- Methods
- Pumping systems
- Mechanical pumping system
- Hydraulic pumping system
- Electric submersible pumping system
- Gas lift system
- Selection of an artificial production system
- References
The artificial production systems are processes used in oil wells to increase pressure within the reservoir and thus encourage the oil rises to the surface.
When the natural impulse energy of the reservoir is not strong enough to push the oil to the surface, an artificial system is used to obtain more material.
Source: pixabay.com
While some wells contain enough pressure for the oil to rise to the surface without having to perform any stimulation, most do not, requiring an artificial system.
Of the estimated 1 million oil and gas wells produced in the world, only 5% flow naturally, making almost all of the world's oil and gas production dependent on efficient operations of artificial production systems.
Even for those wells that initially have a natural flow to the surface, that pressure is depleted over time. For them, the use of an artificial system is also required.
Methods
Although there are several methods to achieve artificial production, the two main types of artificial systems are pump systems and gas lift systems.
For example, in the United States, 82% of wells use mechanical rockers, 10% use gas lift, 4% use electric submersible pumps, and 2% use hydraulic pumps.
Pumping systems
Mechanical pumping system
This system uses equipment on the surface and below it to increase pressure and push hydrocarbons towards the ground. Mechanical pumps are the well-known rocker arms seen in onshore oil wells.
On the surface, the rocker swings back and forth. It is connected to a chain of rods called sucker rods, which sink into the well.
The sucker rods are connected to the sucker rod pump, which is installed as part of the pipes near the bottom of the well.
As the rocker oscillates, this operates the rod chain, sucker rod, and sucker rod pump, working in a similar way to pistons within a cylinder.
The sucker rod pump lifts the oil from the bottom of the well to the surface. Generally, the pumping units are powered electronically or by means of a gasoline engine, called a prime mover.
In order for the pumping system to function properly, a speed reducer is employed to ensure that the pump unit moves steadily.
Hydraulic pumping system
This pumping system applies a hydraulic pump from the bottom of the well, instead of sucker rods, to bring the oil to the surface. Production is forced against the pistons, causing the pressure and the pistons to lift the fluids to the surface.
Similar to the physics applied to the water wheels that drive ancient mills, natural energy is used within the wellbore to bring production to the surface.
Hydraulic pumps are generally made up of two pistons, one on top of the other, connected by a rod that moves up and down inside the pump.
Both surface hydraulic pumps and underground hydraulic pumps are powered by clean oil, previously extracted from the well.
The pump on the surface sends the clean oil through the pipes to the hydraulic pump installed underground at the lowest part of the pipe chain. The reservoir fluids are sent to the surface by a second parallel chain of pipes.
Electric submersible pumping system
Electric submersible pumping systems employ a centrifugal pump below the level of the reservoir fluids. Connected to a long electric motor, the pump is made up of several impellers, or blades, that move the fluids within the well.
The whole system is installed at the bottom of the pipe chain. An electrical cable runs the length of the well and connects the pump to a source of electricity on the surface.
The electric submersible pump applies artificial production by rotating the impellers on the pump shaft, which exert pressure on the surrounding fluids, forcing them to rise to the surface.
Electric submersible pumps are mass producers, and can lift more than 25,000 barrels of fluids per day.
Gas lift system
As an emerging artificial production system, gas lift injects compressed gas into the well to restore pressure, thereby making it produce. Even when a well is flowing without artificial lift, it often uses a natural form of gas lift.
The injected gas, mainly nitrogen, reduces the pressure at the bottom of the well by decreasing the viscosity of the fluids in the well. This, in turn, makes fluids flow more easily to the surface. Typically, the gas that is injected is the same recycled gas that is produced in the oil well.
Although it has very few units on the surface, this system is the optimal choice for application offshore. Downhole, compressed gas is injected into the tube ring, entering the well through numerous access points, called gas lift valves.
As gas enters the tube at these different stages, it forms bubbles, relieves fluids, and decreases pressure.
Selection of an artificial production system
To obtain the maximum development potential from any oil or gas well, the most efficient artificial production system must be selected. The criteria used historically to select the artificial system for a particular well vary widely in the industry:
- Operator experience.
- What artificial systems are available for installations in certain areas of the world.
- The artificial system that is operating in the contiguous or similar wells.
- Determine which systems will be implemented at the desired speed and from the required depths.
- Evaluate lists of advantages and disadvantages.
- Expert systems to discard and select systems.
- Evaluation of initial costs, operating costs, production capacities, etc. with the use of economics as a selection tool, generally on the basis of present value.
In most cases, the artificial production system that has performed best in similar fields serves as the selection criterion. In addition, the equipment and services available can easily determine which artificial production system will be applied.
However, when part of the scenario would require significant costs to maintain high production rates in the wells, it is prudent to consider most of the available evaluation and selection methods.
References
- Rigzone (2019). How Does Artificial Lift Work? Taken from: rigzone.com.
- UNAM (2019). Fundamentals of Artificial Production Systems. Taken from: ptolomeo.unam.mx:8080.
- Schlumberger (2019). Artificial Lift. Taken from: slb.com.
- Petrowiki (2019). Artificial Lift. Taken from: petrowiki.org.
- Wikipedia, the free encyclopedia (2019). Artificial Lift. Taken from: en.wikipedia.org.