Case Study: Adriatic LNG Terminal (Installation and Operation)
Overview of Project
The Adriatic LNG Terminal is the world’s first offshore Gravity Based Structure for unloading,
storing and regasifying Liquefied Natural Gas (LNG). It is located 15 kilometers offshore Porto
Levante, in the northern Adriatic Sea and is set on the sea floor in about 29 meters of water. It
is connected to the Italian national network of gas distribution by a pipeline that runs
underwater from the facility. There are two large LNG tanks encased in concrete that store the
LNG which is unloaded from LNG vessels. A regasification plant is located on the main deck.
This plant supplies about 10 percent of Italy’s natural gas requirements. The project site is
notated as ALNG on the map below.
Weather in the Northern Adriatic Sea
The climate of the northern Adriatic Sea is profoundly influenced by a number of factors making
it a very complex region to forecast the weather. The map below shows the topography of this
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region. The Alps to the north blocks the colder air of northern Europe from making its way
directly to the northern Adriatic Sea. However, this colder air often gets deflected to the
eastern portion of the Alps and makes its way into the Balkan States where the mountains are
much lower. Additionally, the presence of the Appenines, running midway through Italy can
cause a variety of weather features that make this amongst some of the most difficult places to
forecast in the world.
This part of Italy is noted for its warm, humid summers. Winters are fairly cold, but the
extremes are tempered by the warmer waters of the Adriatic Sea. The autumn season is very
short compared to most parts of the world at this latitude, basically lasting only for the month
of October. There are two main concerns for the Adriatic LNG terminal. One is a persistent
southeasterly wind that blows along the entire length of the Adriatic Sea. The southeast winds
at the site may remain fairly low, but they can be much higher to the southeast of the site,
particularly along the coast of Croatia. These strong southeast winds are regionally referred to
as Sirocco winds. Sirocco winds can build over the course of a couple of days and can usually
be forecasted with a certain amount of accuracy.
The other wind of concern is the Bora. The Bora occurs when cold air accumulates over the
Balkan Peninsula. When the depth of the cold air pool reaches the height of the mountain
passes, the Bora will commence. The Bora is most common in the Adriatic Sea where it flows
mainly from the northeast through gaps in the Dinaric Alps. One of these gaps is near Trieste
and is known as the Trieste Gap. On occasion, the Bora can be very localized, extending only a
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few miles offshore. At other times the Bora will dominate the entire Adriatic Sea; when the
pressure differential is large enough the Bora can extend as far south as Malta. The Bora wind
is a down slope wind and its onset is often sudden and at times can be quite violent. Bora wind
gusts have been recorded at over 100 knots in some of the more extreme events.
Bora winds are most common during the cold seasons; usually October through March. (Peak
time for the Adriatic LNG location is Feb-Mar) Summertime Boras tend to be less extreme in
both length and intensity, primarily due to the warmer air that is present over the continent at
that time. The air-sea temperature contrast is muted when compared to the winter events.
The average duration of a continuous gale force Bora over the Adriatic is about 12 hours but
the winds sometimes will last up to two days. The average duration of a Bora that reaches gale
force some time during its history is 40 hours with a maximum duration of 5 day and a record
length of 30 days.
Summer Thunderstorm from LNG Tanker
Details of the Terminal
The terminal began construction in Algeciras, Spain in 2005 and was completed in 2008. It was
towed from Algeciras to Italy in August 2008 and preparations took about a year until the time
that the critical cool down phase was implemented. The Gravity Based Structure (GBS) which
contains the storage tanks is 180 meters long, 88 meters wide, and 47 meters high, most of
which is under water. The storage tanks each have a capacity of 125,000 cubic meters and are
made of a steel and nickel alloy, designed to withstand the temperatures of minus 162° C
needed in order to keep LNG in its liquid form.
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Cool Down of the Storage Tanks
The storage tanks, for the most part were located under water, so the ambient temperature of
the tanks were near 25°C early in August, 2009. The challenge facing the project is that they
could not just start pouring LNG into the tank due to the design of the tanks. Since the tanks
consisted of three modules that were welded together, the concern was that the structural
integrity of the tanks needed to be maintained by an even cooling process. The challenge was
to make sure that the temperatures in the bottom of the tank never got to be too much colder
than those at the top of the tank and not to cool the whole tank off too quickly. This required a
very meticulous cool down process to keep the metallic tanks from contracting too much in the
bottom versus the top of the tank.
Process of Offloading LNG
The LNG that is transported by LNG tankers must be offloaded to the terminal’s storage tanks
via the offloading arms (see attached picture). Because the terminal is a fixed structure and
the tankers are not, this presents problems when the seas are rough and causes tanker
movement relative to the terminal. These specially designed offloading arms are built to
withstand a much greater range of motion than the typical offloading arms in a harbor. This is
necessary because the Northern Adriatic Sea experiences some extreme types of weather that
can occur suddenly and compromise the safety of the unloading process. However, there are
still limits of motion which will prevent an LNG tanker from being able to stay connected to the
loading arms.
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Critical Limits of the Project
The critical phase of the cool down required several days of benign weather in order to get the
first LNG put into the tank. These tolerances restricted wave heights from the northeast or east
to be less than 2.0 meters, but any seas from the southeast had to be less than 1.4 meters. The
differences between these directions were based upon the ship motions associated with seas
emanating from these directions. The distance between the terminal and the Croatian coast to
the northeast and east of the site varies between 30 and 45 nautical miles. This is a short
distance compared to the hundreds of miles of open water to the southeast of the terminal.
The shorter distance to the northeast and east helps to limit the growth of the seas and the
wavelength (distance between wave crests) is typically much shorter than waves that travel
over hundreds of miles. The motion of an ocean vessel depends upon a number of factors,
including its length and width. In general, large vessels like an LNG tanker will not move very
much if the seas are small or the wavelengths are short. This is because there may be several
crests of waves under the vessel at the same time. However, longer wavelengths can have a
much more profound effect upon the motion of a vessel, especially if the bow of the boat is in
the trough of the wave while the stern is at the same time on the crest of the wave. Since the
waves from the southeast have longer wavelengths, they are capable of producing more
motion in the ship than a wave that is higher with a shorter wavelength.
Wilkens Weather On-Site Solution
Since the weather was a critical element in the successful cool down of the tanks, Exxon felt
that an on-site meteorologist was mandatory. The meteorologist would not only prepare the
forecasts from the shore base, but be available for consultation with the key decision makers in
the office. Wilkens Weather was selected for this based upon some research work that was
performed for the project as well as its demonstrated skill of forecasting the weather at the
site. The meteorologist was asked to prepare three forecasts each day with a fourth being
provided by the home base in Houston. Additional duties consisted of verifying forecast
parameters, liaising with Exxon’s project engineers and communicating with offshore
personnel. Additionally, the meteorologist was on call outside of office hours to answer any
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Tel: 713.430.7100
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questions that might arise pertaining to the weather forecast. The daily briefings that were
given helped to build trust between the parties and helped to facilitate a deeper understanding
of what was at stake.
Project Cool Down
There were various delays that delayed the project cool down phase, but the weather was not
one of them. For a period of two weeks, the weather was rather benign except for some
thunderstorms that developed over the site one morning. The cooling of the tanks needed to
be done gradually and methodically before introducing the LNG. This was done primarily with
liquid nitrogen over the period of a few days. Sprayers at the top of the containment tank
helped to equalize the temperature and pressure of the colder liquid nitrogen that settled into
the bottom of the tank. Pumps in the bottom of the tank transported some of the liquid
nitrogen into other parts of the containment vessel where sprayers redistributed the liquid.
Sensors within the tanks monitored the temperatures and pressures at various portions of the
tanks to ensure that critical limits were not breached. Introduction of the LNG would follow,
but during this initial stage it needed to be done carefully and without interruption. This phase
required about 12 hours to complete and that the seas remain below the limits detailed above.
LNG tankers are very stable and seaworthy vessels. When fully loaded, the ships set much
lower in the water than when they do not have any cargo. Captains of these ships are
comfortable operating the vessels in either of these states, but having a ship with only a partial
cargo is problematic in rough sea conditions. That is because of the pressures that build up
from the sloshing of the liquid within the containment vessels can build up extreme pressures
and become very volatile. For that reason, the first offloading of LNG needed to be done in its
entirety without interruption, but at a slower pace to maintain the vessel cool down within
prescribed limits.
The Critical Period – the week of August 17th-23rd
The forecast from Monday, August 17th indicated fairly good conditions at the site until
Saturday night or Sunday morning. The cooling process with the liquid nitrogen was delayed
because of some unplanned mechanical problems, but eventually commenced on Wednesday,
the 19th. The forecasts continued to indicate good weather through the week, but remained
consistent in the timing of a Bora event for Saturday night or Sunday morning. It was on the
morning of Saturday, the 23rd that the project engineers said that they were ready to go
forward with the offloading of the LNG, but that they would require 12 hours in order to
complete the process safely. They were informed that they would have about a 10-12 hour
window before winds and seas would rapidly increase at the site. Since they could not be
assured that they would successfully complete the operation in this amount of time, they
decided against introducing the LNG until after the weather passed. The Bora did commence
that evening within an hour of the predicted time. Seas increased to 2.0 meters from the
northeast, just as predicted and began to subside as forecast the next morning. By later Sunday
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morning, the process of offloading the LNG took place and 12 hours later the operation was
successfully completed.
It is important to note that the project was receiving weather forecasts from other sources that
did not predict the strength of this Bora correctly. Had the operation commenced based upon
that advice, the potential existed for damage to the containment vessel that could have
resulted in the project being scrapped. However, the onsite meteorologist was able to review
all of the sources of data and offer his advice to the client. This demonstrates the value of
having a partner like Wilkens Weather Technologies understand the needs of the client and
being able to offer invaluable advice.
Wilkens Weather’s Current Project Support
Since the initial cool down phase, tankers berth every 4 to 5 days to deliver LNG to the terminal.
Although the critical nature of the first phase has past, a reliable weather forecast is still
required for this project. Typically, it takes about 6 hours for the tankers to offload instead of
the 12 hours required at cool down. The critical limits of 2.0 meter seas from the northeast and
east and the 1.4 meter seas from the southeast are still in place. However, the shorter weather
window gives the terminal more latitude in scheduling.
Since reliable weather forecasts were critical to this project, the terminal continued receiving
forecast from multiple sources during the winter of 2009-2010. They evaluated each of the
forecast firms on their ability to forecast the timing and severity of the weather events that
affected them with the purpose of offering the winning firm a long term contract. Wilkens
Weather was awarded this contract in the summer of 2010.
Exxon expected superior weather forecasts, yet needed to keep within a budget. Wilkens
Weather discussed various options to keep the costs within reason. WWT put out some
options that scaled back on the forecast frequency to twice daily during the summer time when
weather is much less of a factor and increased to four times daily during the winter when things
can change more rapidly. During the summer, we have an office watch in place in which a
meteorologist will monitor the location every hour and send out warnings of rapidly changing
situations like thunderstorms or squalls. Additionally, we have sourced a high resolution
forecast model for the region that is much better at resolving local phenomena like the Bora
winds. Lastly, we have instituted a lightning alert service for the company that gives them
notification if lightning is detected within 50 nautical miles of the platform. We produce
lightning graphic maps that can be animated to show the client how fast the lightning is closing
in on their location.
This customized approach to working with the client is a trademark that distinguishes Wilkens
Weather from other weather providers. There are many forecast companies that can offer a
forecast for a low price. However, it takes an experienced team of meteorologists that truly
understand the client’s needs to provide a service that is second to none.
Wilkens Weather Technologies, A Rockwell Collins Company
2925 Briarpark Dr., 7th Floor Houston, Texas 77042 www.wilkensweather.com
Tel: 713.430.7100
Toll-Free: 800.503.5811 Fax: 713.430.7185
Sample of High Resolution Weather Model Data Used to Support Forecast Service
Another High Resolution Model with Alert levels set to 13 knots
Wilkens Weather Technologies, A Rockwell Collins Company
2925 Briarpark Dr., 7th Floor Houston, Texas 77042 www.wilkensweather.com
Tel: 713.430.7100
Toll-Free: 800.503.5811 Fax: 713.430.7185