The oil system

The set of all the characteristics that lead to the formation of an oil field make up the so-called oil system. This system is made up of the following fundamental elements that will be dealt with in detail in the subsequent paragraphs:

  • the presence of a mother rock (source rock);
  • the presence of a reservoir rock;
  • the presence of a cap rock (seal);
  • the formation of traps with a suitable structure.

The necessary processes comprise:

  • the generation of hydrocarbons (conditions to reach the ‘oil window’);
  • the expulsion and migration of the hydrocarbons from the mother rock to the reservoir rock;
  • the accumulation of hydrocarbons in a reservoir rock within a trap.

The areas that produce the most hydrocarbons are divided into ‘oil fields’ according to their geological and structural characteristics; these in turn are subdivided into smaller provinces characterized by a uniform geological situation and by similar characteristics of the reservoir rocks and of the structure of the traps. The task of the person who is engaged in exploring for hydrocarbons is to locate the areas that have the above-mentioned geological characteristics, those that are the most favourable to the formation of important reserves.

 

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