Paraffin is a costly and complicated problem that varies from area to area and often from well to well. Paraffin commonly refers to a waxy build-up of organic material. Most crude oils contain paraffin in solution, and cooling causes paraffin crystals to clump together and build up on production equipment. Left untreated, the build-up will eventually shut off the flow of oil by completely plugging tubing and flow lines.
The components of petroleum are classified by the number of carbon atoms in the molecule. Methane gas has one carbon atom. Kerosene has between 10 and 14 carbon atoms and paraffins have 18 to 60 carbon atoms per molecule. At a constant pressure each of these molecules has a different boiling point or temperature at which it will vaporize. Short-chain carbon molecules vaporize first when oil is heated. This is essentially the process a refinery uses to make gasoline, kerosene, etc. Cooling an oil causes the reverse to happen – the longer chain molecules crystallize and clump together forming a wax which can have a melting point over 200F. Paraffin occurs when the wax is no longer soluble in the oil. Unfortunately, as wells are produced there is a temperature drop due to gas movement and heat exchange as oil moves up the tubulars. Paraffin often precipitates. Also, the paraffin content of the oil often increases over the life of the well, because the short-chain carbon molecules are more easily produced. Consequently, the result is shorter production periods between paraffin problems. Laboratories can help predict problems by measuring the cloud point, which is the temperature at which the oil will no longer flow. A gas chromatograph can measure paraffin content.