U.S. patent application number 09/281453 was filed with the patent office on 2001-11-15 for universal catenary riser support.
Invention is credited to FINN, LYLE DAVID.
Application Number | 20010041097 09/281453 |
Document ID | / |
Family ID | 23077375 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041097 |
Kind Code |
A1 |
FINN, LYLE DAVID |
November 15, 2001 |
UNIVERSAL CATENARY RISER SUPPORT
Abstract
A universal catenary riser support that can be designed to
accommodate all riser pipe diameters typically considered for
production of offshore hydrocarbons and allows the catenary riser
to exit from the vessel at any azimuth angle and at a wide range of
angles from the vertical. The support structure at the keel of the
offshore structure is provided with a receptacle to receive a
curved riser segment. The curved riser segment is adapted to be
received in the receptacle. The curved riser is also adapted to
receive a vertical riser section through the offshore structure.
Relative motions between the catenary riser and the offshore
structure are accommodated by a tapered section of riser or
flexible joint attached to the curved riser section. A removable
plug may be provided in the curved riser section to prevent water
from entering the catenary riser during installation in the
offshore structure.
Inventors: |
FINN, LYLE DAVID; (SUGAR
LAND, TX) |
Correspondence
Address: |
J. RAY MCDERMOTT, INC.
757 N. ELDRIDGE
HOUSTON
TX
70112
US
|
Family ID: |
23077375 |
Appl. No.: |
09/281453 |
Filed: |
March 30, 1999 |
Current U.S.
Class: |
405/224.2 ;
166/367; 405/184.4 |
Current CPC
Class: |
E21B 17/015 20130101;
E21B 19/004 20130101 |
Class at
Publication: |
405/224.2 ;
405/184.4; 166/367 |
International
Class: |
E02D 005/62 |
Claims
What is claimed as invention is:
1. In a floating offshore structure for producing hydrocarbons
where a catenary riser extends from a sea floor to the floating
structure, a support for the catenary riser, said support
comprising: a. a riser support receptacle in the floating offshore
structure; b. a curved riser segment adapted to be received in said
support receptacle and adapted to receive a vertical riser through
the offshore structure; and c. means attached to said curved riser
segment for accommodating relative motion between the catenary
riser and offshore structure.
2. The catenary riser support of claim 1, wherein said means for
accommodating relative motion between the catenary riser and
offshore structure comprises a stress joint.
3. The catenary riser support of claim 1, wherein said means for
accommodating relative motion between the catenary riser and
offshore structure comprises a flex joint.
4. The catenary riser support of claim 1, further comprising a
fitting attached to said curved riser segment, said fitting
provided with a complementary shape to that of said riser support
receptacle.
5. In a floating offshore structure for producing hydrocarbons
where a catenary riser extends from a sea floor to the floating
structure, a support for the catenary riser, said support
comprising: a. a riser support receptacle in the floating offshore
structure; b. a curved riser segment adapted to be received in said
support receptacle and adapted to receive a vertical riser through
the offshore structure; c. a fitting attached to said curved riser
segment, said fitting provided with a complementary shape to that
of said riser support receptacle; and d. means attached to said
curved riser segment for accommodating relative motion between the
catenary riser and offshore structure, said means comprising a
stress joint.
6. The catenary riser support of claim 5, further comprising means
for latching said fitting to said riser support receptacle.
7. In a floating offshore structure for producing hydrocarbons
where a catenary riser extends from a sea floor to the floating
structure, a support for the catenary riser, said support
comprising: a. a riser support receptacle in the floating offshore
structure; b. a curved riser segment adapted to be received in said
support receptacle and adapted to receive a vertical riser through
the offshore structure; c. a fitting attached to said curved riser
segment, said fitting provided with a complementary shape to that
of said riser support receptacle; and d. means attached to said
curve d riser segment for accommodating relative motion between the
catenary riser and offshore structure, said means comprising a flex
joint.
8. The catenary riser support of claim 7, further comprising means
for latching said fitting to riser support receptacle.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention is generally related to the production of
hydrocarbons from subsea formations and more particularly to the
support of riser pipe used in such production.
[0003] 2. General Background
[0004] In the offshore drilling and production industry, a pipe is
often used to carry product (oil or natural gas) from the offshore
production site to a collection and storage facility which may be a
tanker or an on shore facility. For offshore structures that rest
on the sea floor, such as a jacket or compliant tower, the flexing
effect of environmental conditions such as waves and currents have
a minimal effect on the design considerations when connecting the
pipe to the offshore structure. However, for floating offshore
structures the design of the interface between the pipe and
offshore structure must take into account the bending motions, and
resulting fatigue and stresses, that the pipe and interface must
endure during the life of the structure. The steel catenary
pipeline riser approach is generally considered as the most
cost-effective means for transporting products to and from floating
offshore production vessels.
[0005] For a floating structure such as a TLP (tension leg
platform) or a semi-submersible, the typical configuration of this
riser is for the pipe to be suspended from the side of the floating
vessel from a support platform that is located just below the water
surface (fifty to one hundred feet).
[0006] For a floating structure such as a spar vessel, the pipe for
the riser may enter the interior are of the spar vessel at the keel
or along the side of the spar vessel at a selected depth.
[0007] A disadvantage of previous catenary riser support
configurations for floating structures is that the configuration
normally has been limited to a certain riser diameter and narrow
range of departure angles from the floating structure.
SUMMARY OF THE INVENTION
[0008] The invention addresses the above disadvantage. What is
provided is a universal catenary riser support that can be designed
to accommodate all riser pipe diameters typically considered for
production of offshore hydrocarbons and allows the catenary riser
to exit from the vessel at any azimuth angle and at a wide range of
angles from the vertical. The support structure at the keel of the
offshore structure is provided with a receptacle to receive a
curved riser segment. The curved riser segment is adapted to be
received in the receptacle. The curved riser is also adapted to
receive a vertical riser section through the offshore structure.
Relative motions between the catenary riser and the offshore
structure are accommodated by a tapered section of riser or
flexible joint attached to the curved riser section. A removable
plug may be provided in the curved riser section to prevent water
from entering the catenary riser during installation in the
offshore structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a further understanding of the nature and objects of the
present invention reference should be made to the following
description, taken in conjunction with the accompanying drawing in
which like parts are given like reference numerals, and
wherein:
[0010] FIG. 1 is a side sectional view that illustrates the
invention installed in a spar type vessel.
[0011] FIG. 2 is an enlarged detailed view of the preferred
embodiment of the invention.
[0012] FIG. 3 illustrates an alternate embodiment of the means for
accommodating relative motion between the catenary riser and
floating offshore structure.
[0013] FIGS. 4-6 illustrate the installation of the invention in a
floating offshore structure.
[0014] FIG. 7 illustrates an alternate embodiment of the
invention.
[0015] FIG. 8 illustrates spacer elements attached to the vertical
riser segment in the floating offshore structure.
[0016] FIG. 9 illustrates an alternate embodiment of the means for
accommodating relative motion between the catenary riser and
floating offshore structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] Referring to the drawings, it is seen in FIG. 1 that the
invention is generally indicated by the numeral 10. Catenary riser
support 10 is illustrated installed in a spar type vessel 11 such
as that disclosed in U.S. Pat. No. 4,702,321. It should be
understood that the invention is not limited to use with spar type
vessels and may be used with any floating offshore structure. A
typical situation is illustrated where a catenary riser 13 extends
up from the sea floor 15 to the spar type vessel 11. The spar
vessel 11 illustrated encloses the vertical riser segment 17 that
runs through the vessel. Therefore, minimal guides 19 are required
to provide lateral support to vertical riser segment 17. A top
vertical support 21 is provided for the vertical riser segment 17
at the upper end of the vessel 11.
[0018] As best seen in FIG. 2, the catenary riser support 10 is
generally comprised of receptacle 12, curved riser segment 14, and
means 16 for accommodating relative motion between the offshore
structure 11 and the catenary riser 13.
[0019] Receptacle 12 is received in the support structure 18 in the
keel of the spar vessel 11. The receptacle 12 preferably is axially
symmetric and cone shaped. The cone shape allows it to serve as a
guide during installation of the curved riser segment 14. The
receptacle 12 is provided with a diameter that is large enough to
accept all reasonable sizes of catenary riser pipe.
[0020] As an option, a protective sleeve 20 may be provided to the
receptacle 12 to give additional protection to the vertical riser
segment 17. The sleeve 20 may be attached to the receptacle 12 as
shown or to the support structure 18.
[0021] The curved riser segment 14 is formed from a pipe 22 and a
fitting 24 attached to the pipe 22. The pipe 22 preferably has a
radius of curvature on the order of five to ten pipe diameters for
the purpose of allowing the passage of pipeline pigs there through.
The fitting 24 is provided with a shape that is complementary to
the receptacle 12 such that the fitting is readily received in the
receptacle 12. Means for lifting the curved riser segment 14 into
the receptacle 12 is provided in the form of a cable 26 attached to
the fitting 24 and that is used as a pull-in line. A cable is
merely an example of a suitable pull-in line and it should be
understood that any suitable means such as a chain may also be
used. Curved riser segment 14 is provided with a flange 28 at its
lower end. This allows for attachment to a corresponding flange 23
on means 16 for accommodating the relative motion between the
vessel 11 and catenary riser 13. Curved riser segment 14 may also
be provided with an internal plug 30 that prevents entry of water
into the catenary riser 13 during installation.
[0022] In the preferred embodiment, means 16 for accommodating the
relative motion between the vessel 11 and catenary riser 13 is
provided in the form of a tapered stress joint 32. The tapered
stress joint 32 is provided with a flange 23 at each end for
connection at the upper portion to the curved riser segment 14 and
at the lower portion to the catenary riser 13. In the preferred
embodiment, the tapered stress joint 32 is formed from a riser pipe
that progressively tapers from a thicker wall diameter at the upper
portion to a thinner wall diameter at the lower portion.
[0023] FIG. 3 illustrates an alternate embodiment of means 16 in
the form of a flex joint 34 attached between the catenary riser 13
and the curved riser segment 14. Flex joints are generally known in
the industry.
[0024] Installation is illustrated in FIGS. 4-6. The cable 26 is
used to pull the curved riser segment 14 and accommodation means
16, already connected to catenary riser 13, up into the receptacle
12 in the support structure of the vessel 12 as seen in FIG. 4.
Once the curved riser segment 14 is positioned in the receptacle,
the vertical riser section 17 is lowered through the vessel as seen
in FIG. 5. The vertical riser segment 17 is then attached to the
curved riser segment 14 using a connector 36. Any suitable
connector such as an internal tieback connector may be used. An
external tieback connector may also be used if desired. However,
the use of an external connector will require that the lateral
support guides in the vessel be of a larger diameter than required
for the internal connector in order to allow passage of the
external connector. Once the vertical riser segment 17 is connected
to the curved riser segment 14 and supported vertically by top
vertical support 21, it can be used to support the catenary riser
13 and tension on the cable 26 may be released. As seen in FIG. 6,
after connection of the two sections, the plug 30 is removed by the
use of any suitable means. This would typically be accomplished by
using a drill pipe 38 that is fitted with a tool 40 adapted to
latch onto and release the plug 30 from the curved riser segment
14. The use of such tools for removing plugs is generally known in
the industry. The riser is then ready for production of
hydrocarbons.
[0025] FIG. 7 illustrates an alternate embodiment of the receptacle
12 (indicated by numeral 112) and fitting 24 (indicated by numeral
124). Receptacle 112 is provided with a groove 40 along the inner
circumference. A series of latching dogs 42 are provided on fitting
124 and adapted to be received in groove 40. Once latched in place,
fitting 124 supports the catenary riser 13 and allows the removal
of the lifting chain 44 before the vertical riser segment is
lowered into place and connected to the curved riser segment 14.
The use of circular grooves and corresponding latches is generally
known in the industry.
[0026] FIG. 8 illustrates the vertical riser segment 17 in a spar
type vessel such as that described in U.S. Pat. No. 5,558,467 where
the lower portion of the vessel forms an open truss structure. In
this type of vessel, additional lateral guides 19 are provided
along the length of the vessel to provide lateral support to the
riser against wave and current forces. An insulation material 46
may be provided on the riser to keep the hydrocarbons warm and
reduce the potential for the formation of waxes and hydrates that
could significantly reduce the fluid flow or entirely plug the
riser. Spacer elements 48 may also be provided along the length of
the riser at the locations of the lateral supports 19.
[0027] FIG. 9 illustrates another alternate embodiment of the
receptacle 12 (indicated by numeral 212), curved riser segment 14
(indicated by numeral 214), and the means 16 for accommodating
relative motion between the vessel 11 and the catenary riser 13.
The curved riser segment 214 utilizes a flex joint 50 in the
fitting 224 that receives the pipe 222. The receptacle 212 has an
upper shoulder adapted to receive latching dogs 52 on the fitting
224. The pipe 222 is formed from the catenary riser and is provided
with a bend that matches the required angle. A radius of curvature
on the order of five to ten pipe diameters is sufficient to allow
for the passage of pipeline pigs.
[0028] In this design, the vertical riser segment 17 is fitted with
means 16 for accommodating relative motion between the vessel 11
and pipe 222. Means 16 is a stress joint that is formed from a
tapered section of riser pipe. With this design, the stress joint
accommodates the relative angular motion between the vessel 11 and
the pipe 222. An external tieback connector is illustrated for
connecting the motion accommodating means 16 to the pipe 222.
[0029] The advantage of placing the stress joint above the support
mechanism instead of below as described in the preferred embodiment
is that the axial load in the stress joint with the alternative
design is much lower than in the preferred embodiment. This lower
tension will result in lower bending stresses in the stress joint
and thus a short, thinner, and less expensive tapered stress joint
design. The disadvantage of this alternate design is that the
vertical segment of the riser will move up and down slightly as the
relative angle between the vessel and riser changes. The piping at
the top end of the vertical portion of the riser can be designed to
accommodate this vertical motion.
[0030] Because many varying and differing embodiments may be made
within the scope of the inventive concept herein taught and because
many modifications may be made in the embodiment herein detailed in
accordance with the descriptive requirement of the law, it is to be
understood that the details herein are to be interpreted as
illustrative and not in a limiting sense.
* * * * *