In the late 19th
century, nobody expected oil would become such an important
energy source when the German Nikolaus Otto first used it
to fuel the internal combustion engine. Oil, which
is made up of carbon and hydrogen, is now the world’s
main energy source.
Hydrocarbons Form Rocks
Oil and natural gas come from the accumulation
of organic materials, generally plankton and other microscopic organisms
in an aquatic environment. This is why prospecting for oil and gas
begins with a search for sedimentary basins.
Over time, the sediments and organic materials
in these basins accumulate to form a layer up to several kilometres
thick. In order for an oil or gas deposit to form, the organic materials must
undergo a process that obeys the following stages:
- The organic material must first be buried under kilometres
of sand and mud.
- Then, transformed into oil and gas by the pressure and heat
of the earth.
- The oil or gas then migrates from the parent rock the rock
in which it was formed (generally mudrock) to the reservoir
rock where it can be conserved (a porous rock, generally sandstone
- Lastly, the reservoir must be overlain by an impermeable
rock that blocks the oil or gas from migrating upward.