Summary of Existing Information on Handling Congealing Oils and Paraffin

Abstract

All crude oils become more viscous when chilled, but the only oils thatcongeal and precipitate paraffin to such an extent as actually to causeproduction troubles are those that contain an appreciable amount of wax. In handling these oils of high wax content, three distinct problems may beencountered before the oil reaches the refinery. The first problem is theprecipitation and accumulation of paraffin in the well, either in the oilstring or on the face and in the pores of the sand. The second problem is theaccumulation of paraffin and the congealing of oil in the transportation lines.The third problem is the precipitation of paraffin and the formation of tankbottoms. Factors That Control the Solubility of Paraffin in Crude Oil Two main factors, possibly three, govern the solubility of wax in crude oil.The first of these is temperature. The solubility of wax in crude oil increaseswith an increase in temperature, and as the temperature approaches the meltingpoint, the wax becomes soluble in all proportions in the crude oil. The higherthe melting point of a wax, the less soluble it is in crude oil below itsmelting point. All crude oils containing wax can be chilled to a point wherethe oil is saturated with wax. If the temperature is decreased below thispoint, some of the wax will crystallize from solution. Fig. 1 shows the effectof temperature on the solubility of crude paraffin in oil. The second factor is the amount of volatile constituents and gas removedfrom the crude oil. Evaporation of the volatile constituents and gas lessensthe volume of the oil and concentrates the solution of wax in the oil;therefore less wax can be held in solution at a definite temperature. As thenatural amount of wax present in the oil is constant, this results in the oilbecoming saturated with wax at a higher temperature than if the volatileconstituents and gas were still in the oil.