How crude oil and natural gas is formed? – UPSC GS1

Explain the process of formation of crude oil and natural gas. Examine why there is so much oil in Middle East but less in India

Crude oil and natural gas are obtained from sedimentary rocks. They were formed from remains of dead plants and animal that were buried under sand and rocks. over millions of year, high pressure and heat, in the absence of air, converted them to oil and gas.

1. Sedimentation occurred between 30 degree north and south were temperature was high and organic activity was high. Middle east lied between these range where India missed it.

2. Middle east was at favourable position during mid cretaceous Global warming, coupled with sea level rise and abundance of plankton
3. 500 million years history of sedimentation on continental margins of Gondwana.
4. Though oil is formed in sedimentary rocks but all sedimentary rocks do not contain oil. An oil reservoir must have three pre-requisite conditions–

1. 1. porosity-to accumulate large amount of oil. (middle east rocks are formed of limestone and dolomite which have high porosity. Indian rocks are hard and not so porous) 
   2. Permeability to discharge oil and gas when oil is drilled (dolomite and limestone has high permeability).
   3. porous sand beds, sandstone should be capped by impervious bed so that oil do not dissipate to surrounding rocks.