Note: Descriptions are shown in the official language in which they were submitted.
CA 02785142 2012-08-08
GRAVITY BASE STRUCTURE
FIELD
[001] This disclosure is related to gravity base structures, such as for
supporting hydrocarbon
drilling and extraction facilities in deep arctic seas.
BACKGROUND
[002] Deepwater gravity base structure (GBS) concepts for regions experiencing
significant
sea ice have traditionally been based on large monolithic steel or concrete
substructures
supporting offshore hydrocarbon drilling or production facilities. In deeper
waters, the size,
weight and cost of these structures pose major challenges in terms of design,
construction, and
installation. Traditional GBS designs generally rely on a monolithic caisson,
with or without
discrete vertical legs, filled largely with sea water and/or solid ballast to
resist horizontal loads
from ice and wave interaction. The caisson gross volume and minimum required
on bottom
weight increase rapidly with water depth and horizontal load. This can lead to
difficulty in
satisfying the foundation design requirements, especially in weaker cohesive
soils.
SUMMARY
[003] Embodiments of open gravity base structures for use in deep arctic
waters are
disclosed that comprise wide-set first and second elongated base sections
separated by an
open region and configured to support the on-bottom weight of the structure on
the seabed. An
upper section can be positioned above the open region and configured to extend
at least
partially above the water surface to support topside structures. The structure
can further
comprise a section coupling the wide set base sections to the upper section.
[004]
In some embodiments, the structure can comprise internal fluid storage
chambers that
can be selectively filled partially or entirely with fluid and emptied
partially or entirely of fluid to
lower and raise the structure in the sea. In further embodiments a skirt
structure, which can
comprise a plurality of downwardly open compartments, can be attached to the
base sections to
facilitate positioning the structure on a seabed. In other embodiments the
structure can
comprise a piping system configured to expel or extract fluid from the skirt
cell regions below the
base sections to further facilitate placement of the structure on the seabed
and lift-off of the
structure from the seabed. The structure can be repositioned to different
seabed locations by
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floating the structure up off of the seabed at one location, towing the
structure in a floating
configuration to a second location, and then sinking the structure to the
seabed at the second
location. The depth of floating the structure can be adjusted by adjusting the
fluid level in the
chambers to stabilize the structure when being moved and to accommodate
adverse
environmental conditions such as waves, wind and ice.
[005] The foregoing and other objects, features, and advantages of embodiments
disclosed
herein will become more apparent from the following detailed description,
which proceeds with
reference to the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[006] FIG. 1 illustrates an exemplary embodiment of a gravity base structure
with two
separated base sections.
[007] FIG. 2A is a side profile view of the embodiment of FIG. 1.
[008] FIG. 2B is a front end profile view of the embodiment of FIG. 1.
[009] FIG. 3 is a top plan view of first and second spaced apart base units of
an exemplary
gravity base structure in the direction of arrows 3-3 of FIGS. 2A and 2B.
[010] FIG. 4 is a top plan view of a middle portion of an exemplary gravity
base structure in the
direction of arrows 4-4 of FIGS. 2A and 2B.
[011] FIG. 5 is an end profile view of a base unit of an exemplary gravity
base structure in a
dry dock environment.
[012] FIG. 6 is an end profile view of an at-sea assembly of a portion of an
exemplary gravity
base structure comprising first and second base portions and a first upper
section in position for
assembly.
[013] FIG. 7A is a side profile view of an exemplary gravity base structure
for shallower
waters.
[014] FIG. 7B is a front end profile view of the gravity base structure of
FIG. 7A.
[015] FIG. 8 is a top plan view of a lower portion of the gravity base
structure of FIGS. 7A and
7B.
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[016] FIG. 9 is a side profile view of an exemplary embodiment of a gravity
base structure
having a plurality of internal watertight chambers and resting on a sea floor.
[017] FIG. 10 is an end profile view of the embodiment of FIG. 9.
[018] FIG. 11 is a side profile view of the embodiment of FIG. 9, in an
exemplary state being
partly filled with water and configured for either set-down on the sea floor
or lift-off from the sea
floor.
[019] FIG. 12 is a side profile view of the embodiment of FIG. 9, in an
exemplary state being
mostly empty of water and floating above the sea floor.
[020] FIG.13 is a diagram showing an exemplary seawater filling and discharge
system for the
embodiment of figure 9.
[021] FIG. 14 is a bottom view of a foot portion of the embodiment of FIG. 9,
showing an
exemplary skirt configuration and exemplary locations of fluid outlets for
increasing and
decreasing fluid pressure beneath the gravity base structure.
[022] FIG. 15 is a schematic cross-sectional side view of the foot portion of
FIG. 14 showing
an exemplary arrangement of the skirt and fluid outlets in relation to the
bottom of the gravity
base structure and the seabed.
DETAILED DESCRIPTION
[023] Described here are embodiments of gravity base structures (GBS) that
significantly
reduce the substructure weight required for a given water depth while offering
considerable
advantages in constructability, transportation, installation, relocation, and
removal. The
disclosed embodiments can be used to support drilling or production facilities
in water depths of
up to 200 meters or more. Some embodiments can support topside facilities with
large
installation weights, such as from about 30,000 tonnes to about 90,000 tonnes,
or more. Some
embodiments have the capability to withstand ice, water, and soil conditions
typical of the arctic
and sub-arctic seas, such as in the Beaufort Sea and the Kara Sea.
[024] The embodiments disclosed herein can reduce the traditional conflict
between bearing
load, buoyancy, and footprint area by supporting the topsides on widely
separated base
sections and support struts. These large base sections and support struts can
provide
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manufacturing and construction efficiencies due to modular designs. Components
can also be
symmetric to increase manufacturing efficiency.
[025] FIGS. 1 and 2 show an exemplary embodiment of a GBS 10 comprising a
first base
section 12A and a second base section 12B, a first inclined section 14A, a
second inclined
section 146, a transition section 16, and an upper section 18, and can support
a topside section
20. Some embodiments of the GBS 10 can further comprise one or more cross ties
extending
between the inclined sections 14, such as spaced apart cross ties 22A and 22B
and spaced
apart cross ties 24A and 24B.
[026] Each of the base sections 12 can be configured to be supported on a
seabed and can
support the rest of the GBS 10. The base sections 12 can each comprise a first
foot portion
30A, a second foot portion 30B, and an intermediate portion 34 extending
between the first and
second foot portions. The base sections 12 can be elongated in the direction
between the first
and second foot portions 30A, 30B. The foot portions 30 can have a large
bottom surface area
and can taper in horizontal cross-sectional area moving upward from a base
surface across a
sloped upper surface. The foot portions 30A, 30B can each comprise a chamfered
outer portion
36 that has a gently inclined upper surface, and can comprise an upwardly
projecting portion 38
that can have side surfaces that are more steeply inclined than the surface
36. The foot
portions 30A, 30B can comprise a plurality of flat, polygonal surfaces,
although some
embodiments can comprise curved surfaces or other non-flat and/or non-
polygonal surfaces.
[027] Each of the base sections 12 can have an overall longitudinal length L
and an overall
width W, as shown in FIG. 1. Each foot portion 30 can have a maximum width of
W while the
intermediate portion 34 can have a reduced width, creating a neck or
intermediate section of
reduced width between the two foot portions 30A, 30B. Each of the base
sections 12 can have
an outer sidewall surface and can have a generally straight inner sidewall
surface 40 that
extends the full length of the base section 12 across both of the foot
portions 30A, 30B and the
intermediate portion 34 along the length direction L. Each base section 12 can
be generally
symmetrical about a first vertical plane 63 (see FIG. 3) cutting through the
intermediate portion
34 midway between the foot portions 30. In addition, the base section 12A can
be generally
symmetrical with the base portion 12B about a second vertical plane 64 (see
FIG. 3) extending
in the length direction L half way between the two base sections 12. These
first and second
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vertical planes 63, 64 can each generally bisect the entire GBS 10 into
respective symmetrical
halves on either side of each of the planes, as shown in FIGS. 2A and 2B.
[028] The two base portions 12A and 12B can be widely separated by an open
region 42
between the inner sides 40 of the two base sections. The open region 42 can
extend the entire
length L of the base sections. In embodiments without the cross-ties 22 and
24, the open
region can extend upward to the transition section 16 and separate the two
inclined sections as
well. An embodiment has an "open region" between the two base sections 12A,
12B when the
entire region directly between the two base sections 12A, 12B is obstructed by
less than 10% of
structural components. In some embodiments, the two base sections 12A and 12B
can be
"completely separated" by the open region 42, meaning that there are no
structural components
extending directly between the two base sections 12.
[029] Each base section 12A, 12B can comprise a footprint area defined by the
perimeter of
the bottom surface of the base section that is configured to contact the
underlying seabed.
Exemplary footprint areas are shown in FIG. 3 by the bolded outer perimeter of
the base section
12. The open region 42 between the footprints of the base sections 12 can have
an area that is
greater than either of the footprint areas, or more than 50% of the total area
of the two
footprints. In other embodiments, open region 42 between the footprints of the
base sections 12
can have an area that is at least 25% of the total area of the two footprints.
In some
embodiments, each of the footprints can have an area that is greater than the
maximum
horizontal cross-section area of the upright annular section, or caisson
section, 18.
[030] Each of the inclined sections 14A, 14B can extend upwardly from the
upper portions 38
of the foot portions 30A, 30B of their associated base sections 12A, 12B to
the transition section
16. It should be noted that a stub portion of a corner structure of each of
the sections 14A, 14B
can be included in the associated base section. The inner portions 14A, 14B
can be inclined
such that they lean toward one another. The distance between the two inclined
portions 14A,
14B can decrease moving from the base sections 12 toward the transition
section 16, such that
the two inclined portions can be more readily connected together at the
transition portion 16.
The inclined nature of the inclined sections is best seen in the end view of
FIG. 2B. Thus, the
side portions 14A, 14B can converge, or at least portions thereof can
converge, moving away
from their associated base section 12. Desirably they continuously converge
moving upwardly.
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However, they can less desirably have sections that converge with intervening
non-converging
portions.
[031] Each inclined section 14A, 14B can comprise a first and second strut
44A, 44B and one
or more horizontal cross members, such as 46A and 48A for inclined section 14A
and 46B and
48B for inclined section 14B, which can be parallel to and spread apart one
above the other.
One strut 44A is coupled to one foot portion 30A of each base section 12 and
the other strut
44B is coupled to the other foot portion 30B of each base section. The struts
44A and 44B of
the respective inclined section 14A can converge, in whole or in part toward
one another. The
struts of section 14B can be arranged in the same manner. Thus, the struts of
one section 14A
can slant toward one another and toward the struts of the other inclined
section 14B and these
struts of section 14B can slant toward one another and toward the struts of
section 14A. Each
strut 44 can have a generally square horizontal cross section that decreases
in area with
elevation. Other cross sectional configurations can be employed. The four
struts 44 can have
the same degree of slant and can be generally symmetrical about a vertical
central axis 66 of
the GBS 10 defined by the intersection of the planes of symmetry 63 and 64.
The struts can
continuously converge over their lengths. Alternatively, the struts can have
one or more
converging sections.
[032] Each inclined section 14A, 14B can comprise zero, one, two, or more
horizontal cross
members connecting the struts 44A and 44B together. The embodiment of FIG. 1
comprises a
longer lower cross member 46A and a shorter upper cross member 48A
interconnecting the
struts 44A and 44B of the first inclined section 14A and a longer lower cross
member 46B and a
shorter upper cross member 48B interconnecting the struts 44A and 44B of the
second inclined
section 14B. The cross members 46, 48 can, for example, have a generally
quadrilateral
vertical cross-section with horizontal upper and lower surfaces and inclined
side surfaces.
[033] In embodiments designed for deeper waters, the GBS 10 can comprise cross
ties 22
and/or 24 extending between and coupling the two inclined sections 14A and
14B. One set of
cross ties 22A and 24A can interconnect the two struts 44A and another set of
cross ties 22B
and 24B can interconnect the two struts 44B. The cross ties 22, 24 can be
similar in shape and
elevation to the cross members 46, 48 when present.
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[034] The upper ends of the struts 14 can be connected together by the
transition section 16.
The transition section 16 can be at least partially frustoconical, have the
general shape of a
frustum, or have another shape. The transition section 16 can have a broader
lower perimeter
50 having a first cross sectional area and can taper to a narrower upper
perimeter 52 having a
second cross section less than the first cross sectional area. The transition
section 16 can
comprise an axially extending open inner or central region 48 (FIG. 2). In the
embodiment of
FIG. 1, the transition section 16 has a square lower perimeter 50 and an
octagonal upper
perimeter 52, with polygonal side surfaces. In other embodiments, the
transition section 16 can
have circular upper and lower perimeters and a frustoconical side surface, or
have other
configurations.
[035] The upper section 18 of the GBS 10 can extend upwardly from the upper
perimeter, or
top, 52 of the transition section 16. The upper section 18 can comprise an
upright annular
portion 54 and a flared or enlarged top portion 56. The upper section 18 can
have an open
axially extending inner or central region 58 (FIG. 2). Central region 58 can
be vertically oriented
and can communicate with the open region 48 within the transition section 16.
The upper
section 18 can have a polygonal cross-section, as shown FIG. 1, a circular
cross-section, or any
other suitable shape. The flared portion 56 can have a narrower lower
perimeter 60 with a
smaller cross-sectional area than the upper surface 62 of the flared portion
56. The lower
perimeter 60 is located at the intersection with the top of the annular
upright portion 54. The
flared portion 56 can increase in cross-section area toward a broad upper
surface 62, which can
support the topside structures 20.
[036] The GBS can be sized such that, when supported on a seabed, the upright
annular
portion 54 of the upper section 18 is partially under water and partially
above water. The upright
annular portion 54 can have a smaller horizontal width relative to other
portions the GBS 10
such that it receives less lateral force from waves and ice loads, which are
generally
concentrated near the upper surface of the sea. Various embodiments of the GBS
10 can be
configured to be used in sea depths greater than 60 meters, such as depths
ranging from about
60 meters to about 200 meters, though the GBS 10 can be configured to be used
in other
depths of water as well.
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[037] The dimensions shown in FIGS. 2-4 are merely exemplary and do not limit
the
disclosure in any way. These dimensions illustrate one exemplary embodiment,
and other
embodiments can have different dimensions.
[038] FIGS. 2A and 26 illustrate one exemplary division of the GBS 10 into
three assembly
units 70, 72, and 74. A base unit 70 (shown in regular solid lines X) can
comprise the two base
sections 12A, 126 and lower portions of the two inclined sections 14A, 146
(e.g., lower portions
of the struts 44A, 44B, lower cross members 46, and/or lower cross ties 22).
In some
embodiments, the lower cross members 46A, 468 can be included in the base unit
70. In
addition, the base unit 70 can alternatively also comprise the lower cross
ties 22A, 22B. In
embodiments where the base unit 70 does not include lower cross ties 22A, 22B
(such as for
shallower waters), the base unit 70 can comprise two separate assembly base
units 70A and
706 (as shown in FIG. 3). The middle unit 72 (shown in bolded dashed lines Y
in FIGS. 2A and
2B and also shown in FIG. 4) can comprise upper portions of the inclined
sections 14, the
transition section 16, a lower portion of the upper section 18, and optionally
the upper cross ties
24A, 24B. The top unit 74 (shown in solid bold lines Z) can comprise an upper
portion of the
upper section 18 and optionally the topside structures 20.
[039] Each of the assembly units 70, 72, 74 can be constructed individually in
a large dock.
During assembly of the GBS, the base unit 70 can be positioned first floating
partially
submerged in a sea, then the middle unit 72 can be positioned over and coupled
to the base
unit 70, then the combined base unit 70 and middle unit 72 can be lowered in
the water, then
the top unit 74 can be positioned over and coupled to the middle unit 72. In
some
embodiments, the lower cross ties 22 can be coupled to the base unit 70 and
the upper cross
ties 24 can be coupled to the middle unit 72 before the top unit 74 is
attached. In other
embodiments, the GBS unit 10 can be divided into various other assembly units
and/or sub-
units and can be assembled in various other manners.
[040] FIG. 3 shows a top plan view of the base units 70A, 70B of the
embodiment of FIG. 2
without cross members 46 or cross ties 22. This view illustrates the open
region 42 between
the inner side surfaces 40 of the two base sections 12A and 126. The inner
most edges 41 of
the inner side surfaces 40 can be parallel. This view also illustrates an
exemplary footprint of
the base sections 12 on the seabed, with the narrow intermediate portions 34
and the broader
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foot portion 30. The base units 70A, 70B can be symmetrical with each other
about a vertical
plane 64, while each can be symmetrical about a vertical plane 63. This view
also shows lower
portions of the four struts 44 slanting toward a central axis 66 of the
structure, which is desirably
vertical.
[041] FIG. 4 shows a top plan view of the middle unit 72 of the embodiment of
FIG. 2. This
view illustrates the exemplary square cross sectional peripheral shape created
by the four struts
44, the upper cross members 48A, 480 and the upper cross ties 24A, 24B at the
bottom of the
middle unit 72. This view also illustrates the octagonal cross-section of the
exemplary upright
annular portion 54. The middle portion 72 can be symmetrical about the
vertical planes 63 and
64. In some embodiments, the middle portion 72 can also be symmetrical about
two diagonal
vertical planes (not shown) at 45 to the planes 63 and 64.
[042] FIGS. 5 and 6 illustrate one exemplary construction approach of the base
unit 70 shown
in FIGS. 2A and 2B. In this approach, the base unit 70 is assembled from two
base portions
90A and 90B and a third portion 92 that connects the base portions 90A, 90B.
As shown in FIG.
5, in some embodiments, the two base portions 90 can be constructed
individually in a dry dock
80. FIG. 5 shows a cross-sectional end view of one of the base portions 90 as
constructed in
dry dock 80. In some embodiments, the base portions 90 are extremely large and
require very
large dry docks. One very large dry dock 80 is illustrated. The dry dock 80
can comprise a floor
82 with a width W1 of about 131 meters and a lift 84, such as a goliath lift,
which can have a
maximum lifting height H2 of about 91 meters above the floor 82. The dock 80
can have a
depth H1 of about 14.5 meters, which can be partially filled with water or
other liquids 86, such
as to a height H3 of about 10 meters, in order to help support and construct
the base portions
90. The bottom surfaces of the base portions 90 can be spaced above the floor
82, such as via
blocks 88, about 1.8 meters. Using such a large dry dock 80, each entire base
portion 90 can
be constructed at one time, and then moved as a single unit out of the dry
dock for assembly to
the base portion and the third portion 92 at sea.
[043] In some embodiments, the base portions 90 can include the parts marked
in FIG. 5 as A
and B, and the part marked as C can be constructed with the third portion 92
(as shown in FIG.
6). Base portions comprising only parts A and B can comprise the portion of
FIG. 1 shown
below the dashed lines 1. In other embodiments, given a large enough dry dock,
all three parts
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A, B and C shown in FIG. 5 can be constructed at once with the base portion
90, which can rise
to a height H4 of about 85 meters above the floor 82. Such a base portion with
parts A, B, and
C can comprise the portion of FIG. 1 shown below the dashed lines 2. Two base
portions
comprising parts A, B and C can then be coupled together with the lower cross
ties 22 at sea to
form the base unit 70.
[044] Importantly, the base portions 90 have a base length L (see FIG. 1) that
is much greater
than its base width (W2 shown in FIG. 5), and the dry dock 80 also desirably
has sufficient
length. The open region 42 between the two base sections 12A, 12B allows for
the separate
construction of each of the two discrete base portions 90 in their entirety in
a single dry dock,
one after another, such that they can later be assembled with other components
at sea to form
the GBS 10. This constructability would not be possible for a GBS having a
base structure that
exceeds the width of the dry dock.
[045] As shown in FIG. 6, in some embodiments, the base unit 70 can be
constructed in three
parts. The two base portions 90A and 90B can comprise the portions of the GBS
below the
lower cross members 46 and the lower cross ties 22, which includes the parts
marked as A and
B in FIGS. 5 and 6. The third portion 92 can comprise the lower cross members
46A, 46B, the
lower cross ties 22A, 22B, and intermediate portions of the four struts 44 up
to the bottom of the
upper cross members 48A, 48B and upper cross ties 24A, 24B. To assemble the
three portions
90A, 90B and 92, the portions 90A and 90B can first be positioned in the
floating arrangement
shown in FIG. 6 at sea. To reduce the buoyancy of the portions 90A and 90B,
enclosed internal
regions in the portions 90A and 90B, such as those shown as 94 in FIG. 6, can
be flooded with
seawater, causing them to float lower in the water. Once they are floating at
a desired level and
proper lateral relation to one another, the third portion 92 can be
transported over the top of
them. As shown in FIG. 6, barges 96 can be used to positioned the third
portion 92. Once over
the top of the portions 90A and 90B, the third portion 92 can be lowered into
contact with the
tops of the portions 90A and 90B and the three portions can be coupled
together (e.g., welded)
to form the base unit 70, as shown in FIGS. 2A and 2B. In this embodiment, the
base unit 70
includes the lower cross ties 22, whereas in the embodiment shown in FIG. 3,
the two base
units 70A and 70B can be constructed without the lower cross ties 22, and the
lower cross ties
22 can optionally be added at a later time, or not at all.
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[046] Once the three portions 90A, 90B and 92 shown in FIG. 6 are joined
together to form the
base unit 70, the entire base unit 70 can be lowered in the water by further
flooding the
enclosed internal regions 94 and/or flooding enclosed internal regions in the
third portion 92,
such as the regions 98 shown in FIG. 6. Once the base unit 70 has been lowered
to a desirable
level, the separately constructed middle unit 72 can be positioned over the
top of the third
portion 92 and coupled (e.g., welded) to the base unit 70.
[047] In the embodiment shown in FIGS. 3-5, the two individual base units 70A
and 70B can
likewise be lowered in the water by flooding internal floatation chambers,
and, with the base
units 70A and 70B properly spaced and aligned, the middle unit 72 can be
positioned above the
base units and coupled to them.
[048] Once the middle unit 72 is coupled to the base unit 70, the structure
can be further lower
in the water by flooding one or more internal floatation chambers in the base
unit 70 and/or the
middle unit 72, and the top unit 74 can be positioned above the middle unit 72
can coupled
together. The illustrated top unit 74 desirably has a positive hydrodynamic
stability in an upright
orientation such that it naturally floats with the top surface 62 above water,
even with heavy
facilities pre-coupled to the top surface.
[049] The coupling together of the base unit 70, the middle unit 72, and the
top unit 74 can be
performed at any location with sufficient water depth, be it just off shore
from the dry dock 80
where the units are constructed, or at a drilling site in an arctic sea.
Because the GBS 10
comprises an open structure with large open regions between the base sections
12 and the
inclined section 14, the entire assembled GBS 10 can be transported (towed) in
water with
reduced drag. The assembled GBS 10 is preferably towed in the water in the
length direction L
(see FIG. 1) such that two foot portions 30A or the two foot portion 306 are
leading. When
towed in this orientation, the base sections 12 and the inclined sections 14
have a minimal drag
profile and the large open region 42 is aligned with the direction of travel,
reducing
hydrodynamic drag. In addition, the chamfered base sections 12 can reduce
hydrodynamic
drag as the GBS moves through the sea. Alternatively, the individual assembly
units 70, 72, 74
can be separately towed to the set-down location and then assembled.
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[050] The overall configuration of the GBS has a very favorable hydrodynamic
stability. In a
desirable form, the pyramidal shape with broader, heavier base sections and
narrower, lighter
upper section contribute to the stability. As such, the GBS can be naturally
stable in the upright
position when afloat in water. In addition, the open structure of the GBS
results in a reduced
weight relative to a conventional GBS designed for the same water depth. The
reduced overall
weight, reduced drag, and natural hydrodynamic stability can make the GBS
easier to transport
in its fully assembled form across long distances in water, such as from near
a dry dock to an
arctic drilling location.
[051] Once the assembled GBS 10 is at a desired set-down location, the entire
GBS 10 can
be lowered onto the seabed by further flooding internal floatation chambers
with sea water until
the bottom surfaces of the base sections 12 come into contact with the sea
floor. The sea floor
can be pre-conditioned prior to set-down, such as by leveling the surface,
removing unstable
material, adding material, etc. Desirably, the set-down location has a level
sea floor such that
the entire lower surfaces of the base sections 12 are supported by the sea
floor. One
advantage of the widely spaced base sections is that it reduces the overall
footprint of the GBS
on the seabed and thus reduces the amount of seabed preparation needed prior
to set-down.
In addition, the underside of the base sections 12 can be reinforced to
withstand the pressures
exerted by uneven seabed conditions. In some embodiments, a foundation skirt
can be
provided on or adjacent to the underside of the base section 12 to improve the
stability of the
foundations.
[052] After the GBS is set down on the sea floor, the upper surface level of
the sea is, under
normal conditions, between the top of the transition section 52 and the top of
the upright annular
section 54, such that the upright annular section 54 protrudes through the
surface of the water.
Due to the relatively narrow width of the upright annular section 54, it can
limit the magnitude of
lateral forces imparted on the GBS 10 from wave action and from ice formations
at the surface
of the sea. In addition, the open structure of the base sections 12 and the
inclined sections 14
can allow water currents to pass through the GBS with reduced resistance,
particularly in the
length direction L of the base sections 12. These features can reduce the
total lateral load
imparted on the GBS 10 compared to traditional GBS designs. The GBS can be
oriented with
the length direction oriented toward prevailing water currents to reduce
lateral forces.
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[053] The widely spaced base portions 12 prevent the GBS 10 from overturning
over due to
lateral loads. In addition, the lateral frictional forces between the base
sections 12 and the sea
floor are sufficient to prevent the lateral sliding of the GBS along the sea
floor. Nevertheless, in
some embodiments, although less desirable, the GBS 10 can be further secured
to the sea floor
with piles, anchors, or other mechanisms. The GBS 10 can be configured to be
used in deep
waters with depths up to about 200 meters. One exemplary embodiment can be
configured to
be used in water depths of at least 150 meters, such as a range of water
depths from about 150
meters to about 200 meters, while other exemplary embodiments can be
configured to be used
in other water depth ranges. The range of water depths a particular embodiment
is designed for
can be related to the vertical height of the upright annular portion 54.
[054] Because the GBS is at least partially submerged in water when in use,
the weight of the
GBS can partially be supported by the water and partially be supported by the
seabed. The
portion supported by the seabed can be referred to as on-bottom weight. In the
described
embodiments, the two base sections 12 are configured to transfer substantially
all of the on-
bottom weight of the GBS to the seabed.
[055] FIGS. 7 and 8 show another embodiment of a GBS 110 that is configured to
be used in
water depths down to about 60 meters. One exemplary embodiment of the GBS 110
can be
configured to be used in a range of water depths from about 60 meters to about
100 meters,
while other exemplary embodiments can be configured to be used in other
ranges. The GBS
110 comprises two spaced apart base sections 112 and an upper section 114
extending
upwardly from the base sections 112. FIGS. 7A and 7B shown cross-sectional
side and end
views, respectively, of the GBS 110. FIG. 8 is a partial plan view of the GBS
110 showing
outlines of the two base sections 112 at different heights and a lower profile
of the upper section
114.
[056] The base sections 112 can have a generally rectangular lower footprint
118 with
generally parallel inner edges 120 and outer edges 122, generally parallel end
edges 124, and
diagonal or chamfered outer corner edges 126. Each footprint 118 can have a
longitudinal
length L, which can be about 250 meters, and a width W1, which can be about 85
meters. An
open region 128 between the two base sections 112 can have width W2, which can
be about 70
meters, and can extend the entire length L between the base sections 112. The
base sections
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CA 02785142 2012-08-08
112 can taper (continuously or partially) to an upper perimeter 130. An inner
edge 132 of the
upper perimeter 130 can be inward of the inner edge 120 of the footprint 118
such that the base
sections 112 slant inwardly toward each other.
[057] The upper section 114 can comprise an upright annular body with a
variable horizontal
cross-sectional profile. The upper section 114 can comprises a lower outer
perimeter 134,
which can have an octagonal shape as shown in FIG. 8, or another shape. The
outer perimeter
134 can overlap a portion of the upper surface of the base sections 112 within
the upper
perimeter 130 and can intersect the inner edges 132. The upper section 114 can
further
comprise a lower inner perimeter 136 within the lower outer perimeter 134. The
lower inner
perimeter 136 is positioned over the open region 128 and can share lateral
edges with the inner
edges 132 of the bases sections 112. The upper section 114 can define an open
inner region
140 that extends axially or vertically entirely through the upper section 114
and can have a
variable cross-sectional area. The upper section 114 can taper in cross-
sectional area moving
upwardly from the bass section 112 to a narrowest vertical portion 142 and
then increase in
horizontal cross-sectional area moving upwardly from the vertical portion 142
to an upper
surface 144.
[058] The GBS 110 can be constructed and assembled in a similar manner as the
GBS 10.
For example, the base sections can be constructed individually and the upper
section can be
constructed in one or two parts that are assembled at sea.
[059] The dimensions shown in FIGS. 7 and 8 are merely exemplary and do not
limit the
disclosure in any way. These dimensions illustrate one exemplary embodiment,
and other
embodiments can have different dimensions.
[060] The upper section 18 of the GBS 10 and the upper section 114 of the GBS
110 can
comprise an inner open region through which drilling equipment passes from the
upper platform
to the seabed. This inner open region can be open at the upper and lower ends
such that the
seawater level within the open inner region naturally adjusts to the same
height as the seawater
surrounding the upper section. This inner region can be referred to as a "moon
pool" and the
surrounding upright annular structure can be referred to as a "caisson." In
addition to
structurally supporting the topside structures, the caisson can isolate the
drilling equipment from
waves and ice formations at the surface of the sea. Such ice formations extend
several meters
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CA 02785142 2012-08-08
below sea level and thus the caisson desirably extends at least this far below
sea level in a
desirable embodiment.
[061] The structural components of the GBS embodiments disclosed herein can
comprise any
sufficiently strong, rigid material or materials, such as steel. In some
embodiments, any of the
lower components of the GBS, such as the base sections 12, can comprise
concrete.
[062] In some of the embodiments described herein, the first base section can
comprise a first
point at one end and a second point at the opposite end, the second base
section can comprise
a third point at one end and a fourth point at the opposite end, and the
first, second, third, and
fourth points define the vertices of a horizontal quadrilateral area, such
that all portions of the
GBS with greater elevation than the quadrilateral area are positioned directly
above the
quadrilateral area. For example, in the embodiment 10 of FIG. 1, the entire
first and second
inclined sections, the entire transition section, and the entire upper section
and topsides are
positioned directly above an area defined by the four foot portions 30.
[063] The GBS embodiments disclosed herein can be used for various purposes.
Some
embodiments can be used for exploratory drilling wherein the GBS is moved to
various locations
to explore for desirable condition. Such embodiments can be configured to
support exploratory
drilling structures and equipment on the topsides. Other embodiments can be
used in more
permanent hydrocarbon production operations, wherein the GBS may stay at one
location for a
long period of time, such as several years, while hydrocarbons are extracted
and processed.
Some embodiments can be used for both exploratory purposes and production
purposes. For
exploratory operations, it can be desirable for the GBS to be functional in as
great a range of
water depths as possible. Accordingly, it can be desirable for the caisson
portions to have a
longer vertical height, while maintaining structural stability, such that the
GBS can be used in a
greater range of water depths. When used as a substructure for a permanent
production
facility, which can weigh up to 120,000 tonnes, the GBS can have a broader,
more robust upper
portion as production facilities are typically much larger and heavier than
exploratory drilling
rigs. In any case, the upright annular section, or caisson, can be configured
to support
substantially all of the weight of whatever hydrocarbon extraction
superstructure is positioned on
top of the upright annular section.
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CA 02785142 2012-08-08
[064] The illustrated embodiments can be used on seabeds with cohesive soils
having an
undrained shear strength lower than 30 kPa and larger embodiments (such as in
FIG. 1 with
lower and upper cross ties 22, 24) can withstand multi-year ice loads greater
than 660 MN.
Some of these larger embodiments can have an overall weight of less than
280,000 tonnes, not
including the topside structures, due to the open structure.
[065] In some of the embodiments described herein, any one or more of the
various
components of the GBS can comprise internal chambers that can be used to
temporarily or
permanently store fluids, such as water, hydrocarbons, air, and mixtures of
such fluids.
Desirably, all or most of the major structural components can comprise
internal chambers that
can be selectively filled with and/or emptied of fluid ballast to sink or
raise that component
and/or assemblies comprising that component. In some embodiments, internal
chambers used
for storing hydrocarbons can comprise double-skinned walls to reduce the risk
of spills.
Furthermore, any of the internal chambers of the GBS can comprise solid
ballast.
[066] In preferred embodiments, certain internal chambers are dedicated for
storing
hydrocarbons while other internal chambers, i.e., floatation chambers, are
dedicated for storing
seawater, such that hydrocarbons are not mixed with seawater. This can be
referred to and
"dry" hydrocarbon storage. In such embodiments, the chambers that are filled
with seawater
are designed to remain filled with seawater while the GBS is positioned at a
seabed location, in
order to maintain sufficient gravitational interaction with the seabed, and
the seawater is only
removed in order to lift and move the GBS to another location. In these
embodiments, the
chambers for storing hydrocarbons can be selectively filled and emptied as
desired while the
GBS is at a seabed location, and when they are not full of hydrocarbons, air
or another gas can
be used to fill them. In this way, the hydrocarbons do not mix with seawater.
These
embodiments can maintain sufficient overall density even when the hydrocarbon
chambers are
filled with air or other gasses. In some of these embodiments, the internal
chambers can
comprise from about 150,000 bbl to about 250,000 bbl of dry hydrocarbon
storage. Typically,
such dry hydrocarbon storage chambers can be located in the upper portions of
the GBS, such
as the caisson section 18, the transition section 16, and the upper portions
of the strut sections
14, while dedicated seawater storage chambers can be in located lower portions
of the GBS.
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CA 02785142 2012-08-08
[067] In other embodiments, the same chambers can be used to store both
seawater and
hydrocarbons in a variable proportion such that the chambers are always filled
with seawater
and/or hydrocarbons. As hydrocarbons are added to the chambers, portions of
the seawater in
the chambers can be released into the sea, and as hydrocarbons are removed
from the
chambers, seawater can be added to the chambers. In these embodiments, the
hydrocarbons
can mix with the seawater, requiring that any seawater removed from the
chambers can need to
be cleaned prior to being released to the sea. Such embodiments can be made
smaller and/or
with less volume of internal chambers since all of the chambers are always
full of a liquid,
whereas embodiments with dedicated seawater and hydrocarbon chambers require a
greater
total chamber volume because they are filled with air or other gas when
emptied of fluid and
additional ballast is needed to compensate for the additional buoyancy.
[068] FIGS. 9-12 illustrate an exemplary process for raising an embodiment of
the GBS 10 off
the seabed such that it can be relocated, sinking the GBS, or adjusting the
floating level of the
GBS, such as during towing. Some embodiments of the GBS 10 can comprise a
plurality of
internal watertight subdivisions, or chambers, that can be selectively filled
with liquid and
emptied to adjust the weight of the GBS. The chambers (as well as chambers in
the foot
portions and cross members/cross ties) can be sealed against water leakage
therebetween.
Alternatively, selected chambers can have passageways therebetween so that
they are emptied
and filled together. This also does not preclude the GBS 10 comprising some
chambers that
are always filled with fluid during normal use and towing. The number, size
and arrangement of
such chambers can vary, and the exemplary embodiment shown in FIGS. 9-12 is
just one
possible example.
[069] In the exemplary GBS 10 shown in FIGS. 9 and 10, each of the inclined
struts 44A and
44B are subdivided into a plurality of chambers. Each strut 44 can comprise
one or more
longitudinally extending and uprightly extending dividers and one or more
transversely
extending dividers such as horizontal dividers. For example, each strut 44 can
be divided into
longitudinal quarters by orthogonal dividers 204 and 206 (as shown in FIG. 9A)
that extend
along the entire length of the struts. Each strut 44 can further be divided
transversely by
dividers 208, forming eight chambers in each strut 44 in this example. In the
illustrated
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CA 02785142 2012-08-08
example, some of the chambers are oriented in a side-by-side orientation.
Also, some
chambers are stacked end to end in the struts.
[070] The chambers at lower ends of the struts 44 can be separated from
chambers in foot
portions 30, such as by horizontal dividers 210. Each foot 30 can also be
subdivided into plural
chambers or subdivisions. For example, the upper portions of each foot can be
separated from
the lower portions 36 by another divider 212. Furthermore, the longitudinal
dividers 204, 206
can extend through the foot portions 30 to the bottom of the GBS, dividing
each foot portion into
plural chambers, such as four quadrants each having an upper chamber and a
lower chamber
divided by the divider 212.
[071] The upper portions 16 and 18 of the GBS 10 can also comprise fluid
chambers. The
caisson section 18 can comprise an upper transvers or horizontal divider 220
and can be
separated from the transition section 16 by a transverse or horizontal divider
222. The transition
section can be separated from the upper ends of the struts 44 by transverse or
horizontal
dividers 224. Any of the transverse dividers can alternatively be non-
horizontal in some
embodiments, and need not be planar, although planar dividers is one desirable
form.
[072] The cross members 46 and 48 that connect the struts 44A and 44B can be
subdivided
into plural fluid chambers. In the example shown in FIG. 9, the upper cross
members 48
comprise a middle divider 214 that separates the cross member into two end to
end chambers
and end dividers 215 that separate the two chambers of the cross member 48
from the
chambers of the struts 44. The lower cross members 46 can also comprise plural
chambers,
such as defined by a central or intermediately positioned or middle divider
216 that separates
the cross member into two end-to-end chambers and end dividers 217 that
separate the two
chambers of the cross member 46 from the chambers of the struts 44.
[073] Similarly, the cross ties 22 and 24 can also be subdivided into plural
fluid chambers. In
the example shown in FIG. 10, the upper cross ties 24 comprise a central or
intermediately
positioned or middle divider 226 that separates the cross tie into two
chambers and end dividers
227 that separate the two chambers of the cross tie 24 from the chambers of
the struts 44. The
lower cross tie 22 can comprise divider 228 that separates the cross tie into
two end-to-end
chambers and end dividers 229 that separate the two chambers of the cross tie
22 from the
chambers of the struts 44.
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[074] Each of the foot portions 30A and 306 can also be separated from the
intermediate
portion 34 of the base section 12 by respective dividers 218, as shown in FIG.
9.
[075] FIGS. 9 and 10 show the subdivided GBS 10 resting on the seabed 230 with
the sea
level 200 nearly even with the upper divider 220 of the caisson portion 18.
This can be the
maximum operating water depth of the GBS during normal operating conditions.
To keep the
GBS 10 resting on the seabed 230, a sufficient percentage of the GBS is filled
with seawater
and/or hydrocarbons to overcome the buoyancy of the GBS. In the illustrated
example, all of
the internal chambers of the GBS are filled with seawater up to a filling
level 202, which is
spaced below the sea level 200. In this configuration, the gravitational
forces on the GBS
overcome the buoyant forces and the GBS remains held in place on the seabed.
[076] FIG. 11 shows the GBS with a lower volume of seawater stored in the
internal chambers
than shown in FIGS. 9 and 10. The internal water level 232 is at about the
level of the top of the
upper cross members 48. The caisson section 18 and transition section 16 are
emptied of
seawater and desirably filled with air. In addition, some of the upper
chambers of the struts 44
are partially filled with seawater and partially filled with air. All of the
chambers below the filling
level 232 are completely or at least substantially filled with water. At about
this filling level, the
buoyant forces of the GBS are approximately even with the gravitational
forces. In other
embodiments, the filling level 232 corresponding to an approximately even
buoyancy-gravity
balance can be higher or lower than shown in FIG. 11, depending the
configuration and material
of the GBS. It should be noted that different chambers other than those shown
in FIG. 11 can
be emptied of seawater to achieve the desired GBS gravity-buoyancy balance.
For example,
some or all of the lower chambers of the struts and feet can be emptied while
higher chambers
remain filled.
[077] With a neutral buoyancy-gravity balance, the GBS can be carefully raised
from the
seabed or lowered toward the seabed. If the buoyancy of the GBS is too much
greater than the
gravity, the GBS can tend to rise too rapidly, which can cause damage to the
GBS and other
undesirable consequences. Similarly, if the gravity is too much greater than
the buoyancy, the
GBS can sink too rapidly, which can cause damage to the GBS and other
undesirable
consequences.
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CA 02785142 2012-08-08
[078] It can be desirable to keep the center of gravity of the GBS as low as
possible to prevent
tipping. Thus, it can be desirable to empty the seawater from the GBS starting
from the
uppermost chambers and moving downward. Similarly, it can be desirably to fill
the lowermost
chambers first and gradually fill the chambers moving upward. This concept is
illustrated in
FIGS. 9-12. In other embodiments, however, seawater can be added or removed
from the
chambers in other sequences or patterns, such as gradually from all of the
chambers
simultaneously. Alternative filling and emptying patterns or sequences can
provide other
advantages with regard to force and stress distributions, moment of inertia
control, etc.
[079] FIG. 12 shows the GBS 10 with all of the fluid chambers above the base
sections 12
empty and shows the GBS 10 floating with the sea level 238 at about the level
of the upper
cross members 48. In this configuration, the GBS 10 can be towed through the
sea, such as to
relocate the GBS to a new drilling location where the GBS can be set down on
the seabed by
filling the internal chambers with seawater. The horizontal lines 234 and 236
represent
exemplary lower and upper boundaries, respectively, of a range of possible
draft levels for
towing the GBS through the sea. For example, the lower level 234 can
correspond to a state
where all or nearly all of the internal chambers are empty or nearly empty of
fluid such that the
GBS floats very high in the sea with the sea level about even with the tops of
the base sections
12, while still remaining sufficiently stable. Conversely, the upper level 236
can correspond to a
state where a maximum volume of fluid is stored in the internal chambers and
the sea level is
about even with the caisson section 18, while still remaining buoyant. The
liquid level in the
various chambers can be varied as the GBS is being towed. For example, if seas
and wind are
calm, the GBS can be floated higher in the water column to reduce towing drag.
In contrast, if
winds are high and/or waves are rough, the GBS can be floated lower in the
water column to
increase its stability during towing. In heavy ice conditions, the GBS is can
also be floated lower
such that the narrower and rounded caisson section passes through the ice.
[080] The draft level of the GBS 10 can thus be adjusted to suit particular
conditions while
maintaining hydrodynamic and hydrostatic stability. As another example, to
traverse shallower
waters, the GBS can be floated higher in the sea by storing less fluid in the
internal chambers,
and to traverse deeper waters and/or waters with greater ice formations on the
surface, the
GBS can be floated lower in the sea by storing more fluid in the internal
chambers. The dashed
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CA 02785142 2012-08-08
line 242 shows an exemplary tow line connected to the GBS and connected with a
tug boat or
other towing vessel. The connection location of the towlines can be selected
such that tow
forces are aligned near the center of gravity or other central location of the
GBS to avoid
excessive tipping or rotation of the GBS and to avoid damage to the GBS.
[081] Regardless of the draft level, the towing force must overcome the
resistance of any
current, wind, sea ice and other environmental effects. Due to the rounded
caisson section 18,
open strut sections 14, and spaced apart base sections 12, these forces on the
GBS can be
substantially reduced at any draft level. Furthermore, ice formations at the
surface can be
broken up by other vessels before the towed GBS arrives to further reduce
towing resistance.
[082] FIG. 13 is a diagram of an exemplary system 250 for adjusting the fluid
and gas levels
within exemplary chambers of the GBS. Two chambers are shown having an outer
wall 252
and a divider 254 that separates the two chambers and that seals the two
chambers from one
another and from the environment. Each of the chambers can be partially filled
with fluid 258
(e.g., seawater or hydrocarbons) and partially filled with gas 256 (e.g.,
air). Each chamber can
comprise a fluid pump 260 located near the bottom of the chamber and coupled
to one or more
valves (e.g., a non-return or one-way valve 262 and a discharge valve 264)
configured to expel
the liquid 258 out of the chamber at outlet 266, such as into the sea or into
another chamber.
Each chamber can also have a seawater inlet valve 268 to admit seawater into
the chamber,
such as from the sea or from another chamber. The pump 260 and the inlet valve
268 can be
operated together to control the volume of liquid in the chamber. A valve 270
can connect
adjacent chambers to allow liquid the move between them, such as to ensure
adjacent
chambers maintain an even liquid level. One or more vents or outlet valves 272
can be coupled
to the top of the chambers to allow gas to exit the chambers via outlets 276,
such as to the
atmosphere to another chamber. One or more gas inlet valves 274 can also be
couple to the
top of the chambers to admit gas into the chambers, such as from a compressed
air source or
from another chamber. An additional valve 280 can couple to gas conduits from
adjacent
chambers to ensure even gas pressure distribution between the chambers.
[083] Desirably, the valves are remotely controlled valves. For example, they
can each be
electrically connected to a controller and responsive to a control signal
generated in response to
signals from the controller to pend and/or close the valve. The valves can
also be controllable
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CA 02785142 2012-08-08
in response to manually (e.g. switch activations) generated control signals.
The controls can be
programmed to establish the desired sequence of valve activation to fill or
empty the chambers
to float or sink the GBS.
[084] Plural chambers can be in fluid communication with one another such that
a single valve
can fill or empty the chambers together. A valve can separate these chambers
to selectively
allow fluid communication between them so that they are not filled or emptied
together.
[085] In other embodiments, the GBS can comprise one or more centralize
pumping systems
that remote replace the function of the localized pumps 260 in each chamber.
Such a
centralized pumping system can have one or more pumps located in a centralized
part of the
GBS and can be coupled to each chamber via piping. Similarly, the compressed
gas source
can be centralize and coupled to each chamber via piping. This can provide
more useable
volume in each chamber and reduce the total weight and cost of the gas and
liquid pumping
systems.
[086] Some embodiment of the GBS can also comprise a system of piping and
mechanical
equipment that is configured to introduce and/or extract water or air at the
underside of the GBS
base sections 12 to assist in establishing contact with or separation from the
seabed. Such a
system can assist in creating an even distribution of contact forces across
the underside of the
base sections 12 during set-down of the structure by locally disturbing the
stability of the seabed
surface material. The same or similar system can also be used to assist in the
release of the
structure prior to floatation by loosening compacted soil, breaking suction,
and/or pressurizing
the area between the base sections 12 and the seabed. Such conditions may be
encountered if
the structure is placed on relatively soft cohesive soils, particularly of the
structure is fitted with a
skirt arrangement beneath the base sections 12, as is shown in the exemplary
embodiment of
FIGS. 14 and 15.
[087] FIG. 14 is a bottom view of a portion of one base section 12 showing a
skirt structure
300 attached to the underside of the foot portions 30. FIG. 15 shows a cross-
sectional side
view showing the skirt structure 300 engaged with the seabed. The skirt
structure can define a
plurality of chambers or cells (a few being numbered 310 in FIG. 14) that open
downwardly in
this example. In one specific example, the underside of the base sections 12
can comprise
transverse body members such as horizontal base plates 302 that can also form
bottom walls of
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CA 02785142 2012-08-08
one or more fluid chambers within the GBS. The skirt structure 300 can
comprise a plurality of
projections, such as upright walls, that extend downwardly from the base
sections 12. The
projections can form a grid pattern of intersecting plates that defines a
plurality of open
chambers 310 on the underside of the GBS 10, as shown in FIG. 14. In some
embodiments,
the intersecting walls can be orthogonal to one another and form plural
rectangular or square
compartments. In other embodiments the walls can form triangular compartments
or other
shaped compartments. When the GBS 10 is in place on a seabed 230, as shown in
FIG. 15,
the skirt structure 300 can embed into the soil and enclose the chambers 310
between the soil,
the skirt structure 300, and the lower surface of the base section 12.
[088] The GBS 10 can further comprise a piping system, such as is shown in
FIG. 15, that
includes main pipes 304 positioned in this example above the base plate 302
and within the
base portions 12. The main pipes can be coupled to water and/or air pumps and
downwardly
extending branch pipes 306 that extend from the main pipes 304, through the
base plate 302,
and into the compartments 310. In some embodiments, at least one branch pipe
306 can
extend into each of the compartments 310 (as shown in FIG. 14), and in some
embodiments,
two or more branch pipes can extend into each compartment 310 (as shown in
FIG. 15). The
branch pipes 306 can comprise one or more outlets 308, such as nozzles, that
can be
positioned below the base plate 302. One or more of the outlets 308 can be
positioned below
the soil level and/or one or more outlets 308 can be positioned above the soil
level. Seawater
and/or air can be conducted through the outlets 308, branch pipes 306, and
main pipes 306 to
disturb the soil 230 and/or to manipulate the pressure in the compartments 310
between the soil
230 and the base plate 302. The main pipes 304 can be configured in a loop or
ring
configuration for coupling plural branch pipes together.
[089] In one example, as shown in FIG. 14, the branch pipes 306 can be
clustered at adjacent
corners of the compartments 310, such that the piping systems are simplified
within the base
structures 12. In other embodiments, the branch pipes 306 can be arranged in
other manners.
[090] Prior to lift-off of the GBS 10 from the seabed, air and/or water can be
expelled from the
outlets 308 to help release the skirt structure 300 and base sections 12 from
the seabed 230.
Pressurized air and/or water can break the soil apart and help detach chunks
of the soil that
remain attached to the skirt structure during lift-off. Furthermore, the
expelled air and/or water
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CA 02785142 2012-08-08
can increase the pressure in the compartments 310 to help break suction with
the seabed and
reduce friction between the skirt structure and the soil during lift-off.
[091] During set-down of the GBS 10 onto the seabed, air and/or water can also
be expelled
from the outlets 308 to pre-condition the seabed, such as by leveling the soil
and/or loosening
the soil so the skirt structure 300 can more easily embed into or rest upon
the seabed. In
addition, during set-down, water can be extracted from the compartments 310
through the
outlets/inlets 308. Extracted water can be stored inside chambers of the GBS
and/or can be
expelled to other parts of the sea. Extracting water from the compartments 310
during set-down
can reduce potential high-pressure build up in the compartments as the skirt
structure 300 sinks
into the seabed and the volume of the compartments decreases. In some
embodiments,
different openings 308 can be used for extraction versus expulsion. Different
down pipe
structures can also be used.
General Considerations
[092] For purposes of this description, certain aspects, advantages, and novel
features of the
embodiments of this disclosure are described herein. The disclosed
apparatuses, systems, and
methods should not be construed as limiting in any way. Instead, the present
disclosure is
directed toward all novel and nonobvious features and aspects of the various
disclosed
embodiments, alone and in various combinations and sub-combinations with one
another. The
disclosed embodiments are not limited to any specific aspect or feature or
combination thereof,
nor do the disclosed embodiments require that any one or more specific
advantages be present
or problems be solved.
[093] Although the operations of some of the disclosed methods are described
in a particular,
sequential order for convenient presentation, it should be understood that
this manner of
description encompasses rearrangement, unless a particular ordering is
required by specific
language. For example, operations described sequentially may in some cases be
rearranged or
performed concurrently. Moreover, for the sake of simplicity, the attached
figures may not show
the various ways in which the disclosed methods can be used in conjunction
with other
methods. Additionally, the description sometimes uses terms like "determine"
and "provide" to
describe the disclosed methods. These terms are high-level abstractions of the
actual
operations that are performed. The actual operations that correspond to these
terms may vary
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CA 02785142 2012-08-08
depending on the particular implementation and are readily discernible by one
of ordinary skill in
the art.
[094] As used herein, the terms "a", "an" and "at least one" encompass one or
more of the
specified element. That is, if two of a particular element are present, one of
these elements is
also present and thus "an" element is present. The terms "a plurality of" and
"plural" mean two
or more of the specified element.
[095] As used herein, the term "and/or' used between the last two of a list of
elements means
any one or more of the listed elements. For example, the phrase "A, B, and/or
C" means "A,"
"B," "C," "A and B," "A and C," "B and C" or "A, B and C."
[096] As used herein, the term "coupled" generally means mechanically,
chemically,
magnetically or otherwise physically coupled or linked and does not exclude
the presence of
intermediate elements between the coupled items, unless otherwise described
herein.
[097] In view of the many possible embodiments to which the principles of the
disclosed
invention may be applied, it should be recognized that the illustrated
embodiments are only
desirable examples and should not be taken as limiting the scope of the
disclosure. Rather, the
scope of the disclosure is defined by the following claims. We therefore claim
as our invention
all that comes within the scope of these claims.
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