Effect of ethylene vinyl acetate on pour point and wax deposition characteristics of high-pour-point and viscous waxy crude oil

In this study, the effects of ethylene vinyl acetate copolymers on pour point, wax crystal structure, deposition rate and composition were investigated from macro and micro aspects by using pour point tester, cold finger, polarizing microscopy and high temperature gas chromatography. The results revealed that the copolymers could reduce the pour point of crude oil, but they had mutually selective which depending on their respective composition. Moreover, it observed that the copolymers significantly reduced the wax crystal precipitation, transforming crystal shapes from flake or needle-like forms to rounded, aggregated structures, which became more obvious as the heating temperature increased. It was found that copolymers inhibited the formation of wax deposition, and the rate of wax deposition decreased, tending toward stability as the copolymers concentration increased. But the wax content in the deposits increased, owing to the eutectic effect between the copolymers and the wax molecules resulting in a decrease in the porosity of the network structure covering the deposits, and an increase in the proportion of high-carbon compounds in the deposits. Additionally, the aging of the deposit layer intensified as the critical carbon number increased, while the enrichment of the resins and asphaltenes in the deposits decreased.