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science experiment: oil and water don’t mix
When crude oil accumulates in underground reservoirs, it is often accompanied by natural gas and water.
The natural gas is lighter than the oil, so it rises higher in the reservoir and forms a layer on top of the oil.
The water is heavier than the oil, so it sits on the bottom. You can see this phenomenon at work by carefully
combining ingredients with different densities. This simple experiment will show you how.
what you’ll need:
• 1 clear drinking glass or plastic cup
• 59 ml (1/4 cup) honey
• 118 ml (1/2 cup) water • A few drops of cooking oil
1. Pour the honey into the glass.
3. Finally, pour a few drops of the oil
into the glass.
Can you see the three ingredients
separate according to their densities?
Honey, the heaviest, settles at the
bottom. Water rests in the middle. And
oil, being the lightest, rises to the top.
Can you picture how the water, oil and
gas settle in a reservoir?
To drill for oil in the desert, roads,
airstrips and buildings to house people
and machinery must be built. Water
must be found, or piped in if it can’t be
found nearby, and, often, desalted and
cleaned.
CHAPTER 4
below: Miles and miles of sand dunes
make for incredible challenges.
2. Next, pour the water into the glass.
DRILLING CHALLENGES
Extracting the Oil
You’ve learned a lot so far about how petroleum forms and how it’s
found. Once a well site has been selected, the drilling and exploration
crews haul all of the necessary supplies and equipment to the drilling site
to begin the complicated, and sometimes dangerous, task of retrieving
oil.
The challenges in oil production start with the locations where
petroleum is found, which is often in hard-to-reach locations. In Saudi
Arabia, a great deal of petroleum is found beneath harsh, remote
desert (temperatures at Shaybah field, deep in the Rub‘ al-Khali,
can reach as high as 55 ºC (131 ºF) in the summer months). All the
supplies and equipment necessary for developing these fields must be
Bit by Bit
Most petroleum reservoirs are hundreds or even thousands of meters
underground. That means the drill bits have to go through layer after
layer of soil, rock, salt and whatever other obstacles are in the way. The
the rock (think about what would happen if you rubbed a piece of metal
against a rock really quickly). To cool the bits down, the drilling crew
pours a mixture of chemicals called “mud” down the drillstring. In
addition to cooling the bit, the mud also sweeps away the bits of rock
and debris that can clog the drill. The design of a drilling rig will also
differ depending on whether it will be used on land (onshore) or in a
body of water (offshore).
Since drill bits have to work even harder in unconventional reservoirs,
and they cost oil companies time and money when they break, special
designs have been created to make them even stronger. Saudi Aramco
has worked with outside companies to test many different designs to
find just the right materials to cut through the varied layers of the earth
surrounding petroleum reservoirs. Many recent drill bit designs feature
The term “rig” includes all of
the drilling machinery and the
scaffolding that supports it,
including the platform, derrick, drill, turbines and more.
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drilling 101
small chunks of synthetic diamond covering the head of the bit. Since
above: As tough as they are, drill
bits do get dull and must be replaced
periodically. Unfortunately, one bit will
not make the entire journey from the
surface to the petroleum. Because the
size and shape of the holes being drilled
are not always the same, drill bits are
also made in a variety of patterns.
diamond is one of the hardest substances in the world, it makes an
excellent cutting edge.
Broken Drillstrings
The depth of the wells in Saudi Arabia creates its own set of problems.
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In Chapter 3, you learned that the oil reservoirs in Saudi Arabia are
The massive structures built to drill for oil or gas are called drilling “rigs.” They come in many shapes and
configurations but they all perform the same basic task of drilling. What they’re drilling for may differ.
Drilling rigs are used to drill test wells in search of oil; other times, they are used to drill for core samples
with which to analyze the earth’s composition. In other instances, they are used to drill the wells through
which the oil will actually rise to the earth’s surface.
To drill a typical vertical, onshore well, a preliminary hole is “spudded,” or dug. A derrick—the tall tower
you see in most oil fields—is set up to hold the drill, and casing is set into the hole to keep the sides from
collapsing. Then the drilling resumes. The drill bit is at the end of what’s called the “drillstring.” This is a
sequence of connected pipe sections, with a heavy tube-shaped piece called a drill “collar” at the end to
add extra weight to the drillstring and hold it in place.
CHAPTER 4 | Drilling Challenges
CHAPTER 4 | Drilling Challenges
drill bits heat up tremendously from the friction of grinding through
primarily found in a layer of the earth known as the Arab Zone. The
deeper the hole, the greater the stress on the drillstring, which, over
greater lengths has a tendency to flex or bend. If it bends too much,
it will break, which is not only costly due to the fact that drill bits are
expensive to replace, but also creates other problems.
When a drillstring breaks, drilling on the well must stop while the broken
string is retrieved. This is done by a process called a “fishing operation,”
and the men who perform the fishing operation are called “fishermen.”
The fishing operation varies depending upon where, exactly, the
In the early days of oil
production, actual mud was
used as the coolant that was
poured down the drillstring.
drillstring breaks. Another important factor is whether or not there is
measure density of the rock layers, electromagnetic resistance and more)
toxic material surrounding the drillstring. Once these questions are
are mounted on the drill bits and drillstrings. They can transmit detailed
answered, the fishermen use special tools that can either cut into the
information to drilling crews on the surface, helping the crews detect and
broken piece or attract it (like a magnet) and pull it out.
resolve problems before they become critical. Combined with improved
drill bit design, these advances have greatly reduced the likelihood of
of retrieving oil from hard-to-reach places. However, horizontal wells are
much longer than vertical wells (since they have to go down to the right
level and then run horizontally for a considerable distance) and therefore,
they actually cause more stress to the drillstring.
These days, fiber optic cameras and many kinds of sensors (which
above: If a drillstring (like the one seen
here) breaks, “fishermen” are called in
to perform a fishing operation. First
they have to figure out where the string
is stuck. In an open hole? Inside the
casing? below: Horizontal wells include
a section (or multiple sections) that
runs horizontally through the reservoir.
You’ll learn about horizontal drilling in
Chapter 8.
above: These tiny microchips can be
attached to drill bits and drillstrings to
help collect and transmit information
from the well to the crew on the surface.
Pressure Control
The challenges don’t stop once a well has been drilled. Getting the
petroleum out of the reservoir is also complicated. Remember, the
pressure within the earth is high—higher than it is on the surface—and
this pressure typically pushes the petroleum upward. If petroleum filling
the pore spaces within rocks is like water filling a sponge, reservoir
pressure is like squeezing that sponge into a small bottle, and then filling
CHAPTER 4 | Drilling Challenges
CHAPTER 4 | Drilling Challenges
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broken bits and drillstrings.
The drilling of horizontal wells is an innovative solution to the problem
the bottle with liquid. When the bottle is opened, the liquid will take the
easiest path out—up the neck of the bottle.
above: A well shaft is like the neck of a
soda bottle. When the drill bit pierces
through the cap rock (the dam) covering
the reservoir, it’s like taking the top off
the bottle. What would happen if that
bottle was shaken up first? The pressure
inside the bottle would make the soda
blow out the top. The same thing can
happen when drilling for oil or gas.
This is called a blowout. right: Drilling
crews cap wells with heavy-duty valves
called blowout preventers, seen here, to
help prevent blowouts, but an accurate
understanding of the reservoir is also
critical to predicting overpressure.
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As the oil and gas are removed, the pressure in the reservoir begins to go
1
The platform of Aramco’s
AMDP-1 was shaped like an
isosceles triangle, with two sides
measuring roughly 29 meters
(94 feet) and one side measuring
roughly 32 meters (104 feet). The
platform was about 3.5 meters
(10 feet) thick and enclosed
with steel sides. When moving
through the water, it acted like a
ship’s hull and floated.
2
Because offshore oil rigs are
often built in the middle of the
ocean, helicopters are used to
transport workers to and from
the rig.
3
The legs on an offshore oil rig are
equipped with gears that allow
them to move up, when the rig is
being moved into position, and
down, when the rig is ready to be
planted on the sea floor. The legs
of Aramco’s AMDP-1 were each
about 38 meters (125 feet) long.
down. At some point, it will dip low enough that the oil will stop flowing
up the well shaft. In some cases, oil companies reinject natural gas into
the reservoirs to keep the pressure up. In other cases, the pressure is
supplied by water (most commonly seawater), which is pumped into
CHAPTER 4 | Drilling Challenges
special “injection wells” at the outer edges of the reservoir.
Some petroleum reservoirs, however, are actually under too much
pressure—a condition known as overpressure. Overpressure is caused
by the fact that the deeper underground the reservoir is, the higher the
pressure in it will be. Non associated natural gas reservoirs, for example,
tend to be much deeper than oil reservoirs, so overpressure is always a
concern when drilling into them. In an overpressured reservoir, when the
drill bit pierces the cap rock, the high-pressure in the reservoir can force
2
1
oil or gas to rush up the well shaft to the surface, like soda exploding out
of a bottle that has been shaken up. This is known as a blowout.
3
Formation Damage
You read earlier about drilling mud, the stuff that is poured down the
drillstring to cool and lubricate the drill bit and flush out the pieces of
offshore drilling
rock. Over time, drilling mud has come to have a lot of other ingredients
in it. It can also be either water- or oil-based, depending on the needs of
a particular well.
One issue with the chemicals in drilling mud, however, is they can invade
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the reservoir rock and damage it—a problem known as “formation
damage.” Xanthan and similar chemicals, known as polymers, are used
to form plugs that prevent the chemicals in drilling mud from invading
the reservoir. Polymers also lubricate the drill bit, making it less likely
above: An explosion of soda is easy to
clean up, but gas and oil are not soda.
They are very flammable, and when they
explode out, catastrophic fires can occur.
to snap from the friction of drilling through hard rock. However, the
polymers themselves can create problems for drilling because they can
gum building up on the underside of your school chair), creating a “filter
cake” that can cause the drill bit or drillstring to get stuck or snap. The
polymer residue must be removed, but care must be taken because the
the drilling equipment, create formation damage in the well shaft and
background: Safaniya is the world’s
largest offshore oil field. To find it,
Aramco built its first offshore rig.
To keep the rig from floating away,
Aramco built a platform to hold the
rig and workers, and then anchored
that platform to the seabed.
Aramco geologists suspected that large petroleum reservoirs existed in the seabed underneath the
Arabian Gulf, particularly in an area called Safaniya. The company began searching for those reservoirs in
1949, and built its first offshore drilling rig in 1950. In 1951, it discovered the Safaniya field.
The many layers and obstructions underground mean drillers have to approach each reservoir from
multiple directions (advancements in horizontal drilling help with this today). Because each offshore
oil rig had to be attached to the seabed to keep from floating away, Aramco soon realized it would
take multiple years and drilling rigs to reach all the oil in Safaniya. So, they came up with a solution: a
moveable drilling platform!
build up in the well shaft and in the drillstring (imagine wads of chewing
strong acids commonly used to dissolve the polymers can also destroy
Oil seeps have been discovered in oceans around the world for many
years, and just like the seeps on land, they are taken as clues that
petroleum reservoirs may be buried deep beneath the sea floor. Undersea, or offshore, wells were drilled in shallow coastal areas as
early as the beginning of the 20th century, but extracting petroleum
from the ocean’s depths was not a focus until demand greatly
increased after World War II. Drilling mud is full of chemicals
with names such as xanthan.
If the word xanthan sounds
familiar to you, it is because
xanthan is also found in chewing gum!
After several years of research and development, Aramco launched its first mobile drilling platform in
1958. It was named Aramco Mobile Drilling Platform 1, or AMDP-1. That basic model is still in use today.
damage the surrounding environment. Saudi Aramco chemists have
developed a treatment for filter cake using enzymes specifically targeted
loay mashabi, petroleum engineer
at dissolving the polymers, followed by a treatment with diluted acid to
finish the process.
Reservoir Management
Saudi Aramco has a team dedicated to dealing with all the complexities
that go hand in hand with drilling wells and retrieving the petroleum
from them—the Reservoir Management Department. Reservoir
Management studies and makes computer models of the reservoirs
to determine their exact makeup; chooses the best sites for drilling;
and predicts, prevents or fixes problems such as formation damage,
collapsing well holes, blowouts and more. The task is huge, and
Reservoir Management must work with many people throughout the
Polymers take different forms
as a result of the molecules
that make them up. Molecules
are made from atoms. The
properties of molecules differ
depending upon which atoms
they are made from and how
those atoms bond together.
company, from geologists to computer systems technicians.
After going on to complete the College Preparatory Program (CPP) run by
Saudi Aramco, Mashabi entered King Fahd University of Petroleum and
Minerals (KFUPM), where he completed a degree program in petroleum
engineering.
Mashabi then fulfilled his boyhood dream by beginning work as a
Saudi Aramco production engineer. Despite being just 26 years old and
only having been in his position for three-and-a-half years, he now has
responsibility for 120 wells in the Ghawar field. His job is to ensure the
wells are free of problems, known as “well integrity,” by conducting
numerous tests and surveys, as well as analyzing data provided by other
departments. On average, he spends five to 10 days a month away from
home, mostly to supervise work being carried out on the wells.
above: “My job can be very
demanding but is also very
fulfilling. It gives you a strong
sense of responsibility and
ownership.”
CHAPTER 4 | Drilling Challenges
CHAPTER 4 | Drilling Challenges
After visiting the Saudi Aramco Exhibit in Dhahran as a schoolboy, Loay
Mashabi’s dream was to work for the company. Raised in Jiddah, he knew
little about Saudi Aramco before the trip to Dhahran. The experience,
however, left him knowing exactly what career he wanted to pursue.
Mashabi is an active member of the renowned Society of Petroleum Engineers (SPE). He continues to
advance his learning by taking advantage of the many training courses offered by the company.
In addition to his responsibilities, Mashabi still finds time to scuba dive and play water polo in his free
time. In fact, he is training to become a scuba diving instructor. Mashabi believes that with determination,
others too can fulfill their dreams, “With a positive attitude you will learn a lot,” he said. “Communication
skills are important because 90 percent of what I do is reliant on other people. If you have an open mind
and are able to work with people from various backgrounds, you can fulfill your dreams.”
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above: Enzymes are a type of protein
that helps start or speed up chemical
reactions, such as this one. Saudi
Aramco’s enzyme technique has been
quite effective at removing polymer
buildup without causing formation
damage in the well shaft. left: Making
and studying 3D models of Saudi
Aramco’s petroleum reservoirs is not
just the responsibility of the Reservoir
Management Department.
A production engineer is usually assigned the
responsibility of one or more Gas Oil Separation
Plants (GOSPs) or Water Injection Plants (WIPs) or a
group of oil, water or gas wells.
In many cases, this responsibility is shared with
another engineer. Production engineers monitor
wellbore integrity, ensure the well is performing
efficiently and gather data to enable proper reservoir
management. This is done by designing, planning
and witnessing well testing and surveillance of oil,
water and gas in the designated area.
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