Petroleum extraction is the process of extracting usable petroleum from the earth's sub-surface. Petroleum describes a mixture of hydrocarbons including gasses and solids dissolved in the liquid, and natural or free gas. Extractable petroleum is usually trapped in layers of permeable rock under layers of impermeable rock, and in impermeable but porous rock in which liquids and gasses are trapped.
Petroleum extraction is a complicated process and makes use of different technologies. Petroleum is extracted in three basic stages i.e. primary extraction, secondary extraction, and tertiary extraction. Primary extraction accounts for 5 to 15% of the total amount of petroleum in a deposit. Secondary extraction accounts for 35%-45% of the total deposit and tertiary extraction is also about 5%-15% of the total deposit. The total amount of petroleum that can be extracted from a well is a maximum 60% of available petroleum.
Recovering 100% of petroleum is not economical if the amount of energy invested in extracting petroleum exceeds the amount of energy that can be gained from utilizing that petroleum or EROEI (energy returned on energy invested).