U.S. patent application number 10/213963 was filed with the patent office on 2004-02-12 for production riser with pre-formed curves for accommodating vessel motion.
Invention is credited to Horton, Edward E. III.
Application Number | 20040026083 10/213963 |
Document ID | / |
Family ID | 31494572 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040026083 |
Kind Code |
A1 |
Horton, Edward E. III |
February 12, 2004 |
Production riser with pre-formed curves for accommodating vessel
motion
Abstract
A system for establishing a fluid communication between a
floating-body and a wellhead is provided. The system comprises a
means for fluidly connecting the floating-body and the wellhead
that defines a major axis essentially extending from about the
floating-body to about the wellhead. The system further comprises a
means for absorbing and releasing energy in response to the heave
and surge of the floating-body that flexes in a direction
essentially parallel to the major axis. An apparatus is also
provided for establishing a fluid connection between a
floating-body and a wellhead that is fixed to the seafloor. The
apparatus comprises a riser pipe and a series of pre-formed curves
in the riser pipe that defines a substantially linear axis between
the floating-body and the wellhead.
Inventors: |
Horton, Edward E. III;
(Houston, TX) |
Correspondence
Address: |
Arnold & Associates
Suite 630
2401 Fountainview
Houston
TX
77057
US
|
Family ID: |
31494572 |
Appl. No.: |
10/213963 |
Filed: |
August 7, 2002 |
Current U.S.
Class: |
166/367 ;
166/359 |
Current CPC
Class: |
E21B 17/017 20130101;
E21B 17/015 20130101 |
Class at
Publication: |
166/367 ;
166/359 |
International
Class: |
E21B 017/01 |
Claims
I claim:
1. A system for establishing a fluid communication between a
floating-body and a wellhead, the system comprising: a means for
fluidly connecting the floating-body and the wellhead, wherein said
means for fluidly connecting defines a major axis essentially
extending from about the floating-body to about the wellhead; and a
means for absorbing and releasing energy in response to the heave
and surge of the floating-body, wherein said means for absorbing
and releasing energy flexes in a direction essentially parallel to
the major axis; wherein the means for fluidly connecting comprises
a steel riser; wherein the means for storing and releasing
comprises a series of pre-formed curves in the steel riser; and
wherein the series of pre-formed curves comprise a series of
single-planar, pre-formed curves in the riser.
2. A system as in claim 1 wherein the series of single-planar
curves comprise arcs having a substantially constant radius of
curvature.
3. A system as in claim 1 wherein the series of single-planar
curves comprises sinusoidal shaped curves.
4. A system for establishing a fluid communication between a
floating-body and a wellhead, the system comprising: a means for
fluidly connecting the floating-body and the wellhead, wherein said
means for fluidly connecting defines a major axis essentially
extending from about the floating-body to about the wellhead; and a
means for absorbing and releasing energy in response to the heave
and surge of the floating-body, wherein said means for absorbing
and releasing energy flexes in a direction essentially parallel to
the major axis; wherein the means for fluidly connecting comprises
a steel riser; wherein the means for storing and releasing
comprises a series of pre-formed curves in the steel riser; and
wherein the series of pre-formed curves comprise a series of
multi-planar, pre-formed curves in the riser.
5. A system as in claim 4 wherein the series of multi-planar curves
comprise arcs having a substantially constant radius of
curvature.
6. A system as in claim 4 wherein the series of multi-planar curves
comprises sinusoidal shaped curves.
7. A system as in claim 6 wherein the series of multi-formed curves
comprise helical pre-formed curves.
Description
BACKGROUND
[0001] This invention is generally related to risers that convey
fluid from producing wells on the seafloor to a floating structure
on the sea surface. This invention is also related to a conduit
that is fixed to the seafloor, which must accommodate the motion of
a vessel that is connected to it.
[0002] In offshore drilling and production operations carried out
from a floating vessel, fluid is conveyed from wells on the
seafloor to the vessel stationed on the surface by a conduit often
referred to as a "riser." Various methods and mechanisms are used
to reduce stresses in risers that are affixed to the moving vessel
on the surface and the stationary wellhead at the seafloor. These
include using flexible hose for the riser in lieu of steel pipe,
supporting a steel riser with hydraulic or elastomeric tensioners
that accommodate the relative movement of the vessel, buoyancy cans
that support the pipe at the top and allow the vessel to move (as
shown in, for example, U.S. Pat. No. 4,702,321, incorporated herein
by reference) or some combination of these techniques. Another
method is by using a steel catenary riser (often referred to as a
"SCR"), which comprises an extension of the steel riser pipe a
sufficient horizontal distance from the vessel such that the pipe
forms a rather deep catenary curve. Depending on a number of
factors, the SCR can be designed to accommodate some vessel
motion.
[0003] The above methods all have disadvantages and limitations.
For example, flexible hose is costly, cannot withstand external
compressive loads without internal stiffening, and requires
bend-restrictor devices at the terminations. The SCR are much less
costly and have a long record of reliability; however, their
shortcoming lies in motion compensation. The tensioners and
buoyancy cans are expensive, and they both require a flexible hose
(referred as a jumper line) to accommodate the relative motion
between the top of the riser, which sometimes includes a "Christmas
tree," and a flow manifold (fixed to the vessel).
[0004] There is therefore a need for a relatively low-cost, simple
riser that compensates for the motion of a floating vessel.
SUMMARY OF THE INVENTION
[0005] The above issues are addressed by various aspects of the
invention using a curved riser.
[0006] A system for establishing a fluid communication between a
floating-body and a wellhead is provided. The system comprises a
means for fluidly connecting the floating-body and the wellhead
that defines a major axis essentially extending from about the
floating-body to about the wellhead. The system further comprises a
means for absorbing and releasing energy in response to the heave
and surge of the floating-body that flexes in a direction
essentially parallel to the major axis. In one embodiment, the
means for fluidly connecting comprises a steel riser; and, in a
typical embodiment, the means for storing and releasing comprises a
series of pre-formed curves in the steel riser. In some
embodiments, the series of pre-formed curves comprises a series of
single-planar, pre-formed curves in the riser. These single-planar
curves comprise arcs having a substantially constant radius of
curvature in one embodiment and sinusoidal curves in another
embodiment. In some other embodiments, the series of pre-formed
curves comprises helical pre-formed curves. In various embodiments,
the means for storing and releasing comprises pre-formed curves in
the steel riser. In some embodiments, these pre-formed curves
comprise single-planar curves and in other embodiments, the
pre-formed curves comprise helical curves.
[0007] An apparatus for establishing a fluid connection between a
floating-body and a wellhead, wherein the wellhead is fixed to the
seafloor is also provided. The apparatus comprises a riser pipe and
a series of pre-formed curves in the riser pipe that defines a
substantially linear axis between the floating-body and the
wellhead. In some embodiments the series of pre-formed curves
comprises multi-planar curves, which in one embodiment comprises
helical shaped curves. In some other embodiments, the series of
pre-formed curves comprises single-planar curves, which in one
embodiment comprises sinusoidal curves. The riser pipe comprises
steel in some embodiments, but in some embodiments, the pre-formed
curves comprise a different material than the remainder of the
riser pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a side view of an example embodiment of riser with
a series of pre-formed curves.
[0009] FIG. 2 is a side view of an example embodiment of a
pre-formed helical curve.
[0010] FIG. 3 is a side view of an example embodiment of a
pre-formed curve in a single plane.
DESCRIPTION OF EXAMPLE EMBODIMENTS OF INVENTION
[0011] According to one example embodiment of the invention, seen
in FIG. 1, various shortcomings of prior designs using a riser pipe
14 are addressed by including pre-formed curves 10 in the riser
pipe 14. These curves accommodate the stress generated by the
motion of the floating-body 16. The pre-formed curves 10 flex in
response to the motion of the floating-body 16, so that the forces
generated by the floating-body 16 are not transmitted to the
wellhead 12. By using these pre-formed curves 10, a single, steel
riser pipe 14 becomes feasible to connect the floating-body with
the wellhead 12, without the need for a using catenary curve. In
other embodiments, the pipe is made of steel alloy or some other
similar alloy. By accommodating the motion of the floating-body 16,
the pre-formed curves 10 also eliminate the need for a flexible
section of pipe to connect the riser pipe 14 and the floating-body
16. Using a steel riser pipe 14 further eliminates the need for the
external stiffening associated with using a flexible pipe section
because the steel can withstand the external compressive loads
exerted by the environment. In one embodiment, the pre-formed
curves 10 are fashioned from a different material than the
remainder of the riser pipe 14.
[0012] By absorbing the forces exerted by the floating-body 16
without using a catenary curve, the pre-formed curves 10 also
eliminate the need for additional buoyancy devices. As a result, in
one embodiment, the riser pipe 14 connecting the wellhead 12 to the
floating-body 16 is only suspended from the floating-body 16. In
one embodiment, the suspension from the floating-body 16 supports
the entire weight of the riser pipe 14, while in another
embodiment, part of the riser pipe's 14 weight is supported by the
riser pipe 14 itself.
[0013] In some embodiments, the pre-formed curves 10 do not affect
the overall orientation or direction of the riser pipe 14.
Therefore, in one embodiment, the floating-body 16 suspending the
riser pipe 14 is positioned directly above the wellhead 12. The
riser pipe 14 thereby defines an axis 21 essentially from about the
floating-body 16 to about the wellhead 12. So that the riser pipe
14 can accommodate the motion of the floating-body 16, the
pre-formed curves 10 flex in a direction essentially parallel to
the axis 21 defined by the riser pipe 14. In another embodiment,
positioning the floating-body 16 closer to the wellhead 12
simplifies the installation and design of the subsea systems, in
part by enabling a vertical connection between the riser pipe 14
and the wellhead 12. Tools pass more easily through a vertical
wellhead 12 connection than through a horizontal connection.
[0014] In one embodiment, the series of pre-formed curves 10 is
connected to or close to the wellhead 12 on one end and the
remainder of the steel riser pipe 14 on the other end. In still
other embodiments, the series of pre-formed curves 10 extends from
the wellhead 12 to the floating-body 16. While in still other
embodiments, segments of relatively straight riser pipe 14 are on
either end of the series of pre-formed curves 10. In the example
shown in FIG. 1 the riser pipe 14 connects with a floating-body 16
(in this example, a SPAR-type semi-submersible) and a series of
pre-formed curves 10. Other embodiments of the floating-body 16
include a floating production storage and offloading (FPSO) system,
semi-submersible platforms, a tension leg platform, and others
known to those of ordinary skill in the art. This connection
between the wellhead 12 and the floating-body 16 allows fluid to
flow from one section to another (sometimes referred to as "fluid
communication"). In some examples, this connection also allows
tools to be passed from one section to another, and in one specific
embodiment, the riser pipe 14 is raised using some lifting means
located on the floating-body 16, stretching the series of
pre-formed curves 10 and allowing tools to pass more easily through
the series of pre-formed curves 10.
[0015] Referring now to FIGS. 2 and 3, examples of pre-formed
curves 10 are shown. In FIG. 2, the pre-formed curves 10 comprise
an open coil. In one embodiment, this forms a helical curve. As
shown in FIG. 2, the vertical distance between equivalent points in
the helical curve is called the curve spacing 17, and the curve
diameter 18 describes the diameter of the cross-sectional area of
the curve. In some embodiments, the curve spacing is at least
double that of the curve diameter. In one embodiment, the curve
spacing increases as the helical curve rises higher above the
seafloor.
[0016] The characteristics of one set of example embodiments of a
riser pipe 14 with helical pre-formed curves 10 is shown in Table 1
below.
1TABLE 1 Riser Pipe Embodiments With Helical Pre-Formed Curves No L
A TL OD Wt D/t RF RFr St Kr PS.sub.ksi PS.sub.psf P.sub.ksi *
10.sup.2 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+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
[0017] L represents the curve spacing measured in feet.
[0018] A represents the curve radius measured in feet.
[0019] TL represents the total length of the curve used for
simulation purposes measured in feet.
[0020] OD represents the outer diameter of the riser pipe measured
in inches.
[0021] Wt represents the wall thickness of the riser pipe wall
measured in inches.
[0022] D/t represents the ratio of the outer diameter to the
thickness of the riser pipe wall.
[0023] RF represents the reaction force necessary to displace the
top of the planar sine wave riser 20 feet.
[0024] RFr represents a normalization of the reaction forces to a
base case scenario.
[0025] K represents the stiffness of the riser model.
[0026] Kr represents a normalization of the stiffness to a base
case scenario.
[0027] PS.sub.ksi represents the peak stress in kips per square
inch.
[0028] PS.sub.psf represents the peak stress in pounds per square
foot.
[0029] PS.sub.ksf*100 represents the peak stress in kips per square
foot multiplied by 100.
[0030] L.sub.30ksi represents the length of a curved section with
necessary to maintain a maximum stress of 30 ksi in the riser.
[0031] FIG. 3 shows an example embodiment in which the series of
pre-formed curves 10 comprises curves in a single plane. In some
embodiments, these single-planar, pre-formed curves 10 are
sinusoidal; and, in other embodiments, the pre-formed curves 10
have semi-circular or other shapes. Combinations of such shapes of
varying complexity are included in still further example
embodiments. In one embodiment, the pre-formed curves 10 comprise
several connected segments of pipes. As shown in FIG. 3, the
vertical distance between equivalent points in the sinusoidal curve
is called the wavelength 19, and the amplitude 20 describes the
width of the curve.
[0032] The characteristics of one set of example embodiments of a
sinusoidal riser pipe 14 is shown in Table 2 below.
2TABLE 2 Riser Pipe Embodiments With Sinusoidal Pre-Formed Curves
No L A TL OD Wt D/t RF RFr St Kr PS.sub.ksi PS.sub.psf P.sub.ksf*
10.sup.2 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+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
[0033] L represents the wavelength measured in feet.
[0034] A represents the amplitude measured in feet.
[0035] TL represents the total length of curves used for simulation
purposes measured in feet.
[0036] OD represents the outer diameter of the riser pipe measured
in inches.
[0037] Wt represents the wall thickness of the riser pipe wall
measured in inches.
[0038] D/t represents the ratio of the outer diameter to the
thickness of the riser pipe wall.
[0039] RF represents the reaction force necessary to displace the
top of the planar sine wave riser 20 feet.
[0040] RFr represents a normalization of the reaction forces to a
base case scenario.
[0041] K represents the stiffness of the riser model.
[0042] Kr represents a normalization of the stiffness to a base
case scenario.
[0043] PS.sub.ksi represents the peak stress in kips per square
inch.
[0044] PS.sub.psf represents the peak stress in pounds per square
foot.
[0045] PS.sub.ksf*100 represents the peak stress in kips per square
foot multiplied by 100.
[0046] L.sub.30ksi represents the length of a curved section with
necessary to maintain a maximum stress of 30 ksi in the riser.
[0047] One important benefit derived from including pre-formed
curves 10 is that they add an additional layer of safety for the
structural integrity of the whole riser pipe 14. If, for example,
the top end of the riser pipe 14 should move beyond its normal
operating design limits either horizontally or vertically, the
pre-formed curves 10, in various example embodiments, flex, without
local buckling, and still maintains structural integrity. This
situation might occur if, for example, the surface vessel 16 should
lose buoyancy due to a damaged tank, if the moorings were to come
loose or some other mishap were to occur.
[0048] In addition to the characteristics of a riser pipe 14 with
pre-formed curves 10 shown in the tables above, a number of
additional design factors are considered to develop a site-specific
design. A non-exhaustive list of these additional factors
includes:
[0049] Water depth
[0050] Envelope of surface vessel motion
[0051] Physical properties of the riser
[0052] Ocean currents
[0053] Envelope of deflection curve of the riser to avoid
clashing
[0054] Method of installation and removal of riser
[0055] Limitation of curvature of riser to allow passage of
through-tubing tools (e.g. "pigs").
[0056] The above Summary and Detailed Description are given by way
of example only. Other aspects and examples of the invention will
be understood to be within the spirit of the present invention and
with the scope of or equivalent to that described by the
claims.
* * * * *