Petroleum, also called crude oil and natural gas, is a fossil fuel formed from the remains of ancient sea life. This article explains what petroleum is, how it forms, and the short history of how people began to use it.
What Is Petroleum?
There are many theories about the origin of petroleum, but the most widely accepted is the Organic Theory. For a detailed look at how oil forms, read The Hidden Origins of Oil.
Petroleum is called a fossil fuel because it was formed from the remains of tiny sea plants and animals that died millions of years ago. They sank to the bottom of the oceans and were buried by thousands of feet of sand and silt. Over time, this organic mixture was subjected to enormous pressure and heat as the layers built up. It changed chemically into compounds of hydrogen and carbon atoms, called hydrocarbons. Finally, an oil-saturated rock, much like a wet household sponge, was formed.
Conditions Needed for an Oil Field
Not all organic material turns into oil. Certain geological conditions must exist:
- A source rock rich in organic material, buried deep enough to be heated.
- A reservoir rock with pores to hold the oil. A typical petroleum reservoir is mostly sandstone or limestone.
- A seal (such as salt or clay) that keeps the oil from rising to the surface, and a trap that holds it in place.
Even under these conditions, only a small fraction of the organic material is transformed into oil. Oil in a reservoir may be as thin as gasoline or as thick as tar, and almost clear or black. Reservoir fluids are grouped into several types, as shown in the classification of reservoir fluids.
Petroleum is called a nonrenewable energy source because it takes millions of years to form. We cannot make more in a short time.
A Short History of Oil
People have used naturally available petroleum since ancient times, though they did not know how to find it. The ancient Chinese and Egyptians burned oil for lighting.
Before the 1850s, Americans often used whale oil for light. When whale oil became scarce, people looked for other sources. In some places, oil seeped naturally to the surface of ponds and streams, and people skimmed it and made it into kerosene, which lit many homes before the electric light bulb.
As the demand for kerosene grew, a group of businessmen hired Edwin Drake to drill for oil in Titusville, Pennsylvania. After much hard work and slow progress he found oil in 1859. His well was only 69.5 feet deep, very shallow compared with today’s wells.
Drake refined his oil into kerosene for lighting. Gasoline and other products from refining were simply thrown away, because there was no use for them. That changed with the automobile, which needed gasoline. By 1920 there were around nine million motor vehicles in America alone, and filling stations were opening everywhere.
Frequently Asked Questions
Why is petroleum called a fossil fuel?
Because it formed from the remains of ancient sea plants and animals.
Is petroleum renewable?
No. It takes millions of years to form, so it cannot be replaced in a human lifetime.
Key Takeaways
- Petroleum forms from buried marine organic matter under heat and pressure.
- An oil field needs a source rock, a reservoir rock, a seal and a trap.
- The first commercial oil well was drilled by Edwin Drake in 1859.
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