Question

Look at the figure where petroleum and natural gas deposits are shown. Why do we find oil layer above water layer?

Answer 1

Hint: As we have learnt that petroleum is a naturally occurring liquid which is yellowish-black in colour and normally found beneath the Earth’s surface and natural gas is a source of heat energy and a non-renewable hydrocarbon. Water possesses hydrogen bonds which keeps its molecules together and oils and fats lack such bonding but their molecules are larger in size.

Complete Step by step answer: As discussed that petroleum is a naturally occurring liquid which is yellowish-black in colour and normally found beneath the Earth’s surface. It is refined and used as a fuel and consists of hydrocarbons of different molecular weights. It includes both unprocessed crude oil as well as refined crude oil. Petroleum is refined into products like kerosene, diesel, petrol, etc.
Let us talk about natural gas which is a source of heat energy and a non-renewable hydrocarbon. It has many uses like acting as fuel in vehicles, in plastic manufacturing it is used as chemical feedstock and also used in cooking and generation of electricity.
Now we can learn about the formation of oil and gas. Microscopic plants and animals living in oceans for a long time absorb light energy and store it as carbon molecules in their body and when they die they get settled at the bottom of the sea. Over millions of years, whenever these organisms die they get deposited in layers and buried deeper and deeper in the sea which results in increase of heat and pressure and eventually oil and natural gas is produced, which tends to migrate in surrounding rocks through the tiny pores until they get caught by the impervious rock. These oils and natural gases are now extracted through vertical drilling in Earth’s surface.
The gas, oil and water is present in a layered manner. As we all know that gas is the lightest of all it will be present above water and oil. Next will be oil which is light weighted that water due to the molecular makeup of oils and fats as the oil molecules are large in size and cannot pack together as tightly as water molecules does and that is the reason for denser nature of water also. Therefore, we see the oil layer above the water layer.

Note: Interstellar clouds within our milky way galaxy water have been detected as it is present in abundance because of its most abundant elements that are hydrogen and oxygen. Water becomes less dense when it freezes and has a maximum density at 40C where it sinks to the bottom of oceans and ice formation takes place at the surface.