Effect of temperature on wall sticking of heavy oil in low-temperature transportation

Abstract

After surface adhesion apparatus (SAA) experiments, the mass of oil sticking to wall was found to increase slightly in high-temperature region (70-60 °C), while this mass was increased immediately in low-temperature region (35-25 °C). The contact angle and interfacial tension (IFT) of oil droplets were measured, and the work of adhesion and cohesion were cauculated, indicating that the process of oil sticking to pipeline wall includes the adhesion region and cohesion region. However, the work of adhesion does not change with temperature, but the work of cohesion is positively correlated with temperature. Consisting with this, the Results of the work of adhesion and cohesion using molecular simulation (MD) are the same with experiments and the van der Waals (VDW) interaction of polar substances is the main drive force of adhesion. The polar molecules on iron surface are aggregated at 0.5–2.0 nm along the X and Y directions and close to the iron surface at 0.5–1.0 nm along the Z direction. The polar substances in heavy oil are located on the near-iron plate side and the heteroatoms (i.e., N and S) formed adhesive joints in the processes of oil sticking to wall, especially N element. • A new method for predicting the wall sticking occurrence temperature of heavy oil. • Processes of wall sticking of heavy oil include the adhesion and cohesion region. • The N and S atoms are the bonding joints between heavy oil and pipe wall.