Natural Gas Processing & NGL
Natural gas processing and natural gas liquids (NGL) compressor lubricants are selected for compressors handling feed gas, intermediate process streams, residue gas, and hydrocarbon refrigerants within natural gas processing facilities.
Gas composition varies across these duties. Feed and NGL-rich streams contain methane, ethane, propane, butanes, pentanes, and heavier hydrocarbons; treated residue gas holds a much higher methane concentration. Where the process gas contacts the lubricant, dissolved hydrocarbons reduce its in-service viscosity.
NEXT Lubricants produces mineral, polyalphaolefin (PAO), polyalkylene glycol (PAG), and polyethylene glycol (PEG) formulations for natural gas processing and NGL applications. Mineral and PAO lubricants serve leaner streams where dilution stays controlled. PAG and PEG chemistries resist viscosity reduction in hydrocarbon-rich process and refrigeration duties.
For position-by-position selection across feed gas, refrigeration, fractionation, and residue gas, see NGL Plant Compression: Matching Lubricant to Position, from Inlet to Fractionation.
One plant presents several distinct lubricant challenges. Feed gas, refrigeration, cryogenic recovery, fractionation, and residue gas involve different compositions, pressures, and temperatures. Lubricant selection must therefore be made compressor by compressor rather than site-wide.
Dilution follows the partial pressure of the component dissolving into the lubricant, not total system pressure. A fractionation overhead compressor handling a nearly pure heavy component can experience greater dilution than a rich feed-gas compressor operating at higher pressure.
The most demanding dilution duty in a gas plant is usually at the fractionation end, not the inlet. Each column separates a heavier and purer product than the previous one, and purity is what makes a stream aggressive toward the lubricant.
Refrigeration compressors in a gas plant are refrigeration machines, not process-gas compressors. They operate in a closed loop containing essentially pure refrigerant. Specifying them from the process-gas lubricant list is a common and expensive error.
Where the lubricant never contacts the process gas, dilution resistance provides no benefit. Centrifugal compressors with dry gas seals require turbomachinery properties—including oxidation life, water separation, and air release—which a mineral grade meeting the applicable turbine-oil standards already provides.
Cryogenic duty reverses the requirement. At the cold end, the stream consists almost entirely of methane, so dilution is mild and low-temperature fluidity becomes the primary selection factor.
Recommended NEXT Natural Gas Processing & NGL Compressor Lubricants
NEXT GPL PAG-WS
Medium–Heavy / High-Dilution Hydrocarbon Compression
Base Oil: PAG-WS
ISO Range: 32 – 460
NEXT GPL PAG-EO
Heavy Hydrocarbon / Very Low-Dilution Compression
Base Oil: PEG
ISO Range: 32 – 220
NEXT GPL PAO
Light to Medium Hydrocarbon Compression Lubricant
Base Oil: PAO
ISO Range: 32 – 320
NEXT GPL MIN
Light Hydrocarbon / Wet-Gas Compression
Base Oil: Mineral
ISO Range: 32 – 680
How natural gas processing and NGL recovery work
Feed Gas Compression
Feed-gas compressors raise incoming gas to the pressure required for processing, while residue-gas compressors handle the leaner gas remaining after NGL recovery for downstream transport or export.
NGL Recovery & Cryogenic Processing
Compression supports natural-gas-liquid recovery and process stages associated with deethanizing and fractionation, where recovered hydrocarbons are separated into products such as ethane, propane and butanes.
Hydrocarbon Dew-Point Control
Gas-processing facilities control hydrocarbon dew point to prevent heavier hydrocarbons from condensing after the treated gas leaves the plant. Compressors associated with these processes can handle streams close to condensation conditions.
Gas-Plant Propane Refrigeration
Mechanical refrigeration chills feed gas so heavier hydrocarbons condense and drop out — as the primary recovery method in refrigeration plants, and as supplemental pre-cooling in cryogenic ones. The refrigeration compressor works a closed propane loop, which makes it a refrigeration duty rather than a process gas duty.
Fractionation & NGL Product Handling
Deethanizer, depropanizer and debutanizer systems separate the recovered NGL stream into individual products or defined product mixtures. Compressors may support vapour handling, recompression, refrigeration and product-recovery duties associated with these systems.
LPG Storage & Terminal Refrigeration
Propane and butane are stored refrigerated at atmospheric pressure rather than under pressure, with continuous boil-off reliquefied and returned. These systems commonly run open-cycle, so the stored product acts as the refrigerant and the dilution condition changes with the cargo.
Residue Gas Compression
Residue gas generally creates less hydrocarbon dilution than rich feed or process gas, although the actual lubricant requirements still depend on composition and operating conditions.
Factors Affecting Lubricant Selection
Lubricant behavior follows the interaction between the process stream, compressor design, and operating envelope. These factors set gas solubility, in-service viscosity, phase behavior, thermal stability, and material compatibility.
- Gas Composition Methane and heavier hydrocarbons dissolve differently in the lubricant. Higher ethane, propane, butane and pentane content increases dilution and reduces in-service viscosity.
- Suction and Discharge Conditions Pressure, compression ratio and stage count set gas solubility, mechanical loading, discharge temperature and the viscosity required to maintain the lubricant film.
- Oil and Gas Temperature Temperature sets gas solubility, lubricant viscosity and oxidation rate. Lower oil temperature increases dissolved hydrocarbon; higher temperature increases thermal and oxidative stress.
- Condensate and Liquid Carry-Over Hydrocarbon condensate entering the compressor dilutes the lubricant rapidly, disrupts cylinder-wall lubrication and raises wear, deposits and consumption.
- Water, CO₂ and H₂S Concentration Water, carbon dioxide (CO₂) and hydrogen sulfide (H₂S) drive corrosion risk, lubricant stability and material compatibility. Sour or wet gas requires lubricant chemistry with specific resistance to these conditions.
- Gas and Load Variability Changing gas composition, flow rate and compressor load alter dilution, discharge temperature and lubricant-film requirements across the operating cycle.
What NEXT needs to recommend a lubricant
A lubricant recommendation is based on the information below. Provide whatever information is available; NEXT will identify whether any additional details are required.
- Compressor Details Manufacturer, model, serial number and compressor type, such as reciprocating, rotary screw or centrifugal.
- Current Lubricant and Performance Current oil, oil volume, operating hours and any problems with viscosity, deposits, consumption, carryover or lubricant life.
- Gas Composition Main hydrocarbon components and any water, CO₂, H₂S, nitrogen, oxygen or other substances present. An existing gas-composition report can also be provided.
- Operating Conditions Suction and discharge pressures and temperatures, oil temperature and relevant operating limits for each compression stage.
- Application and Specific Requirements How the compressor is used and any purity, catalyst, material-compatibility, minimum-viscosity or other application-specific requirements.
- Final Recommendation NEXT evaluates the available information and confirms the recommended product, lubricant chemistry and ISO viscosity grade, with compatibility and changeover guidance where required.
Operational Benefits of Correct Lubricant Selection
Selecting the lubricant according to the compressor, gas composition and operating conditions can provide several operational benefits.
- Reduced Unplanned Downtime Prevents lubrication-related wear, overheating, valve problems, deposits and unplanned compressor shutdowns.
- Extended Component Life Protects cylinders, piston rings, packing, bearings, rotors and other lubricated components.
- Stable Operating Viscosity Maintains film strength after hydrocarbons dissolve into and dilute the lubricant.
- Lower Lubricant Consumption Delivers cylinder lubrication that reduces oil use, carryover and top-up frequency.
- Longer, Predictable Service Intervals Resists oxidation, viscosity loss and contamination for controlled maintenance planning.
- Consistent Protection Across Changing Gas Conditions Holds operating viscosity and film strength as process stream, flow rate and gas composition change.
Our technical team can help identify the right product.
Lubricant Selection, Technical Support and Compatibility Documentation
NEXT combines application knowledge, laboratory data and an extensive internal cross-reference database to support lubricant selection, conversions and compressor troubleshooting.
Depending on the application, we can provide:
- Application-Specific Product Recommendations Lubricant recommendations based on gas or refrigerant composition, compressor design, operating conditions and current performance issues.
- Lubricant Cross-Referencing Identifies suitable NEXT alternatives by comparing base-oil chemistry, viscosity, application, specifications and operating requirements.
- Compatibility and Conversion Documentation Provides chemistry comparisons, mixture-test data, material compatibility, flushing requirements and top-off or changeover guidance.
- Dilution Data and PVT Graphs Shows how gas or refrigerant concentration, pressure and temperature affect lubricant dilution, density and operating viscosity.
- Troubleshooting and Root-Cause Support Supports investigations into foaming, oil carryover, dilution, deposits, corrosion, high lubricant consumption and reduced oil life.
What type of oil is used in natural gas processing compressors?
Hydrotreated mineral, polyalphaolefin (PAO), polyalkylene glycol (PAG), water-soluble PAG or polyethylene glycol (PEG) — and a single plant will normally need more than one.
The determining variable is the propane-and-heavier content of the stream each machine handles, which differs enormously across one site. Residue gas runs well under one percent; feed gas runs high single figures; a fractionation overhead approaches a pure single component.
Two further cases sit outside that ladder. Refrigeration compressors work a closed refrigerant loop and follow refrigeration logic. Centrifugal machines with dry gas seals never expose the lubricant to process gas at all.
Why does NGL-rich gas reduce compressor oil viscosity?
Because hydrocarbon gases and most compressor lubricants are chemically alike.
Mineral oils and PAO are non-polar, as are the hydrocarbons, so they mix readily and dissolved gas removes operating viscosity. PAG carries oxygen in its backbone, making it polar, and hydrocarbons are correspondingly less soluble in it.
Two effects amplify it in a gas plant. Heavier components dissolve far more readily than methane, and solubility rises with pressure — so the discharge end of the machine dilutes hardest.
Which compressor in a gas plant is the hardest on the lubricant?
Usually a fractionation overhead, and usually not the one an operator expects.
Dissolution follows the partial pressure of the component doing the dissolving — total pressure multiplied by that component’s mole fraction. A rich feed stream at high pressure still contains mostly methane, so the propane driving force is a fraction of the total. A depropanizer overhead handles a near-pure heavy component, so almost the whole pressure is driving force.
The result is that the overhead machine can dilute considerably harder while running at lower total pressure. The pressure gauge reads lower and the duty is more severe.
Does NGL-rich gas always require a higher ISO viscosity grade?
No. A higher starting viscosity is one way to compensate for dilution; a more dilution-resistant chemistry is often the better one, because it holds viscosity rather than starting higher and falling further.
Grade increases also run out of room. Past a certain severity the grade needed to survive dilution becomes too viscous to feed properly at cold start, and a chemistry change is the correct move instead.
Which of the two applies is settled by calculating in-service viscosity against the compressor manufacturer’s requirement, rather than by a rule.
What is the difference between PAG, PAG-WS and PEG for NGL-rich gas?
They are a severity progression rather than a quality ranking, and each step trades something.
Water-insoluble PAG covers light to medium hydrocarbon service. Water-soluble PAG, an ethylene oxide/propylene oxide copolymer, resists heavier components better. PEG sits at the top with hydrocarbon solubility below 3 wt%, which effectively removes dilution from the calculation.
What each step costs is compatibility and price. Moving further up the ladder than the duty requires buys resistance the machine cannot use, and introduces a chemistry that is incompatible with the rest of the site.
Does propane refrigeration in a natural gas plant use the same lubricant as the process-gas compressors?
No, and treating it as a process gas compressor is one of the most common errors in this application.
A refrigeration compressor works a closed loop of essentially pure propane. Its requirements are set by refrigeration logic: resist dilution by the refrigerant, and still return oil from the chiller. Those two pull against each other, because the miscibility that brings the oil back is the same miscibility that thins it.
One detail catches people out. Suction pressure in these loops is very low, but the oil sits at condensing pressure in an atmosphere of pure propane — so a selection made on suction pressure badly underspecifies the machine.
It also matters commercially in a way that does not look like a lubrication problem. Oil that escapes the separator reaches the chiller, does not boil off, and concentrates there. Heat transfer degrades progressively, and in a gas plant that shows up as lost NGL recovery rather than as an oil complaint — so the process gets investigated before anyone looks at the bottom of the chiller.
Do cryogenic plants still have propane refrigeration?
Usually, yes — and it is frequently overlooked for exactly that reason.
Where feed gas is rich, a propane refrigeration package is commonly integrated into a turboexpander design to provide supplemental pre-cooling ahead of the cold box. A plant described as cryogenic therefore still contains a refrigeration compressor.
Because it sits inside a gas plant rather than in a refrigeration hall, it often gets charged with whatever the process gas compressors run. It should be specified as a refrigeration machine.
How is LPG terminal refrigeration different from gas-plant refrigeration?
The refrigerant is the product, which changes the problem.
A gas-plant propane circuit is closed, with a known charge of essentially pure refrigerant. An LPG storage terminal or carrier typically runs open-cycle: the boil-off compressor draws vapour directly from the storage tanks, compresses and condenses it, and returns the condensate. The tanks are the evaporator and the cargo is the refrigerant.
Three consequences follow. Any lubricant carryover returns into saleable product. The dilution condition changes with the cargo, since a terminal handling propane one week and butane the next presents its compressor with two different problems and no equipment change between them. And commercial LPG is a specification product rather than a pure fluid, so composition moves by source and season.
An open-cycle duty is therefore specified for the heaviest product it will handle, because the compressor cannot be recharged between cargoes.
What is the difference between PAG, PAG-WS and PEG for NGL-rich gas?
They are a severity progression rather than a quality ranking, and each step trades something.
Water-insoluble PAG covers light to medium hydrocarbon service. Water-soluble PAG, an ethylene oxide/propylene oxide copolymer, resists heavier components better. PEG sits at the top with hydrocarbon solubility below 3 wt%, which effectively removes dilution from the calculation.
What each step costs is compatibility and price. Moving further up the ladder than the duty requires buys resistance the machine cannot use, and introduces a chemistry that is incompatible with the rest of the site.
What information is most important when selecting a natural gas processing compressor lubricant?
Compressor make, model and type; the full gas composition for the specific machine including C5 and heavier; suction and discharge pressure and temperature for each stage; oil injection or sump temperature; and any liquid carry-over history.
The C5+ fractions matter more than their small percentages suggest, because lubricants preferentially absorb the heavier components. A composition truncated at butane removes exactly the part that drives the result.
For a gas plant, the form should be completed once per compressor position rather than once per site — the whole point being that the duties differ.
Explore Other Gas Compression Applications
Natural Gas Gathering
Lubricants for compressors handling raw, wet and variable-composition gas from wells and field gathering systems.
Natural Gas Transmission & Storage
Lubricants for compressors handling treated natural gas in pipelines, underground storage and transmission infrastructure.
Vapor Recovery Units
Lubricants for low-pressure hydrocarbon vapour recovery from tanks, production facilities and oil-and-gas operations.
Sour Gas Compression
Lubricants for gas streams containing significant H₂S, CO₂ and other acid-gas components.