Oil Production

There are three different stages of oil recovery from a field. Primary, secondary and tertiary recovery.

Primary recovery: Produces oil using the natural pressure in the ground as a force to push the oil to the surface.

Secondary recovery: The pressure in the ground will eventually fall and it will become necessary(if economical) to use secondary recovery methods to recover the oil. Methods like pumps and injection of gases and liquids to raise the pressure.

Tertiary recovery: In this third step more advanced and sophisticated methods are used. Methods that are reducing the viscosity of the oil. This step is also known as enchanced recovery.

Oil is often divided into conventional and unconventional oil. Conventional oil is defined as oil that's produced by the primary and secondary recovery methods. 95% of the worlds oil production comes from conventional oil. Unconventional methods often are expensive and with todays oil price it's not economically acceptable to use these methods in a larger scale. I will give a deeper explanation of this subject later.

Conventional crude oil reserves includes all oil that is possible to extract from a well using the primary, secondary and tertiary methods. This does not include the unconventional methods. The oil reserves are classified as proven, probable or possible depending on the probability of finding a certain amount of oil in the field.

Proven P90, 90% of finding a certain amount of oil in the field.
Probable P50 50% of finding a certain amount of oil in the field.
Possible P10 10% of finding a certain amount of oil in the field.