Paraffin deposition

What is paraffin deposition?

Crude oil contains paraffins, straight-chain and branched hydrocarbons. The long-chain paraffins, generally those with more than about 18 carbon atoms, stay dissolved while the oil is warm but crystallize into solid wax as it cools. Paraffin deposition is the buildup of that wax on the surfaces the oil flows past. Over time the deposits narrow the flow path, add backpressure, and can block tubing, flowlines or equipment entirely.

The temperature at which wax crystals first appear is the wax appearance temperature, also called the cloud point of the crude. Below it, wax can deposit on any surface colder than the oil.

Where and why paraffin deposits

Oil leaves the reservoir warm and cools as it moves toward the surface and through surface equipment. Deposition is most likely where the oil cools fastest or flows slowest:

• Upper tubing, where the surrounding rock and air are cooler.
• Flowlines and pipelines, especially in cold weather or subsea.
• Tanks, heater-treaters and separators, where oil sits and cools.
• Near the wellbore, where gas expansion and pressure drop cool the oil.

Loss of light components as gas comes out of solution also reduces the oil’s ability to keep wax dissolved. Shutting in a well lets oil cool in place, which is why wells can be harder to restart after a shut-in.

Effects

• Reduced production and higher pumping costs from restricted flow.
• Rod pump and equipment problems.
• Plugged lines and costly interventions.
• In tanks, accumulated solids add to tank bottoms that must be cleaned out.

Paraffin is one of the main threats managed under flow assurance. It often occurs together with asphaltene deposits, which form for different reasons and respond to different treatments.

How paraffin is treated

• Thermal methods. Hot oiling or hot watering melts deposits in tubing and flowlines.
• Mechanical removal. Scrapers, pigs and cutting tools remove wax physically.
• Solvents. Aromatic solvents such as xylene dissolve wax but raise safety and environmental concerns; see BTEX.
• Dispersants. Dispersants and surfactants break deposits into small particles that the oil carries away and help keep them suspended.
• Inhibitors and pour point depressants. Wax crystal modifiers change how wax crystals grow so they are less likely to stick or gel, and lower the oil’s pour point.

Treatment programs are often continuous or periodic, because deposition resumes as long as the oil keeps cooling.

Paraffin and Locus biosurfactants

Locus’s Avert is a solvent-free biosurfactant that Locus describes as remediating and inhibiting paraffin and asphaltene deposits in producing and injection wells, and its AssurEOR FLOW treatment is positioned for near-wellbore paraffin removal.

Frequently asked questions