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OCR for page 245
17.
Arctic Offshore Technology and
Its Relevance to the Antarctic
K. R. Croasdale
INTRODUCTION
In considering the issue of potential antarctic oil and
gas resources, especially offshore, it is perhaps relevant
to look to the Arctic for an analog of what might be
possible. This chapter will provide a briefing on the
technology being used and/or developed for Arctic
offshore oil and gas operations. For our purposes, the
Arctic will be defined as northern offshore areas subject
to major ice coverage. Therefore, the Canadian east
coast, with its iceberg problems, is also included. My
major focus will be on operations in Canada, where most
oil and gas activity has taken place. Other nations
bordering on the Arctic, however, also have interests in
Arctic off-shore resources and are developing technology
similar to that which I will describe.
Where appropriate, reference will be made to the
similarities and contrasts between the Arctic and the
Antarctic. The chapter will conclude with some specific
comments on the possible adaptation of Arctic offshore
technology to the Antarctic.
GEOGRAPHY AND OIL AND GAS RESOURCES
The Arctic consists mainly of a large ocean surrounded by
land that is divided here and there by straits, channels,
and small seas. The Arctic Ocean can be considered a
polar Mediterranean--an inland sea with very little com-
munication, except through the Fram Strait, with the
other oceans of the world.
It is a hostile region, but because of the populated,
surrounding land masses, human presence around the
245
OCR for page 246
246
fringes of the Arctic Ocean has existed for at least
40,000 years. Only during the past three centuries,
however, have Europeans endeavored to explore and exploit
the region. Early ventures used wooden sailing ships and
were conducted either for whaling or for exploration,
especially in the search for a northwest passage to Asia.
Arctic technology used before about 1900 was not really
adequate; many expeditions spent years at a time trapped
by ice in the Arctic, and many of the explorers perished.
Today, the major incentive for Arctic operations is
the exploitation of minerals, primarily oil and gas.
During the past 15 years or so, the Canadian oil industry,
encouraged by government incentives and the prospect of
large discoveries, has been very active in exploring
Canada's Arctic and offshore areas. Although no produc-
tion has yet occurred from Canada's offshore Arctic,
several promising discoveries have been made:
.
· gas and oil in the Beaufort;
· gas and some oil in the High Arctic (Arctic
Islands);
· gas off Labrador;'and
oil off Newfoundland.
Furthermore, there is the promise of large oil and gas
reserves yet undiscovered. Canadian government sources
predict mean potential recoverable reserves of oil for
the Canadian Beaufort of about 8.5 billion barrels; for
the Arctic Islands, about 4.3 billion barrels; and for
the Canadian east coast, about 12 billion barrels. On
the Alaskan continental shelf, a mean value for potential
recoverable reserves is about 818 billion. This, plus
the desirability of North American self-sufficiency in
energy, is the incentive that has led the major oil
companies and governments actively to pursue the
exploitation of Arctic oil and gas (despite its high cost
relative to oil and gas operations in more temperate
regions). Of course, the high cost of Arctic oil and gas
operations is mainly a function of the climate, the
remoteness, and especially the presence of offshore ice
THE ARCTIC OFFSHORE ENVIRONMENT
.
The Arctic Ocean is covered with drifting ice. Only in
the more southerly coastal zones does the ice clear every
summer. The major drift patterns of the Arctic ice are
OCR for page 247
247
shown in Figure 17-1. The Pacific or Beaufort gyral
dominates the ice drift in the North American sector of
the Arctic Ocean, rotating clockwise, completing one
revolution in about 10 years at a rate of several
kilometers per day. It consists mostly of multiyear ice
with an average thickness of about 5 m. Around the edges
of the Arctic Ocean, the ice melts and reforms every
year, creating first-year ice with a maximum thickness of
about 2 m.
Close to shore, out to about 20 m water depth and
between islands, the ice becomes landfast each winter.
The approximate demarcations among the various ice zones
in the winter in the Beaufort Sea are shown in Figure
17-2; this is typical of most of the coastal regions of
the Arctic Ocean.
As depicted in the cross section (Figure 17-3), pres-
sure ridges, both first year and multiyear, can occur in
all the ice zones. The probability of seeing multiyear
ice in the near-shore zones is quite low; in fact, it
usually invades only during those summers when the
permanent polar pack is driven south by onshore winds.
This occurs on average about once every five years.
Pressure ridges, especially multiyear ridges, are the ice
features that create the greatest difficulty for offshore
operations. The movement of multiyear floes and ridges
against offshore platforms causes high lateral loads, and
these also create the most difficult obstacles for ice-
breaking vessels. Multiyear ridges up to about 25 m
thick can occur.
The pressure ridges that ground in the near-shore
zones cause gouging of the seafloor. Numerous gouges
several meters deep have been observed. Any seafloor
facilities, such as pipelines and wellheads, have to be
protected against this ice action. The present approach
is to put such facilities into trenches, so that they are
below the depth of the deepest gouge likely during their
lifetimes.
The open water in the coastal zones does allow floating
operations to be conducted during the short summer season.
In the southern Beaufort Sea, the period of open water
averages about 100 days. This period gets shorter with
increasing distance offshore.
Off Canada's east coast, annual pack ice occurs south
to about 45°N latitude. The open-water period off
Newfoundland can range from about 200 to 365 days per
year. Further north in the Davis Strait, it reduces to
about 100 days.
OCR for page 248
248
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OCR for page 249
249
I 0,
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_ . ,
STATUTE MILES
100 50 0 100 200
:300 400
· ~ ~ __ ~
ARCTIC PACK ICE
; B~/
1 \5~U
A\
MAINLY OLD ICE 3-4 MEtERS THICK MOVING
SLOWLY YEAR ROUND.
SOLID AND UNMOVING
OLD OR FIRST YEAR ICE OR A MIXTURE OF BOTH
COMPLETELY COVER I NO TH E WATERWAY.
MORE THAN 7/8ths
MAINLY FIRST YEAR ICE 1-2 METERS THICK IN
INTERMITTENT RESTRICTED MOTION.
FIGURE 17-2 Typical winter ice conditions in the
Beaufort Sea area (February) (Department of Energy,
Mines, and Resources, 1970) (Reprinted with permission)
\
\
.
OCR for page 250
250
I LANDFAST ICE MOBILE POOR PACK
,. ~ .
BorrOM FLOATING ICE GROUNDED ICE SEASONAL ICE ZONE
FAST ZONE ZONE TRANSITION
FIRST YEAR GROUNDED · ZONE
PRESSURE FIRST
_" ~ MULTI-YEAR FLOES
Ah)
~ ~~ 'I
FIGURE 17-3 Near-shore winter ice conditions
in the Beaufort Sea.
In addition to pack ice, there are many icebergs off
Canada's east coast. The major source of icebergs in the
eastern Arctic is the Greenland ice cap, which annually
calves about 240 km3 of glacier ice into the surrounding
seas. This results in about 20 to 34 thousand icebergs
per year, although on average only about 500 per year
will reach the Grand Banks area off Newfoundland. These
icebergs are much smaller than those in the Antarctic.
There are no icebergs in the Beaufort Sea, but large
pieces of ice shelf ice can occur, which are called ice
islands. Ice islands are calved from a relic Pleistocene
ice shelf that still exists along the north coast of
Ellesmere Island. When calved, the thickness of an ice
island can be greater than 50 m, and ice islands can be
as much as 10 km in extent. However, large ice islands
are so rare (perhaps only one still exists in the Arctic
Ocean) that offshore platforms justifiably need not be
designed for them. The probability of a collision is
extremely low, and ice islands could be detected well
ahead of a collision so that people could be evacuated
and oil wells sealed off below the ocean floor. (A
similar approach is used for hurricanes in the Gulf of
Mexico.)
The water depths of the continental shelves surround-
ing the Arctic Ocean are shallow relative to the Antarc-
tic. In the Arctic the shelf break starts at about 100 m
depth. Most offshore operations to date have been con-
ducted within this water depth (although wells off the
East Coast of Canada have been drilled in water out to
about 1,000 m).
OCR for page 251
251
TECHNOLOGY FOR ARCTIC OFFSHORE PETROLEUM OPERATIONS
General
Potential hydrocarbons have to be drilled into in order
to confirm their presence. So one of the first tasks for
the oil industry in the Beau for t Sea was to consider
various methods of offshore drilling in ice covered
waters. Figure 17-4 was drawn about 10 years ago. It
shows the various concepts being considered at that time.
These ideas range from building artificial islands in
the very shallow waters (which can be used year-round) to
floating drilling in the deeper waters during the ice-
free periods. Also shown are gravity-founded mobile
drilling units, which could be ballasted down onto the
seafloor, and drilling off the landfast ice during the
winter. Active systems using ice cutters in order to
remain on location in moving ice were also proposed.
Some of the systems shown in Figure 17-4 have been put
to use during the past decade, and these will now be
described in the context of main geographic areas.
The Beaufort Sea
Of all the concepts shown, in the Beaufort Sea the
artificial island has been one of the most successful,
especially in water depths out to about 20 m. ESSO
Canada built the first artificial island in 1972. A
typical island in summer conditions is shown in Figure
17-5. To date, well over 20 islands have been built and
PACK ICE
FAST ICE
(YEAR ROUND)
///" //:
GRAVITY CONE
~ OR MONOPOD
GRAVEL ISLANDS
I'd
Hi. .;..; ~ ; . .. , ..; .__
1 , ,
0 2 6 20
WATER DEPTH (m)
~C,, ~
0
— ICE CUTTER —
SEMI
SILT ISLANDS RCRAFT
BARGE
FAST ICE
(WINTER ONLY)
74-='>~
LOCAL ICE
THICKENING
~-
~ ' 1 ' -' ' ' ~
OPEN WATER
DRILLSHIP
DRILL BARGES
-
1 00 700
FIGURE 17-4 Exploratory drilling concepts
for ice infested waters (Croasdale, 1983)
(Reprinted with permission).
OCR for page 252
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OCR for page 253
253
drilled from in the Beaufort (Figure 17-6). This map
also shows locations drilled using ships, which I will
discuss later. Islands constructed in the summer by
dredging have been a favored technique for Canadian
Beaufort exploration in the shallow water. In contrast,
most islands constructed off Alaska have used land
sources of gravel. Islands have proved very adequate in
resisting the ice, but their cost effectiveness decreases
with water depth. In water depths beyond about 20 m the
fill requirements tend to be prohibitive, especially for
in the summer
islands with very shallow slopes. Also, islands are
susceptible to wave erosion during the summer months
particularly during construction. For these reasons
retained islands were conceived both to reduce fill
volumes and to provide immediate wave protection at the
waterline.
One of the first designs for a caisson-retained island
was Esso Canada 's. This consists of a ring of steel
caissons retaining an interior sand fill. The caissons
are placed on a berm, which can be adjusted in size
according to water depth. The Esso retained island has
drilled two exploration walls to ~At" in wager A=~Eh~ ^
to 26 m.
A different design of caisson-retained island was used
—- -,=~ &- A_—_— —~ ~~—~ ~ 11 ~~ ~~ ~C~11= Vim ~
at Tarsiut in about 22 m of water. Here, four concrete
caissons were placed on a berm and filled with sand to
provide the retaining structure for an interior sand
fill. The Tarsiut island also utilized steep dredged
slopes; one in 5 compared with one in 15 on most Esso
islands. The Tarsiut island set a record for drilling at
the very edge of the landfast ice in the winter of
1981/1982 and is shown in Figure 17-7. The island proved
well able to resist the ice forces but had a rather
limited surface area. Another disadvantage of the
retained islands shown so far is the need to Diane
two
~ a land
rig on them after construction. In a short Arctic summer
this can be a problem, and icebreaker support is often
required.
The Gulf Canada Molliqpak was conceived to overcome
this problem by designing it with a rig permanently
mounted on the caisson structure. The caisson has a
hollow core, which is sand filled to provide sliding
resistance. The Molliqpak was constructed in Japan and
is now on location in the Canadian Beaufort, drilling its
first well in 26 m of water.
A similar philosophy of a ready-mounted rig was adopted
with the design of the dome single steel drilling caisson
OCR for page 254
254
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255
.. __
~ ~ _ ~
a: :: :: _
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:Si
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FIGURE 17-7 The Tarsiut Drilling Island in the Beaufort
Sea (Courtesy of Dome Petroleum Ltd.).
(SSDC). This concept was designed for rapid deployment
by water ballasting down onto a prebuilt underwater berm
(at -9 m below seabed).
The main structure of the SSDC is actually the con-
verted for ebody of a very large crude [oil] carrier
specially strengthened to resist the ice loads. It was
designed and brought into the Beaufort ice in less than
nine months. The SSDC also holds the record for the
greatest water-depth drilled by fixed platforms in the
Arctic. This was at Uviluk in 31 m of water, well
outside the landfast ice.
Meanwhile, the U.S. operators have been busy in the
Alaskan Beaufort. Several artificial islands have also
been built there in recent years for exploratory drilling.
This year the Global Marine concrete island drilling
system (CIDS) is drilling its first well for Exxon in 15
m of water. The CIDS is a self-contained caisson system
that relies on water ballast and can, therefore, be
rapidly deployed. Also of significance is that at its
present location no foundation preparation was done; it
was put down directly onto the seafloor. It is also
worth noting that at this location Exxon will be building
a spray-ice barrier to provide additional sliding
resistance against late winter ice. Spray-ice barriers
OCR for page 256
256
and rubble-protected systems may enable exploration
concepts to be used in the future.
In the even deeper Beaufort waters, Dome Petroleum has
pioneered the use of drill ships, which were brought into
the Beaufort in 1976. The drill ships are, of course,
ice strengthened, and when the ice is managed with
icebreakers, drilling can continue into freeze-up.
However, it is not usually possible to drill much beyond
late November or when the ice is about 0.3 m thick. A
late-season drilling situation is depicted in Figure 17-8.
The summer drill ship season is short, hardly long
enough to drill and test one well. For most of the year
the drill ships remain unused in a winter harbor.
To extend the floating drilling season, the Gulf
subsidiary Beaudrill designed and built a round drill
ship, the Kulluk (Figure 17-9). Kulluk is designed to
stay on location with 1.3 m of ice moving against it. It
is held on location with twelve 9 cm mooring lines. Ice
management is provided by two Class 4 icebreakers and two
ice-class supply ships. So far Kulluk has drilled two
discovery wells and apparently has a performance record
that exceeds expectations. Incidentally, Kulluk was
FIGURE 17-8 Late summer drilling in the Beaufort Sea
(Courtesy of Dome Petroleum Ltd.).
OCR for page 257
/
/
/
moo q
- ~
_ 1 1
~ ~-
HULL
TANKS
257
Li me
1 AT
1 ~
Ill
\ - \N
\
a_ DRILL FLOORS
I I T 11 i''j'''''i'''1 ~
_ ll - 44 - . MAIN DECI
ELEVATION (FEET)
~ - ~ 1
HULL
TANKS
1 ~
FIGURE 17-9 Typical cross section of Kulluk, showing
mooring wire routing (Frankovich, 1984) (Reprinted with
permission).
recently approved by the regulatory agency--the Canada
Oil and Gas Lands Administration--as a relief well-
drilling system for the fixed-caisson systems described
earlier. For floating drilling, regulations require that
no drilling into hydrocarbon (or potential hydrocarbon)
zones take place during the last month of the season, in
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258
order that time be available to drill a relief well in
the event of a blowout.
During the decade of Beaufort Sea drilling there have
been no blowouts and (as far as I can judge) no damage to
the environment. However, because of the high logistics
. . .
costs, the special equipment, and the short season of
use, it is not untypical for an exploration well to cost
3100 million.
No commercial fields have yet been found, but many
encouraging finds suggest that oil and gas production
will occur sometime in the next 10 years.
The kinds of Production concepts that have been
considered for ice-covered waters are shown in Figure
17-10. In the near-shore Beaufort Sea it is expected
that artificial islands and/or bottom-founded steel or
concrete structures will be used. Fixed platforms in
ice-covered regions are probably feasible out to 100 m
water depth. Beyond that, some kind of subsea production
technology, which is currently being developed for other
deep-water offshore areas, will likely be needed.
If oil production does occur from the Beaufort Sea,
the oil will be transported to market by either pipeline
or tanker; both alternatives are being studied. On the
U.S. side, the existing Alaskan pipeline will likely be
used for future offshore production. On the Canadian
side, a new pipeline down the Mackenzie Valley would be
required. However, as the reader may be aware, a large-
diameter gas pipeline down the Mackenzie Valley was ruled
out in 1977. At that time, an independent review com-
mission advised the Canadian government that construction
of a large-diameter line would have an adverse effect on
local communities. Since then, however, a small 30 cm
oil line has been built to Normal Wells (halfway down the
valley), and by analogy it could be extended to the
Beaufort by the early 1990s.
.
The alternative, icebreaking tankers, has of course
been under consideration since the late 1960s when the
Manhattan performed trials in the Arctic in 1969. Since
that time, there have been significant advances in ice-
breaker design, motivated by Beaufort Sea exploration.
Some of the small icebreakers designed by Beaufort
operators do incorporate features that could be used on
large icebreaking tankers. It is claimed by their
proponents that icebreaking tankers would be much safer
than conventional tankers. This is because, to combat
the ice, they have to be much stronger and incorporate
significant redundancy. Thus, an icebreaking tanker
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259
TUNNELS
ALL
ICE
ZONES
W I TIN
—PROTECTION A
I— Q —(~ ~) ~ ~
Am, ~ / / / / '7
GRAVITY CONE
OR MONOPOD
ISLANDS
l
/ '/'// / / / / j A-/ _
SUBSEA PRODUCTION
o
l
6 20 100
WATER DEPTH ( m)
7a 0
FIGURE 17-10 Production concepts for ice infested waters
(Croasdale, 1983) (Reprinted with permission).
would have double hulls, twin screws, and twin rudders;
it would also have a much greater power-to-displacement
ratio than conventional tankers.
The other commodity of interest is, of course, natural
gas. From the Beaufort we would see pipelines as the
favored system, either linking with a gas pipeline from
Alaska or being part of a polar gas pipeline bringing gas
from the High Arctic. For the gas from the High Arctic.
liquefied natural gas (LNG) tankers have been considered.
These would ply the Northwest Passage and take gas to
eastern markets or even to Europe. LNG tankers have also
been designed and would contain many of the features
discussed for oil tankers. Currently, the Arctic Pilot
Project, proposing to ship LNG from the High Arctic, has
been shelved, primarily because of lack of markets for
gas rather than concern about technical feasibility.
It should be noted that the distances that the Arctic
tankers would have to travel to reach either Europe or
the eastern United States are about the same as the
distances from the Antarctic to such areas as South
OCR for page 260
260
America, Australia, or New Zealand. Furthermore, they
are less than the distance from the Middle East to the
United States.
The Canadian Arctic Islands (High Arctic)
The ice between the islands of the Canadian archipelago
is quite different from that in the Arctic Ocean,
primarily because it moves less. Over much of the area
it becomes landfast every winter.
This, combined with
the deeper water (typically 200 to 300 m), has enabled
exploration drilling to be conducted using ice as the
platform for the drilling rig (Figure 17-11).
This method requires ice thickening by flooding, to
support the rig and avoid creep failure of the ice under
sustained loading. Such techniques are now routine, and
several oil and gas discoveries have been made using this
very cost effective method. Small ice movements can be
tolerated by the marine riser system (as used in floating
drilling). Larger movements can be accommodated by moving
the rig, but these movements have to be less than about
10 m during the period of drilling the well (say, 30 to
50 days).
Production methods from this area will need to be
based on subsea production technology. A trial subsea
completion for a gas well with pipeline to shore has
already been implemented.
SURFACE B.O.P. STACK
TRIG 770 TONNE
_~ I ~ ~ NATURAL ICE
_ ~~M
BUILT UP ICE i
'I
1
WATER DEPTH 130 M
HYDRAULIC CONNECTOR
130 M
j
_ MARIN E R ISE R
ORILL STRING
~ _ 2~ SUBSEA B.0.P. STACK
OCEAN FLOOR t~ ,.
T: .,,, ~~
FIGURE 17-11 Drilling off the landfast
ice in the Canadian Arctic (Croasdale, 1977)
(Reprinted win permission).
OCR for page 261
261
The Canadian East Coast (Labrador and Newfoundland)
Off Canada's east coast, exploratory drilling has been
under way for about 15 years. All the drilling has been
performed using either drill ships or semisubmersibles
during the pack ice free periods. However, during the
ice-free periods, icebergs can still occur, and
techniques for dealing with them have been developed.
Canadian operators off Labrador and Newfoundland have
pioneered drilling among icebergs. The approach is
essentially one of avoidance. Alert zones are estab-
lished around the vessel; as icebergs enter these alert
zones, various operational responses are implemented. In
the zone farthest from the vessel, typically several
miles, the iceberg is tracked using radar. If the
iceberg continues to move in the direction of the vessel,
then certain actions may be taken in the drilling opera-
tion that would enable the well to be shut in. Also,
towing vessels will be dispatched to tow the iceberg away
from the drill ship. If for some reason this is
unsuccessful, in the next alert zone the well is shut
in. If the iceberg continues to move toward the ship,
then the drill ship disconnects from the seafloor well-
head (and blowout preventer) and moves out of the way of
the iceberg. All vessels used in iceberg areas do not
use mooring lines but are dynamically positioned (using
thrusters). Therefore, the final move off can be
accomplished in minutes. After the iceberg threat is
passed, the drill ship moves back to the wellhead and
continues drilling.
To give some idea of the need for disconnects, it is
useful to quote some statistics for the Labrador Sea,
where drilling started in 1971. In the first season, one
drill ship was used, and the season length was 67 days.
During this period, 167 icebergs were tracked, 10 were
towed, and there was one disconnect. From 1971 to 1982
there were 21 drill-rig seasons. About 2,600 icebergs
were tracked, more than 600 were towed, and there was a
total of 13 disconnects.
It is envisaged that in certain areas of the antarctic
offshore, methods similar to those developed for drilling
off Canada's east coast could be used.
Production from this area will utilize either fixed or
floating platforms. It is considered technically feasible
to build fixed platforms out to about 200 m; at this dis-
tance the platforms can still withstand iceberg impacts.
Floating systems, combined with subsea wellheads, are a
OCR for page 262
2˘2
more likely alternative in deeper waters. Any subsea
wellheads and pipelines would of course be placed in pits
and trenches for protection from grounding icebergs.
CONCLUSIONS
It should be stressed that, even from the point of view
of technology, the Arctic cannot be considered a direct
analog for the Antarctic. There are some obvious differ-
ences. For instance, water depths are generally greater
in the Antarctic, icebergs are larger, and the distances
to support infrastructure and markets are greater. On
the other hand, pack ice conditions are probably less
severe in the Antarctic than in the Arctic.
Nevertheless, despite these differences, some of the
methods developed for the Arctic could be used for
exploration. These include
(1) Drilling off the landfast ice and ice shelves; and
(2) Floating drilling in the summer months combined
with iceberg management, including quick disconnects
from a protected subsea wellhead.
The costs of exploration in the Antarctic are expected
to be as great as or greater than the Arctic, where an
exploration well costing $100 million is not uncommon.
As far as production from the Antarctic is concerned,
only in the narrow zone of shallow water (say, less than
50 m deep) could fixed platforms be used. In deeper
water, subsea production systems combined with seasonal
floating service platforms might be envisaged. These
technologies are under development but have not yet been
widely used.
So far I have said little about research and lead
times. It is important to recognize that in frontier
areas, many years of research and data gathering are
often needed before commencement of operations. For
example, in the Canadian Beaufort, offshore leases were
taken by the oil companies in the mid-1960s.
Environmental data gathering and research commenced in
the late 1960s. Exploratory drilling started offshore in
1973. Production has not yet taken place and is unlikely
to occur before 1990.
By analogy, even if a decision were made now to start
looking for antarctic hydrocarbons, and even if feasible
technology became available, and even if the economics
OCR for page 263
263
were favorable, production and cash flow would probably
be 20 to 30 years away. Furthermore, before then, vast
investments would be required, and extensive research and
data-gathering programs would have to be implemented.
REFERENCES
Croasdale, K. R. 1977. Ice Engineering for offshore
petroleum exploration in Canada. In Proceedings of
Fourth International Conference on Port and Ocean
Engineering under Arctic Conditions, Memorial
University of Newfoundland, Vol. 1:30.
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OCR for page 264
Representative terms from entire chapter:
arctic ocean
