paraffin oil

Oilfield Paraffin and Asphaltene

Petroleum - English
Print Friendly, PDF & Email

Paraffin-in-Crude-Oil


Paraffin control products prevent crude oil precipitation of paraffin wax deposits in production risers, subsea tie-backs, or any other production tubular or transportation pipeline.
Paraffin – Asphaltenes and Inhibitors
Some formulation products are wax crystal modifiers that prevent paraffin formation by interfering with the bonding of aliphatic wax molecules. Composed of branched chain polymers, these modifiers bond to the wax crystal lattice at an active growing site but prevent further growth and interfere with deposition by disrupting the lattice structure.
Although the paraffins remain unstable in solution, they are prevented from growing crystals of adequate size to block production lines; hence production is not impeded even for temperatures below the wax appearance temperature (WAT).
Wax crystal modifiers are applied continuously in the production stream for uninterrupted paraffin control. In pumping wells with low to moderate fluid levels, frequent batch treatments can approximate a continuous injection treatment. Similarly, a continuous supply of chemical can be provided by feedback from a formation squeeze treatment.
Paraffin Deposition
Crude oil is a complex substance formed under high pressure and temperature from vegetable and/or animal organic materials. A broad spectrum of organic chemical components exist in light, paraffinic and heavy oils. These include wax up to C60, esters, organic acids, asphaltenes and napthalenes. Depending on the makeup of these components, the crude oil will have its own characteristics, including specific gravity, wax content, pour point, color, etc.
Crude oil can cause a series of problems:
• Wax deposition
• Viscous gels at low temperatures (from heavy oils)
• Deposition of asphaltenes

read more about Crude Oil Components

Paraffin consists of straight and branched chain hydrocarbons of varying lengths; they are part of the chemical family called alkanes. Paraffin wax molecules contain between 20 to 80 or more carbon atoms in their chain and have a definite melting point. Paraffin waxes often make up 60-90% of a wax deposit. Soft deposits are composed of molecules containing from CI, to C,5 carbon atoms, their melting points are below 150·F. The high molecular weight waxes are referred as microcrystalline waxes and are similar
in chemical structure to the normal paraffin waxes but have a much higher melting point. (150 to 212·F).

Paraffins are aliphatic hydrocarbon waxes that are present in most crude oils. They precipitate from a crude oil at the point where the temperature falls below the WAT.
These deposits reduce the internal diameter of tubulars and pipelines, restrict or block valves, and impede other production equipment to reduce capacity and, in the worst case, stop production.
Factors Influencing Paraffin Deposition:
• Paraffin wax is primarily a solid – liquid phase equilibrium phenomenon; the lowering of temperature is the significant driving force for precipitation. Crude oil is made up of many different properties and freeze points. As the temperature falls below the freeze point of a hydrocarbon, it falls out of solution. The harder waxes deposit first, followed by the softer waxes as the temperature drops.
• Hydrocarbon density – paraffin waxes are increasingly soluble in lighter gravity, low molecular weight hydrocarbons.
• Solution gas – as oil losses light ends it becomes more dense, and paraffin solubility decreases. The light end losses usually occur at pressure drops, which cause the release of the volatile hydrocarbons, which are good solvents for paraffin wax.
• Rough surfaces provide sharp edges, which promote the deposition and agglomeration of wax. Suspended solids also provide surfaces for wax to adhere to and start accumulating.
• Water cut – as the water cut increases in a system it affects the temperature, water carries and retains more heat than oil does. The water reduces the tendency for wax to deposit by increased velocity and water wetting surfaces.

Asphaltene Deposition
Asphaltenes are probably the least understood deposits occurring in the oilfield. They are a complex organic material that are thought to be arranged in stacked, multi-ring structures. They contain nitrogen, oxygen’ and sulfur atoms within the repeating unit.
Asphaltenes have a wide variety of potential structures and vary from reservoir to reservoir. Asphaltenes are not truly soluble in most crude oils. They exist as 35 to 40 micron sized platelets
and are maintained in suspension by materials called maltenes and resins. These smaller similar
suspending molecules are soluble and act in what has been described as a micelle-type
arrangement to keep the asphaltic products in suspension. When stabilizing influences are
removed the asphaltic particles coalesce into larger groups, called flocs, which separate from
the oil. Asphaltene precipitation will occur with the addition of low molecular weight alkanes,
like pentane, hexane, and heptane, and are soluble in aromatic hydrocarbons, like xylene and toluene.

Factors Influencing Asphaltene Deposition
• Rich gas flooding causes destabilization by lowering the carbon to hydrogen ratio. Stripping gas from the oil has been shown to improve the solubility of the asphaltenes.
• The lowering of pH interrupts solution equilibrium and can cause a destabilization of the asphaltene. This may be caused by CO² mineral acid or naturally occurring organic acid. This can cause asphaltene to deposit in the well bore and pumps.
• Mixing of crude and/or condensate streams can cause a shift in pH or change the ratio of light hydrocarbons. Another example is the mixing of a paraffinic oil or condensate with an asphaltenic one.
• Incompatible organic chemicals, like isopropyl alcohol, methyl alcohol, acetone, and even some glycol, alcohol or surfactant based mutual solvents that do not have an aromatic component can selectively wet or attract maltenes and resins and cause the precipitation of asphaltenes.
•The effect of pressure drop and shear on asphaltene behavior may be to shift the tendency to
precipitate asphaltene, similar to a change in equilibrium. Turbulence also has impact on increasing asphaltene precipitation. Asphaltene deposits are frequently found downstream of chokes, liner
slots, valves, and vessels.
•Temperature drop – this may have more to do with indirect destabilization of the solubility of
maltenes and resins or may cause paraffin precipitation, which traps some asphaltenes as it solidifies.
Temperature can also be affected by pressure drop.

Paraffin / Asphaltene Comparison
Paraffin
• Straight and branched chains
• Definite melting point
• Cloud point indicates crystal initiation
• Soluble in crude oil
• Pour Point – no flow of oil due to wax
• Carbon number’s C12 to C66+
Asphaltene
• Friable solids
• No definite melting point
• Swell and pop when heated
• Aromatic rings
• Decompose to coke material
• Stabilized by resins and maltenes
• Not soluble in crude oil
• Contain nitrogen, oxygen and sulphur

Impact of Paraffin / Asphaltene Deposition
The impact of paraffin/asphaltene deposition is very severe and it can increase operating costs as well as
reduce well and system productivity. Examples of the impact are as follows:
• Plugging of perforations and near well bore damage resulting in a decline in reservoir productivity.
• Increased lifting costs from down hole pump maintenance, etc.
• Pressure increases in flow lines and wells resulting in higher operating costs.

Deposition and plugging of production tanks resulting in a difficulty of meeting BS &W requirements.
Pipeline blockage and increased transmission costs.
Wax is present in most crude oils, usually in quantities of less than 5%, but even this much can still cause problems. Wax can be detected by normal analytical methods (IP) and usually represents that fraction of the oil with a carbon number higher than 18. Wax is formed when the oil is cooled as a result of being produced from the well.
• Subsea pipelines
• Heat exchange
• Joule effect
• Gas lift (change in solubility)
The wax crystals are formed at a specific temperature (wax appearance point), and then they become so big that they deposit on the surface and block the pipes or process equipment.

Deposit Identification
Paraffin
• If it melts above l22’F
• If it floats on water
• If it dissolves in hot xylene
Asphaltene
• If it doesn’t melt but dissolves in
• hot xylene.
• Solids (scale, iron sulfide, sand,
• mud, etc.)
Solids
• If it doesn’t melt
• If it doesn’t dissolve in hot xylene
• If it sinks in water