Q1. How do oil and gas form?

Oil and gas are a complex mixture of hydrocarbons and other substances like nitrogen, sulfur, oxygen etc. They are formed through conversion of organic matter (remains of micro-organisms, both plants and animals), under critical range of pressure and temperature conditions, into kerogen and then to oil and gas. This process of oil and gas formation takes tens of millions of years. The rocks in which oil and gas are formed are called source rocks. Examples of source rocks are shale and limestone. These then get migrated to a porous and permeable rock, called reservoir. Example of reservoir rocks are sandstone and limestone, which form 90% of World reservoirs. Other rocks in the vicinity of source rock if fractured or porous can also act as reservoirs.