Accumulations of oil and gas – the fields – exist underground almost everywhere in the world. But all the same it is necessary that certain conditions come together for those accumulations to develop. What is called the genesis of oil follows seven fundamental steps, each one essential and above all very, very slow.
First, it is necessary to have organic matter capable of being transformed into oil, and in sufficient quantities: this is the source rock.
Then all the conditions favourable for the transformation (maturation) of this potential oil and gas must be present.
The new oil and gas then embark on a journey (migration) towards the surface.
During this migration the hydrocarbons must meet a rock capable of hoarding them in large quantities: the reservoir.
This reservoir must be impervious. A barrier (seal or cap) is therefore necessary: that is to say an impermeable rock to prevent the oil and gas from pursuing their way upwards. This rock is the seal or cap rock.
Then, to accumulate quantities of oil and gas sufficient for profitable exploitation, the substratum must have a form sufficiently large and with a closed
geology: this is the trap.
Finally once well tucked away in their trap, our oil and gas must not be destabilised by attacks coming from the exterior.
Good conditions for the
preservation of hydrocarbons are necessary. |