CHAPTER 1
INTRODUCTION
1.0 Background of Study
Oil and Gas is considered to be one of the major sources of energy in the world due to its high energy density, easy transportability, and relative abundance. It is a vital factor in every country’s economy. Almost all items that we buy, use, and consume are products of oil. The EIA (Energy Information Administration) stated that the world consumption of crude oil daily is 85.64 million barrels, which is equivalent to 2 liters of oil per day per person.
Generally, oil can be produced from the reservoir by the stored energy of the oil in the reservoir. This energy is obtained by the difference between the reservoir and wellbore pressures. If this difference is high, the well will be capable of producing naturally. Most oil wells worldwide produce naturally in their early lives until there is a decrease in the reservoir pressure which leads us to enhanced oil recovery.
When a well has been producing for a period of time, there will be decrease in reservoir pressure and as a result the difference between reservoir and wellbore pressure will decline. So, the energy in the well will not be able to lift oil up to surface, or it might lift oil to the surface but in less than economic volume. At this stage, artificial lift is introduced and it can be utilized to overcome this issue by reducing the wellbore pressure. This reduction will bring back the essential difference between the reservoir and wellbore pressure so oil can be extracted and lifted up to the surface.
One of the most important roles of artificial lift is to maximize the production rate from flowing wells. Artificial lift can be divided into two types, based on lifting mechanism: gas lifting and pumps. The gas lifting method makes use of a compressed gas that is injected from the surface to certain points in the tubing. This gas will lower the density of the fluid column in the tubing causing a reduction in the wellbore pressure and therefore increasing production. The pumping method, on the other hand, involves setting the pump at a certain depth inside the tubing that will cause it to be submerged below the liquid level. This pump will lower the wellbore pressure and hence increase the drawdown, thereby boosting production. The most common artificial lift methods used are as follows:
- Electrical Submersible Pump (ESP)
- Sucker Rod Pumps (SRP)
- GasLift (GL)
- Plunger Lift Pumps (PLNG)
- Progressive Cavity Pumps (PCP)
- Hydraulic Pumps (HP)
Bearden (2007), stated that ESP is the most competent and consistent method of artificial lift when moderate to high volume of oil needs to be lifted from the well. He also estimated the lifting capacity of ESPs to be as low as 150 barrels per day and as high as 150,000 barrels per day. Fig 1.1 below shows the various types of artificial lifts and their utilization worldwide.
