Deepwater Oil and Gas
Production in the early days of the oil industry was exclusively onshore, but in due course eyes turned seaward to tap the extensions of fields lying on the coast.
At first, that
was achieved by deviating wells from the shore, and later, by drilling from
steel platforms in shallow waters, as for example in Trinidad, Peru and Lake
Maracaibo.
Later, a rig was mounted on a barge that could
be moved from location to location, which was pioneered in 1949 in the shallow
waters of the Gulf of Mexico, off Louisiana.
The
breakthrough then came with the idea of building the rig on two submerged
pontoons that could rest in relatively tranquil water beneath the wave-base.
The first such rig, Blue Water No.1,
came into operation in 1962, and began to extend the range of drilling to as
much as 200 m of water.
The design was subject to continual
improvement such that it soon became possible to drill routine wells in the
stormy waters of the North Sea.
There are two other types of offshore rig
worth mentioning: the jack-up which sits on long retractable legs resting on
the seabed; and the drillship, having a rig mounted mid-ships on an ordinary
vessel, held in place by anchors or thrusters.
Gradually, the
continental shelves of the world were explored, and delivered some substantial
finds both from the extensions of existing onshore basins and from entirely new
provinces.
Offshore seismic technology also saw great
advances from the early days when a seismic boat let off explosive changes, the
echoes of which bounced off formations far below the seabed to be recorded on
receptors towed behind the vessel.
New sources of
energy were developed and computing power brought great sophistication, such
that offshore surveys are now cheaper and give better results than onshore
ones.
Despite these advances, great challenges
remain in installing the production facilities, such as the massive steel and
concrete platforms of the North Sea.
As the
opportunities of the continental shelves were gradually exhausted, attention
began to turn to the Deepwater domain.
The Brazilian State Company, Petrobras,
pioneered this development, as the country was facing the high cost of imports
during the early 1980s.
To its enormous credit, it successfully began
to find and develop fields in exceptionally deep water.
Parallel developments came in the Gulf of
Mexico, and later off Angola, Nigeria and other countries on the other side of
the South Atlantic.
Offshore oil
resource is playing an increasingly significant role in satisfying our fossil
fuel needs.
According to the U.S. Geological Survey, in
2014, about 47% of the total untapped oil resource comes from the sea.
For the offshore oil industry, it is becoming an
important issue to reliably supply electrical power to the offshore oil
platforms.
At present,
most of the oil platforms far from the land are powered by the independent
power stations built on them.
This power supply mode, however, would lead to
blackout of the platform once the power station thereon shuts down.
Therefore, it
becomes a trend to construct offshore oilfield power systems that can
interconnect every platform to improve the reliability of power supply.
Since 2010,
offshore platforms have been connected electrically along the coast of China.
Many larger-scale offshore power systems are emerging.
Therefore, how to plan a highly reliable power
system suitable for the offshore oilfield is critical for the construction as
well as the effective and safe operation of the offshore oil industry.
The technology
of planning has been widely studied and applied to large-scale inland power
systems for the past decades.
Conventionally,
the process of inland power system planning is divided into two steps, i.e.,
generation expansion planning (GEP) and transmission expansion planning (TEP), for
the following reasons: It is difficult to deal with GEP and TEP simultaneously
due to the huge number of variables.
The
construction of power stations and transmission lines are in the charge of
different sections of the power industry.
Over 80% of the
total expansion cost goes to GEP whereas TEP only accounts for a small fraction
of the investment, which leads to relatively minor errors with the two-step
planning procedure.
Either GEP or
TEP has been widely investigated in the past research.
For GEP, different techniques have been used,
for instance, fuzzy logic, genetic algorithm (GA), particle swarm optimization
(PSO), Tabu search and etc.
However, without the geographical information
of generators and transmissions, all generators were just considered to be at a
single nodal point.
As for TEP,
there are also different methods for example, mixed integer linear programming
(MILP) algorithms, heuristic methods, game theory and artificial intelligence
techniques.
Similarly,
without clear information of generations, the obtained TEP result can hardly be
the most cost-effective one.
However, the
composite generation and transmission system expansion planning is reasonable
for offshore oilfield power systems.
Three reasons are explained for this idea.
First, offshore systems are much smaller than inland systems and have far fewer
stations and lines to be planned, which means the number of decision variables
is much smaller.
Second, both
generation and transmission system are constructed and operated by a single
company (In China, the company is China National Offshore Oil Corporation).
As a result,
simultaneous and integrated planning of generation and transmission is feasible
in the perspectives of both technology and management.
Last but not least, the investment cost of
submarine cables is enormous enough to be comparable to that of generators.
Consequently,
separate execution of TEP and GEP could lead to ill-considered decisions.
Overall, integrated planning is not only
feasible but also necessary for offshore oilfield power systems.
Furthermore,
special attention should be paid to two issues for the planning of offshore
systems.
One is the outage cost, which need be taken
into account for the fact that loss of electricity in the offshore oilfield
would cause serious damage to drilling equipment or even a complete halt of oil
production.
The other is the shipping cost, which should
be explicitly considered for the reason that the distance from the mainland to
offshore platforms is critical for determining the construction costs of
generators and cables.
An integrated
generation-transmission expansion planning model is proposed which includes
outage cost and shipping cost.
A genetic Tabu hybrid algorithm (GTHA) based
optimization method has been developed to solve the integrated planning problem
to find the optimal plan.
If you want
to learn more about Deepwater Oil and Gas you could
do so in my book, economic study of oil and gas well drilling. which is
published on amazon, check it out at the link below.
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