Sour Gas Compression
Sour gas compressor lubricants are selected for compressors handling gas streams that contain hydrogen sulfide (H₂S), frequently together with carbon dioxide (CO₂), moisture and hydrocarbons.
Sour gas adds toxicity, corrosion, containment and material-compatibility requirements beyond those of sweet natural gas. Severity follows H₂S concentration and partial pressure, moisture, CO₂ content, hydrocarbon composition, compressor design and operating conditions.
NEXT Lubricants supplies mineral, polyalphaolefin (PAO), polyalkylene glycol (PAG) and polyethylene glycol (PEG) lubricants for sour gas gathering, gas processing, acid-gas compression, reinjection and sulfur-recovery duty. Product selection accounts for both the sour-service severity and any hydrocarbon dilution that reduces the lubricant’s operating viscosity.
- No single universal H₂S concentration sets the lubricant. Sour-service severity comes from H₂S concentration and partial pressure together with moisture and CO₂ content.
- Free water sharply raises the corrosion risk of H₂S- and CO₂-bearing gas.
- Compressor metallurgy, seals, packing, purge systems and gas containment are the primary sour-service defenses; lubricant selection supplements these engineering controls, it does not replace them.
- Sour streams frequently carry propane, butane and heavier hydrocarbons; heavier hydrocarbons dissolve into the lubricant more readily than lighter ones and reduce in-service viscosity.
- Acid-gas injection compresses concentrated H₂S and CO₂ mixtures to high injection pressure, one of the most demanding sour-service duties.
- Five NEXT lubricants cover sour service across the dilution range: NEXT GPL MIN for wet sour gas; NEXT GPL PAO for sour process gas needing strong corrosion protection and water separation; NEXT GPL PAG for sour light-to-medium hydrocarbon streams; NEXT GPL PAG-WS for sour, high-dilution hydrocarbon service; and NEXT GPL PAG-EO (PEG, hydrocarbon solubility below 3 wt%) for heavy sour hydrocarbons.
How Sour Gas compression works and the compressor's role
Sour gas occurs in oil-and-gas reservoirs and process streams that contain measurable concentrations of H₂S. Before the gas enters a sales pipeline or downstream process, it undergoes compression, dehydration, sweetening and removal of H₂S, CO₂ and other contaminants.
Compressors raise the gas pressure for gathering, processing, treatment, reinjection or movement between process stages. Reciprocating and rotary screw compressors serve sour duty according to gas composition, pressure ratio, flow rate and facility design.
The lubricant protects bearings, cylinders, piston rings, packing, rotors and other moving components. Its exposure to the sour gas follows the compressor design and lubrication point. In reciprocating compressors, the frame lubricant remains isolated from the process gas while the cylinder and packing lubricant contacts it directly. In oil-injected rotary screw compressors, gas–lubricant contact is extensive.
Because H₂S is both toxic and corrosive, sour-gas compressors require specialized metallurgy, packing arrangements, distance pieces, purge systems and controlled venting. The compressor manufacturer and the applicable sour-service standards establish these equipment requirements.
Sour Gas Gathering & Boosting
Field and gathering compressors handle raw natural gas containing H₂S, CO₂, water and hydrocarbons before the gas reaches central treatment facilities.
Gas Processing & Sweetening
Compressors around gas-treatment facilities handle sour feed gas before H₂S and CO₂ removal, along with process streams associated with the sweetening system.
Acid Gas Injection
Acid gas separated during natural-gas sweetening carries concentrated mixtures of H₂S and CO₂. These streams are compressed to high pressure and reinjected underground, which makes acid-gas injection one of the more demanding sour-gas compression applications.
Sour gas reinjection
Sour gas is recompressed and reinjected into a reservoir for disposal, pressure maintenance or hydrocarbon recovery, according to the field-development strategy.
Sulphur Recovery
Sulfur-recovery facilities handle H₂S-rich acid gas removed from sour natural gas and convert hydrogen sulfide into elemental sulfur. Compression and blower duties on these streams require materials and lubricant selection matched to the actual gas composition.
Factors Affecting Lubricant Selection
Sour gas compressor lubrication accounts for the corrosive gas components, moisture, hydrocarbon dilution and compressor operating envelope. The following factors determine the required formulation and viscosity.
- H₂S concentration and partial pressure Establish the severity of the sour service and the corresponding compressor, material and lubricant requirements.
- Moisture and free water Increase corrosion risk in H₂S- and CO₂-containing gas and affect lubricant stability, separation and component protection.
- CO₂ and complete acid-gas composition Influence corrosion severity, phase behavior and lubricant requirements, particularly in concentrated acid-gas streams.
- Hydrocarbon composition and dilution Determine whether propane, butane and heavier components dissolve into the lubricant and reduce its operating viscosity.
- Suction and discharge conditions Set H₂S and CO₂ partial pressure, compressor loading, discharge temperature, gas density and lubricant exposure.
- Lubricant and gas temperature Govern lubricant viscosity, oxidation, gas solubility, condensation and the phase behavior of the complete gas stream.
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 sour-gas composition, compressor and operating conditions can provide several operational benefits.
- Reduced Unplanned Downtime Prevents lubrication-related wear, overheating, valve problems, deposits and unexpected compressor shutdowns.
- Corrosion Protection in Wet Sour Service Protects lubricated surfaces against corrosive attack from H₂S and CO₂ in the presence of moisture.
- Extended Component Life Protects cylinders, piston rings, packing, bearings, rotors and other lubricated components.
- Stable Operating Viscosity Maintains sufficient film strength after hydrocarbons dissolve into and dilute the lubricant.
- Longer and More Predictable Service Intervals Resists oxidation, viscosity loss and contamination for controlled maintenance planning.
- Clean Running and Deposit Control Minimizes varnish, carbon and deposit formation for cleaner valves, cylinders and lubricant-system components.
Recommended NEXT Sour Gas Compressor Lubricants
NEXT GPL PAG
Sour Gas / Light–Medium Hydrocarbon Compression
Base Oil: PAG
ISO Range: 32 – 680
NEXT GPL PAG-WS
Sour Hydrocarbon / High-Dilution Compression
Base Oil: PAG-WS
ISO Range: 32 – 460
NEXT GPL PAG-EO
Heavy Sour Hydrocarbon / Very Low-Dilution Compression
Base Oil: PEG
ISO Range: 32 – 220
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 sour gas compressors?
Sour-gas compressors can use specially formulated mineral, PAO, PAG or PEG lubricants depending on H₂S concentration, moisture, CO₂, hydrocarbon content, compressor design and operating conditions. The lubricant must be suitable for the specific sour-service severity rather than selected solely by viscosity grade.
What H₂S concentration makes a gas compressor a sour-gas application?
There is no single universal lubricant threshold. Compressor manufacturers and materials standards define sour-service requirements according to their own equipment and H₂S exposure criteria. For Ariel reciprocating compressors, 100 ppm to 2% H₂S is classified as Sour Level 1 and above 2% as Sour Level 2, although some materials restrictions become relevant at even lower H₂S concentrations.
Why does sour gas require a special compressor lubricant?
H₂S creates a corrosive and chemically demanding environment, particularly when moisture is present. Sour-gas compressor lubricants therefore require suitable corrosion protection and compatibility with the gas and compressor materials. Ariel specifically states that sour-gas service typically requires a special lubricant for the separate cylinder-lubrication supply.
Can the same lubricant be used for mildly sour gas and acid gas injection?
Not automatically. Mild sour gas and concentrated acid-gas streams can differ enormously in H₂S, CO₂, pressure and moisture. Acid gas injection commonly compresses separated H₂S/CO₂ mixtures to high pressure for underground injection, so lubricant and compressor requirements should be evaluated for that specific duty.
Does CO₂ change sour-gas lubricant selection?
Yes. CO₂ should be evaluated together with H₂S and moisture. In wet conditions, CO₂ contributes additional corrosion risk, while high CO₂ partial pressure can also affect lubricant behavior. The complete gas composition should therefore be provided when selecting a sour-gas lubricant.
When should PAG or PEG be used instead of PAO in sour gas?
PAG or PEG becomes particularly relevant when the sour gas also contains hydrocarbons that significantly dilute conventional oil. PAO provides strong sour-gas corrosion protection and water separation, while PAG-WS and PEG can provide greater resistance to hydrocarbon dilution. The correct choice depends on both sour-gas severity and gas composition. NEXT’s current products explicitly position PAO, PAG-WS and PAG-EO differently for these duties.
Does moisture make sour-gas compression more severe?
Yes. Water significantly increases corrosion concerns in H₂S and CO₂-containing environments. Any free water or high moisture content should therefore be included in the compressor and lubricant assessment.
Is acid gas injection the most demanding sour-gas application?
It can be among the most demanding because the gas being compressed may contain very high concentrations of H₂S and CO₂ and may be compressed to high injection pressure. However, severity still depends on the actual acid-gas composition, pressure, temperature, compressor and water content rather than the application name alone.
Explore Other Gas Compression Applications
CO₂ Compression
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Carbon Capture & CCUS
Natural Gas Gathering
Biogas
Lubricants for methane/CO₂ gas streams where H₂S, moisture and other contaminants influence compressor lubrication.