In oilfields, you often hear questions like: Why isn’t this well using a pumping unit? Why do some wells use ESPs while others use screw pumps? Are ESPs the highest-yielding equipment?
Many newcomers to the oilfield have a misconception: that the more advanced the oil production equipment, the better.
In reality, there’s no absolute “good” or “bad” oil production equipment; it’s all about whether it’s suitable for the specific well. In oil production engineering, there’s a classic saying:
Choosing the right lift method is more important than later maintenance.
For the same oil well, if the wrong lift method is chosen, the following may occur:
- Insufficient fluid supply;
- Increased energy consumption;
- Frequent equipment failures;
- Shortened pump inspection cycles;
- Significantly increased production costs.
Choosing the appropriate artificial lift method can not only increase production but also reduce maintenance costs and extend equipment life. Currently, the three most widely used artificial lift equipment in China’s onshore oilfields are:
• Beam Pump
• Electric Submersible Pump (ESP)
• Progressing Cavity Pump (PCP)
Each type is suitable for different types of oil wells. Today, we will comprehensively analyze the differences between these three types of equipment from multiple perspectives, including working principles, applicable scope, advantages and disadvantages, and cost.
1. Why do oil wells need artificial lift?
In the early stages of oilfield development, underground pressure is sufficient, and many oil wells can flow naturally using formation energy. However, with continuous production:
- Formation pressure decreases;
- Crude oil flow weakens;
- Natural flow stops.
At this point, artificial lift is necessary, with only one purpose: to continuously, safely, and economically lift underground crude oil to the surface. Different reservoirs require different lift methods, thus forming the three most widely used oil production equipment.
Type 1: Beam Pumping Unit – The Most Classic Oil Production Equipment in Onshore Oilfields
If you were to ask which equipment best represents Chinese oilfields, the answer would undoubtedly be: the beam pumping unit, also known as the “nodding donkey” pump.
It has become the most representative equipment in onshore oilfields such as Daqing, Shengli, Changqing, Zhongyuan, and Xinjiang. Working Principle: The pumping unit itself does not directly pump oil; the downhole pump is responsible for lifting the crude oil.
The entire working process is as follows:
- Electric motor
- Gearbox
- Four-bar linkage
- Up-and-down movement of the donkey head
- Up-and-down movement of the sucker rod
- Reciprocating motion of the plunger
- Downhole pump completes oil suction and discharge
- Crude oil enters the surface along the tubing.
The entire process is a mechanical reciprocating lift. Suitable Well Types: The pumping unit is particularly suitable for:
- Low-to-medium production wells
- Old oilfields
- Shallow to medium-medium production wells
- Water-injected development wells
- Low gas-oil ratio wells
The vast majority of onshore oil wells in my country use this method. The biggest advantages are reliability, simple structure, and decades of mature technology. Specifically:
- Long equipment lifespan;
- Convenient maintenance;
- Commonly used parts;
- Rich management experience;
- Lower requirements for the power grid;
- Continuously improving automation.
Many pumping units have been operating continuously for over 20 years and are still running normally.
Disadvantages, of course, also exist.
For example, the deeper the well, the heavier the rod string, leading to decreased efficiency and increased susceptibility to rod breakage, uneven wear, and severe wear.
Advantages of pumping units
Furthermore, the advantages of pumping units are not obvious in high-gas-content wells, deep wells, and high-displacement wells. A field case in a water injection development area of
- Power consumption increased by approximately 35%;
- Pump maintenance costs increased significantly;
- Actual daily oil production increased by only 0.2 tons.
After comprehensive economic evaluation, pumping unit production was resumed. By optimizing stroke, stroke frequency, and pump diameter, production was restored to its original level, with even lower operating costs. Conclusion: For low- to medium-yield old wells, pumping units are often the most economical choice.
The second type: Electric Submersible Pump (ESP) – The “High-Flow Player” for High-Yield Wells
If pumping units represent stability, then ESPs represent high production. In recent years, many new blocks, deep wells, and horizontal wells in China have begun to adopt ESPs extensively. The working principle is self-explanatory: the motor is installed downhole, powered by a cable, driving a multi-stage centrifugal pump to rotate at high speed. The impeller continuously increases the liquid energy, ultimately delivering the crude oil to the surface. It belongs to the category of continuous centrifugal pump lifting. The biggest difference between ESPs and pumping units is the absence of a sucker rod. Applicable well types: ESPs are particularly suitable for:
- Deep wells
- High-displacement wells
- High-yield wells
- High-liquid-volume wells
- Directional wells
- Horizontal wells
Many oil wells producing hundreds of tons of liquid per day can only use ESPs.
Advantages of Electric Submersible Pump (ESP)
Its biggest advantage is its large production capacity. For example, a single well can produce hundreds or even thousands of tons of fluid per day, which is impossible with a pumping unit.
Furthermore, the wellhead equipment is simple, requiring no large pumping units, resulting in a small surface footprint and a high degree of automation.
However, its disadvantages are equally apparent.
For example, the downhole equipment is complex, maintenance is difficult, pump inspection costs are high, it has high requirements for the power grid, and it is particularly vulnerable to sand, wax, gas, and cable failures.
A field case: A deep well in Xinjiang, exceeding 3200 meters in depth, produced nearly 280 tons of fluid per day. Initially, a rod-pumped system was used, resulting in long-term rod fatigue and frequent rod breakage.
Later, it was switched to an ESP (Electrical Pumping Unit), which stabilized the daily fluid production at 320 tons and operated continuously for a year without any major failures. For such deep wells, the advantages of ESP are very clear.
The third type: Screw Pump (PCP) – a “specialized equipment” for heavy oil wells and sand-bearing wells
Many people who see a screw pump for the first time think it looks similar to a screw. In fact, its core component is indeed a special helical rotor.
Working Principle: Downhole pumps mainly consist of a metal rotor and a rubber stator. The rotor rotates continuously, forming a continuous sealed cavity, and the liquid is continuously transported upwards along the spiral cavity.
This type belongs to: volumetric continuous lift.
The biggest characteristic: continuous flow rate, unlike pumping units which move up and down repeatedly.
Particularly suitable for:
- Heavy oil wells
- High-viscosity crude oil
- Sand-bearing wells
- Foamy oil wells
- Easily emulsifiable oil wells
This method is widely used in Canadian heavy oil development. It is also widely applied in heavy oil blocks such as Liaohe, Xinjiang, and Shengli in my country.
Advantages of Screw Pump (PCP)
The biggest advantage is: strong sand resistance, good lifting effect for heavy oil, stable fluid flow, low shear, less prone to emulsification, and relatively long maintenance cycle.
Disadvantages:
However, the biggest weakness of screw pumps is: the rubber stator has limited temperature resistance and is susceptible to: high temperatures, corrosion, and dry friction. Insufficient fluid supply can easily burn out the stator.
Field Case: A heavy oil well in the Liaohe Oilfield with crude oil viscosity exceeding 6000 mPa·s.
Initially, pumping units were used, but due to the high viscosity of the liquid, the sucker rods were overloaded and frequently broke.
Later, screw pumps were used, increasing daily oil production by approximately 40% and extending the maintenance cycle from 4 months to 10 months.
Comparison of Three Oil Production Equipment
| Comparison Projects | Beam pumping unit | Electric Submersible Pump (ESP) | Screw pump (PCP) |
| Working principle | The sucker rod drives the downhole plunger pump in reciprocating motion. | Downhole motor drives multi-stage centrifugal pump for continuous lifting | The rotor rotates within the stator to form a sealed cavity for continuous transport. |
| Applicable well types | Low-to-medium production wells, shallow-to-medium production wells, and old oilfields | Deep wells, high-yield wells, large-volume wells, horizontal wells | Heavy oil wells, sand-bearing wells, high-viscosity oil wells |
| Daily production capacity | Medium | Very high | Medium |
| Well depth adaptability | Shallow wells have more advantages | Deep wells have obvious advantages | Medium to deep wells are more suitable |
| Sand resistance | Ordinary | Poor | Very good |
| Adaptable to high gas content | Ordinary | Poor (easily gets airlocked) | Very good |
| Equipment maintenance | Most convenient | Most complex | Medium |
| Level of automation | Higher | Very high | Higher |
| One investment | Lower | Highest | Medium |
| Operating costs | Lower | Higher | Medium |
| Typical applications | Daqing, Shengli and other old onshore oilfields | Deep wells, high-yield new areas | Liaohe, Xinjiang and other heavy oil blocks |
How to Select Oil Production Equipment on-site?
Experienced oil production engineers don’t simply choose the best equipment; they consider the following factors comprehensively:
- Reservoir conditions: pressure, permeability, fluid supply capacity;
- Well conditions: well depth, well inclination, horizontal section length;
- Fluid properties: crude oil viscosity, sand content, gas-oil ratio, wax content;
- Production goals: high production or low-cost operation;
- Economics: investment, maintenance costs, overhaul cycles, life cycle costs.
In conclusion
In oil production engineering, no single piece of equipment is suitable for all wells.
Pumping rigs, relying on their maturity, reliability, and low cost, have become the mainstay in established onshore oilfields; ESPs, with their high displacement and deep-well adaptability, are widely used in high-yield wells and new area development; screw pumps, with their excellent adaptability to heavy oil and sand content, play an irreplaceable role in special operating conditions.
Truly excellent oil production engineers are not familiar with one type of equipment, but can select the most suitable artificial lift method based on reservoir conditions, well conditions, and economic indicators. In oilfield development, choosing the right equipment is often more important than repeated maintenance later on.
