BP Educational Service
Science at Work
Discovering oil and gas
Oil and gas formation
Without oil and gas our lives would be totally
different. We depend upon them for energy, plastics
and even clothing. But where do oil and gas come
from? The story begins over 150 million years ago.
Ancient oceans
teemed with
microscopic
creatures. When
they died, they sank
to the bottom of the
sea. A layer of dead
matter formed on
the seabed.
Over millions of
years, sand and
mud buried the dead
matter. Sediments
built up, pushing down
on the matter below
them. The pressure and
temperature increased.
High pressures
and temperatures
transformed the
sediments and dead
matter.
The sand and mud
became sedimentary
rocks, such as chalk,
limestone, sandstone
and shale.
The dead matter
became crude oil
and natural gas.
1. Oil and gas took millions of years to form.
Why do you think they are called ‘finite’ and
‘non-renewable’ energy sources?
2. Why do BP geologists look for oil and gas
where they find sedimentary rocks?
1
The oil and gas formed
many kilometres
underground. They
were squeezed by the
high pressures and
pushed into tiny pores
in neighbouring rocks.
Where are oil and gas
found?
BP geologists use their understanding of the rocks
they see on the surface of the Earth to help them
understand the rocks that are buried underground.
They can spot areas where oil and gas might be
trapped underground by looking at aerial
photographs of the surface.
Impermeable rock
Even after oil has formed in the rock, the pressure
continues to rise. This squeezes the oil through
rocks that have pores, or spaces, within them.
Oil is forced into pores in surrounding rocks.
Permeable rock
Impermeable and permeable rocks (greatly magnified)
Some oil eventually
seeps naturally to
the surface.
Most oil meets a layer
of rock that it can’t
move through. This
impermeable rock
forms a seal or trap.
Reservoirs are rock formations that hold oil, natural
gas or both within their pores, like a fossilised
sponge. The pores also contain salt water.
Reservoirs can be massive. Some may be as large
as London.
Very slowly, the oil
builds up to form
a reservoir.
3. How are oil and gas trapped to form
a reservoir?
Oil, salt water and gas have different densities.
These densities change with temperature and
pressure. For example, the density of natural gas
increases when it is put under more pressure.
The density of crude oil can also differ depending
on whether it is a ‘thin’ or ‘thick’ crude.
In one BP oil well, the densities in the reservoir are:
Oil: 910 kg/m3
Salt water: 1,025 kg/m3
Natural gas: 410 kg/m3
4. The oil, water and gas form three layers
in the reservoir. Use the densities above
to explain why, and to put the three layers
in order.
2
Using waves to find
oil and gas
Drilling a well is extremely expensive. It’s
vital that BP can locate exactly where to drill.
BP geophysicists must find the right spots
in each oil field.
5. Why do you think sandstone is less dense
than shale?
BP geophysicists can direct sound waves at a rock
formation from several different points, and measure
how the waves are reflected. They use the data
to work out the size and shape of the formation.
One such formation is a ‘cap’ of heavy shale.
Geophysicists use acoustic surveys – known as
seismic surveys – to locate oil and gas. They use
air guns to fire acoustic pulses down through the
rock. These sound waves bounce back like echoes,
revealing different layers of material and their
depths.
6. Oil is sometimes found trapped beneath
a ‘cap’. Shale is good at reflecting sound
waves underground. Why does this mean
that geophysicists must scan the rocks
with sound waves from different points?
A powerful computer converts the sound patterns
into a view of what lies underground. The data
gives scientists the information they need to map
reservoirs. They can identify whether the reservoirs
are likely to be filled with oil, gas or just water
(but they don’t know for sure until they drill a well).
Different rocks have different densities.
Porous sandstone is less dense than heavy shale.
Geophysicists know the density of each type of
rock, and how fast sound waves travel through
each one.
Survey ship
source of shock waves
(air gun)
hydrophones
(for recording sound)
sea bed
path of
reflected waves
sedimentary
rock layers
gas
impermeable rock
oil
water
ck
oir ro
reserv
s
u
o
r
po
A seismic survey
Seismic operations in Algeria
3
Visualising the world
under your feet
BP uses cutting-edge seismic technology to
picture underground reservoirs.
In a special room called a Highly Immersive Visual
Environment (HIVE), geologists, geophysicists,
computer scientists, drilling engineers and others
come together to view the seismic data. Special
glasses allow them to explore the reservoir in 3D.
Seismic engineers create a series of images in
vertical ‘slices’. HIVE puts these images together,
like slices of bread in a loaf. Geologists can view the
rocks from any angle by using HIVE to rotate the
image.
Inside the HIVE
These images help BP to plan the next step: drilling
into soil and rock to find out for certain whether oil
or gas are present.
7. Why might a detailed, 3D image help BP
to make the most of each oil field?
Scientists and engineers can now take seismic
surveys into the fourth dimension – time. They scan
the oil field every few months or years to build up
a '4D' picture of how the oil and gas have changed
position over time.
These are important tools. In most oil fields,
engineers have to inject water to help push the oil
to the surface. They inject water down wells in the
oil field, and this pushes the oil out through wells
at other locations.
Detailed 3D and 4D surveillance allows the
engineers to inject the water in the most effective
places, and to monitor how the water injection
is working.
‘What’s really exciting
is that seismic surveillance
has a direct impact on
our day-to-day business.’
8. Remember that substances with different
densities reflect sound waves in different
ways. How might the densities of oil and
water allow BP engineers to see how an
oil field has changed over time?
Seismic advisor, BP
4
The products of oil and gas
9. In a small group, list all the products you
can see around you that are made from oil.
How many did you spot? What other
products that come from oil might you
have used since you got up this morning?
Nearly every molecule in oil or gas is made up of
just two elements: hydrogen and carbon. These
elements combine in chains to create molecules
called hydrocarbons.
Chemists can alter hydrocarbon molecules
to change their properties. They can:
Noticeboard pins – one use for plastics made from oil
join small molecules
together to form
longer chains
10. Some crude oils are more valuable than
others. Refineries pay more for thin, pale oils
than for thick, heavy oils. Why do you think
this might be?
or break long-chain
molecules into
smaller ones
Chemists can overcome differences in crude oil.
They help BP refineries to modify the hydrocarbons
each crude contains. This helps each refinery to
meet its customers’ needs.
Hydrocarbon molecules
These processes allow many different products
to be made from crude oil.
Oil and gas from different reservoirs formed under
different conditions. They were created from
different marine creatures, and experienced
different temperatures, pressures and ‘cooking
times’. This makes the oil and gas in each reservoir
unique. For example, some oils from South
America are thick and tarry, while many from
North Africa are thinner and lighter.
5
Hydrocarbons and the future
Oil and gas are essential. They power transport
and homes, and they provide thousands of
products from bottles to medicines.
‘‘Scientists carefully
distinguish among
proven fact, informed
speculation and
blind faith.’
Scientists are certain that oil and gas are finite
resources. Almost since the beginning of the oil
industry over 150 years ago, people have warned
that supplies will run out. No-one knows how long
supplies will last.
Chief scientist, BP
The amount of oil and gas that we know exists
has changed over time, and so has the amount
that can be extracted.
11.
Why might these amounts
of oil and gas change?
BP needs to understand how much oil and gas
might be available in the future. It needs to predict
where new technologies could help to locate and
recover more reserves. For example, many new
oil fields are located under seawater up to 3,000m
deep. BP is investing in new technologies that
allow it to work in these conditions.
Scientists are also developing other technologies:
– Different sources of energy, for example
wind power, or technologies that use
natural gas or hydrogen
– New ways to recycle more waste plastic
12. Why might recycling become more
important as oil reserves get smaller?
Biofuel
6
Glossary
Acoustic – to do with sound; an acoustic wave
is a sound wave.
Density – the mass per unit of volume; shows
how tightly packed together the substance is.
Impermeable – does not allow liquids or gases
to pass through.
Porous – full of tiny holes or passages.
Pressure – the amount of force acting on a surface
or volume.
Reservoir – a place where a volume of oil or gas
is trapped.
Seismic technology – using acoustic waves
to explore rock formations deep underground.
Shale – soft, finely layered sedimentary rock
formed from mud or clay.
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© BP International Ltd 2008