Oil extraction and recovery
It is not so easy to extract this important raw material, as there are no oil lakes that have only to be delivered above ground. In fact the crude oil is mostly embedded together with saltwater in the pores of rock like sandstone or lime rock. Layers of impermeable rock like slate prevent the crude oil from floating up. Oil reservoirs that are finally discovered with the help of extensive methods like 3D seismic technology or test drillings have to be equipped for economical oil extraction.
During the long time of oil production more and more salt water will be delivered together with the oil. During the life time of an oil field this so called “water cut” increases steadily until more water than oil comes to the surface. Well organized oil fields will produce oil profitably even with contents of water higher than 90%. The delivered water usually is saltwater with a medium to very high content of chlorides together with fine solids and remaining hydrocarbons. This water cannot be poured into the surrounding environment due to ecological reasons.
Depending on the size of on oilfield it can take up to decades of years until the oil delivery rates start sinking. In average it is around 40 years.
Primary oil recovery 10-20%
During the first stage of oil production, the primary recovery stage, oil is forced to the surface by the underground pressure – in average up to 10% only.
With decreasing reservoir pressure pumps like beam pumps (“horsehead pumps”) are needed to bring the oil up to the well head.
The recovery factor with this traditional pump technology goes up to 15% to 20% maximum.
Alternatively electric driven multistage submersible pumps that can achieve significantly higher delivery rates than the horsehead pumps are used. Also progressive cavity submersible pumps for higher viscosities and significant content of sand that comes together with the crude oil are used. Another improvement can be generated by using multiphase pumps (special screw pumps or progressive cavity pumps), that are increasing the recovery rate by lowering the wellhead pressure and are pumping crude oil together with gas and formation water to a central separation facility. As real positive displacement pumps multiphase pumps can also deliver gas contents close to 100% und are not changing their delivery rates at so called slugs - a sudden change from high gas content to liquid phase or reversed. As an additional advantage polluting gas flaring on the oil field can be omitted and the gas can be used as valuable additional energy source.