Enhanced Oil Recovery & Gas Injection
Enhanced oil recovery and gas injection compressor lubricants are selected for compressors raising carbon dioxide (CO₂), natural gas, hydrocarbon gas or nitrogen to the pressure required for reservoir injection.
The lubricant challenge follows the injection gas. CO₂ and hydrocarbon gases dissolve into lubricants and reduce operating viscosity. Rich hydrocarbon gas creates severe dilution in conventional mineral and polyalphaolefin (PAO) lubricants, while nitrogen and lean dry gas place greater emphasis on compressor design, cleanliness and long-term lubricant stability.
NEXT Lubricants supplies PAO, polyalkylene glycol (PAG), water-soluble PAG (PAG-WS), polyethylene glycol (PEG) and mineral lubricants for EOR, gas reinjection, reservoir pressure maintenance and associated-gas recycling. General industrial CO₂ compression and the wider carbon-capture, transport and storage chain are covered on separate application pages.
Gas injection forces carbon dioxide, natural gas, hydrocarbon gas, or nitrogen into a reservoir to displace trapped oil or maintain reservoir pressure. It is the highest-pressure duty in gas compression, and the injected gas determines nearly every lubricant requirement.
The same lubricant in the same ISO grade behaves differently in every injection service. Carbon dioxide dissolves readily, hydrocarbon solubility increases with molecular weight, and nitrogen dissolves the least. One lubricant cannot therefore be assumed suitable across several injection trains.
Heavier hydrocarbons cause more dilution than lean gas. The lubricant also absorbs heavier components preferentially, so a gas analysis showing mostly methane can understate what is actually dissolving into the lubricant.
Injection pressure amplifies every dilution mechanism. Solubility increases with pressure, and injection operates at some of the highest pressures on the site. A lubricant that retains sufficient viscosity at pipeline pressure may fail at injection pressure.
Nitrogen is the mildest injection gas, not an absent one. It is chemically inert toward the lubricant and noncorrosive, but it still dissolves into the oil. At injection pressure, that solubility is not negligible.
Reservoir terms describe reservoir behavior, not lubricant behavior. Miscible injection, immiscible injection, and minimum miscibility pressure determine what enters the reservoir and at what pressure. Water-alternating-gas operation does not automatically expose the compressor lubricant to water; that depends on compressor-side separation and process conditions.
How enhanced oil recovery and gas injection work
After primary and secondary production, part of the reservoir oil remains trapped within the rock. Gas injection introduces CO₂, natural gas, enriched hydrocarbon gas or nitrogen to maintain pressure, improve displacement, swell the oil or reduce its effective viscosity.
The compressor raises the injection gas from its supply or recovery pressure to the pressure required by the reservoir-injection system. In many pressure-maintenance and gas-recycling applications, produced gas is also separated, treated, recompressed and reinjected.
Reciprocating, integrally geared and centrifugal compressors serve injection duty according to gas composition, flow, pressure ratio and required discharge pressure. Lubricant exposure differs by compressor design: cylinder-lubricated and oil-injected compressors create direct gas–lubricant contact, while dry-sealed or separately lubricated designs isolate the process gas from the bearing lubricant.
CO₂ Injection
CO₂ is compressed for miscible or immiscible reservoir injection. CO₂/lubricant contact, pressure and operating viscosity drive lubricant selection.
Hydrocarbon Gas Injection & Reinjection
Natural gas, associated gas or enriched hydrocarbon gas is recompressed and injected for pressure maintenance or enhanced recovery. Richer gas dilutes conventional lubricant more aggressively.
Nitrogen Injection
Nitrogen provides an alternative injection gas for reservoir pressure support and oil displacement where reservoir and project conditions suit it. As an inert, non-diluting gas, it shifts the emphasis to compressor cleanliness and lubricant stability.
Water-Alternating-Gas (WAG)
WAG alternates periods of gas and water injection to improve reservoir sweep. The compressor handles the gas-injection portion; separate injection pumps handle the water.
Factors Affecting Lubricant Selection
Gas injection is not one lubricant duty. The injection gas, compressor and complete operating envelope are evaluated together.
- Compressor Design and Gas–Lubricant Contact Determine which components require lubrication and whether the lubricant contacts the injection gas directly or stays isolated in bearings, crankcases, seals or auxiliary systems.
- Injection-Gas Composition and Dilution Determine how CO₂, methane, heavier hydrocarbons, nitrogen and other components interact with the lubricant and reduce operating viscosity.
- Pressure, Temperature and Operating Viscosity Determine gas solubility, compressor loading and the film strength available across every compression stage.
- Moisture, H₂S and Process Contaminants Influence corrosion risk, lubricant stability, water separation, deposit formation and material compatibility.
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 Injection-gas type and any water, CO₂, H₂S, nitrogen, oxygen or other substances present. An existing gas-composition report also serves.
- 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 injection gas, compressor and operating conditions delivers reliable high-pressure compression.
- Reduced Unplanned Downtime Prevents lubrication-related wear, overheating, deposits, valve problems and unexpected compressor shutdowns.
- Component Protection Protects bearings, cylinders, piston rings, packing, rotors, gears and other lubricated components.
- Stable Operating Viscosity Maintains film strength after gas dilution and operating temperature reduce it.
- Reduced Lubricant Consumption Low-volatility, gas-appropriate formulations limit carryover, lubricant losses and unnecessary top-ups.
- Clean Running and Deposit Control Oxidation stability and deposit control keep valves, cylinders and lubricant-system components clean.
- Longer and More Predictable Service Life Resists dilution, oxidation and contamination for controlled maintenance intervals.
Recommended NEXT EOR & Gas Injection Compressor Lubricants
NEXT GPL PAG
Light–Medium Hydrocarbon Injection / Reinjection
Base Oil: PAG
ISO Range: 32 – 680
NEXT GPL PAG-WS
Rich / Heavy Hydrocarbon Reinjection
Base Oil: PAG-WS
ISO Range: 32 – 460
NEXT GPL PAG-EO
Severe-Dilution Heavy Hydrocarbon Injection
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 gases are used for enhanced oil recovery?
Carbon dioxide, natural gas or richer hydrocarbon gas, and nitrogen. Reservoir pressure and temperature, crude oil properties, gas availability and project economics decide which.
From the compressor’s point of view, they are four different problems rather than four options for one problem. Carbon dioxide dissolves aggressively at injection pressure. Rich hydrocarbon gas dilutes hardest of all. Lean natural gas dilutes moderately. Nitrogen dilutes least.
That range is why this page carries the full product line rather than one or two grades — it is the only application on the site that uses all six.
Why does the same lubricant behave differently in different injection wells?
Because dilution is set by what is being injected, not by the grade on the drum.
An ISO viscosity grade is measured at 40 °C (104 °F) on undiluted oil. Once the injection gas dissolves into it, the working viscosity is lower — and how much lower depends on the gas.
Run one grade across a carbon dioxide train, a nitrogen train and a rich gas reinjection train and three different operating viscosities result. Only one of them may meet what the compressor needs.
This is the practical reason a lubricant that has performed well on one injection service can fail on another at the same site, with no change to the product.
Why does rich hydrocarbon gas dilute more than lean gas?
Two reasons, and the second one is the one people miss.
Heavier hydrocarbons dissolve into a lubricant more readily than methane does, so a stream carrying propane, butane and heavier components dilutes more than one that is mostly methane.
But the lubricant also takes them up preferentially. Sampling of used oil from operating compressors shows a higher proportion of the heavier components dissolved in the oil than their proportion in the gas stream.
So a gas analysis reading ninety-plus percent methane does not mean the dissolved gas in the lubricant is ninety-plus percent methane. The small numbers at the heavy end of the analysis are doing more damage than they appear to, which is why truncating a composition at butane removes exactly the part that matters.
Does injection pressure change the lubricant requirement?
Yes, and it is the reason this duty is harder than it looks.
Gas solubility rises with pressure. Injection is the highest-pressure application in gas compression, so the same composition that is manageable in a gathering or pipeline machine can be severe at injection discharge.
Two consequences follow. Stage-by-stage assessment is not optional — a multi-stage injection machine presents very different conditions at the first stage and the last. And the final stage governs: whatever grade satisfies the last stage will be adequate everywhere upstream, but not the reverse.
Is nitrogen injection easy on the lubricant?
Easier than the alternatives, but not free.
Nitrogen is chemically inert toward the lubricant and introduces no corrosion mechanism, which removes two problems that carbon dioxide and hydrocarbon service bring. That is a real advantage.
What it does not do is stay out of the oil. Nitrogen has measurable solubility in lubricating fluids, and injection pressures are high enough that a real amount dissolves. An operator who selected a grade assuming zero dilution has no margin.
The correct framing is that nitrogen is the mildest of the injection gases rather than an absent one. Low-temperature fluidity, cleanliness and long-term stability become the deciding properties instead of dilution resistance.
What lubricant is used for CO₂ EOR compression?
Normally a polyalphaolefin, because the problem is carbon dioxide solubility rather than hydrocarbon dilution.
Carbon dioxide dissolves readily into most lubricants, and at injection pressures it behaves as a dense fluid with solvent character rather than as an ordinary gas. Viscosity loss is driven by pressure rather than by hydrocarbon content — there may be no hydrocarbons in the stream at all.
That makes it a different property from the one the polyalkylene glycol grades are chosen for. A lubricant with low carbon dioxide solubility is worth more here than one with low hydrocarbon solubility.
NEXT PAO covers this duty, with chemical stability across carbon dioxide, nitrogen and other inert gases and a pour point reaching −68 °C (−90 °F).
Why are PAG lubricants used for hydrocarbon gas reinjection?
Because hydrocarbons and conventional lubricants are chemically alike, and polyalkylene glycol is not.
Mineral oils and polyalphaolefin are non-polar, as are hydrocarbon gases, so they mix readily and dissolved gas removes viscosity. Polyalkylene glycol carries oxygen in its backbone, which makes it polar — and hydrocarbons are correspondingly less soluble in it.
That is the whole mechanism. It is also why moving from a mineral oil to a polyalphaolefin does not solve a dilution problem: both are non-polar, so the dilution resistance is comparable. Anyone changing to a synthetic to fix dilution has bought the wrong property.
When should NEXT GPL PAG-WS or PAG-EO be considered?
As the injected gas gets richer, and at the point where a heavier viscosity grade stops being a workable answer.
GPL PAG-WS covers rich and heavy hydrocarbon reinjection. GPL PAG-EO, with hydrocarbon solubility below 3 wt%, covers the severe end where dilution needs to be near-eliminated rather than reduced.
The useful test is whether a grade increase can still do the job. In carbon dioxide, nitrogen and lean gas service, moving up one or two ISO grades is often the right correction. In rich hydrocarbon service it usually is not — the grade needed becomes too viscous to feed properly at cold start, and a chemistry change is the correct move instead.
Calculating the in-service viscosity is what identifies where that transition sits for a specific stream.
Explore Other Gas Compression Applications
Natural Gas Processing & NGL
Natural Gas Gathering
Lubricants for compressors handling raw, wet and variable-composition gas from wells and field gathering systems.
CO₂ Compression
Core CO₂/lubricant solubility and operating-viscosity selection for industrial process CO₂.