Experiments on the characteristics of upgrading and viscosity reduction of heavy oil under supercritical water conditions

This paper investigates the macroscopic and microscopic characteristics of viscosity reduction and quality improvement of heavy oil in a supercritical water environment through laboratory experiments and testing. The effect of three reaction parameters, i.e. reaction temperature, reaction time and oil-water ratio, is analyzed on the product and their correlation with viscosity. The results show that the flow state of heavy oil is significantly improved with a viscosity reduction of 99.4% in average after the reaction in the supercritical water. Excessively high reaction temperature leads to a higher content of resins and asphaltenes, with significantly increasing production of coke. The optimal temperature ranges in 380–420 °C. Prolonged reaction time could continuously increase the yield of light oil, but it will also results in the growth of resins and asphaltenes, with the optimal reaction time of 150 min. Reducing the oil-water ratio helps improve the diffusion environment within the reaction system and reduce the content of resins and asphaltenes, but it will increase the cost of heavy oil treatment. An oil-water ratio of 1︰2 is considered as optimum to balance the quality improvement, viscosity reduction and reaction economics. The correlation of the three reaction parameters relative to the oil sample viscosity is ranked as temperature, time and oil-water ratio. Among the four fractions of heavy oil, the viscosity is dominated by asphaltene content, followed by aromatic content and less affected by resins and saturates contents.