U.S. patent application number 10/626044 was filed with the patent office on 2004-08-26 for offshore well production riser.
This patent application is currently assigned to Deepwater Technologies, Inc.. Invention is credited to Horton, Edward E. III.
Application Number | 20040163817 10/626044 |
Document ID | / |
Family ID | 31721403 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040163817 |
Kind Code |
A1 |
Horton, Edward E. III |
August 26, 2004 |
Offshore well production riser
Abstract
An offshore oil well riser system that compensates for the
motions of an associated floating platform comprises a vertical
pipe section supported by the floating vessel and extending
downward from the vessel substantially perpendicular to the sea
floor, and a horizontal pipe section connected to the associated
sub-sea well equipment and extending away from the equipment
substantially parallel to the sea floor. A angled elbow pipe
connects the horizontal pipe to the vertical pipe. At least one of
the horizontal and the vertical pipes incorporates a flexing
portion comprising a plurality of recurvate sections of pipe
connected end-to-end with alternating curvatures. In one
embodiment, the central axis of the flexing portion lies in a
single plane and takes a sinusoid path. In another embodiment, the
central axis of the flexing portion takes a three dimensional
helical path.
Inventors: |
Horton, Edward E. III;
(Houston, TX) |
Correspondence
Address: |
KLEIN, O'NEILL & SINGH
2 PARK PLAZA
SUITE 510
IRVINE
CA
92614
US
|
Assignee: |
Deepwater Technologies,
Inc.
Houston
TX
|
Family ID: |
31721403 |
Appl. No.: |
10/626044 |
Filed: |
July 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10626044 |
Jul 24, 2003 |
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10213966 |
Aug 7, 2002 |
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10626044 |
Jul 24, 2003 |
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10213963 |
Aug 7, 2002 |
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Current U.S.
Class: |
166/367 |
Current CPC
Class: |
E21B 17/085 20130101;
E21B 19/006 20130101; E21B 17/015 20130101; E21B 17/017
20130101 |
Class at
Publication: |
166/367 |
International
Class: |
E21B 017/01 |
Claims
What is claimed is:
1. An offshore oil well riser system extending from a floating
vessel on the sea surface to a sub-sea well equipment located on
the sea floor, the riser system comprising: an elongated,
substantially vertical section of pipe supported by the floating
body and extending downward towards the sea floor; an elongated,
substantially horizontal section of pipe connected to the sub-sea
well equipment; an angled elbow section of pipe connecting the
vertical pipe section to the horizontal pipe section such that the
vertical and horizontal pipe sections resiliently flex in a
direction generally perpendicular to their respective long axes in
response to motion of the floating vessel. and, an elongated
flexing portion of pipe disposed axially within at least one of the
vertical and the horizontal pipe sections and arranged therein to
resiliently flex in directions both generally perpendicular and
parallel to its long axis in response to motion of the floating
vessel.
2. The riser system of claim 1, wherein the flexing portion of pipe
comprises a plurality of recurvate sections of pipe connected
end-to-end with alternating curvatures.
3. The riser system of claim 1, wherein the flexing portion of pipe
is disposed in the vertical, the horizontal, or both the vertical
and the horizontal sections of pipe.
4. The riser system of claim 1, wherein a central axis of the
flexing portion of pipe lies in a single plane.
5. The riser system of claim 1, wherein the flexing portion pipe is
generally sinusoidal in shape.
6. The riser system of claim 1, wherein the flexing portion of pipe
is generally helical in shape.
7. The riser system of claim 1, wherein the flexing portion of pipe
has a two-dimensional shape.
8. The riser system of claim 1, wherein the flexing portion of pipe
has a three-dimensional shape.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a continuation-in-part of co-pending
U.S. pat. app. Ser. Nos. 10/213,966 and 10/213,963, both filed Aug.
7, 2002.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] (Not Applicable)
REFERENCE TO APPENDIX
[0003] (Not Applicable)
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates, in general, to offshore oil well
risers that convey petroleum from producing wells on the sea floor
to a floating platform on the sea surface, and in particular, to
risers that are capable of accommodating large motions of the
platform relative to the wells without damage.
[0006] 2. Description of Related Art
[0007] Conventional "dry tree" floating offshore platforms for
drilling and production of oil and gas typically include such "low
heave" designs as Spar platforms, Tension Leg Platforms ("TLPs"),
and Deep-Draft semi-submersible platforms. These platforms are
capable of supporting a plurality of vertical production and/or
drilling "risers," i.e., long pipes extending up from oil and gas
wells on the sea floor to the platforms. The platforms typically
comprise a "well deck," where surface "trees," i.e., control valves
disposed on the top ends of the risers, are located, and a
production deck, where the crude oil is collected from the risers
and fed to a processing facility for separation of water, oil and
gas. In conventional dry tree offshore platforms, the risers extend
from the respective well heads to the well deck and are supported
thereon by a tensioning apparatus, and such risers are thus termed
Top-Tensioned Risers ("TTRs").
[0008] One known TTR design uses "active" hydraulic tensioners
located on the well deck to support each riser independently of the
others. Each riser extends vertically from the well head to a
tensioner located on the well deck of the platform, and is
supported there by hydraulic cylinders connected to the well deck.
The cylinders enable the platform to move up and down relative to
the risers, and thereby partially isolate the risers from the heave
motions of the hull. A surface tree is attached at the top of each
riser, and a flexible, high-pressure jumper hose connects the
surface tree to the production deck. However, as the tension force
and displacement requirements of the hydraulic cylinders increase,
these active tensioners become prohibitively expensive. Further,
the offshore platform must be capable of supporting the combined
load of all the risers.
[0009] A second TTR design uses passive "buoyancy cans" to support
the risers independently of the platform, as illustrated in the
schematic elevation view of FIG. 1 of the accompanying drawings. In
this design, each riser 100 extends vertically from the well head
through the keel of the floating platform and into a "stem pipe,"
to which the buoyancy cans are attached. This stem pipe extends
above the buoyancy cans and supports a platform to which the risers
and the surface trees are attached. A flexible, high pressure
jumper hose connects the surface trees to the production deck of
the platform. Since the risers are independently supported by the
buoyancy cans relative to the hull of the platform, the hull is
able to move up and down relative to the risers, and thus, the
risers are isolated from the heave motions of the platform. The
buoyancy cans must provide sufficient buoyancy to supply the
required top tension in the risers, as well as support the weight
of the can, stem, and the surface tree. At greater depths, the
buoyancy required to support the riser system is proportionately
greater, resulting in relatively large buoyancy cans. Consequently,
the deck space required to accommodate all the risers increases
substantially. Designing and manufacturing individual buoyancy cans
for each riser in deep water applications is therefore costly.
[0010] Conventional "wet tree" offshore platforms include Floating
Production Storage and Off-loading ("FPSO") and semi submersible
platforms. These types of platforms have relatively large motions
that make it impractical for them to support vertical production
and drilling risers, and accordingly, are generally used in
connection with a sub-sea completion system, i.e., sub-sea trees,
which are arranged on the seafloor. Produced crude oil is typically
conveyed along the seafloor with flow-lines and gathered in a
manifold. Production risers then carry the crude oil from the
manifold or sub-sea tree to the process equipment of the floating
support. As the floating support has relatively large motions (both
heave and horizontal), the production risers must be designed to
accommodate these large motions.
[0011] Production risers can also comprise flexible, reinforced
elastomeric risers. Flexible risers are connected directly to the
floating platform, and thus take the shape of a catenary that
extends from the floating support to the sea floor, as illustrated
schematically in FIG. 2, in which a flexible riser 200 is shown.
Because of their shape and construction, and particularly their
flexibility, flexible risers are better able to accommodate the
motions of the platform. However, they are also relatively heavy
and expensive. Alternatively, the risers can comprise so-called
Steel Catenary Risers ("SCRs"). These connect directly to the
floating support through a flexible joint or similar mechanism and
also present a catenary shape when deployed. Because they are made
of steel, SCRs are less expensive than flexible risers, but because
they are also stiffer, are prone to fatigue problems caused by
dynamic motions and require greater lengths to absorb the vessel
motion.
[0012] Another known dry tree riser system is the so-called "riser
tower." In this system, the riser tower comprises one or more rigid
vertical pipes connected to the seafloor through a pivot connection
or stress joint. The pipes are supported by a large top buoyancy
device which provides sufficient buoyancy to support the pipes and
prevent them from going slack or vibrating in response to ocean
currents. Flexible jumpers are used to connect the vertical pipes
to the floating support. This type of riser system is both
expensive and difficult to install.
[0013] In light of the foregoing, a long felt but as yet
unsatisfied need exists in the petroleum industry for a low-cost,
simple, yet reliable offshore oil well riser system that
compensates for the motions of an associated floating platform.
BRIEF SUMMARY OF THE INVENTION
[0014] In accordance with the present invention, an offshore oil
well riser system is provided that compensates for the motions of
an associated floating drilling or production platform. The riser
system is relatively inexpensive, simple to fabricate and deploy,
and reliable in operation.
[0015] The novel riser comprises a rigid vertical pipe section that
is supported by the floating vessel, and which extends downward
from the vessel substantially perpendicular to the sea floor, and a
rigid horizontal pipe section that is connected to the associated
sub-sea well equipment (i.e., the well head, sub-sea tree, split
tree, manifold, or the like), and which extends away from the
equipment substantially parallel to the sea floor. A relatively
short, inflexible angled pipe section, i.e., an "elbow," connects
the horizontal pipe to the vertical pipe. In a preferred
embodiment, the vertical pipe section predominates over the others
such that the overall riser system presents a substantially
vertical shape, and only a relatively small, substantially
horizontal pipe section is used to connect the riser to the sub-sea
well head equipment.
[0016] Since the riser is directly supported by the floating
platform, motions of the platform (i.e., heave, surge, sway, pitch,
roll, and yaw) are transmitted to the riser, and must therefore be
absorbed by the horizontal and vertical pipes. To limit the
resulting stress and fatigue in these two sections, at least one of
them is provided with a flexing portion that is able to absorb the
motion of the platform imparted to the riser. This flexing portion
can be arranged in the vertical pipe section, in the horizontal
pipe section, or in both. The flexing portion comprises a plurality
of recurvate sections of pipe connected end-to-end with alternating
curvatures. In one possible embodiment thereof, the central axis of
the flexing portion lies in a single plane and takes a sinuous
path, e.g., that of a sinusoid. In another possible embodiment, the
central axis of the flexing portion takes a three dimensional path,
e.g., that of a helix. Many other configurations of the flexing
portion are possible.
[0017] Both the angled pipe section, i.e., the elbow, and the
flexing portion of the novel riser can be designed to easily
accommodate wire line, coiled tubing or "pigging" operations
internally. The floating vessel supports the riser, and thus, no
expensive buoyancy cans are required. Since all vessel motions are
absorbed by the riser, neither a flexible jumper nor a long length
of pipe is required to accommodate the motion. Additionally, since
the major portion of the riser is substantially vertical, the total
length of riser required is substantially reduced, relative to a
catenary shape, and since it is made entirely of steel pipe, it is
cost-effective to make.
[0018] A better understanding of the above and many other features
and advantages of the present invention may be obtained from a
consideration of the detailed description thereof below, especially
if such consideration is made in conjunction with the views of the
appended drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] FIG. 1 is a schematic elevation view of a prior art offshore
oil well riser system;
[0020] FIG. 2 is a schematic elevation view of another prior art
riser system;
[0021] FIG. 3 is schematic elevation view of an exemplary
embodiment of an offshore oil well riser system in accordance with
the present invention;
[0022] FIG. 4 is an enlarged elevation view of the exemplary riser
system shown in FIG. 3;
[0023] FIG. 5 is an elevation view of exemplary embodiment of an
another riser system in accordance with the present invention;
[0024] FIGS. 6 and 7 are perspective views of the centerline of the
riser of the system illustrated in FIG. 4, showing displacements of
the riser in response to surface platform movements;
[0025] FIG. 8 is a partial elevation view of a riser in accordance
with another exemplary embodiment the present invention;
[0026] FIG. 9 is a partial elevation view of a riser in accordance
with another exemplary embodiment the present invention;
[0027] FIG. 10 is an elevation view of an exemplary embodiment of
an another riser system in accordance with the present
invention;
[0028] FIGS. 11-13 are schematic elevation views of exemplary
embodiments of other riser systems in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] An offshore oil well riser system 10 in accordance with one
exemplary embodiment of the present invention is illustrated in the
respective schematic and enlarged elevation views of FIGS. 3 and 4.
The riser system comprises a substantially horizontal well entry
pipe section 12 connected to a wellhead 14 located on the sea floor
16. An angulated elbow section of pipe 18 connects the horizontal
well entry pipe 12 to a substantially vertical riser pipe section
20, which in turn, is connected to and supported by a vessel 22
that floats on the surface of the water, e.g., a Spar platform, an
FPSO, or any type of floating platform. In one advantageous
embodiment, the horizontal well entry pipe, the elbow and the
vertical riser pipe are all made of steel. Although steel risers
are relatively much stiffer than flexible risers, they nevertheless
have sufficient resilience and elasticity to bend and flex in
response to the motions of the floating vessel, such that the
forces thereby exerted on the riser are substantially isolated from
the wellhead.
[0030] As a practical matter, because of the relatively large
depths in which the riser system 10 is deployed, the length of the
vertical pipe section 20 is much greater than that of the
horizontal pipe section 12, and accordingly, the overall riser 10
presents a substantially vertical aspect. Also, as will appreciated
by those of skill in the art, "substantially horizontal" and
"substantially vertical" are relative terms, as both the horizontal
and vertical sections of pipe move through relatively large angles
relative to the sea floor 16 in response to movement of the surface
vessel 22, as illustrated schematically in FIGS. 6 and 7, in which
movement of the central axis 24 of the riser with respect to the
sea floor in response to surface vessel movement is shown before
(solid line) and after (dashed line) displacement.
[0031] An alternative exemplary embodiment of a riser system 10 in
accordance with the present invention is illustrated in FIG. 5. In
this embodiment, a riser "spur" pipe 24, comprising a short,
substantially vertical pipe section, is connected at one end to the
wellhead 14. As in the first embodiment above, an elbow section 18
connects the other end of the spur pipe to a substantially vertical
riser pipe section 20, which in turn, is connected to and supported
by the floating vessel 22. In the first embodiment of FIG. 1, the
elbow section 18 is bent at an angle of about 90.degree. to
accommodate the horizontal and vertical sections of pipe. In the
second embodiment of FIG. 5, the elbow is bent at an angle of about
a 45.degree. to accommodate the substantially vertical stub pipe,
and accordingly, the lower end portion 24 of the vertical pipe
section 20 is curved tangentially at about 45.degree. to attach to
the elbow. Of course, a plurality of elbows having a variety of
other included angles may be used to connect the sections of the
riser together, and in some possible embodiments, the walls of the
elbows can incorporate bellows-like convolutions to render them
more flexible.
[0032] The flexing of the riser system 10 illustrated in FIGS. 6
and 7 comprises flexing of the horizontal and vertical pipe
sections 12 and 20 in a direction generally perpendicular to their
respective long axes. By such flexing, the riser can absorb a
considerable amount of the energy associated with movement of the
floating-vessel 22 without buckling. However, as described in more
detail below, it is possible to further increase the amount of
surface vessel motion that the riser system can accommodate by
incorporating one or more "flexing portions" into the pipe sections
of the riser that enable the sections to flex in directions both
perpendicular and parallel to their respective long axes.
[0033] As illustrated in FIGS. 8 and 9, the flexing portion 30 of
the riser 10 comprises a plurality of recurvate pipe sections 32
that are connected end-to-end, e.g., with flanges or by welding,
with their respective curvatures in an alternating arrangement. In
one advantageous embodiment, the central axis of the flexing
portion lies in a single plane and takes a sinuous path, e.g., that
of a sinusoid, as illustrated in FIG. 8. In another advantageous
embodiment, the curved sections also include an axial twist, such
that the central axis of the flexing portion takes a three
dimensional path, e.g., that of a helix. Of course, the flexing
portions may advantageously have many other possible two- and
three-dimensional geometries. The dimension P between equivalent
points in adjacent recurvate sections of the flexing portion is
referred to herein as the wavelength of the portion, for a
two-dimensional configuration, or its pitch, for a
three-dimensional configuration, and the dimension R relates to the
amplitude of the portion, for a two-dimensional configuration, or
its radius, for a three-dimensional configuration. In one
advantageous embodiment, the wavelength or pitch of the flexing
portion is at least four times that of its amplitude or radius. In
another advantageous embodiment, the pitch increases as the flexing
portion extends higher above the seafloor 16. The recurvate section
both flexes resiliently in a direction generally perpendicular to
its long axis, and expands and contracts in a direction parallel to
its long axis, to accommodate the motion of the floating-body
22.
[0034] The flexing portion 30 enables a wellhead 14 to be connected
directly to a floating platform 22 with single steel riser 10
without requiring either a flexible, reinforced elastomeric section
of pipe, as illustrated in the prior art riser system of FIG. 1,
and/or a catenary curve in the riser, as illustrated in FIG. 2.
Further, since the steel of the risers can withstand the external
compressive loads exerted by the environment, the need for
reinforcement of a flexible elastomeric pipe section is also
eliminated. Additionally, by eliminating the need for a catenary
curve in the riser and its correspondingly greater weight, the need
for the riser tension loads supported by the floating vessel are
significantly.
[0035] It should be understood that the riser system 10 of the
invention can be used in conjunction with many types of known
platforms, including an FPSO platform, a TLP platform, a
semi-submersible platform, or other types of such platforms that
are known to those of skill in the art.
[0036] The characteristics of an exemplary vertical riser pipe 20
incorporating a flexing portion 30 having a sinusoidal
configuration, such as that illustrated in FIG. 8, is shown in
Table 1 below,
1TABLE 1 Vertical Riser Pipe With Sinusoidal Flexible Portion No. P
R TL OD Wm D/t RF RFr St Kr PS.sub.ksi PS.sub.psf P.sub.ksf*100
L.sub.30ksi 1 30 2.0 210 6.625 0.4321 15.3 425.4 2.8 21.3 2.8 815.5
1.17E+08 1174.3 5708 2 30 3.4 210 6.625 0.4321 15.3 150.4 1.0 7.5
1.0 461.9 6.65E+07 665.1 3233 3 20 3.4 220 6.625 0.4321 15.3 135.5
0.9 6.8 0.9 411.0 5.92E+07 591.8 3014 4 40 3.4 200 6.625 0.4321
15.3 85.8 0.6 4.3 0.6 508.8 7.33E.div.07 732.7 3392 5 30 3.4 420
6.625 0.4321 15.3 72.1 0.5 3.6 0.5 228.3 3.29E+07 328.7 3196 6 30
5.0 210 6.625 0.4321 15.3 63.2 0.4 3.2 0.4 288.7 4.16E+07 415.8
2021 7 30 2.0 210 6.625 0.2161 30.7 235.4 1.6 11.8 1.6 844.3
1.22E+08 1215.8 5910 8 30 3.4 220 6.625 0.2161 30.7 75.0 0.5 3.7
0.5 425.4 6.13E+07 612.5 3119 9 40 3.4 200 6.625 0.2161 30.7 85.8
0.6 4.3 0.6 508.8 7.33E+07 732.7 3392 10 20 3.4 220 6.625 0.2161
30.7 75.0 0.5 3.7 0.5 425.4 6.13E+07 612.5 3119 11 30 3.4 420 6.625
0.2161 30.7 39.9 0.3 2.0 0.3 236.3 3.40E+07 340.3 3308 12 30 5.0
210 6.625 0.2161 30.7 34.0 0.2 1.7 0.2 298.9 4.30E+07 430.4 2092 13
30 3.4 210 8 0.5229 15.3 318.8 2.1 15.9 2.1 559.0 8.05E+07 805.0
3913 wherein, P = flexing portion wavelength, in feet; R = flexing
portion amplitude, in feet; TL = total lenght of flexing portion,
in feet; OD = outer diameter of riser pipe, in inches; Wt = wall
thickness of riser pipe, in inches; D/t = ratio of riser outer
diameter to wall thickness; RF = reaction force necessary to
displace top of riser 20 feet; RFr = normalization of reaction
forces relative to straight pipe; K = stiffness of riser; Kr =
normalization of stiffness relative to a straight pipe; PSksi =
peak stress in riser, in kips per square inch; PS.sub.psf= peak
stress, pounds per square foot; PS.sub.ksi*100 = peak stress, kips
per square foot times 100; and, L.sub.30ksi = length of a curved
section necessary to limit maximum stress in riser to 30 ksi.
[0037] The characteristics of an exemplary vertical riser pipe 20
incorporating a flexing portion 30 with a helical configuration,
such as that illustrated in FIG. 9, is shown in Table 2 below,
2TABLE 2 Vertical Riser Pipe With Helical Flexing Portion No. P R
TL OD Wt D/t RF RFr St Kr PS.sub.ksi PS.sub.psf P.sub.ksf*100
L.sub.30ksi 1 30 3.4 240 6.625 0.4321 15.3 24.6 1.0 1.2 1.0 127.1
1.83E+07 183.0 1016.7 2 20 3.4 240 6.625 0.4321 15.3 19.5 0.8 1.0
0.8 85.1 1.23E.+-.07 122.5 680.6 3 30 2 240 6.625 0.4321 15.3 84.6
3.4 4.2 3.4 294.4 4.24E+07 424.0 2355.6 4 30 5 240 6.625 0.4321
15.3 9.2 0.4 0.5 0.4 59.0 8.49E.div.06 84.9 471.7 5 40 3.4 240
6.625 0.4321 15.3 27.5 1.1 1.4 1.1 153.9 2.22E+07 221.6 1231.1 6 20
3.4 240 6.625 0.2161 30.7 10.8 0.4 0.5 0.4 88.1 1.27E+07 126.8
704.4 7 30 2 240 6.625 0.2161 30.7 46.9 1.9 2.3 1.9 304.9 4.39E+07
439.0 2438.9 8 30 3.4 240 6.625 0.2161 30.7 13.6 0.6 0.7 0.6 131.3
1.89E+07 189.0 1050.0 9 30 5 240 6.625 0.2161 30.5 5.1 0.2 0.3 0.2
61.0 8.79E+06 87.9 488.3 10 40 3.4 240 6.625 0.2161 30.7 15.3 0.6
0.8 0.6 159.0 2.29E+07 229.0 1272.2 11 30 3.4 240 8 0.5229 15.3
52.1 2.1 2.6 2.1 153.6 2.21E+07 221.3 1229.2 wherein, P = flexing
portion pitch, in feet; R = flexing portion radius, in feet; TL =
total lenght of flexing portion, in feet; OD = outer diameter of
riser pipe, in inches; Wt = wall thickness of riser pipe, in
inches; D/t = ratio of riser pipe outer diameter to wall thickness;
RF = reaction force necessary to displace top of riser 20 feet; RFr
= normalization of reaction forces relative to straight pipe riser;
K = riser stiffness; Kr = normalization of riser stiffness relative
to a straight pipe riser; PS.sub.ksl = peak stress, kips per sqare
inch; PS.sub.psf = peak stress, pounds per square foot;
PS.sub.ksf*100 = peak stress, kips per square foot times 100; and,
L.sub.30ksf = length of flexing portion necessary to limit maximum
stress in riser to 30 ksi.
[0038] An important advantage provided by the flexing portions 30
is the additional "layer" of safety that they afford to the
structural integrity of the entire riser system 10. If, for
example, the top end of the riser pipe 20 should move beyond its
normal operating design limits, either horizontally or vertically,
the flexing portions will responsively expand or contract, without
local buckling, and thereby maintain the structural integrity of
the riser. This situation might occur if, for example, the surface
vessel 22 were to lose buoyancy due to a damaged tank, or if it
should inadvertently slip its moorings.
[0039] In addition to the riser pipe characteristics shown in
Tables 1 and 2 above, a number of additional design factors should
be considered in developing a site-specific riser system 10 design.
These additional factors include:
[0040] Water depth;
[0041] Envelope of surface vessel motion;
[0042] Physical properties of the riser;
[0043] Ocean currents;
[0044] Envelope of deflection curve of the riser to avoid riser
collisions;
[0045] Method of installation and removal of riser; and,
[0046] Limitation of riser curvature to allow passage of
through-tubing tools (e.g. "pigs").
[0047] As illustrated in FIG. 10, the benefits of the flexing
portions 30 can be advantageously combined with those of the riser
systems 10 having elbows described above in connection with FIGS. 4
and 5. In FIG. 10, a flexing portion has been incorporated in the
vertical pipe section 20, such that movements of the floating
platform 22 are accommodated by flexure of the horizontal and
vertical sections of pipe in a direction perpendicular to their
respective longitudinal axes, as well as by flexure of the flexing
portion in a direction parallel to its longitudinal axis.
Embodiments of riser systems incorporating a flexing portion in the
horizontal, vertical, and both the horizontal and vertical pipe
sections of the riser are illustrated schematically in FIGS. 11, 12
and 13, respectively.
[0048] As will by now be apparent to those of skill in the art,
many modifications, alterations and substitutions are possible to
the materials, methods and configurations of the riser systems of
the present invention without departing from its spirit and scope.
Accordingly, the scope of the present invention should not be
limited to the particular embodiments described and illustrated
herein, as these are merely exemplary in nature. Rather, the scope
of the present invention should be commensurate with that of the
claims appended hereafter, and their functional equivalents.
* * * * *