Unseen Comprehension - 09 Alim (Mineral Oil)

Mineral Oil. 

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The world needs a large amount of mineral oil because it is a very useful fuel. Different kinds of oil are  always in use. Aircrafts need finer oil than cars or railway engines .

Engineers in many  countries drill the ground for  oil . The oil is taken away in big tankers .  Some of the latest tankers are ships of 1,00,000 tons. The mineral oil in the ground is called petroleum. Very often there is gas with it , and both are under pressure . The oil  cannot escape because rock  or clay holds it down ; but it can escape when the drill makes a hole. Then the oil sometimes rushes up through the hole and rises high into the air above the  ground.

The natural gas itself is very  useful . In some countries it is distributed through pipes to different cities. It is very useful for heating houses and other buildings in cold countries. 
When the oil  does not rush  up through the hole , it can be raised by pumps . One well may supply  us with a lot of  mineral oil, but usually there are several wells together . A group of well form an oil-field. There are many oil-fields in Iran, Saudi Arabia and Kuwait. It is usually difficult to find a new oil-field, but modern  instruments and machines are very helpful. We can recognise an oil-field because we can see a lot of derricks. A dirrick is a tall steel framework over an oil-well for holding the drill. If the sea is near, a tanker may be waiting to take oil on board. 
The petroleum from a well is usually thick and brown, and we cannot use that in a car or an aircraft. We have to make it finer. This is done in a refinery.