How is natural gas formed?

Millions of years ago marine plants and animals died and settled on the sea floor. They were buried by the sediments which were brought by rivers and deposited on the sea floor.

 These sediments grew thicker. The weight of these layers of sedimentary rock and the action of bacteria caused the dead plants and animals to decompose and turn into both crude oil and natural gas.

Sedimentary rocks have pores (tiny spaces) that allow ground water, oil and gas to flow through. Do you know why the gas is above the oil and the oil is above the water? 

This migration occurs because oil and gas are less dense than water. This difference in density causes the oil and gas to rise towards the surface so that they are above groundwater with the gas settling above the oil.

 The water, oil and gas collect underground when there is a fold in the strata. An up-fold such as this is called an anticline.

The pores of different layers of rocks vary in size. The rock through which the water, oil and gas flow easily has big pores and is called permeable rock.