, the upper transition unit 26. A short taper 30
may or may
not be used at the pipe up ends where the transition is made. At the top, the
upper
transition unit 26 may include a weld profile to be welded at the bottom of
the tendon top
segment 20. The pipe strings 38 may also be attached to the bottom transition
unit 28
that interfaces with the tendon bottom segment 24. The pipes in the strings 38
are welded
to, or mechanically connected to, the bottom transition unit 28. A short taper
32 may or
may not be used at the pipe bottom ends where the transition is made. At the
bottom, the
11
CA 02857910 2014-07-30
=
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
bottom transition unit 28 may have a weld profile to be welded to the top of
the tendon
bottom. segment 24.
10046] The physical arrangement of pipe sections 38 may vary, and
may depend on the
depth of service, the expected environmental conditions, and other factors. In
some
embodiments, the pipe strings 38 may be arranged such that the pipe strings
run
alongside each other. In other embodiments, the pipe strings 38 may be spaced
apart
from each other.
[0047] For example, in some embodiments, the pipe strings 38 may
be spaced apart using
a centralizer 40, a guide frame 42, or a combination of the two. Centralizers
40 may be
made of non-ferric material, with or without the metallic guide frames 42, and
may be
used to bundle the pipe strings together and keep all the strings acting as a
mechanically
composite unit to meet the tendon strength and fatigue requirements. Figure 2
and Figure
3 show one possible arrangement of the centralizer 40.
[0048] Compartmentalization of the pipes may be used to reduce the
in-water weight of
the tendon when a leak occurs in one pipe string 38. For example, as shown in
Figure 4,
single or multiple compartments 44, 46 may be formed inside the pipe strings,
as well as
the tendon top segment 20 and the tendon bottom segment 24, by using bulkhead
48. The
bulkheads 48 may be used together with the guide frame 42 in some embodiments.
For
example, the guide frames 42 and bulkheads 48 may be inserted proximate an end
of a =
pipe segment, facilitating connection to the next pipe segment forming the
pipe string 38,
spacing of the pipe strings, as well as segregation of the pipe segments into
sealed
chambers 44, 46.
[0049] Buoyancy modules 50 may be used partially or fully along
the Cellular Tendon
length to provide buoyancy necessary for installation of the tendons. Material
used to
form the buoyancy modules may be synthetic foams or other suitable light
material.
Open-bottom air cans or other types of buoyancy devices may also be used.
Further, the
buoyancy of the buoyancy modules 50 may vary along the length of pipe strings
38.
[0050] The buoyancy modules 50 may also be used as a fabrication
aid when the pipe
strings 38 are assembled on shore. For example, using a centralizer 40,
internal to a pipe
segment group, encapsulation of multiple pipe segments with a buoyancy module
50 may
12
=
CA 02857910 2014-07-30
=
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
facilitate disposition of the ends of the pipe segment for connection of guide
frames 42,
bulkheads 44, and/or connection of the pipe segment to the subsequent pipe
segment. In
some embodiments, the buoyancy modules 50 may be fastened to the pipe strings
38 by
non-ferric or metallic straps 52, which may be recessed within a buoyancy
module or
may be placed at the surface around a buoyancy module.
[0051] A buoyancy arrest collar 54 may be used, such as with the metallic
guide frames
42 as shown in Figure 4, to facilitate placement and retention of the buoyancy
module 50
around the pipe strings 38, both during construction and in service. For
example,
buoyancy arrest collar 54 may include one or more mechanic parts configured to
engage
corresponding profiles in the buoyancy module. In other embodiments, buoyancy
arrest
collar may include a disc-like structure encompassing the pipe strings 38, the
outer
portions of the disc engaging circumferential grooves in the buoyancy modules
50, or
engaging a terminal end of the buoyancy modules 50.
[0052] Referring now to Figure 5, an elevation view of a floating platform
1, such as a
TLP, moored to seabed 2 using hybrid or modular cellular tendon systems
according to
embodiments herein is illustrated, where like numerals represent like parts.
As described
above with respect to Figure 1, the platform 1 may have a plurality of columns
4, and a
horizontal section 6 may extend between the columns 4. Columns 4 and
horizontal
pontoons 6 provide buoyancy, and may be adapted to be selectively ballasted
with water.
Platform I may also include one or more decks 8 for supporting a variety of
equipment
for offshore operations, such as drilling and/or production, such as through
top tensioned
risers 10.
[0053] Similar to the cellular tendon system described above, upper tendon
supports 12
are mounted to platform 1 at each column 4 for attachment to an upper end 13
of each
tendon 14. Minimum two tendons 14 may be supported at each tendon support 12,
and
thus a platform 1 with four corners would have minimum eight separate tendons
14. The
lower end 16 of each tendon 14 is secured to a piling or foundation 18.
[0054] Figure 5 illustrates two possible hybrid cellular tendons according
to
embodiments herein. Hybrid tendons 70 include an upper tendon module 72 that
is a
conventional, single string, tendon connected to a lower tendon module 74 that
is a
13
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
cellular tendon, such as that described above with respect to Figure 2. Hybrid
tendons 76
include an upper tendon module 78 that is a cellular tendon section, such as
that
described above with respect to Figure 2, connected to a lower tendon module
80, which
may also be a cellular tendon similar to that as described above with respect
to Figure 2,
where the modules 78, 80 may be of the same or different design, which may be
varied to
appropriately meet design criteria for intended depth of use.
[0055] Figure 6 is a side view of a hybrid tendon 70 according to
embodiments herein,
where like numerals represent like parts. Tendon 70 may include an upper
tendon
module 72 that is a conventional, single string, tendon connected to a lower
tendon
module 74 that is a cellular tendon.
[0056] Upper tendon module 72 may include a tendon module top segment 81, a
tendon
module main body section 82, and a tendon module bottom segment 84. The top of
the
uppermost pipe segment in tendon top segment 81 may be terminated with a
connector
assembly 25, commonly referred to as a length adjustment joint (LAI) that is
arranged
and designed to connect to the 'TLP hull. Conventional tendon module 72 main
body
section 82 may be formed from a single pipe string 86 including one or more
segments 88
of pipe axially connected end-to-end.
[0057] The top of tendon main body section 82 is axially connected to the
bottom of
tendon top segment 81, and the bottom of tendon main body section 82 is
axially
connected to the top of tendon bottom segment 84. The bottom of the tendon
bottom
segment 84 is terminated with a connector assembly 87, which may be similar to
a
bottom latch assembly,
[0058] The connector 87 may be designed to be received and locked into a
receiver
assembly 90, having a receptacle 92, which may be designed similar to
connector
assemblies for attachment of a tendon to a piling, for example. The receiver
assembly 90
may be connected, directly or indirectly, to bottom tendon module 74. For
example,
receiver assembly 90 may be part of a transition module (not shown) for
latching
connector assembly 87 and likewise latching to a connector assembly (not
shown)
forming an upper terminal end of bottom tendon module 74. In other
embodiments, such
14
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
=
as illustrated in Figure 6, connector assembly 87 may form the upper terminal
end 94 of
bottom tendon module 74.
[0059] Bottom tendon module 74 may be similar to that as described above
with respect
to Figures 2-4, where like numerals represent like parts. The top of bottom
tendon main
body section 22 is axially connected to the bottom of upper tendon module 72,
as
described above, and the bottom of tendon main body section 22 is axially
connected to
the top of a tendon bottom segment 24. The bottom of the tendon bottom segment
24 is
terminated with a connector assembly 27, commonly referred to as a bottom
latch
assembly that is arranged and designed to be received and locked into a piling
18 or other
foundation structure on the seabed.
[0060] Figure 7 is a side view of a hybrid tendon 76 according to
embodiments herein,
where like numerals represent like parts. Tendon 76 may include an upper
tendon
module 78 that is a cellular tendon connected to a lower tendon module 80 that
is also a
cellular tendon.
[0061] Upper tendon module 78 may include a tendon module top segment 101,
a tendon
module main body section 102, and a tendon module bottom segment 104, The top
of the
uppermost pipe segment in tendon top segment 101 may be terminated with a
connector
assembly 25, commonly referred to as a length adjustment joint (LAJ) that is
arranged
and designed to connect to the TLP hull.
[0062] The top of tendon main body section 102 is axially connected to the
bottom of
tendon top segment 101, and the bottom of tendon main body section 102 is
axially
connected to the top of tendon bottom segment 104. The bottom of the tendon
bottom
segment 104 is terminated with a connector assembly 107, which may be similar
to a
bottom latch assembly.
[0063] The connector 107 may be designed to be received and locked into a
receiver
assembly 110, having a receptacle 112, which may be designed similar to
connector
assemblies for attachment of a tendon to a piling, for example. The receiver
assembly
110 may be connected, directly or indirectly, to bottom tendon module 80. For
example,
receiver assembly 112 may be part of a transition module (not shown) for
latching
connector assembly 107 and likewise latching to a connector assembly (not
shown)
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
forming an upper terminal end of bottom tendon module 80. In other
embodiments, such
as illustrated in Figure 7, connector assembly 107 may form the upper terminal
end 114
of bottom tendon module 80.
10064] The top of bottom tendon main body section 122 is axially connected
to the
bottom of upper tendon module 72, as described above, via connector assembly
107, and
the bottom of tendon main body section 122 is axially connected to the top of
a tendon
bottom segment 124. The bottom of the tendon bottom segment 124 is terminated
with a
connector assembly 127, commonly referred to as a bottom latch assembly that
is
arranged and designed to be received and locked into a piling 18 or other
foundation
structure on the seabed.
[0065] Upper tendon module 78 and bottom tendon module 80 may otherwise be
similar
to the cellular tendons as shown and described above with respect to Figures 2-
4, where
like numerals represent like parts.
[0066] In the various tendon modules 78, 80, as well as for intermediate
modules that
may be placed between and connecting modules 78, 80 for embodiments including
more
than two tendon modules, the size, number, and physical arrangement of pipe
sections 38
may vary, and may depend on the depth of service, the expected environmental
conditions, and other factors. In some embodiments, the pipe strings 38 may be
arranged
such that the pipe strings run alongside each other. In other embodiments, the
pipe
strings 38 may be spaced apart from each other. For example, as described
above with
respect to Figures 2-4, in some embodiments, the pipe strings 38 may be spaced
apart
using a centralizer 40, a guide frame 42, or a combination of the two, as well
as with a
buoyancy module 50.
[0067] The upper tendon modules, such as modules 72, 78, as well as the
bottom tendon
modules, such as modules 74, 80, may include transition units 130, similar to
transition
units 26, 28, connecting the respective tendon main body segments 22, 82, 102,
122 to
the tendon top segments and tendon bottom segments, as well as any
intermediate
connector segments used along the length of the hybrid tendon system.
[0068] Assembly of the cellular tendons according to embodiments herein may
be
performed in any number of manners. The main body section 22 may be assembled
pipe
16
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/D23002
segment by pipe segment. In some embodiments, the top and bottom transition
units and
tendon top and bottom segments may be connected in order of depth or height
(top-to-
bottom or bottom-to-top) along with the main tendon body pipe strings, or
these
components may be individually assembled and connected to the main tendon body
pipe
stings following completion of the main tendon body pipe strings.
100691 Methods of assembling a tendon system according to embodiments
herein may
thus include assembling a tendon main body section including two or more pipe
strings.
The two or more pipe strings forming the tendon main body may be individually
assembled by axially connecting two or more pipe segments to form a pipe
string. The
two or more pipe strings, having roughly equivalent length, may be axially
connected at
the respective ends to a tendon top segment and a tendon bottom segment. An
upper
transition unit and a bottom transition unit may be used to facilitate
connection of the
tendon main body section with the tendon top segment and the tendon bottom
segment.
As noted above, the tendon bottom segment and the tendon top segment may each
be
terminated with a connector assembly.
[0070] As noted above, it may be desired to space the pipe strings forming
the tendon
main body section apart from one another. Guide frames, centralizers, and/or a
buoyancy
module may be used to achieve the desired spacing, either during collective
manufacture
of the individual pipe strings or following manufacture of the individual pipe
strings
individually. A bulkhead may periodically be disposed in the pipe strings
during
assembly, and buoyancy arrest collars may be disposed along the length of the
pipe
strings, either during collective assembly of the individual pipe strings or
following
manufacture of the individual pipe strings individually.
[0071] In some embodiments, the main tendon body pipe strings may be
assembled
collectively as follows. A buoyancy module section, such as a semi-circular
section, may
be placed horizontally, with the interior of the module facing upward. The
buoyancy
module section may be configured, similar to that as illustrated in Figure 3,
having
pockets 60 in which the pipe segments may be disposed or laid. Centralizer 40
may then
be disposed on the pipes and buoyancy modules, such as into a groove in the
buoyancy
module section or by welding to pipes 38. The upper pipe segments may then be
17
CA 02857910 2014-07-30
=
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964/023002
disposed on or connected to centralizer 40, subsequently encapsulated with a
second
buoyancy module section, and then the buoyancy module sections may be cinched
or
secured to the structure using straps 52. Disposing of a centralizer and
buoyancy module
proximate each end of a pipe segment, such as within a couple feet of an end,
may thus
allow for disposal of guide frames 42, bulkheads 48, and buoyancy arrest
collars 54, as
required, and connection of two corresponding pipe segments forming an
individual pipe
string to be welded or otherwise connected to each other with relative ease.
[0072] One possible arrangement for buoyancy modules 50 is thus as
illustrated and
described with respect to Figure 3, which may be used to facilitate tendon
fabrication as
described above, Other various arrangements for buoyancy modules that may
facilitate
fabrication and spacing of strings 38 during fabrication are illustrated in
Figures 8-10.
[0073] As illustrated in Figure 8, for example, a buoyancy module 150 may
include two
or more arms defining two or more recesses 154 in which the strings 38 may be
disposed.
Non-ferric or metallic straps 52 may be placed at the surface around the
buoyancy
module 150 and the strings 38. As illustrated, buoyancy module 150 includes
four arms
152 / recesses 154; other embodiments may include three, five, six or more
arms/recesses
for placement of the strings 38.
[0074] As illustrated in Figure 9, as another example, a buoyancy module
160 may be
used to space strings 38 via corner recesses 162. Similarly, shapes having
three, five, six
or more corners may be used, where recessed corners are designed for placement
and/or
retention of strings 38 during fabrication and/or use of the cellular tendon
or cellular
tendon modules.
[0075] As illustrated in Figure 10, as another example, a buoyancy module
170 may be
used to space strings 38 via recesses 172. Recesses 172 may be located
proximate a
comer of the shaped buoyancy module, as well as along the length of the sides
of the
shaped buoyancy module. As illustrated in Figure 10, the buoyancy module 170
includes
a recess 172 proximate the top corner of the triangular buoyancy module 170,
as well as
two recesses 172 located along the sides of the triangular buoyancy module
170. In this
manner, the bottom 174 of the buoyancy module may be used to support the
strings 38
18
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO 17964/023002
during fabrication, providing a flat surface for disposal of the buoyancy
module and
:
strings 38 during fabrication.
[0076] The buoyancy modules as illustrated in Figures 8-10 may provide for
the desired
buoyancy of the cellular tendon modules. Additionally, these and similar
configurations
provide openings along the length of the string, allowing access to the pipes
in the strings
for inspection. Additionally, such embodiments may allow for removal and/or
replacement of one or more strings offshore.
[0077] Similar to the embodiments for buoyancy modules illustrated in
Figures 3 and 8-
10, guide frames may also be formed from a variety of shapes so as to properly
space
strings 38 and facilitate fabrication of the cellular tendons or tendon
modules.
[0078] After assembly on shore, the cellular tendon system 14 as described
above may be
transported, or towed out, in single units, pairs, or other convenient
connection numbers,
to the offshore site. The towing can be carried out as surface tow or
submerged tow. At
the offshore site, the cellular tendon system 14 is upended and attached to
the foundation
18. The tendon top segment 20 is pulled in and locked at the tension leg
platform 1
tendon porch 12 via the length adjustment joint (LAJ) 25. After the tendon
pretension
reaches the design value, the tendon is ready for the in-place services.
[0079] To add flexibility in the TLP construction schedule, the Cellular
Tendon system
14 can be pre-installed. In the pre-installed condition, a temporary tendon
supporting
buoy may be used to maintain the near vertical position of the tendons and
meet the
strength and fatigue requirements from the wave and current loads, similar to
those used
in conventional tendon systems.
[0080] When multiple tendon modules are used to form a single tendon, such
as
illustrated in Figures 5-7, the cellular tendon modules may be fabricated
onshore as
described above. After assembly onshore, the modules (such as 72, 74 or 78,
80) may be
towed out, in single units or in pairs, to the offshore site. The towing can
be carried out
as surface tow or submerged tow. At the offshore site, the bottom tendon
module may be
upended and attached to the foundation. To add the flexibility in the TLP
construction
schedule, the bottom modules can be pre-installed prior to arrival of the
upper modules.
After towed to the site, the upper modules may be upended and latched, or
otherwise
19
CA 02857910 2014-07-30
PATENT APPLICATION
ATTORNEY DOCKET NO. 17964)023002
attached, to the receiving module at the upper end of the lower module. The
top tendon
segment of the uppermost module is pulled in and locked at the TLP tendon
porch via the
length adjustment joint (LAJ). After the tendon pretension has reached the
design value,
the tendon is ready for the in-place services. In other embodiments, the upper
and lower
modules of the tendon system may be assembled offshore prior to submerging and
upending.
[0081] As described above, tendons according to embodiments herein include
a tendon
main body section that includes multiple metallic or composite tubular
members, bundled
together acting as the main body of a tendon system for a Tension Leg Platform
(TLP).
These "cellular" tendons have unique features which enable the TLP technology
and
application in hydrocarbon production in ultra-deep water and/or with heavy
topsides. In
addition, the advantages of the cellular tendon over the conventional tendons
reside in the
technical robustness, local fabrication, and cost savings.
[0082] The cellular tendon design has technical merits for actual field
developments
using TLPs with representative large, medium or small payloads in water depths
between
1500 meters and 3000 meters, and possibly deeper. The cellular tendon system
has the
following advantages over the conventional tendons: provides sufficient
vertical and
lateral stiffness, while also ensuring sufficient resistance to tension-
collapse; provides
more neutrally buoyant tendons that reduce TLP displacement and temporary
buoyancy
requirement during tendon installation; provides more structural redundancy
for the
tendon main body where the multiple tube construction in the Cellular Tendon
warrants
additional structural redundancy in the event of one string damaged; enhances
(and in
some cases enables) the local fabrication content, where applicable; provides
material
cost savings as a result of eliminating mechanical couplings; and provides
installation
cost savings as a result of eliminating the need for heavy lift vessels.
[00831 While the disclosure includes a limited number of embodiments, those
skilled in
the art, having benefit of this disclosure, will appreciate that other
embodiments may be
devised which do not depart from the scope of the present disclosure.
Accordingly, the
scope should be limited only by the attached claims.
