conversation about oil - 1 | Текст песни

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• conversation about oil
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T = teacher, А, В = students

T As you all know oil and gas are fossil fuels. Can someone tell me what that means?

A It means that they are formed from plants and animals.

T Yes, plants and animals that lived millions of years ago. The oil and gas we extract today were formed between ten and 160 million years ago. Seas and wet areas are rich in bacteria and microscopic plants and animals, known as phytoplankton and zooplankton. When they die, they sink to the bottom of the water and form thick layers of organic matter. This gets slowly covered in layers of mud, sand, and other mineral deposits. These sedimentary layers build up on top of each other. What do you think happens to the temperature and pressure, Dani?

В Er... the pressure increases?

T That's right. As the layers increase, the pressure and temperature rise too. There is no air in the organic matter but anaerobic bacteria, which live without oxygen, begin to work on the organic matter and change it. As this happens, wax, fat, and oil from the buried organic matter form dark spots called kerogen. Rocks that contain oil and gas in this form are known as source rocks. In this diagram, you can see that the source rock is the bottom layer. Deeper down, the temperature rises further. Chains of hydrocarbons became shorter and break away to give light oil and gas.

В I've heard that oil from the North Sea is light oil.

T Yes, that's right. Well, we know that oil and gas are less dense than water, so the oil and gas that have formed in this way begin to slowly move upwards into porous rocks that have larger spaces in them. These spaces are known as pores. Can someone tell me the name of a porous rock?

A Sandstone?

T Yes, that's a good example. These porous rocks are reservoir rocks. However, oil and gas continue to rise until they reach the surface of the ground or become trapped under a layer of impermeable trap or cap rock. You can see this in the diagram, here...

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