To increase the pressure in the reservoir (the oil well, precisely) and bring up the oil to the surface, the process of artificial lift is used. In case the natural energy is not enough or is way less to itself push up the oil towards the surface, artificial lift is put into use in order to get more production and recovery. Some oil wells generally do not require the artificial lift but in the US, most of the wells, around 96%, require an artificial lift from the inception when they are built. Even the wells that contain the natural force and flow for the oil to come up to the surface lose their pressure with time and a need for the artificial lift arises. Therefore, during the production life of a well, an artificial lift is always used, sooner or later when it is built.
There are many ways to make up for an artificial lift, but the main methods are pumping systems and gas lifts.
In the pumping system, the most common type is beam pumping. In beam pumping, equipment is fitted on and below the surface to increase the pressure so that the oil pushes itself up. Now, this equipment is made up of a sucker rod pump and sucker rod string. These beam pumps are commonly found on the onshore oil wells and are sometimes called jack pumps.
On the surface, the beam pumping system goes up and down, back and forth. This system is attached to a sucker rod which plunges itself into the wellbore. Now further, these sucker rods are linked with the sucker rod pump, which is fitted near the base of the wall as a part of the tubing string. Now as the beam pumping system goes back and forth, the rod string, sucker rod pump and sucker rods are operated as well. Now the sucker rod pump pulls up the oil through the well from the reservoir to the surface.
Generally, this is pumped for 20 times in a minute and these units for pumping are powered through electricity or gas engine, which is also called a prime mover. With the goal to make the beam system work efficiently, a speed reducer is also used to ensure that the pump moves steadily instead of the 600 revolutions in one minute which the engine takes.
Another system for artificial lift is hydraulic pumping. In this system, hydraulic pumping equipment is through its hydraulic pump picks up the oil and lift it to the surface, unlike the sucker rod pumps. In this system, the production is put against the pistons which creates a lot of pressure so that the pistons can lift up all or any of the fluids towards the surface. These hydraulic pumps are generally made of two pistons over each other that is further connected to a rod which goes up and down inside the pump. These pumps are powered with the help of power oil which is initially lifted up using the pump itself.
An electrical submersible pump is another system for creating the required pressure to bring oil to the surface. It has a centrifugal pump made up of blades that move the oil within the well and thus putting pressure upwards to take them to the surface. An electric submersible pump is considered to lift 25,000 barrels of oil in one day.
There is another emerging method of the artificial lift called gas lift which puts in compressed gas into the oil well to help the oil regain its natural pressure that helps in production. Typically, the gas which is put in is a recycled gas produced from the well. This gas decreases the pressure at the base of the well and thus helps the fluids to move up easily to the surface. As the gas enters into the well and decreases the pressure, it also reduces the weight of the fluid.
Gas lift is considered as the most effective choice to be used in an offshore oil well. In the USA, almost 80% of the oil wells use the beam pump because it is easy to use and largely available and the sucker rod pumps are considered good to go.