Primary Recovery

Primary recovery is the first stage of petroleum and gas production. Crude oil extraction from a new well relies on the natural rise of the oil due to pressure differences between the oil field and the bottom-hole of the well. Mechanical lift systems such as a rod pump are also a primary recovery method.

Primary recovery is also known as primary production.

Primary recovery is less expensive than secondary and enhanced oil recovery (EOR). Enhanced oil recovery techniques are costly and use gases, chemicals, and heat to extract the oil. EOR is expensive and not always useful. Primary recovery takes advantage of the natural tendency for crude oil to rise to the surface once a well punctures the underground oil field.

The crude oil, contained in the ground, is under intense pressure, whereas the hollow well shaft is at lower pressure. Oil will flow rapidly into the area of lowest pressure into the well and up to the surface. When oil under pressure is uncontained, it can result in an oil geyser, spouting from the earth. During primary recovery typically only 5- to 15-percent of a well’s total of potential hydrocarbons are extracted.

Hydrocarbons are organic chemical compounds, composed exclusively of hydrogen and carbon atoms. Hydrocarbons can be solids, liquids or gasses. Petroleum and natural gas are made primarily of hydrocarbons. These compounds combust in the presence of sufficient oxygen and produce carbon dioxide, water, and heat. Methane is the primary component of natural gas and is the simplest hydrocarbon because of its structured. 

Oil and gas companies will use an estimated ultimate recovery (EUR) calculation to determine if the oil or gas contained in a field has the potential to make the hydrocarbon recovery profitable.

Various factors can cause the natural pressures that drive oil to the surface during primary recovery. One common primary recovery method is a gas drive. The gas drive uses the energy of expanding underground gas to force the oil to the surface. Another recovery method is the water drive. Water drives use underground aquifers to exert pressure on the oil. Also, in some shallow and steeply graded oil fields, the oil will drain to the surface with the force of gravity.

As production continues, the reservoir pressure will decrease, and hence the differential pressure will decrease. This decrease in pressure may necessitate the use of an artificial lifting system to continue production. The most common artificial lift for use in primary recovery is the rod pump. The rod pump employs a beam-and-crank assembly to create a reciprocating motion which transfers to vertical lift through a series of plungers and valves. This method is the classic oil derrick with its distinctive bobbing horse head.

Eventually, the primary recovery reaches its limit. This limit happens when the reservoir pressure is too low, or when the mix of gas or water into the output stream is too high. At this point, even artificial lift systems are not economical for the continued extraction of the hydrocarbons. 

The next stage involves the use of secondary recovery techniques such as water injections, which attempts to force the oil to the surface through applied pressure. The final recovery stage is enhanced oil recovery (EOR), which goes beyond applying pressure to altering the properties of the oil itself.