Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to improvements in the drilling of oil
and gas wells in polar regions. More particularly, it relates to
improved techniques for effectuating such drilling in the wintertime in
the Arctic Ocean and more especially in the Beaufort Sea, although it is
feasible for application in other areas where similar conditions exist.
Still more particularly, it relates to a method and apparatus for provid-
ing an ice-free zone around a drillship to enable such wintertime
drilling.
At the present time drilling in offshore Arctic regions is
carried out in the summertime either by the use of drillship anchored
at a drill site where the risk of impingement by ice floes is minimal,
or through the use of artificial islands. Summertime drilling is
feasible for depths from 60 to 200 feet or more. Artificial islands
currently being used in the shallow water regions of the Beaufort Sea
become excessively expensive in water depths of 40 feet or greater. It
appears uneconomical at the present t:Lme to build artificial islands for
exploratory drilling wells in water depths exceeding 40 feet. It may be
economical to drill production wells from artificial platforms in water
depths exceeding 40 feet. Moreover, :Lt is presentLy not feasible to
drill exploratory wells from floating ice islands in the regions where
ice movement is too great (i.e., more than few feet).
One of the chief obstacles to overcome in drilling in Arctic
regions is the Arctic pack ice. The ice grows to a thickness of approxi-
mately 6 feet and is laced with pressure ridges and ice islands which can
reach thicknesses of over 100 feet. The pack ice moves at speeds from
0 to 20 or more miles per day with an average movement of approximately
2 miles per day.
If drilling were to take place in waters where there was con-
siderable ice movement, a very solid structure would be required in order
to withstand the forces exerted upon it by the ice pack and yet to be
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able to remain on position in order to drill a well. For exploratory
drilling operations, a solid bottom founded structure should be provided
which could resist the movement of the ice pack and yet would be mobile
enough to be transported from one exploratory drilling site to another.
Drilling with structures on the sea bottom has numerous prob-
lems. Firstly, there is the problem of designing hulls whic~ could with-
stand tne ice forces from deep ice keels against these structures. In
the second place, subsea systems would have problems of buoyancy, life-
support systems, power supply, and access for crews and maintenance.
It woula, therefore, be desirable to develop another technique
that would a~low exploratory drilling during winter months. Such system
should also be able to extend operational capability into the shorefast
ice. This technique has the potential for drilling wells more economi-
cally than any other method in the shorefast ice regions. Using the
technique, the rate of exploration in the Beaufort Sea would be increased
by a factor of from two to four times. This technology of using drill-
ships in shorefast ice could be applied to other regions of the Canadian
Arctic. The techniques used for drilling in shorefast ice are a logical
step toward developing year-round drilling systems in pack ice regions.
The development of such technology is important since the risks
to the environment of a drilling system in the shorefast ice are rela-
tively low. One advantage of operating in shorefast ice is that the
ice moves very little throughout the winter. Any oil spilled underneath
the ice would be confined to a very small area where it could be removed
from the environment.
The initial problem which the present invention proposes to
overcome is the maintenance of a substantially ice-free area around the
drillship, and in particular, an ice-free area around a drillship opera-
ting in shorefast ice zones during winter.
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An object of a principal aspect of the present invention
is to provide an apparatus for maintaining a substantially ice-
free area around a drillship out to at least 100 feet from the
vessel, including the combination of a set of floating barges
around the perimeter of the ship.
An object of yet another aspect of the present invention
is to provide an apparatus which is simple to construct and may
be easily deployed.
This inventioA in its broadest aspects provides an appar-
atus for providing a substantially ice-free ~one around a vessel
out to 100 feet or more, comprising, in combination with the ves-
sel:
~a) a plurality of floating modules disposed
around, and each connected at one end to,
said vessel;
~b) a continuous, downwardly depending skirt
extending completely around the outer per-
iphery of said plural:Lty of floating mod-
ules;
20 and (c) an air/water heat exchanger in each of a
selected plurality of said floating mod-
ules.
; By one variant of the apparatus of an aspect of this
invention, the plurality of floating modules comprises a series
of alternating floating barges interconnected by roof modules.
By another variant, each floating module comprises a
floating barge provided with an air/water heat exchanger.
By another variant of this apparatus, each floating
module comprises a fLoating barge including a floating barge
section and a cantilevered canopy section.
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By a further variant, each floating module comprises
a floating barge provided with an air/water heat exchanger and
also with a cantilevered canopy section.
In the accompanying drawings,
Figure 1 is a perspective of an embodiment of an ~apparatus
of one aspect of the present invention;
Figure 2 is a partial top view of an embodiment of an
apparatus of an aspect of thè present invention;
- Figure 3 is a section through line III-III of Figure 2; and
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Figure 4 is a side view of the transportation system for
deploying the barges used in the apparatus of an aspect of the present
invention.
Referring to Figure 1, a drillship 10 is shown, the drillship
being generally of the type used in offshore drilling operations and
particularly in Arctic zones. When operating in this environment, there
is a severe hazard associated with the effect of ice encroaching on the
drillship itself and consequently, the invention disclosed and claimed in
copending Canadian application Serial No. 294,056 filed December 29, 1977,
provided an ice-free zone close to the drillship. Another manner of main-
taining such substantially ice-free zone around the drillship involves
the deployment of such canopy system of an aspect of this invention about
the perimeter of the drillship, as shown in Figure 1.
As seen in Figure 1, the canopy system 20 includes floating
modules 30 and roof modules 40, as well as membrane 50 which covers the
non-linear areas in close proximity with the drillship 10 and within the
periphery of the canopy system not covered by floating modules 30 and
roof modules 40. Floating modules 30 and roof modules 40 are provided
with flexible downwardly depending skirts 35 and 45s respectively, which
: 20 extend downwardly from the outer edge of floating module 30 and roof
module 40 to slightly below the water surface 60.
As seen in Figures 2 and 3, floating modules 30 comprise a
: floating barge section 32 and a cantilever section 33. Skirt 35 depends
from the outboard end of cantilever section 33 to slightly below the
water surface 60, thereby forming an air compartment 36 below the canti-
lever section 33.
Barge section 32 is provided with a forced air heating system
70 which makes use of heat, partially the waste thermal energy from the
drillship 10. Warm waste water pipe 37 from the drillship 10 is connected
to the warm water input of an indirect contact heat exchanger 39, and the
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thus cooled water returns to the drillship lO via return line 38. The
heating system 70 is provided with the use of suitable fans and ducts
(not shown) in order to distribute hot air in a manner and quantity suffi-
cient to prevent formation of ice under tlle canopy system.
Disposed between each floating module 30 and connected therein
is a roof module 40. The warm air from the forced air heating system 70
is circulated through the floating barge section 32, then through canti-
lever section 33 and thence into the roof module 40 and back again to the
heating system 70.
A stream of warm air is injected into the skirt 35 to keep the
skirt free of ice. This method and structure is disclosed and claimed
in copending Canadian application Serial No. 305,628 filed June 16, 1978.
While Figure 1 shows the barge system already deployed, it is
nevertheless necessary to transport the barge system easily from one
location to another, as the drillship 10 is shifted from one drilling
; site to another. Figure 4 shows an embodiment of the present invention
for transporting and relocating the barge modules. Special carrier
barge 80 is used to support the barge modules in a stacked formation.
Once at the site, the modules are moved from the carrier barge 80 by
means of a ship's crane. An appropriate spreader system is used to dis-
tribu~e and support the modules. Pre-assembled roof modules are simi-
larly put in place. Deployment of the pre-assembled barge and roof
modules once they arrive on site is carried out expeditiously. Activa-
tion of the heating system involves only connection of two flexible hoses
and a power supply to each of the barge modules.
Disconnection of the barge system can be carried out, for
example, within a few hours. It requires hose and power, mooring line,
and membrane cover (over the cap between barge and ship) disconnection.
If the ship changes location, the barges can either be towed in a train
or restacked on the carrier barge and transported.
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To summarize, the present invention provides a method and
apparatus of maintaining a substantially ice-free zone around a drillship,
consisting of the set of floating barges deployed around the perimeter
of the ship, spaced one barge width apart with an intermodular roof con-
necting the barges. The entire perimeter of the system is enclosed with
a flexible skirt which permits ice movement underneath while sealing the
heat within into the system. A forced air heating system is integrated
into the barge modules to distribute air at least partially heated by
the drillship waste heat, in a manner and quantity sufficient to prevent
ice formation under the barge hulls and roofs.
Once deployed, the barge system operates virtually automatical-
ly. The barge system is thermostatically controlled for optimal heat
distribution. Snow clearing and temperature and ice movement monitoring
are the only operating functions apart from regular inspections and
maintenance required for barge system operation.
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