“Secondary recovery involves the feasibility of the fields. Water or gas is pumped into the reservoir to produce more pressure on the oil. When natural pressure is too low to bring the oil to the well.”
Incentives such as the operator knew where the oil was, the owning of the mineral rights, and having the facilities for processing was already in place. Such incentives led to the development of several techniques that are called “secondary recovery.”
“The four basic possibilities in such recovery are mining, squeezing, pushing, and sucking.”
Mining involves removing the oil bearing rock from its position several hundreds or thousands of feet below the surface of the earth. It is brought to the surface for processing as an ore. This method proved to be uneconomical because of the concentration of ore is low and the depths of most deposits make mining difficult.
Squeezing has to do with the pressing out the oil from the rock by force.
Pushing is the most successful secondary recovery. This is done by displacing the oil from the rock with some other substance.
Sucking is a type of variation of pushing. The air in the atmosphere is used as a pusher.
The primary techniques are supplemented by the injection of water or gas in the secondary recovery technique. They do not displace all of the oil. That which is trapped by capillaries force in the pores is called residual oil.