Primary recovery: During the primary recovery stage, oil drilling companies make use of several natural processes to drive the reservoir, including the expansion of gas contained within the crude oil itself, the displacement of oil by natural water flowing downward into the well, a proliferation of natural gas near the top of the reservoir, and gravity drainage. In most cases, oil is forced to the surface by the collecting of underground pressure in the oil reservoir. Many companies choose to install a network of valves to funnel the oil into a pipeline, which greatly facilitates transportation and storage. In general, the primary recovery process yields a 5 to 15 percent recovery rate.
Secondary recovery: After the initial pressure contained within the well falls below a certain level, drilling companies must then utilize a number of different techniques to extract the oil from the earth, referred to as secondary recovery methods. Secondary recovery techniques typically rely on the use of an external power source to drive the reservoir and make it easier to obtain the oil from the well. In addition to beam pumps and electrical submersible pumps, two of the most common ways to extract oil after the dissipation of the initial pressure, secondary recovery methods include techniques such as natural gas reinjection, water injection, and gas lift. Because the secondary recovery draws upon energy from manmade sources, it is able to produce a recovery rate of more than 30 percent.
Tertiary recovery: After secondary recovery methods have extracted as much oil as they possibly can, tertiary recovery techniques allow driller to extract another 5 to 15 percent of the oil reservoir. In most cases, tertiary recovery involves increasing the mobility of the oil to make it more viscous and easy to extract. Common methods to increasing oil mobility include steam injection, the introduction of surfactants to break up surface tension, and flooding the well with carbon dioxide.