During primary production “Mother Nature” supplies the energy necessary for oil production. A reservoir produces approximately 10 percent to 20 percent of oil in this stage.
During “primary production” nature provides the fluid and force to move the oil. Gas associated with oil or water from an aquifer forces the fluid and moves the oil through the rock. For primary production the oil simply pumps to the surface.
When the cost of pumping oil exceeds the value of oil, due to the loss of the driving force, then another method for producing oil must be selected.