1.1 Artificial Lifting

Most oil wells in the early stages of their lives flow naturally to the surface and are called flowing wells. Flowing production means that the pressure at the well bottom is sufficient to overcome the sum of pressure losses occurring along the flow path to the separator. When this criterion is not met, natural flow ends and the well dies.

Wells may die for two main reasons: either their flowing bottomhole pressure drops below the total pressure losses in the well, or the opposite happens and pressure losses in the well become greater than the bottomhole pressure needed for moving the wellstream to the surface. The first case occurs when a gradual decrease in reservoir pressure takes place because of the removal of fluids from the underground reservoir. The second case involves an increasing flow resistance in the well, generally caused by (a) an increase in the density of the flowing fluid as a result of decreased gas production; or (b) various mechanical problems like a small tubing size, downhole restrictions, etc. Surface conditions, such as separator pressure or flowline size, also directly impact total pressure losses and can prevent a well from flowing.

Artificial lifting methods are used to produce fluids from wells already dead or to increase the production rate from flowing wells; and several lifting mechanisms are available to choose from. One widely used type of artificial lift method uses a pump set below the liquid level in the well to increase the pressure...