An oil reservoir typically has enou

An oil reservoir typically has enough pressure to move petroleum from the subsurface to the surface, where production equipment is located. However, reservoir pressure declines over time, and oil production is reduced as a result. Different approaches, such as injecting water or gas into the reservoir or installing a pump in the well, enhance oil recovery from the reservoir; these processes are called advanced oil recovery or artificial lift. Advanced oil recovery that is accomplished by injecting gas into the reservoir is called a gas lift.Fig.1.20 portrays a drilling well that is penetrating into the reservoir rock. Production tubing is run into the drilled well to produce oil, gas, and water. Gas is injected into the area between the tubing and wellbore for advanced oil recovery, resulting in the fluid is being forced up and out of the wellbore through the production tubing.