Petroleum extraction is the whole process by which hydrocarbons (petroleum) is extracted and removed from the earth. The process is divided in three different stages: location, drilling and the actual oil extraction and recovery.
- Location: Using seismic surveys the aim of petroleum geologists is to find deposits of hydrocarbons. Gravimeters or magnetometers are also used in the search.
- Drilling: An oil well is created by drilling into the earth with an oil rig. Offshore an oil rig is the platform from which the well is drilled. The actual hole is filled with a pipe made of steel. The idea is to fortify the integrity of the drilled hole. The bottom of the hole is finally perforated to allow oil to pass into the wellbore. On top of the well a structure with multiple valves is placed, called ironically „Christmas tree".
- Oil extraction and recovery: The actually oil extraction and recovery after locating and drilling is subdivided into three stages.
Primary recovery: Harvesting the oil from a well "as is". Natural water can be utilized, displacing oil downward into the well. This leads to an expansion of the natural gas at the top of the reservoir. The expansion of the gas results in a flow of oil within the reservoir from the upper to the lower parts where the wells are located.
Secondary recovery: Pressure within an oil well does not remain stable throughout its lifetime. It will fall and ultimately diminish. Secondary recovery applies at this stage, where the natural pressure has disappeared. This can be achieved by injecting water, natural gas or other gases into the reservoir to increase pressure again. Pumps (electrical submersible pumps) can be used as well.
Tertiary recovery: Tertiary recovery is applied where primary or secondary recovery fail to produce any more recovery. Mostly, the so-called "TEOR" method is applied. Thermally enjanced oil recovery methods, which aim at heating the remaining oil within the reservoir to reduce the viscosity (make it more "fluid") so that extraction is easier.
This type of recovery though needs external energy which comes from e.g. a gas turbine to create electricity or steam. Burning some oil from the reservoir is another mean of "TEOR". In rare cases, additional chemicals can be injected to the well to achieve a decrease of surface tension and thus again increasing fluidity of the oil within the well. Another form of tertiary recovery is based on the idea of injecting microbes into the well that in a set of complex, organic chemical processes break down hydrocarbons to more fluid components.