Oil and Gas Basics

Exploring and Drilling for Oil and GasPrepared by Tom Sheeran

What are Oil and Gas?Oil and Gas are substances found within the earths 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 its natural state can be thick or thin, black or light colored.

When oil is refined, many products can be obtained:

Energy for powerGasoline for carsDiesel fuel for trucks and trainsHi-octane fuels for planesHeating oil for housesMany other materials also come from petroleum:

PlasticsMaterials for clothes (example: polyester fabrics)Chemicals for everyday use PaintsPrepared by Tom Sheeran

Did you know that 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.Thats 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

OilHeres 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?Prepared by Tom Sheeran

GasHeres an example of a Gas reservoir.Again, note the impermeable layer of rock preventing the gas fromescaping.Prepared by Tom Sheeran

GasHeres an example of an Oil reservoir with a Gas capOilWhy 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.sourcereceiverst = 1 sect = 1.2 sect = 1.42 secPrepared by Tom Sheeran

What do we do after we find a reservoir????Prepared by Tom Sheeran

We Drill Into It ! ! !

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What do we drill with ? Prepared by Tom Sheeran

A Drilling Rig ! Here are a few different types of drilling rigs available:Drill ships and semi-submersible rigs are for drilling in water depths from 100 to 5000+ ft.Jackup RigFor drilling in water depths from 15 ft to +/- 350 ft.Inland BargeFor drilling in water depths from 8 to 30 ft.Prepared by Tom Sheeran

Whats 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? Thats as deep as Mt. Everest is tall!Prepared by Tom Sheeran

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.substructureThis 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 pipeThis shows a 30 foot section of drill pipe being added to the drill pipe already in the hole.Prepared by Tom Sheeran

Heres 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. Prepared by Tom Sheeran

3) the mixture of drilling mud and drill cuttings are circulated up the annulusscreens5) the drill cuttings are removed, and form a cuttings pile. This can be hauled off and disposed of. 4) the mixture iscirculated acrossscreens at surface1) 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 pitsThe Drilling Mud Cyclemud pumpPrepared by Tom Sheeran

Heres 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.0200Prepared by Tom Sheeran

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.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

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?Prepared by Tom Sheeran

SandShaleSiltstoneShaleSiltstoneDolomiteShaleHeres 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 theres no oil).Prepared by Tom Sheeran

Can you tell where the geologist would complete this well?GammaRadiation200

500

3000ElectricalResistivityPorosityLookslike goodsandqualitygood resistivity,may have oil or gaspoor resistivity,probably watergood porositypoor porositygood porositypoor resistivity,probably waterpoor porositygood porosity}Right here! This shows a clean sand, with good porosity and resistivity.good porositypoor porosityPrepared by Tom Sheeran

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

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

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Production tubing is run, with a packer to isolate the produced zone from the casing above.tubingPackerPrepared 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 gas, oil, and water into their separate phases.Prepared by Tom Sheeran

Production SeparatorOilProduced WaterProduced GasFrom there, the oil and gas may be refined further before being ready to market.Oil RefineryStorage TanksPrepared by Tom Sheeran

Finally, the gas and oil can be sold to power cars and heat houses.Prepared by Tom Sheeran

And Thats 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. SheeranSr. Drilling EngineerChevron Nigeria [email protected]

TAS Oct. 1998