The critical role of natural gas compressors in the oil and gas industry

In today’s world energy structure, natural gas, as a clean and efficient fossil fuel, is becoming increasingly important. From extraction to transportation to final utilization, every link of natural gas is inseparable from a vital equipment natural gas compressor. Natural gas compressors increase the pressure of natural gas so that it can overcome pipeline resistance, enter storage facilities or meet specific process requirements. It can be said that natural gas compressors are the veritable “heart” of the oil and gas industry, and their performance and efficiency directly affect the operating costs, safety and environmental performance of the entire industry. This article will explore in depth the basic working principle of natural gas compressors, their key role in oil and gas extraction, transportation and storage, as well as their trends in improving production efficiency and future development, aiming to fully demonstrate the indispensable position of natural gas compressors in the oil and gas industry.

1.Basic Working Principle of Natural Gas Compressors

The core function of natural gas compressors is to raise low-pressure gas to high pressure. Its working principle can be broadly divided into two categories: positive displacement compressors and dynamic compressors.

① Positive displacement compressors:

This type of compressor compresses gas by changing the volume of the working chamber. When the volume of the working chamber decreases, the gas is compressed and the pressure increases. Common positive displacement compressors include:

◉ Piston compressors: The reciprocating motion of the piston in the cylinder is used to compress the gas. When the piston moves inward, the cylinder volume decreases and the gas is compressed. Piston compressors have a simple structure and high reliability, and are suitable for various pressure ranges, especially in high-pressure applications. They can be single-stage or multi-stage compression to achieve a higher pressure ratio. Piston compressors can be divided into electric, gas or diesel drive according to the drive mode. According to the arrangement of the cylinders, they can be divided into vertical, horizontal, opposed, etc. Its advantages are a wide range of pressure applications, high efficiency, and strong adaptability to changes in gas components. The disadvantages are that there are more easily worn parts, relatively large maintenance, and possible high noise and vibration.

◉ Screw compressors: A pair of intermeshing spiral rotors rotate in the casing to compress the gas. When the rotors rotate, the gas is sucked into the cavity between the rotors. As the rotors rotate, the cavity volume decreases and the gas is compressed. Screw compressors have compact structure, smooth operation, low noise, and are suitable for medium and low pressure ranges. They are often used in gas gathering stations and gas processing plants. According to the number of rotors, they can be divided into single screw and twin screw. Twin screw compressors are more widely used and have the advantages of high efficiency, small size, and easy maintenance. Screw compressors are less sensitive to solid particles in the gas and are suitable for processing gases containing impurities. Its advantages are simple and compact structure, smooth and reliable operation, and easy maintenance. The disadvantages are relatively low efficiency, high requirements for gas purity, and not suitable for high-pressure occasions.

◉ Vane compressor: The vanes on the rotor are used to rotate in the stator cavity to compress the gas. When the vanes rotate, cavities with gradually decreasing volumes are formed, in which the gas is compressed. Vane compressors have simple structure, small size, and easy maintenance. They are often used in small gas recovery and boosting occasions. Its advantages are simple structure, small size, light weight, and reliable operation. The disadvantages are low efficiency, high requirements for gas purity, and not suitable for large displacement and high-pressure occasions.

◉Roots blower: Although it is usually called a blower, Roots blower is also a positive displacement compressor, which conveys and pressurizes gas by rotating two “8”-shaped rotors in the casing. Its compression ratio is relatively low, and it is mainly used for gas transportation and low-pressure supercharging. It is often used in sewage treatment, pneumatic transportation and other fields. Its advantages are simple structure, easy maintenance and high reliability. The disadvantages are low efficiency, high noise and low compression ratio.

② Dynamic compressor:

This type of compressor transfers energy to the gas through a high-speed rotating impeller, increases the speed and kinetic energy of the gas, and then converts the kinetic energy into pressure energy through a diffuser, thereby achieving gas compression. Common dynamic compressors include:

◉ Centrifugal compressor: The high-speed rotating impeller is used to throw the gas to the periphery, and the centrifugal force is used to increase the speed and pressure of the gas. Centrifugal compressors have large flow, compact structure and stable operation. They are suitable for large flow, medium and low pressure occasions. They are commonly used compressors in long-distance natural gas pipelines and large liquefaction plants. Its advantages are simple structure, small size, light weight, easy maintenance and stable operation. The disadvantage is that it is suitable for medium and low pressure occasions, is sensitive to changes in gas composition, and has low efficiency in high pressure occasions.

◉ Axial flow compressor: A series of impellers and guide vanes are used to compress the gas step by step along the axial direction. Axial flow compressors have large flow and high efficiency, and are suitable for large flow and high pressure occasions. They are often used in large natural gas processing plants and gas turbines. Its advantages are high efficiency, large flow, and suitable for high pressure occasions. The disadvantages are complex structure, high cost, and high gas purity requirements.

2.The role of natural gas compressors in oil and gas production

Natural gas compressors play a vital role in the oil and gas production stage. Their main functions include:

◈Enhanced Oil Recovery (EOR): In the later stages of oil production, reservoir pressure decreases and crude oil production decreases. By injecting gases such as natural gas or carbon dioxide into the reservoir, the reservoir pressure can be increased and the viscosity of crude oil can be reduced, thereby improving the crude oil recovery rate. The natural gas compressors is responsible for compressing the injected gas to the required pressure for injection into the ground. This is called tertiary oil recovery technology such as “gas drive” or “miscible drive”. The performance and reliability of the compressor directly affect the efficiency and economy of the EOR project.

◈Associated gas processing and recovery: A large amount of natural gas is produced during the oil extraction process, which is called “associated gas”. In order to make full use of these valuable resources, the associated gas needs to be collected, separated, purified and compressed. In this process, the natural gas compressors is responsible for pressurizing the associated gas so that it can be transported to the processing plant or directly used. In the past, associated gas was often directly burned (vented), which not only wasted resources but also caused environmental pollution. Nowadays, with the improvement of environmental awareness and the advancement of technology, the recycling of associated gas has received more and more attention. As a key equipment in the associated gas recovery system, the efficiency and reliability of the compressor directly affect the recovery rate and economic benefits.

◈Shale gas and tight oil and gas extraction: Shale gas and tight oil and gas are usually stored in low-permeability formations and need to be released through technologies such as hydraulic fracturing. After fracturing, the produced gas needs to be pressurized and processed. Natural gas compressors are used in shale gas and tight oil and gas extraction to pressurize the produced gas so that it can be sent to the processing plant or gas pipeline. Since these gases may contain high levels of hydrocarbon liquids and impurities, higher requirements are placed on the design and materials of the compressor.

◈Wellhead pressurization: In some old oil fields or low-yield gas wells, due to the drop in formation pressure, the produced natural gas pressure is low and cannot directly enter the gathering and transportation system. By installing small natural gas compressors at the wellhead, the produced gas can be pressurized so that it can enter the gas gathering station or processing plant. Wellhead pressurization can effectively extend the economic life of low-yield gas wells and improve the recovery rate of a single well.

◈Gas gathering station pressurization: Natural gas produced from various gas wells is usually collected at a gas gathering station. At the gas gathering station, natural gas needs to be initially processed and pressurized so that it can be transported to the natural gas processing plant through a pipeline. The compressors used in the gas gathering station are usually piston or screw compressors, and the appropriate model is selected according to the gas volume and pressure requirements. The compressor at the gas gathering station is a key link in the natural gas gathering and transportation system, and its stable operation is crucial to ensuring the supply of natural gas.

◈Gas processing plant inlet pressurization: Before natural gas is transported to the processing plant, it may need to be further pressurized to meet the requirements of the processing process. The natural gas processing plant is responsible for removing non-hydrocarbon components (such as water, carbon dioxide, hydrogen sulfide, etc.) from natural gas and separating hydrocarbons of different components (such as methane, ethane, propane, etc.). The intake compressor ensures that the processing plant can obtain raw gas with sufficient pressure and flow.

◈Carbon dioxide capture and storage (CCS): In some carbon capture and storage projects, natural gas compressors are used to compress the captured carbon dioxide for transportation and underground storage. High-pressure compression is one of the key steps in carbon dioxide transportation and storage.

◈Nitrogen boosting: In some oil and gas fields, nitrogen is used as gas for reservoir boosting or downhole operations. Natural gas compressors can also be used to compress nitrogen to meet these needs.

3.The key role of natural gas compressors in transportation and storage

Natural gas has the characteristics of large volume and low energy density. In order to achieve long-distance, large-scale transportation and storage, it must be pressurized or liquefied. Natural gas compressors play a core role in the transportation and storage of natural gas:

Long-distance pipeline transportation: Natural gas is transported from the production site to the consumption site through long-distance pipelines. Due to the friction resistance of the inner wall of the pipeline and the height difference along the way, the pressure of natural gas will gradually decrease when it flows in the pipeline. In order to maintain the flow and pressure in the pipeline, it is necessary to set up a compressor station along the way and use natural gas compressors to pressurize the natural gas. The compressor station is the “power source” of the long-distance pipeline. Its number and distribution depend on the length, diameter, transportation volume and terrain along the way. Usually a compressor station is set up every few hundred kilometers. Long-distance pipelines usually use centrifugal compressors because they have large flow and stable operation and are suitable for continuous operation. The efficiency of the compressor directly affects the cost of gas transmission. Efficient compressors can reduce energy consumption and reduce operating costs. The safe operation of the compressor station is crucial to ensuring the safety of natural gas supply.

Natural gas storage: There are two main ways to store natural gas: underground storage and ground storage.

   ◉ Underground storage: Mainly use depleted oil and gas reservoirs, salt caverns or aquifers to store natural gas. During the low period of natural gas demand, excess natural gas is injected into underground storage facilities; during the peak period of demand, natural gas is extracted. Both the injection and extraction processes require natural gas compressors to provide the required pressure. When injected, natural gas needs to be compressed to a pressure higher than that of the underground reservoir; when produced, the produced gas needs to be pressurized to be sent to the gas pipeline. Underground gas storage can play the role of peak load regulation, emergency reserve and strategic reserve, and improve the flexibility and reliability of natural gas supply.

   ◉ Ground storage: Mainly through liquefied natural gas (LNG). Natural gas is cooled to an extremely low temperature (about -162°C) to liquefy it, and its volume can be reduced by about 600 times, which is convenient for storage and transportation. LNG receiving stations receive liquefied natural gas from LNG carriers, then gasify it and transport it to users through pipelines. LNG plants are responsible for liquefying natural gas and storing it in cryogenic storage tanks. Natural gas compressors play an important role in both the production and reception of LNG. In LNG plants, compressors are used for refrigeration cycles and to increase the pressure of natural gas; in LNG receiving stations, compressors are used for the external transmission of gasified natural gas.

Urban gas pipeline network transportation: To transport natural gas from long-distance pipeline receiving stations to end users, it is necessary to pass through the urban gas pipeline network. Before entering the urban pipeline network, natural gas needs to be depressurized through regional pressure regulating stations and building pressure regulating stations. In some cases, in order to meet the pressure requirements at the end of the pipeline network, it may also be necessary to set up a small booster station and use natural gas compressors to boost the natural gas.

Direct gas supply to industrial users: Some large industrial users receive natural gas directly from high-pressure natural gas pipelines. In order to meet the pressure required for their process flow, it may be necessary to install natural gas compressors on the user side for boosting.

CNG and LNG filling stations: Compressed natural gas (CNG) and liquefied natural gas (LNG) are becoming increasingly popular as automotive fuels. CNG filling stations need to compress natural gas to high pressure (usually 20-25MPa) and store it in gas cylinders; LNG filling stations need to gasify and compress liquefied natural gas to a certain pressure. Natural gas compressors are the core equipment of CNG and LNG filling stations.

4.Efficiency improvement of natural gas compressors in oil and gas production

Under the increasingly fierce market competition and increasingly stringent environmental protection requirements, it is of great significance to improve the efficiency of natural gas compressors and reduce energy consumption and operating costs. The efficiency improvement of natural gas compressors can be achieved from multiple aspects:

Improve the design and manufacturing level of the compressor itself:

✔Aerodynamic design optimization: By improving the aerodynamic design of components such as impellers, guide vanes, and volutes, the flow loss of gas inside the compressor is reduced and the compression efficiency is improved.

✔Rotor dynamics optimization: Optimize the rotor structure and bearing system, improve the running stability of the rotor, reduce vibration and noise, and extend the life of the equipment.

✔Material selection and surface treatment: Select high-strength, corrosion-resistant, and wear-resistant materials, and perform surface treatment on key components to improve the reliability and durability of the compressor.

✔Precision machining and assembly: Improve the machining accuracy and assembly quality of components, reduce gaps, reduce leakage, and improve the efficiency of the compressor.

Optimize the operation of the compressor system:

✔Frequency conversion speed regulation technology: The speed of the compressor motor is adjusted by the frequency converter to match its output flow and pressure with actual needs to avoid unnecessary energy waste. This is especially important for situations where the gas volume fluctuates in the natural gas transmission pipeline.

✔Intelligent control system: Using advanced control algorithms and sensor technology, the operating status of the compressor is monitored in real time, the control parameters are optimized, the compressor is optimally operated, and efficiency is improved.

✔Multi-unit collaborative control: In situations where multiple compressors are operated in parallel, the overall efficiency of the system is optimized by optimizing the start and stop and load distribution of each unit.

✔Gas cooling system optimization: In the multi-stage compression process, intermediate cooling can effectively reduce the temperature of the gas and improve the compression efficiency of the next stage. Optimizing the design and operation of the cooling system can improve the overall compression efficiency.

Reduce energy loss:

✔Reduce pipeline resistance: Optimize pipeline design, reduce pipe diameter changes and the number of elbows, and reduce the flow resistance of gas in the pipeline.

✔Reduce leakage: Regularly inspect and maintain the compressor and pipeline system to reduce gas leakage and energy loss.

✔Waste heat recovery: Natural gas compressors generate a lot of heat during operation. Using this heat for heating, power generation or industrial processes through waste heat recovery systems can improve energy efficiency.

Choose the right drive mode:

✔High-efficiency motor: Choose a high-efficiency motor as the drive device of the compressor to reduce power consumption.

✔Gas turbine: In long-distance pipelines and other occasions, gas turbines as the drive device of the compressor have the advantages of high power and high efficiency, and can directly use the transported natural gas as fuel to reduce dependence on external energy.

✔Fuel cell: As a new type of energy conversion technology, fuel cells have the advantages of high efficiency and low pollution, and are expected to be used in the drive of natural gas compressors in the future.

Remote monitoring and fault diagnosis: Through the remote monitoring system, the operating parameters of the compressor are monitored in real time, and faults are discovered and eliminated in time to avoid downtime and efficiency reduction caused by faults. Through big data analysis and artificial intelligence technology, the operating data of the compressor is analyzed to predict potential faults, achieve preventive maintenance, reduce maintenance costs, and improve operating efficiency.

Application of energy-saving technology: For example, the expander energy recovery technology can recover part of the energy from the expansion of high-pressure natural gas to drive compressors or other equipment.

Conclusion

As an indispensable key equipment in the oil and gas industry, the importance of natural gas compressors is self-evident. From oil and gas extraction, associated gas recovery, to long-distance pipeline transportation, underground storage, LNG production and reception, to urban gas pipeline networks and end users, natural gas compressors play a core role. It not only improves the recovery rate and utilization efficiency of oil and gas resources, ensures the safe, efficient transportation and reliable storage of natural gas, but also makes important contributions to the efficiency improvement of oil and gas production.

With the continuous advancement of technology and the transformation of energy structure, natural gas compressors will develop in a more efficient, intelligent and environmentally friendly direction. In the future, natural gas compressors will be more closely integrated with new energy and play a more important role in building a clean, low-carbon and safe modern energy system. A deep understanding of the principles, applications and development trends of natural gas compressors is of great significance to professionals engaged in the oil and gas industry and readers who are concerned about the energy field. Natural gas compressors, the “heart” of this silent industry, will continue to provide strong impetus for global energy supply and economic development.