U.S. patent application number 10/011661 was filed with the patent office on 2002-06-27 for offshore platform.
Invention is credited to Meek, Harke Jan, Sliggers, Pieter Gerardus Frank.
Application Number | 20020081157 10/011661 |
Document ID | / |
Family ID | 8172377 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081157 |
Kind Code |
A1 |
Meek, Harke Jan ; et
al. |
June 27, 2002 |
Offshore platform
Abstract
Offshore platform comprising a bottom structure (1) comprising a
polygonal base (5) resting on the sea floor (2) having suction
piles (10) joined to its corners and a first support frame (8)
connected to the polygonal base (5) including interconnected
open-ended pipes (15), conductors (33) extending from above the
water surface (36) into the seabed through the open-ended pipes
(15) of the first support frame (8), and at least one further
support frame (22, 24) including interconnected open-ended pipes
(25) extending around the conductors (33), wherein each further
support frame (22, 24) is secured to the conductors (33) at a
predetermined level.
Inventors: |
Meek, Harke Jan; ( The
Hague, NL) ; Sliggers, Pieter Gerardus Frank; (
Rijswijk, NL) |
Correspondence
Address: |
Eugene R. Montalvo
Shell Oil Company
Legal - Intellectual Property
P.O. Box 2463
Houston
TX
77252-2463
US
|
Family ID: |
8172377 |
Appl. No.: |
10/011661 |
Filed: |
December 5, 2001 |
Current U.S.
Class: |
405/227 |
Current CPC
Class: |
E02B 17/027 20130101;
E02D 2250/0053 20130101 |
Class at
Publication: |
405/227 |
International
Class: |
E02D 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2000 |
EP |
00204340.4 |
Claims
We claim:
1. A method of installing an offshore platform on a sea floor,
which method comprises the steps of: (a) providing the sea floor
with a set of releasably interconnected support frames comprising a
bottom structure including a polygonal base having suction piles
joined to its corners and a first support frame connected to the
polygonal base including interconnected open-ended pipes that are
arranged perpendicular to the base, and at least one further
support frame, wherein each further support frame includes
interconnected open-ended pipes and has the same cross-section as
the first support frame, and wherein the suction piles are fixed in
the seabed; (b) lowering conductors into the seabed to a
predetermined depth through open-ended passages formed by the
open-ended pipes of the at least one further support frame and the
first support frame such that the upper ends of the conductors
extend to above the water surface; and (c) lifting the at least one
further support frame to a predetermined level and securing the at
least one further support frame to the conductors.
2. The method according to claim 1, wherein step (a) comprises
lowering to the sea floor the bottom structure; allowing the
suction piles to enter into the seabed; and lowering the at least
one further support frame to the bottom structure so as to form the
set of interconnected support frames.
3. The method according to claim 1, wherein step (a) comprises
lowering to the sea floor the set of releasably interconnected
support frames comprising the bottom structure and the at least one
further support frame; and allowing the suction piles to enter into
the seabed.
4. The method according to claim 1, wherein the set of releasably
interconnected support frames comprises at least two further
support frames.
5. The method according to claim 1, wherein the uppermost further
support frame is provided with a platform deck.
6. An offshore platform comprising a bottom structure comprising a
polygonal base resting on the sea floor having suction piles joined
to its corners and fixed in the seabed and a first support frame
connected to the polygonal base including interconnected open-ended
pipes that are arranged perpendicular to the base, conductors
extending from above the water surface into the seabed through the
open-ended pipes of the first support frame, and at least one
further support frame having the same cross-section as the first
support frame and including interconnected open-ended pipes
extending around the conductors, wherein each further support frame
is secured to if the conductors at a predetermined level.
7. The offshore platform according to claim 6, comprising at least
two further support frames.
8. The offshore platform according to claim 6, wherein the
uppermost further support frame is provided with a platform deck.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of installing an
offshore platform. In particular the present invention relates to
installing an offshore production platform, which is an offshore
platform that is provided with wellhead and/or production equipment
only and not with drilling equipment. The platform is suitably
installed in water depths in the range of from 15 to 100 m. The
present invention further relates to an offshore platform.
BACKGROUND OF THE INVENTION
[0002] U.S. Pat. No. 4,739,840 discloses a method of installing an
offshore platform. The known method comprises lowering to the sea
floor a support frame including interconnected open-ended vertical
pipes; lowering conductors into the seabed to a predetermined depth
through the open-ended pipes of the support frame such that the
upper ends of the conductors extend above the water surface; and
lifting the support frame to a predetermined level and securing the
support frame to the conductors.
[0003] Because the support frame is in one piece, this method
allows installation of an offshore platform in relatively shallow
water only, wherein relatively shallow waters have water depths in
the range of from 15 to 50 m.
[0004] British patent specification No. 2 222 189 discloses a
method of installing an offshore platform, which method comprises
lowering to the sea floor a first support frame including
interconnected open-ended vertical pipes; lowering conductors into
the seabed to a predetermined depth through the open-ended pipes of
the support frame such that the upper ends of the conductors extend
above the water surface; and attaching to the upper ends of the
conductors a further support frame that is provided with a platform
deck.
[0005] The later method is more flexible and can be used in deeper
waters, because the platform includes two separate support
frames.
[0006] In both methods, the conductors serve as foundation piles
and as the legs of the offshore platform.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to improve the
foundation of the offshore platform.
[0008] To this end the method of installing an offshore platform
according to the present invention comprises the steps of:
[0009] (a) providing the sea floor with a set of releasably
interconnected support frames comprising a bottom structure
including a polygonal base having suction piles joined to its
corners and a first support frame connected to the polygonal base
including interconnected open-ended pipes that are arranged
perpendicular to the base, and at least one further support frame,
wherein each further support frame includes interconnected
open-ended pipes and has the same cross-section as the first
support frame, and wherein the suction piles are fixed in the
seabed;
[0010] (b) lowering conductors into the seabed to a predetermined
depth through open-ended passages formed by the open-ended pipes of
the at least one further support frame and the first support frame
such that the upper ends of the conductors extend to above the
water surface; and
[0011] (c) lifting the at least one further support frame to a
predetermined level and securing the at least one further support
frame to the conductors.
[0012] The present invention further relates to an offshore
platform comprising a bottom structure comprising a polygonal base
resting on the sea floor having suction piles joined to its corners
and fixed in the seabed and a first support frame connected to the
polygonal base including interconnected open-ended pipes that are
arranged perpendicular to the base, conductors extending from above
the water surface into the seabed through the open-ended pipes of
the first support frame, and at least one further support frame
having the same cross-section as the first support frame and
including interconnected open-ended pipes extending around the
conductors, wherein each further support frame is secured to the
conductors at a predetermined level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows schematically an initial stage of the method of
installing an offshore platform according to the present
invention.
[0014] FIG. 2 shows schematically a further stage of the method
according to the present invention.
[0015] FIG. 3 shows schematically the platform according to the
present invention.
DETAILED DESCRIPTION
[0016] Reference is now made to FIG. 1. The first step of the
method of installing an offshore platform according to the present
invention comprises lowering a bottom structure 1 to the sea floor
2. The bottom structure 1 comprises a polygonal base 5 and a first
support frame 8 that is connected to the polygonal base 5. The
polygonal base 5 has suction piles 10 joined to its corners 11. In
FIG. 1 only two of the three suction piles 10 are shown. The first
support frame 8 is connected to the polygonal base 5 by means of
structural elements 12 and structural elements 13, and the first
support frame 8 includes open-ended pipes 15 that are arranged
perpendicular to the polygonal base 5. The open-ended pipes 15 are
interconnected by means of horizontal structural elements 17 at
their lower ends, horizontal structural elements 19 at their upper
end and inclined structural elements 20.
[0017] Lowering the bottom structure 1 is done using a crane on a
barge or the hoisting means of a drilling rig that is arranged on a
jack-up platform. Neither the barge nor the jackup platform are
shown.
[0018] In the position as shown in FIG. 1 the lower ends of the
three suction piles 10 rest on the sea floor 2.
[0019] Next pumps (not shown) on the suctions piles 10 are
activated to remove water from the interior of the suction piles 10
so as to cause the suction piles 10 to enter into the seabed,
driven by the pressure differential. When this step is completed,
the polygonal base 5 rests on the sea floor 2, and the suction
piles 10 are fixed in the seabed below the sea floor 2.
[0020] To discuss the next steps of the method according to the
present invention, reference is now made to FIG. 2. For the sake of
clarity we do not include the reference numerals for all the
features that were discussed with reference to FIG. 1.
[0021] The polygonal base 5 rests on the sea floor 2, and two
further support frames 22 and 24 are lowered to the bottom
structure 1 so as to form a set of support frames 8, 22 and 24 that
are releasably interconnected. Each further support frame 22 and 24
includes open-ended pipes 25, which open-ended pipes 25 are
interconnected by means of horizontal structural elements 27 at
their lower ends, horizontal structural elements 29 at their upper
end and inclined structural elements 30. For the sake of clarity
not all structural elements have been referred to by means of a
reference numeral.
[0022] In order to allow the support frames 8, 22 and 24 to get
releasably interconnected, each further support frame 22 and 24 has
the same cross-section as the first support frame 8. Elements that
facilitate the interconnection are not shown.
[0023] When the further support frames 22 and 24 have been put on
the bottom structure 1, conductors 33 are lowered into the seabed
to a predetermined depth below the sea floor 2. The conductors 33
are driven through the open-ended passages formed by the open-ended
pipes 25 and 15 of the two further support frames 24 and 22 and the
first support frame 8. The length of the conductors 33 is so
selected that the upper ends 34 of the conductors 33 extend to
above the water surface 36.
[0024] Driving the conductors 33 is done using suitable
pile-driving equipment from the barge or the jack-up platform (not
shown).
[0025] When the driving operation is completed, the two further
support frames 24 and 22 are lifted to a predetermined level above
the sea floor 2. In this case, the further support frame 22 is
raised to about half way the distance between the sea floor 2 and
the water surface 36, and the further support frame 22 is raised to
the top of the conductors 33. Having raised the further support
frames, they are secured to the conductors 33 by any suitable
means, such as welding, swaging and grouting.
[0026] It will be understood that the offshore platform according
to the invention is used in the production of hydrocarbons from an
underground formation via a well. In order to get the well a
borehole is drilled and completed in the known manner. This
borehole is drilled when the platform is in the stage as shown in
FIG. 2, thus before lifting the further support frames 22 and 24.
To drill the borehole, a jack-up platform provided with a drilling
rig is used, and drilling and completing the borehole is done
through the conductors 33. The lateral spacing of the conductors 33
is limited by the lateral skidding of the drilling rig. If applied
in relatively deep water, suitably, the further support frames are
raised and the lowermost further support frame is secured at its
predetermined position before drilling commences. This way of
supporting the conductors improves the stability of the conductors
during drilling.
[0027] The fact that the drilling rig on a jack-up platform can
only be displaced over a limited distance limits the lateral
spacing of the conductors. With the known offshore platform, the
conductors form the foundation of the known offshore platform, and
consequently, if the foundation needs to be improved, the lateral
spacing of the conductors has to be enlarged. However, there is a
limitation to the lateral spacing. In contrast to the known
offshore platforms, the foundation of the offshore platform of the
invention is improved because it comprises the conductors and the
suction piles. Consequently, there is no need to enlarge the
lateral spacing of the conductors.
[0028] In the embodiment as discussed with reference to the
Figures, the first step of the method comprises lowering to the sea
floor the bottom structure; allowing the suction piles to enter
into the seabed; and lowering the at least one further support
frame to the bottom structure so as to form the set of
interconnected support frames. Alternatively, the first step of the
method comprises lowering to the sea floor the set of releasably
interconnected support frames comprising the bottom structure and
the at least one further support frame; and allowing the suction
piles to enter into the seabed.
[0029] In order to place the wellhead and/or production equipment,
the platform is provided with a deck. Schematically the deck is
shown in dashed lines in FIG. 3, and the deck is referred to with
reference numeral 40. The deck can be placed on the uppermost
further support frame 24 after the support frame 24 has been lifted
to its predetermined level and secured to the conductors 33.
Alternatively the deck is already present on the further support
frame 24, when this support frame is lowered to the bottom
structure 1. When lifting the further support frame 24, the deck is
raised as well.
[0030] In the embodiment of the invention as described with
reference to the Figures, the polygonal base of the bottom
structure is a triangle. Alternatively, the polygonal base is a
square or a rectangle. The same applies to the shape of the
cross-section of the first support frame and the further support
frames.
[0031] In the embodiment of the invention as described with
reference to the Figures, each structural element 13 is connected
to the middle of the corresponding open-ended pipe 15.
Alternatively the structural element 13 is connected to the top of
the open-ended pipe 15 where it intersects with the structural
elements 19.
[0032] In the embodiment of the invention as described with
reference to the Figures, there are two further support frames, 22
and 24. An advantage of having a small number of further support
frames is that the wave loading on the platform is reduced. Thus
the number of further support frames is so selected that an optimum
is found between wave loading and structural integrity. Suitably
the number of further support frames is at least two, and more
suitably 2, 3 or 4.
[0033] In the specification and the claims, the term suction piles
is used. This term is intended to cover as well devices that are
known in the art as suction anchors or suction cans.
* * * * *