Oil and Gas Basics

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Exploring and Drilling
for Oil and Gas

Prepared by Tom Sheeran

What are Oil and Gas?
• Oil and Gas are substances found within the earth’s crust.
• They are thought to come from decomposed plant and animal
matter.
• Scientists believe the plants and animals died long ago, and were
slowly buried by thick layers of sediments. Over a long period
of time, and with pressure and temperature, the organic materials
were converted into the oil and gas which are found today.
(For example, we know that present day garbage dumps give off methane gas)

Prepared by Tom Sheeran

What else do we know about oil and gas?
Oil in it’s natural state can be thick
or thin, black or light colored.

When oil is refined, many
products can be obtained:






Energy for power
Gasoline for cars
Diesel fuel for trucks and trains
Hi-octane fuels for planes
Heating oil for houses

Many other materials also come
from petroleum:
• Plastics
• Materials for clothes (example:
polyester fabrics)
• Chemicals for everyday use
• Paints
Prepared by Tom Sheeran

Did you know that oil has natural gas in it?
When oil is produced, some gas is produced
with the oil.

The natural gas is in solution, just like the
carbon dioxide which is put inside of pop to
give it its fizz.

A barrel of oil may contain anywhere from
1 cubic ft of gas, to over 10,000 cubic ft,
depending on the type of reservoir.

That’s enough gas in a single barrel of oil to
fill your whole house!

Prepared by Tom Sheeran

Where can we find Oil and Gas?

Prepared by Tom Sheeran

Some people think that oil is in big pools underground.

Actually, most oil is trapped in the tiny pore spaces between
grains of rock or sand. Most of these pores are too small to
be seen with the naked eye.

Prepared by Tom Sheeran

So, how do we find oil-bearing rocks?

• Oil and gas are found in natural traps within the earth.
• These traps consist of domes or faults. Impermeable rock
above the trap prevents the oil and gas from migrating up
to surface. An “impermeable” rock is one that fluid
cannot pass through.
• without traps, the oil and gas could migrate all the way to
the surface and evaporate.
Prepared by Tom Sheeran

Here’s an example of a dome-shaped
Oil reservoir.

Oil
Water

Note the layer of impermeable rock which prevents the oil from migrating upwards.
Also, note the layer of water below which prevents the oil from escaping down. Why?
Prepared by Tom Sheeran

Here’s an example of a Gas reservoir.

Gas
Water
Again, note the impermeable layer of rock preventing the gas from
escaping.

Prepared by Tom Sheeran

Here’s an example of an Oil reservoir with a Gas cap

Gas
Oil
Water
Why do you suppose the gas is on top?

Prepared by Tom Sheeran

How do we find the oil reservoirs?
• Geophysicists find reservoirs by bouncing sound waves off them, and timing how long it
takes for the sound to come back

• Computers process the data to construct pictures of what the earth looks like underground.

source

t = 1.42 sec

t = 1.2 sec
t = 1 sec

receivers

Gas
Oil

Prepared by Tom Sheeran

What do we do after we find a
reservoir?

?
?

?
Prepared by Tom Sheeran

We Drill Into It ! ! !

Prepared by Tom Sheeran

What do we drill with ?

Prepared by Tom Sheeran

A Drilling Rig !
Here are a few different types of drilling rigs available:
Jackup Rig
Land Rig

For drilling in water
depths from 15 ft
to +/- 350 ft.

For drilling on land.

Inland Barge

Drill Ship

Semi-Submersible Rig
For drilling in water depths
from 8 to 30 ft.

Drill ships and semi-submersible rigs are for drilling in
water depths from 100 to 5000+ ft.
Prepared by Tom Sheeran

What’s a drilling rig ?

Prepared by Tom Sheeran

A Drilling Rig is:
A package of special equipment put together to enable us to
drill into the earth.
• A drilling rig has many different parts:
a derrick, a substructure, hoisting equipment, engines for
power, drill pipe, steel tanks, pumps, solids control
equipment, and many other pieces.
• Did you know that some drilling rigs can drill as deep as 6
miles? That’s as deep as Mt. Everest is tall!
Prepared by Tom Sheeran

This picture shows the hoisting equipment on a rig.
This equipment is used to raise or lower the drillstring, which is
picked up in 30 foot long segments, or “joints”, of drill pipe.
The hoisting equipment
consists of:

derrick

a crown block,
a traveling block,
drilling line,
and a drawworks to
pull the drilling line up
or down.

This shows a 30 foot section
of drill pipe being added to
the drill pipe already in the
hole.

substructure
Drill string
Drill bit

spare drill pipe

Prepared by Tom Sheeran

Here’s a picture of the drill bit drilling the rock.

The drill string is turned at
surface, which turns the bit
at the bottom of the hole.

The teeth on the drill bit
grind the rock into
fragments, or “cuttings”.

Drilling mud is
pumped down the inside
of the drill pipe, through
jet nozzles in the bit,
and into the “annulus”.
This is the space
between the sides of the
hole and the drill pipe.
The mud lifts the
cuttings and circulates
them back to surface
where they are removed.
Prepared by Tom Sheeran

The Drilling Mud Cycle
1) Clean drilling mud is taken from the steel
mud tanks and pumped down the inside of the
drill pipe.
4) the mixture is
circulated across
screens at surface

screens

6) Clean mud falls
through the screens
and is returned to the
pits

3) the mixture of drilling mud and
drill cuttings are circulated up the
annulus

mud pump

5) the drill cuttings are removed, and
form a cuttings pile. This can be
hauled off and disposed of.

2) the mud is circulated through the drill bit into the
annulus, lifting the cuttings removed by the drill bit.
Prepared by Tom Sheeran

Here’s a sequence showing how holes are drilled,
First, a large drill bit is used to drill
a short interval of hole.

Then, steel casing is run and cemented on
the outside to keep the hole from
collapsing.
0’

200’

Prepared by Tom Sheeran

0’

Next,
a smaller bit is
run inside the
first casing.
This bit drills
out the bottom
of the casing,
and drills new
hole.

Then, this new
hole is also
cased off and
cemented.

200’

500’
Prepared by Tom Sheeran

Again, a smaller
hole is drilled out,

and smaller
casing is run
to keep the
hole from
falling in.
Prepared by Tom Sheeran

In this way, the hole is drilled in stages, until the target reservoir rock is penetrated. At
this point, the geologists must figure out if there is oil or gas in it.

Prepared by Tom Sheeran

How do Geologists tell if the reservoir has oil or gas?
They do this by running logs across the zone.

Logs are tools run on electric cable
(“wireline”) which record the physical properties in the rock such as resistivity, porosity,
density, radioactivity, and pore pressure.

Prepared by Tom Sheeran

Here’s an example of what a log looks like.

Geologists look at logs to decide
whether or not to complete a well (if there is oil), or abandon it (if there’s no oil).
Gamma
Radiation

Electrical
Resistivity

Sand

Porosity

good
porosity

Shale

200’

Siltstone

poor
resistivity,
probably
water

Shale
Siltstone
Dolomite

poor
porosity

500’

Shale

Looks
like
good
sand
quality

good
resistivity,
may have
oil or gas

3000’

poor
resistivity,
probably
water

good
porosity

poor
porosity
good
porosity

Prepared by Tom Sheeran

Can you tell where the geologist would complete this well?
Gamma
Radiation

Electrical
Resistivity

Porosity
good porosity

200’
poor
resistivity,
probably
water

poor porosity

good porosity

500’

poor porosity

good
resistivity,
may have oil
or gas

Looks
like
good
sand
quality

good porosity

}Right here! This shows a clean sand,
with good porosity and resistivity.

poor
porosity
poor
resistivity,
probably water

3000’

good porosity

Prepared by Tom Sheeran

If the well looks good on the logs, we run a final string
of casing across the production zone, and cement it in place.

Prepared by Tom Sheeran

Then, we run perforating guns in the hole and perforate (shoot
holes ) in the casing across the productive zone.

Prepared by Tom Sheeran

Production tubing is run, with a packer to isolate the produced
zone from the casing above.

tubing

Packer

Prepared by Tom Sheeran

Finally, the well is produced into
a pipeline, which takes it to
production facilities on surface.

Prepared by Tom Sheeran

The production facilities on surface separate out the

Produced Gas

gas, oil, and water into their separate phases.

Oil
Production Separator

Produced
Water

Prepared by Tom Sheeran

From there, the oil and gas may
be refined further before being
ready to market.

Produced Gas

Storage Tanks

Oil

Oil Refinery

Production Separator
Produced Water

Prepared by Tom Sheeran

Finally, the gas and oil can be sold to
power cars and heat houses.

Prepared by Tom Sheeran

And That’s Where Oil and Gas Come From!

The End.
Prepared by Tom Sheeran

About the Author:
Tom Sheeran has been working in the oil and gas industry for over 18
years. He worked summers on a drilling rig while going to school to earn
a degree in Petroleum Engineering. After graduating, he went to work for
Chevron in the Rocky Mountains. In 1990 he began working for Chevron
Overseas Petroleum, and since then has worked all over the world, in
Scotland, Australia, Papua New Guinea, Venezuela, Angola and Nigeria.
Tom is currently employed by Chevron Nigeria Ltd. and is living and
working as a resident in Lagos, Nigeria.
Tom and his wife Shallini have 2 children, and home-schooled in the U.S.
for several years before moving overseas. Tom developed this
presentation for kids so they may learn more about the oil industry.
You may contact Tom at:
Tom A. Sheeran
Sr. Drilling Engineer
Chevron Nigeria Ltd.
[email protected]
TAS Oct. 1998

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