Exploring and Drilling for Oil and Gas

After 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)

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

What else do we know about oil and gas?

Oil has natural gas in it

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

When oil is produced, some gas is produced with the oil.

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!

Where can we find Oil and Gas?

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.

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.

Oil

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

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?

Water

Gas

Here’s an example of a Gas reservoir.

Again, note the impermeable layer of rock preventing the gas fromescaping.

Water

Gas

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

Oil

Why do you suppose the gas is on top?

Water

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.

GasOil

source

receivers

t = 1 sect = 1.2 sec

t = 1.42 sec

What do we do after we find a reservoir?

??

?

We Drill Into It ! ! !

What do we drill with ?

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

Land Rig

For drilling on land.

Drill Ship

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

Semi-Submersible Rig

Jackup Rig

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

Inland Barge

For drilling in water depths from 8 to 30 ft.

What’s a drilling rig ?

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!

Drill stringDrill bit

The hoisting equipment consists of:

a crown block, a traveling block,

drilling line,and a drawworks to

pull the drilling line up or down.

substructure

derrick

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.

spare drill pipe

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

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

The drill string is turned at surface, which turns the bitat 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.

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

screens

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

4) the mixture iscirculated acrossscreens at surface

1) Clean drilling mud is taken from the steel mud tanks and pumped down the inside of the drill pipe.

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

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

The Drilling Mud Cycle

mud pump

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’

Next,a smaller bit is run inside the first casing.

This bit drills out the bottom of the casing, and drills new hole.

200’

0’

500’

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

Again, a smaller hole is drilled out, and smaller

casing is run to keep the hole from falling in.

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.

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.

How do Geologists tell if the reservoir has oil or gas?

Sand

Shale

Siltstone

Shale

Siltstone

Dolomite

Shale

Here’s an example of what a log looks like. Geologists look at logs to decidewhether or not to complete a well (if there is oil), or abandon it (if there’s no oil).

GammaRadiation

200’

500’

3000’

ElectricalResistivity

Porosity

Lookslike goodsandquality

good resistivity,may have oil or gas

poor resistivity,probably water

good porosity

poor porosity

good porosity

poor resistivity,probably water

poor porosity

good porosity

Can you tell where the geologist would complete this well?

GammaRadiation

200’

500’

3000’

ElectricalResistivity

Porosity

Lookslike goodsandquality

good resistivity,may have oil or gas

poor resistivity,probably water

good porosity

poor porosity

good porosity

poor resistivity,probably water

poor porosity

good porosity

}Right here! This shows a clean sand,

with good porosity and resistivity.

good porosity

poor porosity

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

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

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

tubing

Packer

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

The production facilities on surface separate out the gas, oil, and water into their separate phases.

Production Separator

Oil

Produced Water

Produced Gas

Production Separator

Oil

Produced Water

Produced Gas

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

Oil Refinery

Storage Tanks

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

And That’s Where Oil and Gas Come From!

The End.

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. SheeranSr. Drilling EngineerChevron Nigeria Ltd.SHTA@chevron.com

TAS Oct. 1998