January
2016
Oilfield Technology
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47
(Massachusetts Institute of Technology) studies on meteorological
prediction rates, errors in cyclone prediction “have a substantial
effect on the damage done to a certain area. A difference of one
hundred miles could determine whether or not people (and rigs)
are forced to evacuate. These are large distances for errors in
forecasting landfall.”
1
In the last five years the National Oceanic and
Atmospheric Administration (NOAA), one of the major players in
storm tracking, has reported an average error of 241.6 miles and
14.8 knots at just 120 hours (five days) before the cyclone hits.
Cyclones are 100 miles in diameter on average, and most rigs can
easily weather storms with sustained wind speeds at or below
60 knots. This means that weather tracking often completely
misses the mark in cyclone prediction and weatherability.
Another concern is that a vessel, not knowing the cyclone’s
path, could head off in the wrong direction and end up getting
caught on the ‘dirty’ side of the storm (where wind speeds are
higher and danger increases).
That can spell big trouble for MODUs. Moored DP vessels
require an average of five days to execute a site move. But at
five days, the accuracy of cyclone prediction is so uncertain it
often leads to unnecessary rig moves, which can cost a company
millions of dollars. This loss comes mainly from lack of drilling
time, fuel expended, and the cost of the rig and secondary
support vessels.
The new system significantly reduces transit time (T-time)
needed, saving four hours per mooring line, on average.
With generally 8 – 12 mooring lines per rig, this time adds up
significantly, reducing T-time by up to 48 hours. This reduced
time means the rig can continue drilling for longer. Plus,
since prediction accuracy increases as the cyclone gets closer
(at 48 hours average error falls to 88.7 miles and 13.3 knots
according to the same NOAA study), the rig has more time to
make an informed decision about evacuation.
2
In addition, when paired with active winching, the system
does not require the use of secondary support vessels to release
mooring lines. This can eliminate costly spot rates for AHVs,
which can run in excess of US$100 000/d.
Since DQR activation requires limited personnel involvement
on the back deck, it also poses an increased level of safety to
onboard employees. During harsh weather conditions, the back
deck of an AHV can pose a significant threat of bodily trauma and
man-overboard scenarios.
Conversely, the system also allows companies to quickly
escape a storm that had been previously predicted to miss their
vessel or has suddenly escalated in intensity. In situations like
these, a rig crew may have no choice but to cut the mooring
lines during harsh metocean conditions and hope for the best,
which places personnel and equipment in a perilous situation.
In rare cases there is not time for even this, which poses a very
significant threat to the lives of the crew onboard as well as the
vessel itself. The system mitigates this risk somewhat by allowing
the vessel to leave the danger area in a shorter window of notice.
Agreener future
When it comes to offshore drilling, one of the chief concerns
for the general population is environmental. Though it was
some years ago, the Macondo oil spill of 2010 is still fresh in the
public mind. It is the largest accidental spill in history and its
environmental effects are still being felt today.
Though the incident was not related to mooring failures, it
represents the shortcomings of oil drilling and highlights the need
for extra precautions to operators. The risk for oil companies is
not just environmental either, the Macondo incident resulted in a
price tag of more than US$42 billion in clean-up fees and a record
US$18.7 billion fine from the US government.
3
That plus the loss
of 11 priceless lives makes offshore disasters one of the most
frightening risks oil companies face.
The DQR is also a greener and more economic option for
DP vessels. Normally these vessels expend a lot of fuel, and
therefore greater pollution, to stay on location. By mooring them
instead, less fuel is required and less pollution is released into
the atmosphere.
Thus, there is quite a bit of appeal in DP moored vessels
that could be moved to escape storms instead of being forced
to weather them out. Plus having the system onboard also
means companies might have an easier time acquiring leases
to drill in more protected areas due to reduced emissions and
environmental impact. The risk of damaging surrounding subsea
infrastructure by drifting MODUs in a storm event is eliminated
with DP moored rigs on a quick release system.
Theroadahead
The new system is expected to have an immediate impact
offshore. The first eight systems are already in operation on a
semi-submersible MODU in the Gulf of Mexico.
Making drilling safer and more cost-effective is a top priority
for drilling companies. The Delmar Quick Release takes a key
step in that direction. It represents a promising beginning for
new innovations in offshore mooring, as well as a bright future of
possibilities for drilling operators.
References
1.
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hurricanes/hurricanes-prediction.html
2.
3.
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deepwater-horizon-oil-spill-claims-1435842739
Figure 2.
Trigger sleeve andDQRassembly.
