Because there are only about 33 million people living in a huge area of 13,100,000 km2. It is very cold in Siberia and the conditions are not good for people's lives, and therefore the population density is only 2,5 inhabitants per square kilometer.
The reserves of oil and natural gas are formed and found in the sedimentary and igneous rocks mostly in the porous rocks as they have pores that allow for the water in small quantities to pass through them.
As the naturally occurring oil is drilled and mined from the ground in the oceans and lakes and mapping of their location is called as hydrocarbon kitchens
