December
2014
Oilfield Technology
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33
in a harsh environment. There
is also a variant of the CJ54
that is fully compliant with
NORSOK standards.
Anewsystem
The X‑Y cantilever was
introduced in 2000. The
X‑Y skidding system allows
the combined drill floor,
substructure and cantilever
to be moved in longitudinal
and transversal direction.
The effect is immense. The
X‑Y cantilever has a drilling
envelope that is approximately
two times larger than a
conventional cantilever. The
jack‑up therefore needs to
be moved less frequently. Of
course, the transverse reach –
the Y‑direction – is much larger,
as the cantilever moves back
and forth over the deck instead
of the derrick moving over the
width of the cantilever.
But the large envelope is
not its only advantage. The
well centre is always located
near the centre line of the
cantilever, thus the weight
and loads are always evenly
distributed. As a result, the
cantilever steel weight is lower, the combined load is constant
over the transverse reach and the longitudinal reach is
greater. The capacity of the X‑Y cantilever is approximately
1.5 times higher than a comparable conventional cantilever.
The drilling process is more efficient and the reduction in
the number of flexible lines allows for an improvement in
BOP handling.
Finally, the position of the X‑Y cantilever above the main
deck is approximately 3.5 m. This characteristically elevated
position of the cantilever, together with the reduced width
of the cantilever, minimises deck obstruction and ensures a
larger usable deck area.
The advantages of the X‑Y cantilever and skidding system
have been recognised by world’s leading players in the
offshore industry. The system has been fitted on jack‑ups
units belonging to Maersk, Statoil, Noble, COSL and Seadrill.
Investorsare lookingfor certainty
Although the demand for large cantilever jack‑ups has grown
strongly in recent years, the biggest demand increase in
numbers is for the smaller types of jack‑ups, such as the CJ46
and CJ50. This success can also be attributed to the reliability
of the CJs. Chinese shipyards, which focus traditionally on
building merchant vessels, are receiving fewer orders as
a result of the worldwide economic slowdown. A number
of these shipyards have shifted their focus to the offshore
industry. Within a short period of time, these shipyards
have developed into serious competitors for the established
offshore shipyards. Investors, primarily from Singapore
and China, have ordered a significant number of jack‑ups
from these Chinese shipyards. With an existing track record
based on the CJ46s built in China, GustoMSC was selected
by many of these yards. The main reasons for this are that it
is an independent design house and has a good track record
with proven designs. The market for the CJ46s and CJ50s is
considerable, as deeper waters are being explored and the
market for the replacement of existing over‑aged units is
starting to pick up.
Roomfornewjack‑ups
The growth of the new build market has only just started.
Approximately half of the jack‑up fleet has been in operation
now for over 30 years and is scheduled to be phased out
in the coming years. Even mature fields are not likely to be
exhausted in the immediate future. The new generation of
jack‑ups are using more efficient drilling equipment and
new drilling technologies, so that this remaining oil can
also be accessed relatively easily. In addition to the mature
fields, new fields are still being discovered and developed,
for example the Johan Sverdrup field in the North Sea.
There is growth offshore Mexico, West Africa, Middle East
and South East Asia. Large sections of these areas are very
suitable for jack‑ups as far as water depths and conditions
are concerned. Therefore, the existing active fleet of drilling
jack‑ups will have to grow. It is estimated that at least
150 ‑ 200 new jackups will need to be built in the coming
years, in addition to the 135 jack‑ups that are currently under
construction.
Figure 4.
Maersk Innovator, based onGustoMSC’s CJ70 designwith the X‑Y cantilever skidding system.
