Effect of Polyethylene Pipe on Wall Sticking of Waxy Oil in Low-Temperature Transportation

Abstract With the rapid development of the modern oil industry, oilfields have gradually transformed from a phase of high crude oil production to a period of high water cut. Consequently, heat transportation, which involves significant economic expenditure, is no longer feasible. Therefore, low temperature gathering and transportation technology has been proposed and applied. It enables the safe transportation of high water cut crude oil at temperatures below the pour point and the technical cost is increased pipe friction, which is less than heating loss. The low-temperature transportation of high water cut waxy crude oil was an energy conservation compared with heat transportation. In some oil fields, polyethylene (PE) pipes were used for low-temperature transportation of high water cut waxy crude oil in order to solve economic and environmental problem caused by pipeline corrosion. Unfortunately, few studies on effect of polyethylene pipe on wall sticking of waxy oil at low-temperature has been conducted. In this study, the critical velocity of wall sticking of waxy crude oil in the polyethylene pipes was found to be lower than that in the stainless-steel (SS) pipes in low-temperature transportation. The shear effect and structural strength of oil-wax gel, the most important factors to influence wall sticking of waxy crude oil, were calculated and compared. The shear effect was found to be similar in two pipes and the radial temperature gradient in polyethylene pipes was lower than that in stainless-steel pipes, which resulted in higher interface temperature in PE pipes. Under the influence of higher interface temperature, the solid wax content at oil-water interface in PE pipes was lower than that in SS pipes. The structural strength was affected by the solid wax content and strength enhanced with increase of the solid wax content. The strength of gelled oil in polyethylene pipes was lower than that in stainless-steel pipes, which implied that gelled oil sticking on wall was easier to be stripped from pipe wall in PE pipes. Therefore, the difference of radial temperature gradient in PE and SS pipes dominated the wall sticking process of waxy oil sticking and resulted in the lower wall sticking critical velocity of gelled oil in PE pipes.