For instance, crude oil with a high sulfur content (usually in
the form of hydrogen sulfide) is called sour. Crude oil with
Hydrogen sulfide isn’t the only
thing that has to be removed
from crude oil. Contaminants,
such as metals or nitrogen
need to be removed from any
oil that is going to be used in
end products that come into
close contact with living things.
Some examples of these types
of products are animal feed
and cosmetics. Removing these
contaminants is an added
expense, so crude oil with a lot
of contaminants is considered
less valuable.
a low sulfur content is referred to as sweet. The hydrogen
sulfide in sour crude oil is poisonous when in gas form,
and is so corrosive (meaning it will destroy or permanently
damage anything it comes in contact with) in liquid form
that it must be removed before the oil can be transported.
Sweet crude oil is considered more valuable than sour
because it doesn’t require the difficult and expensive step of
removing the sulfur.
Another important characteristic is specific gravity, which
measures the density of a substance compared to the density
of water. The most widely used measuring system for oil’s
specific gravity was devised by the American Petroleum
Institute in 1921 and is known as API gravity. Within this
CHAPTER 5 | Processing Petroleum
Just because a grade of crude oil
is “sweet,” does not necessarily
mean that it is “light” (or “sour” and
“heavy”). Because the classifications
measure two different things,
though rare, it is possible to have
“heavy sweet” or “light sour” oil.
classification system, Arabian crude oil can range from super
light all the way to heavy. Crude oils with a high API gravity
are considered light, and generally contain few large (longchain) hydrocarbon molecules. The smaller molecules don’t
need to be broken apart in the refining process, so light
crude oil will produce a greater percentage of highvalue end products.
A variety of crude oils are found in the
CHAPTER 5
PROCESSING PETROLEUM
Classifying the Crude Oil
When you think of oil, you probably think of it as being a dark, sticky
Kingdom. About 75 percent of the
country’s proven reserves are light,
below: Gasoline and jet fuel are
examples of the high-value end products
that are made from light crude. Light
crude oil is also easier to pump out of
the ground because it is thinner and
requires less pressure.
sweet crude—most of this coming
from Ghawar (the world’s largest
oil field), Shaybah field and
the fields of central Saudi
Arabia. The rest of the
nation’s reserves are
liquid. But the crude oil that comes out of the ground can take on a range
of characteristics. Take the color blue. There are many different shades of
blue, including teal, baby blue, powder blue, aquamarine, midnight, navy,
etc. Oil comes in many shades as well. The oil industry recognizes many
different grades of oil, and has given them different names depending
upon their characteristics.
top right: Crude oil.
right: Image of subsurface
structure of Ghawar, the
world’s largest oil field.
a variety of grades,
ranging all the way
to heavy sour.
45
Cleansing the Crude Oil
Domestic
Customers
You already know that when petroleum comes out of the ground it
almost always contains contaminants that must be removed before it can
Industrial City
with Shipping
Terminal
be refined or shipped. This is accomplished during the processing phase,
which involves several different steps.
1
The first step in turning crude oil into a usable product is separating
out the gas that often comes with it. This occurs in plants that are often
located near the drilling sites within the oil field.
2
During the refining process, oil is separated into its different
components. These componets can then be blended into different
end products. While Saudi Aramco operates multiple refineries, some
petroleum is shipped to other countries in its crude form, and refined
once it reaches its destination.
3
After the gas is separated from the crude oil, it is fractionated, or
separated into different usable components. Most of the gas that Saudi
Aramco recovers is used to power industry in the Kingdom of Saudi
Arabia. Some of the natural gas liquids (NGL) are exported.
4
Oil and gas are stored in huge tanks like these. When mutiple tanks are
situated together, it is called a tank farm.
5
Oil and NGL are loaded onto tankers waiting at the terminal. The large
vessels carry these products to destinations around the world.
Non-Associated
Gas Plant
3 Fractionation
Gas
Plant
GOSP
Oil Field
46
4
Oil Field 1
LEGEND
GOSP
Oil Field
Gas
Oil
47
pressure deep underground can cause natural gas to take liquid form, but
a gas.
2
GOSP
plant, where natural gas and water are removed. We know that the intense
when it reaches the surface, where the pressure is much lower, it becomes
Refinery
Tank Farm
GOSPs
The first stop for crude oil is usually the GOSP, or gas-oil separation
Associated
Gas Plant
Export
Terminal
CHAPTER 5 | Processing Petroleum
CHAPTER 5 | Processing Petroleum
5
Gas Field
left: At the GOSP, crude oil travels
through a series of drums, or cylinders,
where the gases that rise off it are
collected in “separators.” In this way,
these hydrocarbons can be collected in
a safe and controlled manner. Water is
removed from the bottom. near right:
Huge tanks, like the ones seen here,
can be used to store the separated gas.
middle right: Aerial view of the refinery
at Rabigh. far right: GOSPs are usually
located on or near the oil fields, even
offshore, such as this one.
quick quiz:
Which of these common household appliances can be powered directly by natural gas?
Stove
Refrigerator
Television
Microwave
Barbecue
48
Outdoor lights
Clothes dryer
answer: Everything except the TV and the microwave can be
powered directly by natural gas. The TV and the microwave can
only run on electricity—which can be provided by a natural gas
powered source!
master gas system
In the past, Saudi Aramco (and other oil companies) used to “flare off”
most of its natural gas in controlled amounts by burning it as it emerged
from the well. Only a small amount of natural gas was kept for the
company’s own use. Most of it was reinjected into petroleum reservoirs
to keep the internal pressure high enough to continue the flow of oil.
Aramco was one of the few companies that tried to find customers for its
natural gas, but since most existing power plants were designed to burn
either coal or heating oil, there was not much demand for it.
Space heater
above: As part of the development
of its Master Gas System, the
company built special gas
processing plants at Shedgum,
Ju‘aymah, ‘Uthmaniyah (seen here),
Yanbu’ and other sites; added a
natural gas liquids (NGL) pipeline to
its East-West Pipeline project; and
constructed new piers specifically
designed for loading natural gas
products onto ships.
CHAPTER 5 | Processing Petroleum
CHAPTER 5 | Processing Petroleum
When flaring was a common
practice, the burned-off gas
looked like huge flares, which is
where the term flaring comes
from. Widespread flaring was
stopped in the ’70s. Today, that
gas, a valuable commodity, is
captured and sold to customers
within Saudi Arabia, and
flaring is used for safety/
emergency purposes.
Dehydration and Desalting
In the 1970s, though, fuel prices began to rise dramatically all over the
world. Concern over air pollution was also growing, and it was known
that burning natural gas caused less pollution than burning coal or
heating oil. In 1975, the government of Saudi Arabia asked Aramco to design and construct a Master
Gas System, with the goal of producing as much natural gas nationwide as possible. At that time, the
Saudi government instructed Aramco to establish a consolidated electric system in the Eastern Province,
which led to the building of natural gas power plants to provide the electricity.
When petroleum comes up out of the ground, it almost always has
In the 1980s, Aramco began to focus on locating and developing the Kingdom’s large reservoirs of nonassociated gas. Remember, these are gas reservoirs without any oil, just natural gas, which typically lie
in an even deeper layer of the earth than oil reservoirs. More gas processing plants were constructed,
and the older ones were expanded, to handle increased production of natural gas.
salt and other minerals that must be removed through a process called
Today, the natural gas collected by the Master Gas System is used to power parts of the Kingdom, like
water desalinization plants. What’s more, Saudi Aramco is the world’s top producer and exporter of
natural gas liquids (NGL).
separation. In this method, an electric current is sent through the oil
some water in it. This is because the same conditions that create
petroleum reservoirs—the layers of cap rock that act like seals holding
the liquid in—also create water reservoirs, or aquifers. The oil and water
mix underground, and must be separated at the surface through a
process called dehydration. In addition, the water is often full of dissolved
desalination or desalting.
Both of these processes are done at the same time, using electrostatic
and water mixture to speed up the natural separation of the two that
would happen eventually by gravity.
below: This illustration shows how a
simple reservoir could be structured.
49
Refining
Stabilization
After the natural gas has been separated out at the GOSP, and the water
and minerals have been removed, the crude oil is usually piped to a
stabilizer to be “sweetened,” or in other words, to have the hydrogen
sulfide removed.
Hydrogen sulfide gas has a very distinctive odor—it smells like rotten
eggs. Like many things in nature (think of a skunk), that smell is a
warning to keep your distance. You already know that hydrogen sulfide
above left: This stabilizer is part of the
Abqaiq plant. Remember the difference
between sweet and sour oil? If the oil is
already sweet, sending it to the stabilizer
is not necessary, which is what makes
some grades of oil more valuable than
others. above right: After being sent
though the stabilization column, seen
here, and then cooled, the oil is ready to
be transported, either to the refinery for
further processing, or to terminals for
export.
below: Ras Tanura, located in Saudi
Arabia’s Eastern Province on the Arabian
Gulf, is the site of a marine terminal and
the country’s largest refinery.
The last step in the process of turning crude oil into usable products is
refining—separating the crude oil into useful fractions, or components,
such as gasoline, diesel, jet fuel and fuel oil.
Each refinery is a little different, but there are several steps that most
typical oil refineries follow. By the time it reaches the refinery, the crude
oil has been sweetened, de-gassed, dehydrated and de-salted, and now
it is ready for the fractional distillation unit. Here, it is piped through a
column that is heated with steam at the bottom. The heat causes the
hydrocarbons in the crude oil to boil off into vapor, which rises up the
column. As it reaches cooler areas of the column, the vapor begins to
condense back into liquid. The liquid collects in trays that line the sides
of the column.
Fractional distillation typically produces only about 40 percent
CHAPTER 5 | Processing Petroleum
CHAPTER 5 | Processing Petroleum
Two of Saudi Aramco’s
refineries (Saudi Aramco Shell
Refinery Company, or SASREF,
at Jubail and Saudi Aramco
Mobil Refinery Company
Ltd., or SAMREF, at Yanbu‘)
are joint ventures with other
companies. Have you ever
worked on a group project in
school? It’s a similar concept.
In a joint venture, two or
more companies combine
their resources to finance a
project and then share in the
responsibility for and profits
from that project.
gasoline (one of the most valuable end products), so petroleum chemists
developed ways of altering the hydrocarbons to get a higher percentage
of the fractions they want. There are three basic ways to chemically
alter hydrocarbons:
is poisonous as a gas and corrosive if it mixes with water to form
50
sulfuric acid. (It could actually eat away the steel lining of a transport
51
truck or tanker in the time it took to transport the crude oil to its next
destination.) So, removing hydrogen sulfide from crude oil is essential.
In the stabilizer, the crude oil is sent down a long column, where it
is gradually heated. The heat causes the hydrogen sulfide and other
compounds (including water and leftover natural gas that wasn’t
removed at the GOSP) to become gaseous and rise to the top of the
column. From there they are sent to a “scrubber,” which collects any
useful hydrocarbons that might be trapped among the waste gases.
The sweetened crude oil is sent to cooling tanks to prevent any more
hydrocarbons from evaporating.
Cars run on gasoline, which
is made up of different
hydrocarbons with different
boiling points. Some of
them will turn into vapor
at temperatures as cool as
the temperature inside your
house or school. Have you ever
seen gasoline spilled at a gas
station? It evaporates very
quickly, especially if it is
warm outside.
Fractional
Distillation Column
science experiment: be a chemist!
Liquid Petroleum
Gas (LPG) - Refrigerator
After extracting crude oil from the ground, Saudi Aramco pipes it to huge plants so the oil can go through
all of the processes necessary to make it ready for use. Steps such as separating out the gas and water,
CHAPTER 5 | Processing Petroleum
stabilizing the oil (removing the hydrogen sulfide) and refining it all use heat to create chemical changes.
You can watch a chemical change take place in your own kitchen with a few simple ingredients.
Naphtha - Plastic
Gasoline - Automobile Fuel
what you’ll need:
• 2 avocados
• A kitchen knife
• A spoon
• 2 small bowls
• Lemon juice
2. Take the second avocado and repeat
the process, scooping the flesh into
the other bowl.
What is the result? Do you see a
difference between the plain avocado
and the one with lemon juice?
3. Squeeze some lemon juice onto the
avocado in one of the bowls, using
enough so all of the flesh is covered.
The avocado that did not have any
lemon juice turned brown because of a
process called oxidation, which is when
oxygen molecules come into contact
with another substance and cause a
chemical change. In this case, when the
flesh of the avocado became exposed to
the oxygen in the air, it began to break
down, therefore turning brown. The acid
in the lemon juice, however, slows down
the chemical reaction between the
avocado and the air, thereby keeping the
flesh greener, longer.
Kerosene - Jet Fuel
Diesel - Truck Fuel
Furnace
Fuel Oil - Utilities/Power
Asphalt
52
• Cracking: Breaking apart heavy hydrocarbons into lighter ones.
• Unification: Combining smaller hydrocarbons to make larger ones.
• Isomerization: Rearranging the molecules of one hydrocarbon to make
a different one.
The final steps in refining include treating the petroleum fractions to
remove any remaining impurities and blending the fractions into the
end products. These include various grades of gasoline, diesel fuel,
kerosene, jet fuel and petrochemical feedstock for use in making plastics
and other products.
above: As the crude oil rises through
the fractional distillation column, the
heavier hydrocarbons, which have higher
boiling points, turn into liquid at the
warmer, lower parts of the column. The
lightest hydrocarbons, which have lower
boiling points, condense at the very
top. The medium and lighter fractions,
especially gasoline, kerosene and diesel,
are among the most valuable end
products of the refining process.
1. Take one of the avocados and slice
it open. Remove the seed and, using
your spoon, scoop the flesh into a
bowl.
4. Let both bowls of avocado sit for a
few hours.
In processing petroleum, heat is used to
create chemical changes within crude
oil. Here, oxygen creates the chemical
change. Can you think of another
element that could cause a chemical
change?