Note: Descriptions are shown in the official language in which they were submitted.
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ICE WORTHY JACK-UP DRILLING UNIT WITH CONICAL PILED
MONOPOD AND SOCKETS
FIELD OF THE INVENTION
[0001] This invention relates to mobile offshore drilling units, often
called "jack-up"
drilling units or rigs that are used in shallow water, typically less than 400
feet, for
drilling for hydrocarbons.
BACKGROUND OF THE INVENTION
[0002] In the never-ending search for hydrocarbons, many oil and gas
reservoirs have
been discovered over the last one hundred and fifty years. Many technologies
have been
developed to find new reservoirs and resources and most areas of the world
have been
scoured looking for new discoveries. Few expect that any large, undiscovered
resources
remain to be found near populated areas and in places that would be easily
accessed.
Instead, new large reserves are being found in more challenging and difficult
to reach
areas.
[0003] One promising area is in the offshore Arctic. However, the Arctic is
remote
and cold where ice on the water creates considerable challenges for
prospecting for and
producing hydrocarbons. Over the years, it has generally been regarded that
six
unprofitable wells must be drilled for every profitable well. If this is
actually true, one
must hope that the unprofitable wells will not be expensive to drill. However,
in the
Arctic, little, if anything, is inexpensive.
[0004] Currently, in the shallow waters of cold weather places like the
Arctic, a
jack-up or mobile offshore drilling unit (MODU) can be used for about 45-90
days in the
short, open-water summer season. Predicting when the drilling season starts
and ends is a
game of chance and many efforts are undertaken to determine when the jack-up
may be
safely towed to the drilling location and drilling may be started. Once
started, there is
considerable urgency to complete the well to avoid having to disconnect and
retreat in the
event of ice incursion before the well is complete. Even during the few weeks
of open
water, ice floes present a significant hazard to jack-up drilling rigs where
the drilling rig
is on location and legs of the jack-up drilling rig are exposed and quite
vulnerable to
damage.
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[0005] Jack-up rigs are mobile, self-elevating, offshore drilling and
workover
platforms equipped with legs that are arranged to be lowered to the sea floor
and then to
lift the hull out of the water. Jack-up rigs typically include the drilling
and/or workover
equipment, leg-jacking system, crew quarters, loading and unloading
facilities, storage
areas for bulk and liquid materials, helicopter landing deck and other related
facilities and
equipment.
[0006] A jack-up rig is designed to be towed to the drilling site and
jacked-up out of
the water so that the wave action of the sea only impacts the legs which have
a fairly
small cross section and thus allows the wave action to pass by without
imparting
significant movement to the jack-up rig. However, the legs of a jack-up
provide little
defense against ice floe collisions and an ice floe of any notable size is
capable of causing
structural damage to one or more legs and/or pushing the rig off location. If
this type of
event were to happen before the drilling operations were suspended and
suitable secure
and abandon had been completed, a hydrocarbon leak would possibly occur. Even
a
small risk of such a leak is completely unacceptable in the oil and gas
industry, to the
regulators and to the public.
[0007] Thus, once it is determined that a potentially profitable well has
been drilled
during this short season, a very large, gravity based production system, or
similar
structure may be brought in and set on the sea floor for the long process of
drilling and
producing the hydrocarbons. These gravity based structures are very large and
very
expensive, but are built to withstand the ice forces year around. Any
opportunity to
safely reduce development costs in the Arctic can save very substantial
amounts of
money.
BRIEF SUMMARY OF THE DISCLOSURE
[0008] The invention more particularly relates to a system including an ice
worthy
jack-up rig for drilling for hydrocarbons in potential ice conditions in
offshore areas
including a flotation hull having a relatively flat deck at the upper portion
thereof. The
flotation hull further includes an ice bending shape along the lower portion
thereof and
extending downwardly and inwardly around the periphery of the hull where the
ice
bending shape extends from an area of the hull near the level of the deck and
extends
downwardly near the bottom of the hull. An ice deflecting portion is arranged
to extend
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around the perimeter of the bottom of the hull to direct ice around the hull
and not under
the hull. At least three legs are positioned within the perimeter of the
bottom of the
flotation hull wherein the legs are arranged to be lifted up off the seafloor
so that the rig
may be towed through shallow water and also extend to the sea floor and extend
further
to lift the hull partially or fully out of the water. A jack-up device is
associated with each
leg to both lift the leg from the sea bottom so that the ice worthy jack up
rig may float by
the buoyancy of the hull and push the legs down to the seafloor and push the
hull
partially up and out of the water when ice floes threaten the rig and fully
out of the water
when ice is not present. The system further includes a conical piled monopod
having a
body with a base at the bottom and a top deck at the top wherein the base is
attached to
pilings that are driven into the seafloor when the conical piled monopod
structure is
installed for use. The body of the conical pile monopod includes an inclined
ice engaging
surface around the body extending from a wider lower region to a narrower
upper region
where the lower region is below the sea surface and the upper region is above
the sea
surface. The conical piled monopod further includes tabs with sockets arranged
to
receive a foot on at least one of the legs to be attached and held in place
for drilling
through the conical piled monopod. The rig is arranged to work with the
conical piled
monopod by lifting its hull out of the water and extend over the conical piled
monopod to
drill down through the conical piled monopod, lower itself into the water to
assume an ice
defensive position such that ice would contact the ice bending shape of the
rig when thin
ice is present, and be moved away when thick ice is present.
[0009] The
invention further relates to a method for drilling wells in ice prone waters.
The method includes providing a conical piled monopod having a body with a
base at the
bottom and a top deck at the top and an inclined ice engaging surface around
the body
extending from a wider lower region to a narrower upper region where the lower
region
is below the sea surface and the upper region is above the sea surface wherein
the conical
piled monopod includes at least one tab with a socket for receiving and
holding a foot of
a jack-up drilling rig. Pilings are driven into the seafloor and attaching the
pilings to the
conical piled monopod to fix the conical piled monopod to the sea floor. A rig
is
provided have flotation hull and a relatively flat deck at the upper portion
thereof and an
ice bending shape along the lower portion thereof where the ice bending shape
extends
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from an area of the hull near the level of the deck and extends downwardly
near the
bottom of the hull. An ice deflecting portion is provided to extend around the
perimeter
of the bottom of the hull to direct ice around the hull and not under the
hull. At least
three legs are positioned within the perimeter of the bottom of the hull. Each
leg is
jacked down in a manner that at least one foot on the bottom of one of the
legs engages
the socket on the tab of the conical piled monopod and the remaining feet
engage the sea
floor or another socket on a tab and lifts the hull up and fully out of the
water when ice is
not threatening the rig while the rig is drilling a well on a drill site. The
hull is further
lowered into the water into an ice defensive configuration so that the ice
bending shape
extends above and below the sea surface to bend ice that comes against the rig
to cause
the ice to submerge under the water and endure bending forces that break the
ice where
the ice flows past the rig. A well is drilled from the rig over the side of
the deck and
down through the conical piled monopod.
BRIEF DESCRIPTION OF THE DRAWINGS
100101 A more complete understanding of the present invention and benefits
thereof
may be acquired by referring to the follow description taken in conjunction
with the
accompanying drawings in which:
[0011] Figure 1 is an elevation view of the present invention where the
drilling rig is
floating in the water and available to be towed to a well drilling site;
[0012] Figure 2 is an elevation view of the present invention where the
drilling rig is
jacked up out of the water;
[0013] Figure 3 is an elevation view of the first embodiment of the present
invention
where the drilling rig is partially lowered into the ice/water interface, but
still supported
by its legs, in a defensive configuration for drilling during potential ice
conditions;
[0014] Figure 4 is an enlarged fragmentary elevation view showing one end
of the
first embodiment of the present invention in the Figure 3 configuration with
ice moving
against the rig;
[0015] Figure 5 is an elevation view showing the drilling rig moving to a
conical
piled monopod for drilling down through the conical piled monopod;
[0016] Figure 6 is an elevation view showing the drilling rig arranged over
the
conical piled monopod to drill down through the conical piled monopod;
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[0017] Figure 7 is an elevation view showing the drilling rig arranged
adjacent to the
conical piled monopod in it ice defensive configuration; and
[0018] Figure 8 is a top view showing the drilling rig positioned to drill
down
through the conical piled monopod.
DETAILED DESCRIPTION
[0019] Turning now to the detailed description of the preferred arrangement
or
arrangements of the present invention, it should be understood that the
inventive features
and concepts may be manifested in other arrangements and that the scope of the
invention
is not limited to the embodiments described or illustrated. The scope of the
invention is
intended only to be limited by the scope of the claims that follow.
[0020] As shown in Figure 1, an ice worthy jack-up rig is generally
indicated by the
arrow 10. In Figure 1, jack-up rig 10 is shown with its hull 20 floating in
the sea and legs
25 in a lifted arrangement where much of the length of the legs 25 extend
above the deck
21 of the hull 20. On the deck 21 is derrick 30 mounted to drilling cantilever
24 and with
other conventional equipment and systems, facilitate the drill of wells. In
the
configuration shown in Figure 1, the jack-up rig 10 may be towed from one
drilling site
to another and to and from shore bases for maintenance and other shore
service.
[0021] When the jack-up rig 10 is towed to a drilling site in generally
shallow water,
the legs 25 are lowered through the openings 27 in hull 20 until the feet 26
at the bottom
ends of the legs 25 engage the seafloor 15 as shown in Figure 2. In a
preferred
embodiment, the feet 26 are connected to spud cans 28 to secure the rig 10 to
the
seafloor. Once the feet 26 engage the seafloor 15, jacking rigs within
openings 27 push
the legs 25 down and therefore, the hull 20 is lifted out of the water. With
the hull 20
fully jacked-up and out of the water, any wave action and heavy seas more
easily break
past the legs 25 as compared to the effect of waves against a large buoyant
object like the
hull 20.
[0022] When ice begins to form on the sea surface 12, the risk of an ice
floe
contacting and damaging the legs 25 or simply bulldozing the jack-up rig 10
off the
drilling site becomes a significant concern for conventional jack-up rigs and
such rigs are
typically removed from drill sites by the end of the open water season. The
ice-worthy
jack-up drilling rig 10 of the present invention is designed to resist ice
floes by assuming
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an ice defensive, hull-in-water configuration as shown in Figure 3. In Figure
3, ice tends
to dampen waves and rough seas, so the sea surface 12 appears less
threatening, however,
the hazards of the marine environment have only altered, and not lessened.
[0023] When the ice-worthy jack-up rig 10 assumes its ice defensive, hull-
in-water
configuration, the hull 20 is lowered into the water to contact same, but not
to the extent
that the hull 20 would begin to float. A significant portion of the weight of
the rig 10
preferably remains on the legs 25 to hold the position of the rig 10 on the
drill site against
any pressure an ice flow might bring. The rig 10 is lowered so that inwardly
sloped,
ice-bending surface 41, as best seen in Figure 4 bridges the sea surface 12 to
engage any
floating ice that may come upon the rig 10.
[0024] The sloped ice-bending surface 41 runs from shoulder 42, which is at
the edge
of the deck 26, down to neckline 44. Ice deflector 45 extends downward from
neckline
44. Thus, when an ice floe, such as shown at 51 comes to the rig 10, the ice-
bending
surface 41 causes the leading edge of the ice floe 51 to submerge under the
sea surface 12
and apply a significant bending force that breaks large ice floes into
smaller, less
damaging, less hazardous bits of ice. For example, it is conceivable that an
ice floe being
hundreds of feet and maybe miles across could come toward the rig 10. If the
ice floe is
broken into bits that are less than twenty feet in the longest dimension, such
bits are able
to pass around the rig 10 with much less concern.
[0025] In Figure 5, a conical piled monopod, generally indicated by the
numeral 60,
has been pre-installed to the seafloor. The conical piled monopod 60 is a
structure that
may be used in ice-prone, offshore locations at much lower cost as compared to
a
conventional gravity based structure (GBS). A conical piled monopod 60
includes a
body 65, a base 67 and a top deck 70. The base 67 preferably has the form of a
flange
with holes or perforations spaced around the perimeter of the conical piled
monopod 60.
The base 67 is arranged to rest on the seafloor 15. While the conical piled
monopod 60
rests on the seafloor, the weight of the conical piled monopod is preferably
carried by a
plurality of pilings 68 that are driven deep into the seafloor 15 and then
attached to the
conical piled monopod 60. It is typical to drive the pilings 68 between about
35 and
about 75 meters into the seabed to permanently fix the conical piled monopod
60 in its
offshore location. The pilings 68 are typically strong, but hollow tubes or
pipe like
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structures that act like long nails and provide a very structurally efficient
arrangement for
a permanent platform for offshore hydrocarbon drilling and production
operations. The
pilings have a relatively large diameter of between 1 and 3 meters with a wall
thickness
of about 2 to 10 cm. One particular advantage of the present invention is that
with the
weight of the conical piled monopod 60 supported by the pilings 68, little or
no seabed
preparation is necessary prior to installation and to the extent there is any
seabed
preparation, it is principally to create a level seafloor to set the conical
piled monopod 60
onto as the pilings 68 are installed. A seabed comprising soft, muddy
materials is not
likely to be excavated and replaced with firmer materials.
[0026] With the conical piled monopod 60 supported by the pilings 68,
preparation of
the seafloor for installation of the conical piled monopod 60 is minimal or
none. Once
the pilings 68 are driven into the seafloor and firmly attached to the base
67, the pilings
68 provide resistance to: (a) forces that cause structures to slide along the
seafloor, (b)
forces that cause structures to overturn such as forces acting several meters
above the
base of a structure; and (c) forces that cause vertical movement both upwardly
and
downwardly. The resistance to both upward and downward motion or movement is
important in resisting toppling forces that may be imposed by ice. The pilings
68 at the
front side of the conical piled monopod 60 resist lifting forces that ice may
impose on the
upstream side to resist toppling over while the pilings 68 at the far side or
back side or
downstream side of the conical piled monopod 60 resist downward motion that
would
allow the back side to roll deeper into the seafloor 15. Using such long
pilings provides a
structurally efficient base for year around operations in an ice prone
offshore ice
environment that must resist ice loads that can be quite substantial. The
pilings act like
nails that hold the platform in place and are structurally more efficient than
in the case of
a GBS where resistance to overturning is provided only by the size and weight
of the
structure.
[0027] The length and number of the pilings 68 will be dictated by the
magnitude of
the predicted vertical and lateral forces and by the strength of the soil
layers into which
the pilings are driven. Preferably, the pilings are strategically arranged
around the
periphery of the base 67 to provide resistance to sliding and toppling forces
with
maximum structural efficiency. The base may include at least eight and
preferably at
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least 16 pilings, and up to as many as 64 pilings, around the periphery at a
spacing that
would maximize structural efficiency and create a pile cluster where the
number of
clusters work together to resist lateral forces and support the conical piled
monopod 60.
The pilings 68 typically extend between 35 and 75 meters into the seabed
depending on
predicted loads and the strength characteristics of the soil. The conical
piled monopod 60
is shown as an eight sided faceted structure but a round or circular
configuration may also
be employed. It is preferred that the structure be faceted for ease of
fabrication having
six, eight, or even 12 sides, preferably all being equal in dimension and
where the conical
piled monopod 60 is symmetrical.
100281 The body 65 of the conical piled monopod 60 includes a sloped, ice-
engaging
surface 72 that extends from below the sea surface 12 to above the sea surface
12 such
that ice in the sea, particularly floating ice, engages the body 65 at the
sloped,
ice-engaging surface 72. The ice-engaging surface 72 extends around the
periphery of
the conical piled monopod 60 so that ice from any direction will come into
contact with
the body 65 at the ice-engaging surface 72. The slope of the ice-engaging
surface 72
causes any sheet of ice to rise up the slope and bend to a point of breaking
and is
typically between 40 degrees and 60 degrees from the horizontal and more
preferably
about 55 degrees from the horizontal. Broken ice chunks, called rubble, will
work their
way around the body 65, driven by the sea current or wind. Above the ice-
engaging
surface 72 the conical piled monopod includes a shape to turn away ice that
pushes all the
way up ice-engaging surface 72. A deck 70 is at the top of the conical piled
monopod 60
may be equipped with a drilling template for drilling many wells.
100291 The conical piled monopod 60 is a substantial structure typically
having a
dimension of deck 70 being more than 75 meters across. While being large and
strong,
one advantage of a conical piled monopod over a gravity based structure is
that it is
generally lighter in weight or more particularly, density, prior to any water
ballasting.
Solid ballast material is generally not needed for a conical piled monopod.
While a
gravity based structure (GBS) typically has a density of from 0.21 tonnes/m3
to 0.25
tonnes/m3, a conical piled monopod may be constructed to be 0.20 tonnes/m3
down to
about 0.18 tonnes/m3. Often, a GBS would need solid ballast to increase its
weight to
provide resistance to sliding and overturning. By using piles or a cluster of
pilings 68,
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the conical piled monopod 60 may be designed to be in lighter weight. The
lighter
density of a conical piled monopod may also translate into lower fabrication
and
transportation cost, not including the lower installation cost due to the
avoided site
preparation costs for preparing the seafloor for a large GBS system and for
the high
density ballast material often added to a GBS.
[0030] While
conical piled monopods 60 may be equipped with a derrick and systems
for drilling wells, there is a cost savings if the wells can be drilled by a
jack-up rig as the
conical piled monopod may be sized somewhat smaller and of course having cost
savings
on size alone, not to mention the cost savings for all the drilling related
equipment and
systems. Drilling well through the conical piled monopod with an ice worthy
drilling rig
such as rig 10 provides additional cost savings in that the rig does not
necessarily have to
be towed away at the first sign of ice. More wells may be drilled per year
with an ice
worthy rig 10 that can stay on station longer into the fall when other drill
rigs are long
gone.
[0031] With
the conical piled monopod 60 fixed to the sea floor 15, the drilling rig 10
moves in as shown in Figure 5 and sets up to drill down through the conical
piled
monopod 60 as shown in Figure 6. In one particular aspect of the present
invention are
tabs 75 extending out from base 67 that include pilings 68 to be secured to
the seafloor
15. Spud cans 28 closest to the conical piled monopod 60 are aligned to set
into sockets
on the top of the tabs 75 and held in place by clasps 78. Thus, the rig 10 is
provided
additional resistance to movement by ice pressure by attaching to the conical
piled
monopod. This arrangement has been described as an "Ahab Socket" referring to
the
captain in Moby Dick inserting his peg leg into a knothole in the boat to
stabilize himself
while hunting whales.
[0032] Once
secured into the sockets, the legs 25 of the ice-worthy drilling rig 10,
which will be constructed stronger than conventional legs for jack-up rigs
will be able to
withstand limited ice threats. However, in the event that more significant ice
threats
present themselves, the ice-worthy drilling rig 10 has the option to stay on
location,
suspend drilling operations and assume an ice defensive configuration as shown
in Figure
7. In this position, ice that comes into contact with either or both of the
rig 10 and
conical piled monopod 60 will be broken up and directed to pass around the
system.
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When the ice is abated, drilling may resume and when the ice becomes too
thick, the rig
may be fully removed from the location until the following drilling season. It
is the
shape of the hull 20 (as well as its strength) that provides ice bending and
breaking
capabilities and expands the time window for drilling that substantially
lowers costs for
ice prone locations. While it is preferred that the rig 10 sets up adjacent
one of the facets
of the conical piled monopod as shown in Figure 8, but may approach from any
direction
as indicated by 20A.
[0033] The
hull 20 preferably has a faceted or multisided shape that provides the
advantages of a circular or oval shape, and may be less expensive to
construct. The
plates that make up the hull would likely be formed of flat sheets and so that
the entire
structure comprises segments of flat material such as steel would likely
require less
complication. The ice-breaking surface would preferably extend at least about
five
meters above the water level, recognizing that water levels shift up and down
with tides
and storms and perhaps other influences. The
height above the water level
accommodates ice floes that are quite thick or having ridges that extend well
above the
sea surface 12, but since the height of the shoulder 42 is well above the sea
surface 12,
the tall ice floes will be forced down as they come into contact with the rig
10. At the
same time, the deck 21 at the top of the hull 20 should be far enough above
the water line
so that waves are not able to wash across the deck. As such, the deck 25 is
preferred to
be at least 7 to 8 meters above the sea surface 12. Conversely, the neckline
42 is
preferred to be at least 4 to 8 meters below the sea surface 12 to adequately
bend the ice
floes to break them up into more harmless bits. Thus, the hull 20 is
preferably in the
range of 5-16 meters in height from the flat of bottom to the deck 20, more
preferably
8-16 meters or 11-16 meters.
[0034] It
should also be noted that the legs 25 and the openings 27 through which
they are connected to the hull 20 are within the perimeter of the ice
deflector 45 so that
the ice floes are less likely to contact the legs while the rig 10 is in its
defensive ice
condition configuration as shown in Figure 3 and sometimes called hull-in-
water
configuration. Moreover, the rig 10 does not have to handle every ice floe
threat to
significantly add value to oil and gas companies. If rig 10 can extend the
drilling season
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by as little as a month, that would be a fifty percent improvement in some ice
prone areas
and therefore provide a very real cost saving benefit to the industry.
[0035] In closing, it should be noted that the discussion of any reference
is not an
admission that it is prior art to the present invention, especially any
reference that may
have a publication date after the priority date of this application. At the
same time, each
and every claim below is hereby incorporated into this detailed description or
specification as an additional embodiment of the present invention.
[0036] The scope of the claims should not be limited by the preferred
embodiments set forth
in the examples, but should be given the broadest interpretation consistent
with the Description
as a whole.
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